simplify SimValue Debug format, making complex structures much easier to read

If we ever add Verilog files, we can "or" both results, I guess.

crates/fayalite-proc-macros-impl/src/hdl_bundle.rs

@@ -396,15 +396,29 @@ impl ToTokens for Builder {
         quote_spanned! {self.ident.span()=>
             #[automatically_derived]
             #[allow(non_camel_case_types, dead_code, private_interfaces)]
-            impl #filled_impl_generics ::fayalite::expr::ToExpr for #filled_ty
+            impl #filled_impl_generics ::fayalite::expr::ValueType for #filled_ty
             #filled_where_clause
             {
                 type Type = #target #type_generics;
+                type ValueCategory = ::fayalite::expr::value_category::ValueCategoryExpr;
+
+                fn ty(&self) -> <Self as ::fayalite::expr::ValueType>::Type {
+                    #target {
+                        #(#field_idents: ::fayalite::expr::ValueType::ty(&self.#field_idents),)*
+                    }
+                }
+            }
+
+            #[automatically_derived]
+            #[allow(non_camel_case_types, dead_code, private_interfaces)]
+            impl #filled_impl_generics ::fayalite::expr::ToExpr for #filled_ty
+            #filled_where_clause
+            {
                 fn to_expr(
                     &self,
-                ) -> ::fayalite::expr::Expr<<Self as ::fayalite::expr::ToExpr>::Type> {
+                ) -> ::fayalite::expr::Expr<<Self as ::fayalite::expr::ValueType>::Type> {
                     let __ty = #target {
-                        #(#field_idents: ::fayalite::expr::Expr::ty(self.#field_idents),)*
+                        #(#field_idents: ::fayalite::expr::ValueType::ty(&self.#field_idents),)*
                     };
                     let __field_values = [
                         #(::fayalite::expr::Expr::canonical(self.#field_idents),)*
@@ -695,10 +709,10 @@ impl ToTokens for ParsedBundle {
                 v.field(&value.#ident);
             }
         }));
-        let to_sim_value_fields = Vec::from_iter(fields.named().into_iter().map(|field| {
+        let value_type_fields = Vec::from_iter(fields.named().into_iter().map(|field| {
             let ident: &Ident = field.ident().as_ref().unwrap();
             quote_spanned! {span=>
-                #ident: ::fayalite::sim::value::SimValue::ty(&self.#ident),
+                #ident: ::fayalite::expr::ValueType::ty(&self.#ident),
             }
         }));
         let fields_len = fields.named().into_iter().len();
@@ -806,28 +820,39 @@ impl ToTokens for ParsedBundle {
                 }
             }
             #[automatically_derived]
-            impl #impl_generics ::fayalite::sim::value::ToSimValue for #mask_type_sim_value_ident #type_generics
+            impl #impl_generics ::fayalite::expr::ValueType for #mask_type_sim_value_ident #type_generics
             #where_clause
             {
                 type Type = #mask_type_ident #type_generics;
+                type ValueCategory = ::fayalite::expr::value_category::ValueCategorySimValue;
 
+                fn ty(&self) -> <Self as ::fayalite::expr::ValueType>::Type {
+                    #mask_type_ident {
+                        #(#value_type_fields)*
+                    }
+                }
+            }
+            #[automatically_derived]
+            impl #impl_generics ::fayalite::sim::value::ToSimValue for #mask_type_sim_value_ident #type_generics
+            #where_clause
+            {
                 fn to_sim_value(
                     &self,
                 ) -> ::fayalite::sim::value::SimValue<
-                    <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                    <Self as ::fayalite::expr::ValueType>::Type,
                 > {
                     let ty = #mask_type_ident {
-                        #(#to_sim_value_fields)*
+                        #(#value_type_fields)*
                     };
                     ::fayalite::sim::value::SimValue::from_value(ty, ::fayalite::__std::clone::Clone::clone(self))
                 }
                 fn into_sim_value(
                     self,
                 ) -> ::fayalite::sim::value::SimValue<
-                    <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                    <Self as ::fayalite::expr::ValueType>::Type,
                 > {
                     let ty = #mask_type_ident {
-                        #(#to_sim_value_fields)*
+                        #(#value_type_fields)*
                     };
                     ::fayalite::sim::value::SimValue::from_value(ty, self)
                 }
@@ -955,28 +980,39 @@ impl ToTokens for ParsedBundle {
                 }
             }
             #[automatically_derived]
-            impl #impl_generics ::fayalite::sim::value::ToSimValue for #sim_value_ident #type_generics
+            impl #impl_generics ::fayalite::expr::ValueType for #sim_value_ident #type_generics
             #where_clause
             {
                 type Type = #target #type_generics;
+                type ValueCategory = ::fayalite::expr::value_category::ValueCategorySimValue;
 
+                fn ty(&self) -> <Self as ::fayalite::expr::ValueType>::Type {
+                    #target {
+                        #(#value_type_fields)*
+                    }
+                }
+            }
+            #[automatically_derived]
+            impl #impl_generics ::fayalite::sim::value::ToSimValue for #sim_value_ident #type_generics
+            #where_clause
+            {
                 fn to_sim_value(
                     &self,
                 ) -> ::fayalite::sim::value::SimValue<
-                    <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                    <Self as ::fayalite::expr::ValueType>::Type,
                 > {
                     let ty = #target {
-                        #(#to_sim_value_fields)*
+                        #(#value_type_fields)*
                     };
                     ::fayalite::sim::value::SimValue::from_value(ty, ::fayalite::__std::clone::Clone::clone(self))
                 }
                 fn into_sim_value(
                     self,
                 ) -> ::fayalite::sim::value::SimValue<
-                    <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                    <Self as ::fayalite::expr::ValueType>::Type,
                 > {
                     let ty = #target {
-                        #(#to_sim_value_fields)*
+                        #(#value_type_fields)*
                     };
                     ::fayalite::sim::value::SimValue::from_value(ty, self)
                 }
@@ -1002,91 +1038,172 @@ impl ToTokens for ParsedBundle {
         }
         .to_tokens(tokens);
         if let Some((cmp_eq,)) = cmp_eq {
-            let mut expr_where_clause =
+            let mut cmp_eq_where_clause =
                 Generics::from(generics)
                     .where_clause
                     .unwrap_or_else(|| syn::WhereClause {
                         where_token: Token![where](span),
                         predicates: Punctuated::new(),
                     });
-            let mut sim_value_where_clause = expr_where_clause.clone();
-            let mut fields_sim_value_eq = vec![];
-            let mut fields_cmp_eq = vec![];
-            let mut fields_cmp_ne = vec![];
+            let mut fields_value_eq = vec![];
+            let mut fields_value_ne = vec![];
+            let mut fields_expr_eq = vec![];
+            let mut fields_expr_ne = vec![];
+            let mut fields_valueless_eq = vec![];
+            let mut fields_valueless_ne = vec![];
             for field in fields.named() {
                 let field_ident = field.ident();
                 let field_ty = field.ty();
-                expr_where_clause
+                cmp_eq_where_clause
                     .predicates
                     .push(parse_quote_spanned! {cmp_eq.span=>
-                        #field_ty: ::fayalite::expr::ops::ExprPartialEq<#field_ty>
+                        #field_ty: ::fayalite::expr::HdlPartialEqImpl<#field_ty>
                     });
-                sim_value_where_clause
-                    .predicates
-                    .push(parse_quote_spanned! {cmp_eq.span=>
-                        #field_ty: ::fayalite::sim::value::SimValuePartialEq<#field_ty>
-                    });
-                fields_sim_value_eq.push(quote_spanned! {span=>
-                    ::fayalite::sim::value::SimValuePartialEq::sim_value_eq(&__lhs.#field_ident, &__rhs.#field_ident)
+                fields_value_eq.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_value_eq(
+                        __lhs.#field_ident,
+                        ::fayalite::__std::borrow::Cow::Borrowed(&__lhs_value.#field_ident),
+                        __rhs.#field_ident,
+                        ::fayalite::__std::borrow::Cow::Borrowed(&__rhs_value.#field_ident),
+                    )
                 });
-                fields_cmp_eq.push(quote_spanned! {span=>
-                    ::fayalite::expr::ops::ExprPartialEq::cmp_eq(__lhs.#field_ident, __rhs.#field_ident)
+                fields_value_ne.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_value_ne(
+                        __lhs.#field_ident,
+                        ::fayalite::__std::borrow::Cow::Borrowed(&__lhs_value.#field_ident),
+                        __rhs.#field_ident,
+                        ::fayalite::__std::borrow::Cow::Borrowed(&__rhs_value.#field_ident),
+                    )
                 });
-                fields_cmp_ne.push(quote_spanned! {span=>
-                    ::fayalite::expr::ops::ExprPartialEq::cmp_ne(__lhs.#field_ident, __rhs.#field_ident)
+                fields_expr_eq.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_expr_eq(
+                        __lhs.#field_ident,
+                        __rhs.#field_ident,
+                    )
+                });
+                fields_expr_ne.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_expr_ne(
+                        __lhs.#field_ident,
+                        __rhs.#field_ident,
+                    )
+                });
+                fields_valueless_eq.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_valueless_eq(
+                        ::fayalite::expr::Valueless::new(__lhs.#field_ident),
+                        ::fayalite::expr::Valueless::new(__rhs.#field_ident),
+                    )
+                });
+                fields_valueless_ne.push(quote_spanned! {span=>
+                    ::fayalite::expr::HdlPartialEqImpl::cmp_valueless_ne(
+                        ::fayalite::expr::Valueless::new(__lhs.#field_ident),
+                        ::fayalite::expr::Valueless::new(__rhs.#field_ident),
+                    )
                 });
             }
-            let sim_value_eq_body;
-            let cmp_eq_body;
-            let cmp_ne_body;
+            let value_eq_body;
+            let value_ne_body;
+            let expr_eq_body;
+            let expr_ne_body;
+            let valueless_eq_body;
+            let valueless_ne_body;
             if fields_len == 0 {
-                sim_value_eq_body = quote_spanned! {span=>
+                value_eq_body = quote_spanned! {span=>
                     true
                 };
-                cmp_eq_body = quote_spanned! {span=>
+                value_ne_body = quote_spanned! {span=>
+                    false
+                };
+                expr_eq_body = quote_spanned! {span=>
                     ::fayalite::expr::ToExpr::to_expr(&true)
                 };
-                cmp_ne_body = quote_spanned! {span=>
+                expr_ne_body = quote_spanned! {span=>
                     ::fayalite::expr::ToExpr::to_expr(&false)
                 };
+                valueless_eq_body = quote_spanned! {span=>
+                    ::fayalite::expr::Valueless::new(::fayalite::int::Bool)
+                };
+                valueless_ne_body = quote_spanned! {span=>
+                    ::fayalite::expr::Valueless::new(::fayalite::int::Bool)
+                };
             } else {
-                sim_value_eq_body = quote_spanned! {span=>
-                    #(#fields_sim_value_eq)&&*
+                value_eq_body = quote_spanned! {span=>
+                    #(#fields_value_eq)&*
                 };
-                cmp_eq_body = quote_spanned! {span=>
-                    #(#fields_cmp_eq)&*
+                value_ne_body = quote_spanned! {span=>
+                    #(#fields_value_ne)|*
                 };
-                cmp_ne_body = quote_spanned! {span=>
-                    #(#fields_cmp_ne)|*
+                expr_eq_body = quote_spanned! {span=>
+                    #(#fields_expr_eq)&*
+                };
+                expr_ne_body = quote_spanned! {span=>
+                    #(#fields_expr_ne)|*
+                };
+                valueless_eq_body = quote_spanned! {span=>
+                    let __lhs = ::fayalite::expr::ValueType::ty(&__lhs);
+                    let __rhs = ::fayalite::expr::ValueType::ty(&__rhs);
+                    #(#fields_valueless_eq)|*
+                };
+                valueless_ne_body = quote_spanned! {span=>
+                    let __lhs = ::fayalite::expr::ValueType::ty(&__lhs);
+                    let __rhs = ::fayalite::expr::ValueType::ty(&__rhs);
+                    #(#fields_valueless_ne)|*
                 };
             };
             quote_spanned! {span=>
                 #[automatically_derived]
-                impl #impl_generics ::fayalite::expr::ops::ExprPartialEq<Self> for #target #type_generics
-                #expr_where_clause
+                impl #impl_generics ::fayalite::expr::HdlPartialEqImpl<Self> for #target #type_generics
+                #cmp_eq_where_clause
                 {
-                    fn cmp_eq(
+                    #[track_caller]
+                    fn cmp_value_eq(
+                        __lhs: Self,
+                        __lhs_value: ::fayalite::__std::borrow::Cow<'_, <Self as ::fayalite::ty::Type>::SimValue>,
+                        __rhs: Self,
+                        __rhs_value: ::fayalite::__std::borrow::Cow<'_, <Self as ::fayalite::ty::Type>::SimValue>,
+                    ) -> ::fayalite::__std::primitive::bool {
+                        #value_eq_body
+                    }
+
+                    #[track_caller]
+                    fn cmp_value_ne(
+                        __lhs: Self,
+                        __lhs_value: ::fayalite::__std::borrow::Cow<'_, <Self as ::fayalite::ty::Type>::SimValue>,
+                        __rhs: Self,
+                        __rhs_value: ::fayalite::__std::borrow::Cow<'_, <Self as ::fayalite::ty::Type>::SimValue>,
+                    ) -> ::fayalite::__std::primitive::bool {
+                        #value_ne_body
+                    }
+
+                    #[track_caller]
+                    fn cmp_expr_eq(
                         __lhs: ::fayalite::expr::Expr<Self>,
                         __rhs: ::fayalite::expr::Expr<Self>,
                     ) -> ::fayalite::expr::Expr<::fayalite::int::Bool> {
-                        #cmp_eq_body
+                        #expr_eq_body
                     }
-                    fn cmp_ne(
+
+                    #[track_caller]
+                    fn cmp_expr_ne(
                         __lhs: ::fayalite::expr::Expr<Self>,
                         __rhs: ::fayalite::expr::Expr<Self>,
                     ) -> ::fayalite::expr::Expr<::fayalite::int::Bool> {
-                        #cmp_ne_body
+                        #expr_ne_body
                     }
-                }
-                #[automatically_derived]
-                impl #impl_generics ::fayalite::sim::value::SimValuePartialEq<Self> for #target #type_generics
-                #sim_value_where_clause
-                {
-                    fn sim_value_eq(
-                        __lhs: &::fayalite::sim::value::SimValue<Self>,
-                        __rhs: &::fayalite::sim::value::SimValue<Self>,
-                    ) -> bool {
-                        #sim_value_eq_body
+
+                    #[track_caller]
+                    fn cmp_valueless_eq(
+                        __lhs: ::fayalite::expr::Valueless<Self>,
+                        __rhs: ::fayalite::expr::Valueless<Self>,
+                    ) -> ::fayalite::expr::Valueless<::fayalite::int::Bool> {
+                        #valueless_eq_body
+                    }
+
+                    #[track_caller]
+                    fn cmp_valueless_ne(
+                        __lhs: ::fayalite::expr::Valueless<Self>,
+                        __rhs: ::fayalite::expr::Valueless<Self>,
+                    ) -> ::fayalite::expr::Valueless<::fayalite::int::Bool> {
+                        #valueless_ne_body
                     }
                 }
             }

crates/fayalite-proc-macros-impl/src/hdl_enum.rs

@@ -1024,16 +1024,26 @@ impl ToTokens for ParsedEnum {
                         <::fayalite::int::Bool as ::fayalite::ty::StaticType>::TYPE_PROPERTIES;
                 }
                 #[automatically_derived]
-                impl #static_impl_generics ::fayalite::sim::value::ToSimValue
+                impl #static_impl_generics ::fayalite::expr::ValueType
                 for #sim_value_ident #static_type_generics
                 #static_where_clause
                 {
                     type Type = #target #static_type_generics;
+                    type ValueCategory = ::fayalite::expr::value_category::ValueCategorySimValue;
 
+                    fn ty(&self) -> <Self as ::fayalite::expr::ValueType>::Type {
+                        ::fayalite::ty::StaticType::TYPE
+                    }
+                }
+                #[automatically_derived]
+                impl #static_impl_generics ::fayalite::sim::value::ToSimValue
+                for #sim_value_ident #static_type_generics
+                #static_where_clause
+                {
                     fn to_sim_value(
                         &self,
                     ) -> ::fayalite::sim::value::SimValue<
-                        <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                        <Self as ::fayalite::expr::ValueType>::Type,
                     > {
                         ::fayalite::sim::value::SimValue::from_value(
                             ::fayalite::ty::StaticType::TYPE,
@@ -1043,7 +1053,7 @@ impl ToTokens for ParsedEnum {
                     fn into_sim_value(
                         self,
                     ) -> ::fayalite::sim::value::SimValue<
-                        <Self as ::fayalite::sim::value::ToSimValue>::Type,
+                        <Self as ::fayalite::expr::ValueType>::Type,
                     > {
                         ::fayalite::sim::value::SimValue::from_value(
                             ::fayalite::ty::StaticType::TYPE,

crates/fayalite-proc-macros-impl/src/lib.rs

@@ -887,7 +887,13 @@ pub(crate) fn outline_generated(contents: TokenStream, prefix: &str) -> TokenStr
         }
     }
     let _print_on_panic = PrintOnPanic(&contents);
-    let contents = prettyplease::unparse(&parse_quote! { #contents });
+    let mut parse_err = None;
+    let (Ok(contents) | Err(contents)) = syn::parse2(contents.clone())
+        .map(|file| prettyplease::unparse(&file))
+        .map_err(|e| {
+            parse_err = Some(e);
+            contents.to_string()
+        });
     let hash = <sha2::Sha256 as sha2::Digest>::digest(&contents);
     let hash = base16ct::HexDisplay(&hash[..5]);
     file.write_all(contents.as_bytes()).unwrap();
@@ -899,9 +905,26 @@ pub(crate) fn outline_generated(contents: TokenStream, prefix: &str) -> TokenStr
             e.unwrap();
         }
     }
-    eprintln!("generated {}", dest_file.display());
+    let log_msg = if let Some(parse_err) = parse_err {
+        format!(
+            "fayalite-proc-macros-impl internal error:\nfailed to parse generated output: {parse_err}\nunformatted output is in: {}\n",
+            dest_file.display()
+        )
+    } else {
+        format!("generated {}\n", dest_file.display())
+    };
+    // write message atomically if possible
+    let mut stderr = std::io::stderr().lock();
+    let write_result = stderr.write_all(log_msg.as_bytes());
+    let flush_result = stderr.flush();
+    drop(stderr); // unlock before we try to panic
+    write_result.unwrap();
+    flush_result.unwrap();
+    std::io::stderr()
+        .lock()
+        .write_all(log_msg.as_bytes())
+        .unwrap();
     let dest_file = dest_file.to_str().unwrap();
-
     quote! {
         include!(#dest_file);
     }

crates/fayalite-proc-macros-impl/src/module/transform_body/expand_aggregate_literals.rs

@@ -88,6 +88,9 @@ impl Visitor<'_> {
                 field.expr = parse_quote_spanned! {field.member.span()=>
                     ::fayalite::sim::value::ToSimValue::to_sim_value(&(#expr))
                 };
+                field
+                    .colon_token
+                    .get_or_insert(Token![:](field.member.span()));
             }
             return parse_quote_spanned! {name_span=>
                 {

crates/fayalite-proc-macros-impl/src/module/transform_body/expand_match.rs

@@ -10,7 +10,7 @@ use crate::{
 };
 use proc_macro2::{Span, TokenStream};
 use quote::{ToTokens, TokenStreamExt, format_ident, quote_spanned};
-use std::collections::BTreeSet;
+use std::collections::BTreeMap;
 use syn::{
     Arm, Attribute, Expr, ExprMatch, FieldPat, Ident, Local, Member, Pat, PatIdent, PatOr,
     PatParen, PatPath, PatRest, PatStruct, PatTuple, PatTupleStruct, PatWild, Path, PathSegment,
@@ -24,65 +24,65 @@ use syn::{
 
 macro_rules! visit_trait {
     (
-        $($vis:vis fn $fn:ident($state:ident: _, $value:ident: &$Value:ty) $block:block)*
+        $($vis:vis fn $fn:ident($state:ident: _, $value:ident: &mut $Value:ty) $block:block)*
     ) => {
         trait VisitMatchPat<'a> {
-            $(fn $fn(&mut self, $value: &'a $Value) {
+            $(fn $fn(&mut self, $value: &'a mut $Value) {
                 $fn(self, $value);
             })*
         }
 
-        $($vis fn $fn<'a>($state: &mut (impl ?Sized + VisitMatchPat<'a>), $value: &'a $Value) $block)*
+        $($vis fn $fn<'a>($state: &mut (impl ?Sized + VisitMatchPat<'a>), $value: &'a mut $Value) $block)*
     };
 }
 
 visit_trait! {
-    fn visit_match_pat_binding(_state: _, v: &MatchPatBinding) {
-        let MatchPatBinding { ident: _ } = v;
+    fn visit_match_pat_binding(_state: _, v: &mut MatchPatBinding) {
+        let MatchPatBinding { mutability: _, ident: _ } = v;
     }
-    fn visit_match_pat_wild(_state: _, v: &MatchPatWild) {
+    fn visit_match_pat_wild(_state: _, v: &mut MatchPatWild) {
         let MatchPatWild { underscore_token: _ } = v;
     }
-    fn visit_match_pat_rest(_state: _, v: &MatchPatRest) {
+    fn visit_match_pat_rest(_state: _, v: &mut MatchPatRest) {
         let MatchPatRest { dot2_token: _ } = v;
     }
-    fn visit_match_pat_paren(state: _, v: &MatchPatParen<MatchPat>) {
+    fn visit_match_pat_paren(state: _, v: &mut MatchPatParen<MatchPat>) {
         let MatchPatParen { paren_token: _, pat } = v;
         state.visit_match_pat(pat);
     }
-    fn visit_match_pat_paren_simple(state: _, v: &MatchPatParen<MatchPatSimple>) {
+    fn visit_match_pat_paren_simple(state: _, v: &mut MatchPatParen<MatchPatSimple>) {
         let MatchPatParen { paren_token: _, pat } = v;
         state.visit_match_pat_simple(pat);
     }
-    fn visit_match_pat_or(state: _, v: &MatchPatOr<MatchPat>) {
+    fn visit_match_pat_or(state: _, v: &mut MatchPatOr<MatchPat>) {
         let MatchPatOr { leading_vert: _, cases } = v;
         for v in cases {
             state.visit_match_pat(v);
         }
     }
-    fn visit_match_pat_or_simple(state: _, v: &MatchPatOr<MatchPatSimple>) {
+    fn visit_match_pat_or_simple(state: _, v: &mut MatchPatOr<MatchPatSimple>) {
         let MatchPatOr { leading_vert: _, cases } = v;
         for v in cases {
             state.visit_match_pat_simple(v);
         }
     }
-    fn visit_match_pat_struct_field(state: _, v: &MatchPatStructField) {
+    fn visit_match_pat_struct_field(state: _, v: &mut MatchPatStructField) {
         let MatchPatStructField { field_name: _, colon_token: _, pat } = v;
         state.visit_match_pat_simple(pat);
     }
-    fn visit_match_pat_struct(state: _, v: &MatchPatStruct) {
+    fn visit_match_pat_struct(state: _, v: &mut MatchPatStruct) {
         let MatchPatStruct { match_span: _, path: _, brace_token: _, fields, rest: _ } = v;
         for v in fields {
             state.visit_match_pat_struct_field(v);
         }
     }
-    fn visit_match_pat_tuple(state: _, v: &MatchPatTuple) {
+    fn visit_match_pat_tuple(state: _, v: &mut MatchPatTuple) {
         let MatchPatTuple { paren_token: _, fields } = v;
         for v in fields {
             state.visit_match_pat_simple(v);
         }
     }
-    fn visit_match_pat_enum_variant(state: _, v: &MatchPatEnumVariant) {
+    fn visit_match_pat_enum_variant(state: _, v: &mut MatchPatEnumVariant) {
         let MatchPatEnumVariant {
             match_span:_,
             sim:_,
@@ -95,7 +95,7 @@ visit_trait! {
             state.visit_match_pat_simple(v);
         }
     }
-    fn visit_match_pat_simple(state: _, v: &MatchPatSimple) {
+    fn visit_match_pat_simple(state: _, v: &mut MatchPatSimple) {
         match v {
             MatchPatSimple::Paren(v) => state.visit_match_pat_paren_simple(v),
             MatchPatSimple::Or(v) => state.visit_match_pat_or_simple(v),
@@ -104,7 +104,7 @@ visit_trait! {
             MatchPatSimple::Rest(v) => state.visit_match_pat_rest(v),
         }
     }
-    fn visit_match_pat(state: _, v: &MatchPat) {
+    fn visit_match_pat(state: _, v: &mut MatchPat) {
         match v {
             MatchPat::Simple(v) => state.visit_match_pat_simple(v),
             MatchPat::Or(v) => state.visit_match_pat_or(v),
@@ -118,13 +118,15 @@ visit_trait! {
 
 with_debug_clone_and_fold! {
     struct MatchPatBinding<> {
+        mutability: Option<Token![mut]>,
         ident: Ident,
     }
 }
 
 impl ToTokens for MatchPatBinding {
     fn to_tokens(&self, tokens: &mut TokenStream) {
-        let Self { ident } = self;
+        let Self { mutability, ident } = self;
+        mutability.to_tokens(tokens);
         ident.to_tokens(tokens);
     }
 }
@@ -211,12 +213,20 @@ impl ToTokens for MatchPatStructField {
             colon_token,
             pat,
         } = self;
-        field_name.to_tokens(tokens);
-        if let (None, MatchPatSimple::Binding(MatchPatBinding { ident })) = (colon_token, pat) {
+        if let (
+            None,
+            MatchPatSimple::Binding(MatchPatBinding {
+                mutability: _,
+                ident,
+            }),
+        ) = (colon_token, pat)
+        {
             if field_name == ident {
+                pat.to_tokens(tokens);
                 return;
             }
         }
+        field_name.to_tokens(tokens);
         colon_token
             .unwrap_or_else(|| Token![:](field_name.span()))
             .to_tokens(tokens);
@@ -450,7 +460,7 @@ trait ParseMatchPat: Sized {
             Pat::Ident(PatIdent {
                 attrs: _,
                 by_ref,
-                mutability,
+                mut mutability,
                 ident,
                 subpat,
             }) => {
@@ -459,10 +469,13 @@ trait ParseMatchPat: Sized {
                         .errors
                         .error(by_ref, "ref not allowed in #[hdl] patterns");
                 }
-                if let Some(mutability) = mutability {
-                    state
-                        .errors
-                        .error(mutability, "mut not allowed in #[hdl] patterns");
+                if let Some(mut_token) = mutability {
+                    if state.sim.is_none() {
+                        state
+                            .errors
+                            .error(mut_token, "mut not allowed in #[hdl] patterns");
+                        mutability = None; // avoid duplicate errors
+                    }
                 }
                 if let Some((at_token, _)) = subpat {
                     state
@@ -474,18 +487,26 @@ trait ParseMatchPat: Sized {
                         variant_path,
                         enum_path,
                         variant_name,
-                    }) => Self::enum_variant(
-                        state,
-                        MatchPatEnumVariant {
-                            match_span: state.match_span,
-                            sim: state.sim,
-                            variant_path,
-                            enum_path,
-                            variant_name,
-                            field: None,
-                        },
-                    ),
+                    }) => {
+                        if let Some(mut_token) = mutability {
+                            state
+                                .errors
+                                .error(mut_token, "mut not allowed on unit variants");
+                        }
+                        Self::enum_variant(
+                            state,
+                            MatchPatEnumVariant {
+                                match_span: state.match_span,
+                                sim: state.sim,
+                                variant_path,
+                                enum_path,
+                                variant_name,
+                                field: None,
+                            },
+                        )
+                    }
                     Err(ident) => Ok(Self::simple(MatchPatSimple::Binding(MatchPatBinding {
+                        mutability,
                         ident,
                     }))),
                 }
@@ -980,15 +1001,16 @@ struct HdlMatchParseState<'a> {
 
 struct HdlLetPatVisitState<'a> {
     errors: &'a mut Errors,
-    bindings: BTreeSet<&'a Ident>,
+    bindings: BTreeMap<Ident, MatchPatBinding>,
 }
 
 impl<'a> VisitMatchPat<'a> for HdlLetPatVisitState<'a> {
-    fn visit_match_pat_binding(&mut self, v: &'a MatchPatBinding) {
-        self.bindings.insert(&v.ident);
+    fn visit_match_pat_binding(&mut self, v: &'a mut MatchPatBinding) {
+        self.bindings.insert(v.ident.clone(), v.clone());
+        v.mutability = None;
     }
 
-    fn visit_match_pat_or(&mut self, v: &'a MatchPatOr<MatchPat>) {
+    fn visit_match_pat_or(&mut self, v: &'a mut MatchPatOr<MatchPat>) {
         if let Some(first_inner_vert) = v.first_inner_vert() {
             self.errors.error(
                 first_inner_vert,
@@ -998,7 +1020,7 @@ impl<'a> VisitMatchPat<'a> for HdlLetPatVisitState<'a> {
         visit_match_pat_or(self, v);
     }
 
-    fn visit_match_pat_or_simple(&mut self, v: &'a MatchPatOr<MatchPatSimple>) {
+    fn visit_match_pat_or_simple(&mut self, v: &'a mut MatchPatOr<MatchPatSimple>) {
         if let Some(first_inner_vert) = v.first_inner_vert() {
             self.errors.error(
                 first_inner_vert,
@@ -1008,7 +1030,7 @@ impl<'a> VisitMatchPat<'a> for HdlLetPatVisitState<'a> {
         visit_match_pat_or_simple(self, v);
     }
 
-    fn visit_match_pat_enum_variant(&mut self, v: &'a MatchPatEnumVariant) {
+    fn visit_match_pat_enum_variant(&mut self, v: &'a mut MatchPatEnumVariant) {
         self.errors.error(v, "refutable pattern in let statement");
     }
 }
@@ -1048,7 +1070,7 @@ impl Visitor<'_> {
                 .error(else_, "#[hdl] let ... else { ... } is not implemented");
             return empty_let();
         }
-        let Ok(pat) = MatchPat::parse(
+        let Ok(mut pat) = MatchPat::parse(
             &mut HdlMatchParseState {
                 sim,
                 match_span: span,
@@ -1060,20 +1082,27 @@ impl Visitor<'_> {
         };
         let mut state = HdlLetPatVisitState {
             errors: &mut self.errors,
-            bindings: BTreeSet::new(),
+            bindings: BTreeMap::new(),
         };
-        state.visit_match_pat(&pat);
+        state.visit_match_pat(&mut pat);
         let HdlLetPatVisitState {
             errors: _,
             bindings,
         } = state;
+        let bindings_idents = bindings.keys();
+        let bindings = bindings.values();
         let retval = if sim.is_some() {
             parse_quote_spanned! {span=>
                 let (#(#bindings,)*) = {
                     type __MatchTy<T> = <T as ::fayalite::ty::Type>::SimValue;
-                    let __match_value = ::fayalite::sim::value::ToSimValue::to_sim_value(&(#expr));
-                    #let_token #pat #eq_token ::fayalite::sim::value::SimValue::into_value(__match_value) #semi_token
-                    (#(#bindings,)*)
+                    let __match_value = #expr;
+                    let __match_value = {
+                        use ::fayalite::sim::value::match_sim_value::*;
+                        // use method syntax to deduce the correct trait to call
+                        ::fayalite::sim::value::match_sim_value::MatchSimValueHelper::new(__match_value).__fayalite_match_sim_value()
+                    };
+                    #let_token #pat #eq_token __match_value #semi_token
+                    (#(#bindings_idents,)*)
                 };
             }
         } else {
@@ -1105,7 +1134,7 @@ impl Visitor<'_> {
                             __match_variant,
                         );
                     #let_token #pat #eq_token __match_variant #semi_token
-                    (#(#bindings,)* __scope,)
+                    (#(#bindings_idents,)* __scope,)
                 };
             }
         };
@@ -1142,8 +1171,13 @@ impl Visitor<'_> {
             quote_spanned! {span=>
                 {
                     type __MatchTy<T> = <T as ::fayalite::ty::Type>::SimValue;
-                    let __match_expr = ::fayalite::sim::value::ToSimValue::to_sim_value(&(#expr));
-                    #match_token ::fayalite::sim::value::SimValue::into_value(__match_expr) {
+                    let __match_value = #expr;
+                    let __match_value = {
+                        use ::fayalite::sim::value::match_sim_value::*;
+                        // use method syntax to deduce the correct trait to call
+                        ::fayalite::sim::value::match_sim_value::MatchSimValueHelper::new(__match_value).__fayalite_match_sim_value()
+                    };
+                    #match_token __match_value {
                         #(#arms)*
                     }
                 }

crates/fayalite/examples/blinky.rs

@@ -12,7 +12,7 @@ fn blinky(platform_io_builder: PlatformIOBuilder<'_>) {
         clk: clk_input.clk,
         rst,
     };
-    let max_value = (Expr::ty(clk_input).frequency() / 2.0).round_ties_even() as u64 - 1;
+    let max_value = (clk_input.ty().frequency() / 2.0).round_ties_even() as u64 - 1;
     let int_ty = UInt::range_inclusive(0..=max_value);
     #[hdl]
     let counter_reg: UInt = reg_builder().clock_domain(cd).reset(0u8.cast_to(int_ty));

crates/fayalite/examples/tx_only_uart.rs

@@ -105,7 +105,7 @@ fn tx_only_uart(
     connect(tx, tx_bits[uart_state_reg]);
 
     #[hdl]
-    if uart_state_reg.cmp_eq(Expr::ty(tx_bits).len() - 1) {
+    if uart_state_reg.cmp_eq(tx_bits.ty().len() - 1) {
         connect(next_uart_state, 0_hdl_u4);
         let next_addr_val = addr_reg + 1u8;
         #[hdl]

crates/fayalite/src/_docs/modules/module_bodies/hdl_let_statements/destructuring.rs

@@ -31,3 +31,81 @@
 //!     }
 //! }
 //! ```
+//!
+//! You can also use `#[hdl(sim)] let` to destructure [`SimValue`]s (or anything that implements [`ToSimValue`]).
+//!
+//! [`SimValue`]: crate::sim::value::SimValue
+//! [`ToSimValue`]: crate::sim::value::ToSimValue
+//!
+//! ```
+//! # use fayalite::prelude::*;
+//! #[hdl]
+//! struct MyStruct<T> {
+//!     a: UInt<8>,
+//!     b: Bool,
+//!     c: T,
+//! }
+//!
+//! #[hdl]
+//! fn destructure<T: Type>(v: SimValue<MyStruct<T>>) {
+//!     #[hdl(sim)]
+//!     let MyStruct::<T> {
+//!         a,
+//!         mut b,
+//!         c,
+//!     } = v;
+//!
+//!     // that gives these types:
+//!     let _: SimValue<UInt<8>> = a;
+//!     let _: SimValue<Bool> = b;
+//!     let _: SimValue<T> = c;
+//!     *b = false; // can modify b since mut was used
+//! }
+//!
+//! #[hdl]
+//! fn destructure_ref<'a, T: Type>(v: &'a SimValue<MyStruct<T>>) {
+//!     #[hdl(sim)]
+//!     let MyStruct::<T> {
+//!         a,
+//!         b,
+//!         c,
+//!     } = v;
+//!
+//!     // that gives these types:
+//!     let _: &'a SimValue<UInt<8>> = a;
+//!     let _: &'a SimValue<Bool> = b;
+//!     let _: &'a SimValue<T> = c;
+//! }
+//!
+//! #[hdl]
+//! fn destructure_mut<'a, T: Type>(v: &'a mut SimValue<MyStruct<T>>) {
+//!     #[hdl(sim)]
+//!     let MyStruct::<T> {
+//!         a,
+//!         b,
+//!         c,
+//!     } = v;
+//!
+//!     **b = true; // you can modify v by modifying b which borrows from it
+//!
+//!     // that gives these types:
+//!     let _: &'a mut SimValue<UInt<8>> = a;
+//!     let _: &'a mut SimValue<Bool> = b;
+//!     let _: &'a mut SimValue<T> = c;
+//! }
+//!
+//! #[hdl]
+//! fn destructure_to_sim_value<'a, T: Type>(v: impl ToSimValue<Type = MyStruct<T>>) {
+//!     #[hdl(sim)]
+//!     let MyStruct::<T> {
+//!         a,
+//!         b,
+//!         c,
+//!     } = v;
+//!
+//!     // that gives these types:
+//!     let _: SimValue<UInt<8>> = a;
+//!     let _: SimValue<Bool> = b;
+//!     let _: SimValue<T> = c;
+//! }
+//! ```

crates/fayalite/src/_docs/modules/module_bodies/hdl_match_statements.rs

@@ -9,3 +9,78 @@
 //!
 //! `#[hdl] match` statements can only match one level of struct/tuple/enum pattern for now,
 //! e.g. you can match with the pattern `HdlSome(v)`, but not `HdlSome(HdlSome(_))`.
+//!
+//! You can also use `#[hdl(sim)] match` to match [`SimValue`]s (or anything that implements [`ToSimValue`]).
+//!
+//! `#[hdl(sim)] match` statements' bodies may have any type, unlike `#[hdl] match`.
+//!
+//! [`SimValue`]: crate::sim::value::SimValue
+//! [`ToSimValue`]: crate::sim::value::ToSimValue
+//!
+//! ```
+//! # use fayalite::prelude::*;
+//! #[hdl]
+//! enum MyEnum<T> {
+//!     A,
+//!     B(Bool),
+//!     C(T),
+//! }
+//!
+//! #[hdl]
+//! fn match_move<T: Type>(v: SimValue<MyEnum<T>>) -> String {
+//!     #[hdl(sim)]
+//!     match v {
+//!         MyEnum::<T>::A => String::from("got A"),
+//!         MyEnum::<T>::B(mut b) => {
+//!             let _: SimValue<Bool> = b; // b has this type
+//!             let text = format!("got B({b})");
+//!             *b = true; // can modify b since mut was used
+//!             text
+//!         }
+//!         _ => String::from("something else"),
+//!     }
+//! }
+//!
+//! #[hdl]
+//! fn match_ref<'a, T: Type>(v: &'a SimValue<MyEnum<T>>) -> u32 {
+//!     #[hdl(sim)]
+//!     match v {
+//!         MyEnum::<T>::A => 1,
+//!         MyEnum::<T>::B(b) => {
+//!             let _: &'a SimValue<Bool> = b; // b has this type
+//!             println!("got B({b})");
+//!             5
+//!         }
+//!         _ => 42,
+//!     }
+//! }
+//!
+//! #[hdl]
+//! fn match_mut<'a, T: Type>(v: &'a mut SimValue<MyEnum<T>>) -> Option<&'a mut SimValue<T>> {
+//!     #[hdl(sim)]
+//!     match v {
+//!         MyEnum::<T>::A => None,
+//!         MyEnum::<T>::B(b) => {
+//!             println!("got B({b})");
+//!             **b = true; // you can modify v by modifying b which borrows from it
+//!             let _: &'a mut SimValue<Bool> = b; // b has this type
+//!             None
+//!         }
+//!         MyEnum::<T>::C(v) => Some(v), // you can return matched values
+//!         _ => None, // HDL enums can have invalid discriminants, so we need this extra match arm
+//!     }
+//! }
+//!
+//! #[hdl]
+//! fn match_to_sim_value<'a, T: Type>(v: impl ToSimValue<Type = MyEnum<T>>) {
+//!     #[hdl(sim)]
+//!     match v {
+//!         MyEnum::<T>::A => println!("got A"),
+//!         MyEnum::<T>::B(b) => {
+//!             let _: SimValue<Bool> = b; // b has this type
+//!             println!("got B({b})");
+//!         }
+//!         _ => println!("something else"),
+//!     }
+//! }
+//! ```

crates/fayalite/src/array.rs

@@ -3,13 +3,13 @@
 
 use crate::{
     expr::{
-        CastToBits, Expr, HdlPartialEq, ReduceBits, ToExpr,
-        ops::{ArrayLiteral, ExprFromIterator, ExprIntoIterator, ExprPartialEq},
+        CastToBits, Expr, HdlPartialEq, HdlPartialEqImpl, ReduceBits, ToExpr, ValueType, Valueless,
+        ops::{ArrayLiteral, ExprFromIterator, ExprIntoIterator},
     },
     int::{Bool, DYN_SIZE, DynSize, KnownSize, Size, SizeType},
     intern::{Intern, Interned, LazyInterned},
     module::transform::visit::{Fold, Folder, Visit, Visitor},
-    sim::value::{SimValue, SimValuePartialEq},
+    sim::value::SimValue,
     source_location::SourceLocation,
     ty::{
         CanonicalType, MatchVariantWithoutScope, OpaqueSimValueSlice, OpaqueSimValueWriter,
@@ -19,7 +19,7 @@ use crate::{
     util::ConstUsize,
 };
 use serde::{Deserialize, Deserializer, Serialize, Serializer, de::Error};
-use std::{iter::FusedIterator, ops::Index};
+use std::{borrow::Cow, iter::FusedIterator, ops::Index};
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash)]
 pub struct ArrayType<T: Type = CanonicalType, Len: Size = DynSize> {
@@ -221,7 +221,7 @@ impl<T: Type, Len: Size> Type for ArrayType<T, Len> {
         let value = AsMut::<[SimValue<T>]>::as_mut(value);
         assert_eq!(self.len(), value.len());
         for element_value in value {
-            assert_eq!(SimValue::ty(element_value), element_ty);
+            assert_eq!(element_value.ty(), element_ty);
             let (element_opaque, rest) = opaque.split_at(element_size);
             SimValue::opaque_mut(element_value).clone_from_slice(element_opaque);
             opaque = rest;
@@ -238,7 +238,7 @@ impl<T: Type, Len: Size> Type for ArrayType<T, Len> {
         let value = AsRef::<[SimValue<T>]>::as_ref(value);
         assert_eq!(self.len(), value.len());
         for element_value in value {
-            assert_eq!(SimValue::ty(element_value), element_ty);
+            assert_eq!(element_value.ty(), element_ty);
             writer.fill_prefix_with(element_size, |writer| {
                 writer.fill_cloned_from_slice(SimValue::opaque(element_value).as_slice())
             });
@@ -326,14 +326,30 @@ impl<T: Type, L: SizeType> Index<L> for ArrayWithoutLen<T> {
     }
 }
 
-impl<Lhs: Type, Rhs: Type, Len: Size> ExprPartialEq<ArrayType<Rhs, Len>> for ArrayType<Lhs, Len>
+impl<Lhs: Type, Rhs: Type, Len: Size> HdlPartialEqImpl<ArrayType<Rhs, Len>> for ArrayType<Lhs, Len>
 where
-    Lhs: ExprPartialEq<Rhs>,
+    Lhs: HdlPartialEqImpl<Rhs>,
 {
-    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
-        let lhs_ty = Expr::ty(lhs);
-        let rhs_ty = Expr::ty(rhs);
-        assert_eq!(lhs_ty.len(), rhs_ty.len());
+    fn cmp_value_eq(
+        lhs: Self,
+        lhs_value: Cow<'_, Self::SimValue>,
+        rhs: ArrayType<Rhs, Len>,
+        rhs_value: Cow<'_, <ArrayType<Rhs, Len> as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs.len(), rhs.len());
+        let lhs = lhs.element();
+        let rhs = rhs.element();
+        let lhs_value: &[_] = (*lhs_value).as_ref();
+        let rhs_value: &[_] = (*rhs_value).as_ref();
+        for (lhs_value, rhs_value) in lhs_value.iter().zip(rhs_value) {
+            if !Lhs::cmp_value_eq(lhs, Cow::Borrowed(lhs_value), rhs, Cow::Borrowed(rhs_value)) {
+                return false;
+            }
+        }
+        true
+    }
+    fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
+        assert_eq!(lhs.ty().len(), rhs.ty().len());
         lhs.into_iter()
             .zip(rhs)
             .map(|(l, r)| l.cmp_eq(r))
@@ -341,11 +357,8 @@ where
             .cast_to_bits()
             .all_one_bits()
     }
-
-    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
-        let lhs_ty = Expr::ty(lhs);
-        let rhs_ty = Expr::ty(rhs);
-        assert_eq!(lhs_ty.len(), rhs_ty.len());
+    fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<ArrayType<Rhs, Len>>) -> Expr<Bool> {
+        assert_eq!(lhs.ty().len(), rhs.ty().len());
         lhs.into_iter()
             .zip(rhs)
             .map(|(l, r)| l.cmp_ne(r))
@@ -353,17 +366,19 @@ where
             .cast_to_bits()
             .any_one_bits()
     }
-}
-
-impl<Lhs: Type, Rhs: Type, Len: Size> SimValuePartialEq<ArrayType<Rhs, Len>> for ArrayType<Lhs, Len>
-where
-    Lhs: SimValuePartialEq<Rhs>,
-{
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<ArrayType<Rhs, Len>>) -> bool {
-        AsRef::<[_]>::as_ref(&**this)
-            .iter()
-            .zip(AsRef::<[_]>::as_ref(&**other))
-            .all(|(l, r)| SimValuePartialEq::sim_value_eq(l, r))
+    fn cmp_valueless_eq(
+        lhs: Valueless<Self>,
+        rhs: Valueless<ArrayType<Rhs, Len>>,
+    ) -> Valueless<Bool> {
+        assert_eq!(lhs.ty().len(), rhs.ty().len());
+        Valueless::new(Bool)
+    }
+    fn cmp_valueless_ne(
+        lhs: Valueless<Self>,
+        rhs: Valueless<ArrayType<Rhs, Len>>,
+    ) -> Valueless<Bool> {
+        assert_eq!(lhs.ty().len(), rhs.ty().len());
+        Valueless::new(Bool)
     }
 }
 
@@ -374,7 +389,7 @@ impl<T: Type, Len: Size> ExprIntoIterator for ArrayType<T, Len> {
     fn expr_into_iter(e: Expr<Self>) -> Self::ExprIntoIter {
         ExprArrayIter {
             base: e,
-            indexes: 0..Expr::ty(e).len(),
+            indexes: 0..e.ty().len(),
         }
     }
 }

crates/fayalite/src/bundle.rs

@@ -3,12 +3,14 @@
 
 use crate::{
     expr::{
-        CastToBits, Expr, ReduceBits, ToExpr,
-        ops::{ArrayLiteral, BundleLiteral, ExprPartialEq},
+        CastToBits, Expr, HdlPartialEqImpl, ReduceBits, ToExpr, ToSimValueInner, ValueType,
+        Valueless,
+        ops::{ArrayLiteral, BundleLiteral},
+        value_category::{ValueCategoryCommon, ValueCategoryExpr, ValueCategoryValue},
     },
     int::{Bool, DynSize},
     intern::{Intern, InternSlice, Interned},
-    sim::value::{SimValue, SimValuePartialEq, ToSimValue, ToSimValueWithType},
+    sim::value::{SimValue, SimValueEq, ToSimValue, ToSimValueWithType},
     source_location::SourceLocation,
     ty::{
         CanonicalType, MatchVariantWithoutScope, OpaqueSimValue, OpaqueSimValueSize,
@@ -18,7 +20,7 @@ use crate::{
     util::HashMap,
 };
 use serde::{Deserialize, Serialize};
-use std::{fmt, marker::PhantomData};
+use std::{borrow::Cow, fmt, marker::PhantomData};
 
 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, Serialize, Deserialize)]
 pub struct BundleField {
@@ -317,7 +319,7 @@ impl<'a> BundleSimValueFromOpaque<'a> {
     #[track_caller]
     pub fn field_clone_from_opaque<T: Type>(&mut self, field_value: &mut SimValue<T>) {
         let (field_ty, field_opaque) = self.field_ty_and_opaque::<T>();
-        assert_eq!(field_ty, SimValue::ty(field_value));
+        assert_eq!(field_ty, field_value.ty());
         SimValue::opaque_mut(field_value).clone_from_slice(field_opaque);
     }
 }
@@ -353,7 +355,7 @@ impl<'a> BundleSimValueToOpaque<'a> {
         else {
             panic!("tried to write too many fields with BundleSimValueToOpaque");
         };
-        assert_eq!(T::from_canonical(ty), SimValue::ty(field_value));
+        assert_eq!(T::from_canonical(ty), field_value.ty());
         self.writer.fill_prefix_with(ty.size(), |writer| {
             writer.fill_cloned_from_slice(SimValue::opaque(field_value).as_slice())
         });
@@ -566,23 +568,54 @@ macro_rules! impl_tuples {
                 builder.finish()
             };
         }
-        impl<$($T: ToExpr,)*> ToExpr for ($($T,)*) {
+        impl<'a, $($T: ToSimValue,)*> ToSimValueInner<'a> for ($($T,)*)
+        where
+            Self: ValueType<Type = ($($T::Type,)*)>,
+        {
+            fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+                let ($($var,)*) = this;
+                Cow::Owned(($($var.to_sim_value(),)*))
+            }
+            fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+                let ($($var,)*) = this;
+                Cow::Owned(($($var.into_sim_value(),)*))
+            }
+        }
+        impl<$($T: ValueType,)*> ValueType for ($($T,)*)
+        where
+            ValueCategoryValue: ValueCategoryCommon<($($T::ValueCategory,)*)>,
+        {
             type Type = ($($T::Type,)*);
-
+            type ValueCategory = <ValueCategoryValue as ValueCategoryCommon<($($T::ValueCategory,)*)>>::Common;
+            fn ty(&self) -> Self::Type {
+                let ($($var,)*) = self;
+                ($($var.ty(),)*)
+            }
+        }
+        impl<$($T: ToExpr,)*> ToExpr for ($($T,)*)
+        where
+            Self: ValueType<Type = ($($T::Type,)*)>,
+        {
             fn to_expr(&self) -> Expr<Self::Type> {
                 let ($($var,)*) = self;
                 $(let $var = $var.to_expr();)*
-                let ty = ($(Expr::ty($var),)*);
+                let ty = ($($var.ty(),)*);
                 let field_values = [$(Expr::canonical($var)),*];
                 BundleLiteral::new(ty, field_values.intern_slice()).to_expr()
             }
         }
-        impl<$($T: Type,)*> ToExpr for TupleBuilder<($(Expr<$T>,)*)> {
+        impl<$($T: Type,)*> ValueType for TupleBuilder<($(Expr<$T>,)*)> {
             type Type = ($($T,)*);
-
+            type ValueCategory = ValueCategoryExpr;
+            fn ty(&self) -> Self::Type {
+                let ($($var,)*) = self.0;
+                ($($var.ty(),)*)
+            }
+        }
+        impl<$($T: Type,)*> ToExpr for TupleBuilder<($(Expr<$T>,)*)> {
             fn to_expr(&self) -> Expr<Self::Type> {
                 let ($($var,)*) = self.0;
-                let ty = ($(Expr::ty($var),)*);
+                let ty = ($($var.ty(),)*);
                 let field_values = [$(Expr::canonical($var)),*];
                 BundleLiteral::new(ty, field_values.intern_slice()).to_expr()
             }
@@ -618,7 +651,7 @@ macro_rules! impl_tuples {
                 };
                 let mut opaque = OpaqueSimValue::empty();
                 $(let $var = $var.into_sim_value_with_type($ty_var.ty);
-                assert_eq!(SimValue::ty(&$var), $ty_var.ty);
+                assert_eq!($var.ty(), $ty_var.ty);
                 opaque.extend_from_slice(SimValue::opaque(&$var).as_slice());
                 )*
                 SimValue::from_opaque(ty, opaque)
@@ -640,53 +673,82 @@ macro_rules! impl_tuples {
                 SimValue::from_value(ty, ($($var,)*))
             }
         }
-        impl<$($T: ToSimValue,)*> ToSimValue for ($($T,)*) {
-            type Type = ($($T::Type,)*);
+        impl<$($T: ToSimValue,)*> ToSimValue for ($($T,)*)
+        where
+            Self: ValueType<Type = ($($T::Type,)*)>,
+        {
             #[track_caller]
             fn to_sim_value(&self) -> SimValue<Self::Type> {
                 let ($($var,)*) = self;
                 $(let $var = $var.to_sim_value();)*
-                SimValue::from_value(($(SimValue::ty(&$var),)*), ($($var,)*))
+                SimValue::from_value(($($var.ty(),)*), ($($var,)*))
             }
             #[track_caller]
             fn into_sim_value(self) -> SimValue<Self::Type> {
                 let ($($var,)*) = self;
                 $(let $var = $var.to_sim_value();)*
-                SimValue::from_value(($(SimValue::ty(&$var),)*), ($($var,)*))
+                SimValue::from_value(($($var.ty(),)*), ($($var,)*))
             }
         }
-        impl<$($Lhs: Type + ExprPartialEq<$Rhs>, $Rhs: Type,)*> ExprPartialEq<($($Rhs,)*)> for ($($Lhs,)*) {
-            fn cmp_eq(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
+        impl<$($Lhs: Type + HdlPartialEqImpl<$Rhs>, $Rhs: Type,)*> HdlPartialEqImpl<($($Rhs,)*)> for ($($Lhs,)*) {
+            #[track_caller]
+            fn cmp_value_eq(
+                lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                rhs: ($($Rhs,)*),
+                rhs_value: Cow<'_, <($($Rhs,)*) as Type>::SimValue>,
+            ) -> bool {
+                #![allow(unused_variables)]
+                let ($($lhs_var,)*) = &*lhs_value;
+                let ($($rhs_var,)*) = &*rhs_value;
+                let retval = true;
+                $(let retval = retval && $Lhs::cmp_value_eq(lhs.$num, Cow::Borrowed($lhs_var), rhs.$num, Cow::Borrowed($rhs_var));)*
+                retval
+            }
+
+            #[track_caller]
+            fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
                 let ($($lhs_var,)*) = *lhs;
                 let ($($rhs_var,)*) = *rhs;
                 ArrayLiteral::<Bool, DynSize>::new(
                     Bool,
-                    FromIterator::from_iter([$(Expr::canonical(ExprPartialEq::cmp_eq($lhs_var, $rhs_var)),)*]),
+                    FromIterator::from_iter([$(Expr::canonical($Lhs::cmp_expr_eq($lhs_var, $rhs_var)),)*]),
                 )
                 .cast_to_bits()
                 .all_one_bits()
             }
 
-            fn cmp_ne(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
+            #[track_caller]
+            fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<($($Rhs,)*)>) -> Expr<Bool> {
                 let ($($lhs_var,)*) = *lhs;
                 let ($($rhs_var,)*) = *rhs;
                 ArrayLiteral::<Bool, DynSize>::new(
                     Bool,
-                    FromIterator::from_iter([$(Expr::canonical(ExprPartialEq::cmp_ne($lhs_var, $rhs_var)),)*]),
+                    FromIterator::from_iter([$(Expr::canonical($Lhs::cmp_expr_ne($lhs_var, $rhs_var)),)*]),
                 )
                 .cast_to_bits()
                 .any_one_bits()
             }
-        }
-        impl<$($Lhs: SimValuePartialEq<$Rhs>, $Rhs: Type,)*> SimValuePartialEq<($($Rhs,)*)> for ($($Lhs,)*) {
-            fn sim_value_eq(lhs: &SimValue<Self>, rhs: &SimValue<($($Rhs,)*)>) -> bool {
-                let ($($lhs_var,)*) = &**lhs;
-                let ($($rhs_var,)*) = &**rhs;
-                let retval = true;
-                $(let retval = retval && $lhs_var == $rhs_var;)*
-                retval
+
+            #[track_caller]
+            fn cmp_valueless_eq(lhs: Valueless<Self>, rhs: Valueless<($($Rhs,)*)>) -> Valueless<Bool> {
+                let ($($lhs_var,)*) = lhs.ty();
+                let ($($rhs_var,)*) = rhs.ty();
+                // let them check that the types can be compared
+                $($Lhs::cmp_valueless_eq(Valueless::new($lhs_var), Valueless::new($rhs_var));)*
+                Valueless::new(Bool)
+            }
+
+            #[track_caller]
+            fn cmp_valueless_ne(lhs: Valueless<Self>, rhs: Valueless<($($Rhs,)*)>) -> Valueless<Bool> {
+                let ($($lhs_var,)*) = lhs.ty();
+                let ($($rhs_var,)*) = rhs.ty();
+                // let them check that the types can be compared
+                $($Lhs::cmp_valueless_ne(Valueless::new($lhs_var), Valueless::new($rhs_var));)*
+                Valueless::new(Bool)
             }
         }
+        impl<$($T: SimValueEq + HdlPartialEqImpl<$T>,)*> SimValueEq for ($($T,)*) {}
     };
     ([$($lhs:tt)*] [$rhs_first:tt $($rhs:tt)*]) => {
         impl_tuples!([$($lhs)*] []);
@@ -775,9 +837,16 @@ impl<T: ?Sized + Send + Sync + 'static> Default for PhantomDataBuilder<T> {
     }
 }
 
-impl<T: ?Sized + Send + Sync + 'static> ToExpr for PhantomDataBuilder<T> {
+impl<T: ?Sized + Send + Sync + 'static> ValueType for PhantomDataBuilder<T> {
     type Type = PhantomData<T>;
+    type ValueCategory = ValueCategoryValue;
 
+    fn ty(&self) -> Self::Type {
+        PhantomData
+    }
+}
+
+impl<T: ?Sized + Send + Sync + 'static> ToExpr for PhantomDataBuilder<T> {
     fn to_expr(&self) -> Expr<Self::Type> {
         PhantomData.to_expr()
     }
@@ -803,17 +872,22 @@ impl<T: ?Sized + Send + Sync + 'static> StaticType for PhantomData<T> {
     const MASK_TYPE_PROPERTIES: TypeProperties = <()>::TYPE_PROPERTIES;
 }
 
-impl<T: ?Sized + Send + Sync + 'static> ToExpr for PhantomData<T> {
+impl<T: ?Sized + Send + Sync + 'static> ValueType for PhantomData<T> {
     type Type = PhantomData<T>;
+    type ValueCategory = ValueCategoryValue;
 
+    fn ty(&self) -> Self::Type {
+        PhantomData
+    }
+}
+
+impl<T: ?Sized + Send + Sync + 'static> ToExpr for PhantomData<T> {
     fn to_expr(&self) -> Expr<Self::Type> {
         BundleLiteral::new(PhantomData, Interned::default()).to_expr()
     }
 }
 
 impl<T: ?Sized + Send + Sync + 'static> ToSimValue for PhantomData<T> {
-    type Type = PhantomData<T>;
-
     #[track_caller]
     fn to_sim_value(&self) -> SimValue<Self> {
         SimValue::from_value(*self, *self)

crates/fayalite/src/clock.rs

@@ -1,10 +1,11 @@
 // SPDX-License-Identifier: LGPL-3.0-or-later
 // See Notices.txt for copyright information
 use crate::{
-    expr::{Expr, ToExpr},
+    expr::{Expr, ValueType},
     hdl,
     int::Bool,
     reset::{Reset, ResetType},
+    sim::value::SimValue,
     source_location::SourceLocation,
     ty::{
         CanonicalType, OpaqueSimValueSize, OpaqueSimValueSlice, OpaqueSimValueWriter,
@@ -91,29 +92,34 @@ impl StaticType for Clock {
 }
 
 pub trait ToClock {
-    fn to_clock(&self) -> Expr<Clock>;
+    type Output: ValueType<Type = Clock>;
+    fn to_clock(&self) -> Self::Output;
 }
 
 impl<T: ?Sized + ToClock> ToClock for &'_ T {
-    fn to_clock(&self) -> Expr<Clock> {
+    type Output = T::Output;
+    fn to_clock(&self) -> Self::Output {
         (**self).to_clock()
     }
 }
 
 impl<T: ?Sized + ToClock> ToClock for &'_ mut T {
-    fn to_clock(&self) -> Expr<Clock> {
+    type Output = T::Output;
+    fn to_clock(&self) -> Self::Output {
         (**self).to_clock()
     }
 }
 
 impl<T: ?Sized + ToClock> ToClock for Box<T> {
-    fn to_clock(&self) -> Expr<Clock> {
+    type Output = T::Output;
+    fn to_clock(&self) -> Self::Output {
         (**self).to_clock()
     }
 }
 
 impl ToClock for Expr<Clock> {
-    fn to_clock(&self) -> Expr<Clock> {
+    type Output = Expr<Clock>;
+    fn to_clock(&self) -> Self::Output {
         *self
     }
 }
@@ -125,7 +131,25 @@ pub struct ClockDomain<R: ResetType = Reset> {
 }
 
 impl ToClock for bool {
-    fn to_clock(&self) -> Expr<Clock> {
-        self.to_expr().to_clock()
+    type Output = SimValue<Clock>;
+
+    fn to_clock(&self) -> Self::Output {
+        SimValue::from_value(Clock, *self)
+    }
+}
+
+impl ToClock for SimValue<Bool> {
+    type Output = SimValue<Clock>;
+
+    fn to_clock(&self) -> Self::Output {
+        SimValue::from_value(Clock, **self)
+    }
+}
+
+impl ToClock for SimValue<Clock> {
+    type Output = SimValue<Clock>;
+
+    fn to_clock(&self) -> Self::Output {
+        self.clone()
     }
 }

crates/fayalite/src/enum_.rs

@@ -2,10 +2,7 @@
 // See Notices.txt for copyright information
 
 use crate::{
-    expr::{
-        Expr, ToExpr,
-        ops::{ExprPartialEq, VariantAccess},
-    },
+    expr::{Expr, HdlPartialEq, HdlPartialEqImpl, ToExpr, ValueType, ops::VariantAccess},
     hdl,
     int::{Bool, UIntValue},
     intern::{Intern, Interned},
@@ -13,7 +10,7 @@ use crate::{
         EnumMatchVariantAndInactiveScopeImpl, EnumMatchVariantsIterImpl, Scope, connect,
         enum_match_variants_helper, incomplete_wire, wire,
     },
-    sim::value::{SimValue, SimValuePartialEq},
+    sim::value::SimValue,
     source_location::SourceLocation,
     ty::{
         CanonicalType, MatchVariantAndInactiveScope, OpaqueSimValue, OpaqueSimValueSize,
@@ -24,7 +21,7 @@ use crate::{
 };
 use bitvec::{order::Lsb0, slice::BitSlice, view::BitView};
 use serde::{Deserialize, Serialize};
-use std::{convert::Infallible, fmt, iter::FusedIterator, sync::Arc};
+use std::{borrow::Cow, convert::Infallible, fmt, iter::FusedIterator, sync::Arc};
 
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Serialize, Deserialize)]
 pub struct EnumVariant {
@@ -599,7 +596,7 @@ impl<'a> EnumSimValueFromOpaque<'a> {
         let (Some(variant_ty), variant_bits, padding_bits) = self.known_variant(true) else {
             self.usage_error(true);
         };
-        assert_eq!(SimValue::ty(value), T::from_canonical(variant_ty));
+        assert_eq!(value.ty(), T::from_canonical(variant_ty));
         SimValue::bits_mut(value)
             .bits_mut()
             .copy_from_bitslice(variant_bits);
@@ -711,7 +708,7 @@ impl<'a> EnumSimValueToOpaque<'a> {
         let Some(variant_ty) = self.variants[discriminant].ty else {
             panic!("expected variant to have no field");
         };
-        assert_eq!(SimValue::ty(value), T::from_canonical(variant_ty));
+        assert_eq!(value.ty(), T::from_canonical(variant_ty));
         self.known_variant(discriminant, Some(SimValue::opaque(value)), padding)
     }
 }
@@ -732,9 +729,38 @@ pub enum HdlOption<T: Type> {
     HdlSome(T),
 }
 
-impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> for HdlOption<Lhs> {
+impl<Lhs: Type + HdlPartialEqImpl<Rhs>, Rhs: Type> HdlPartialEqImpl<HdlOption<Rhs>>
+    for HdlOption<Lhs>
+{
+    fn cmp_value_eq(
+        lhs: Self,
+        lhs_value: Cow<'_, Self::SimValue>,
+        rhs: HdlOption<Rhs>,
+        rhs_value: Cow<'_, <HdlOption<Rhs> as Type>::SimValue>,
+    ) -> bool {
+        type SimValueMatch<T> = <T as Type>::SimValue;
+        match (&*lhs_value, &*rhs_value) {
+            (SimValueMatch::<Self>::HdlNone(_), SimValueMatch::<HdlOption<Rhs>>::HdlNone(_)) => {
+                true
+            }
+            (SimValueMatch::<Self>::HdlSome(..), SimValueMatch::<HdlOption<Rhs>>::HdlNone(_))
+            | (SimValueMatch::<Self>::HdlNone(_), SimValueMatch::<HdlOption<Rhs>>::HdlSome(..)) => {
+                false
+            }
+            (
+                SimValueMatch::<Self>::HdlSome(l, _),
+                SimValueMatch::<HdlOption<Rhs>>::HdlSome(r, _),
+            ) => HdlPartialEqImpl::cmp_value_eq(
+                lhs.HdlSome,
+                Cow::Borrowed(&**l),
+                rhs.HdlSome,
+                Cow::Borrowed(&**r),
+            ),
+        }
+    }
+
     #[hdl]
-    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
+    fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
         #[hdl]
         let cmp_eq = wire();
         #[hdl]
@@ -743,7 +769,7 @@ impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> fo
             {
                 #[hdl]
                 match rhs {
-                    HdlSome(rhs) => connect(cmp_eq, ExprPartialEq::cmp_eq(lhs, rhs)),
+                    HdlSome(rhs) => connect(cmp_eq, lhs.cmp_eq(rhs)),
                     HdlNone => connect(cmp_eq, false),
                 }
             }
@@ -760,7 +786,7 @@ impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> fo
     }
 
     #[hdl]
-    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
+    fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<HdlOption<Rhs>>) -> Expr<Bool> {
         #[hdl]
         let cmp_ne = wire();
         #[hdl]
@@ -769,7 +795,7 @@ impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> fo
             {
                 #[hdl]
                 match rhs {
-                    HdlSome(rhs) => connect(cmp_ne, ExprPartialEq::cmp_ne(lhs, rhs)),
+                    HdlSome(rhs) => connect(cmp_ne, lhs.cmp_ne(rhs)),
                     HdlNone => connect(cmp_ne, true),
                 }
             }
@@ -786,25 +812,6 @@ impl<Lhs: Type + ExprPartialEq<Rhs>, Rhs: Type> ExprPartialEq<HdlOption<Rhs>> fo
     }
 }
 
-impl<Lhs: SimValuePartialEq<Rhs>, Rhs: Type> SimValuePartialEq<HdlOption<Rhs>> for HdlOption<Lhs> {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<HdlOption<Rhs>>) -> bool {
-        type SimValueMatch<T> = <T as Type>::SimValue;
-        match (&**this, &**other) {
-            (SimValueMatch::<Self>::HdlNone(_), SimValueMatch::<HdlOption<Rhs>>::HdlNone(_)) => {
-                true
-            }
-            (SimValueMatch::<Self>::HdlSome(..), SimValueMatch::<HdlOption<Rhs>>::HdlNone(_))
-            | (SimValueMatch::<Self>::HdlNone(_), SimValueMatch::<HdlOption<Rhs>>::HdlSome(..)) => {
-                false
-            }
-            (
-                SimValueMatch::<Self>::HdlSome(l, _),
-                SimValueMatch::<HdlOption<Rhs>>::HdlSome(r, _),
-            ) => l == r,
-        }
-    }
-}
-
 #[allow(non_snake_case)]
 pub fn HdlNone<T: StaticType>() -> Expr<HdlOption<T>> {
     HdlOption[T::TYPE].HdlNone()
@@ -813,7 +820,7 @@ pub fn HdlNone<T: StaticType>() -> Expr<HdlOption<T>> {
 #[allow(non_snake_case)]
 pub fn HdlSome<T: Type>(value: impl ToExpr<Type = T>) -> Expr<HdlOption<T>> {
     let value = value.to_expr();
-    HdlOption[Expr::ty(value)].HdlSome(value)
+    HdlOption[value.ty()].HdlSome(value)
 }
 
 impl<T: Type> HdlOption<T> {
@@ -853,7 +860,7 @@ impl<T: Type> HdlOption<T> {
         let value = f(value).inspect_err(|_| {
             and_then_out.complete(()); // avoid error
         })?;
-        let and_then_out = and_then_out.complete(Expr::ty(value));
+        let and_then_out = and_then_out.complete(value.ty());
         connect(and_then_out, value);
         drop(some_scope);
         let (Wrap::<<Self as Type>::MatchVariant>::HdlNone, none_scope) =
@@ -861,7 +868,7 @@ impl<T: Type> HdlOption<T> {
         else {
             unreachable!();
         };
-        connect(and_then_out, Expr::ty(and_then_out).HdlNone());
+        connect(and_then_out, and_then_out.ty().HdlNone());
         drop(none_scope);
         Ok(and_then_out)
     }
@@ -879,8 +886,8 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn and<U: Type>(expr: Expr<Self>, opt_b: Expr<HdlOption<U>>) -> Expr<HdlOption<U>> {
         #[hdl]
-        let and_out = wire(Expr::ty(opt_b));
-        connect(and_out, Expr::ty(opt_b).HdlNone());
+        let and_out = wire(opt_b.ty());
+        connect(and_out, opt_b.ty().HdlNone());
         #[hdl]
         if let HdlSome(_) = expr {
             connect(and_out, opt_b);
@@ -894,8 +901,8 @@ impl<T: Type> HdlOption<T> {
         f: impl FnOnce(Expr<T>) -> Result<Expr<Bool>, E>,
     ) -> Result<Expr<Self>, E> {
         #[hdl]
-        let filtered = wire(Expr::ty(expr));
-        connect(filtered, Expr::ty(expr).HdlNone());
+        let filtered = wire(expr.ty());
+        connect(filtered, expr.ty().HdlNone());
         let mut f = Some(f);
         #[hdl]
         if let HdlSome(v) = expr {
@@ -969,7 +976,7 @@ impl<T: Type> HdlOption<T> {
         f: impl FnOnce(Expr<T>) -> Expr<R>,
     ) -> Expr<R> {
         #[hdl]
-        let mapped = wire(Expr::ty(default));
+        let mapped = wire(default.ty());
         let mut f = Some(f);
         #[hdl]
         match expr {
@@ -994,12 +1001,12 @@ impl<T: Type> HdlOption<T> {
         match expr {
             HdlSome(v) => {
                 let v = f.take().unwrap()(v);
-                let mapped = *retval.get_or_insert_with(|| mapped.complete(Expr::ty(v)));
+                let mapped = *retval.get_or_insert_with(|| mapped.complete(v.ty()));
                 connect(mapped, v);
             }
             HdlNone => {
                 let v = default.take().unwrap()();
-                let mapped = *retval.get_or_insert_with(|| mapped.complete(Expr::ty(v)));
+                let mapped = *retval.get_or_insert_with(|| mapped.complete(v.ty()));
                 connect(mapped, v);
             }
         }
@@ -1009,7 +1016,7 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn or(expr: Expr<Self>, opt_b: Expr<Self>) -> Expr<Self> {
         #[hdl]
-        let or_out = wire(Expr::ty(expr));
+        let or_out = wire(expr.ty());
         connect(or_out, opt_b);
         #[hdl]
         if let HdlSome(_) = expr {
@@ -1021,7 +1028,7 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn or_else(expr: Expr<Self>, f: impl FnOnce() -> Expr<Self>) -> Expr<Self> {
         #[hdl]
-        let or_else_out = wire(Expr::ty(expr));
+        let or_else_out = wire(expr.ty());
         connect(or_else_out, f());
         #[hdl]
         if let HdlSome(_) = expr {
@@ -1033,7 +1040,7 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn unwrap_or(expr: Expr<Self>, default: Expr<T>) -> Expr<T> {
         #[hdl]
-        let unwrap_or_else_out = wire(Expr::ty(default));
+        let unwrap_or_else_out = wire(default.ty());
         connect(unwrap_or_else_out, default);
         #[hdl]
         if let HdlSome(v) = expr {
@@ -1045,7 +1052,7 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn unwrap_or_else(expr: Expr<Self>, f: impl FnOnce() -> Expr<T>) -> Expr<T> {
         #[hdl]
-        let unwrap_or_else_out = wire(Expr::ty(expr).HdlSome);
+        let unwrap_or_else_out = wire(expr.ty().HdlSome);
         connect(unwrap_or_else_out, f());
         #[hdl]
         if let HdlSome(v) = expr {
@@ -1057,14 +1064,14 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn xor(expr: Expr<Self>, opt_b: Expr<Self>) -> Expr<Self> {
         #[hdl]
-        let xor_out = wire(Expr::ty(expr));
+        let xor_out = wire(expr.ty());
         #[hdl]
         if let HdlSome(_) = expr {
             #[hdl]
             if let HdlNone = opt_b {
                 connect(xor_out, expr);
             } else {
-                connect(xor_out, Expr::ty(expr).HdlNone());
+                connect(xor_out, expr.ty().HdlNone());
             }
         } else {
             connect(xor_out, opt_b);
@@ -1075,8 +1082,8 @@ impl<T: Type> HdlOption<T> {
     #[track_caller]
     pub fn zip<U: Type>(expr: Expr<Self>, other: Expr<HdlOption<U>>) -> Expr<HdlOption<(T, U)>> {
         #[hdl]
-        let zip_out = wire(HdlOption[(Expr::ty(expr).HdlSome, Expr::ty(other).HdlSome)]);
-        connect(zip_out, Expr::ty(zip_out).HdlNone());
+        let zip_out = wire(HdlOption[(expr.ty().HdlSome, other.ty().HdlSome)]);
+        connect(zip_out, zip_out.ty().HdlNone());
         #[hdl]
         if let HdlSome(l) = expr {
             #[hdl]
@@ -1093,11 +1100,11 @@ impl<T: Type> HdlOption<HdlOption<T>> {
     #[track_caller]
     pub fn flatten(expr: Expr<Self>) -> Expr<HdlOption<T>> {
         #[hdl]
-        let flattened = wire(Expr::ty(expr).HdlSome);
+        let flattened = wire(expr.ty().HdlSome);
         #[hdl]
         match expr {
             HdlSome(v) => connect(flattened, v),
-            HdlNone => connect(flattened, Expr::ty(expr).HdlSome.HdlNone()),
+            HdlNone => connect(flattened, expr.ty().HdlSome.HdlNone()),
         }
         flattened
     }
@@ -1107,7 +1114,7 @@ impl<T: Type, U: Type> HdlOption<(T, U)> {
     #[hdl]
     #[track_caller]
     pub fn unzip(expr: Expr<Self>) -> Expr<(HdlOption<T>, HdlOption<U>)> {
-        let (t, u) = Expr::ty(expr).HdlSome;
+        let (t, u) = expr.ty().HdlSome;
         #[hdl]
         let unzipped = wire((HdlOption[t], HdlOption[u]));
         connect(unzipped, (HdlOption[t].HdlNone(), HdlOption[u].HdlNone()));

crates/fayalite/src/expr/ops/test_ops_impls.rs

@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+use crate::{expr::Valueless, expr::ops::make_impls, prelude::*};
+use std::num::NonZero;
+
+macro_rules! assert_neg_impls {
+    ([$($Lifetimes:tt)*][$($Bounds:tt)*] ($ty:ty),) => {
+        const _: () = {
+            fn _check_neg_impl<$($Lifetimes)*$($Bounds)*>(v: $ty)
+            -> impl ValueType<
+                ValueCategory = <$ty as ValueType>::ValueCategory,
+                Type = <<Valueless<<$ty as ValueType>::Type> as std::ops::Neg>::Output as ValueType>::Type,
+            > {
+                std::ops::Neg::neg(v)
+            }
+        };
+    };
+}
+
+make_impls! {
+    #[kinds((sint_local<'a, Width>))]
+    assert_neg_impls! {}
+}
+
+macro_rules! assert_not_impls {
+    ([$($Lifetimes:tt)*][$($Bounds:tt)*] ($ty:ty),) => {
+        const _: () = {
+            fn _check_not_impl<$($Lifetimes)*$($Bounds)*>(v: $ty)
+            -> impl ValueType<
+                ValueCategory = <$ty as ValueType>::ValueCategory,
+                Type = <<Valueless<<$ty as ValueType>::Type> as std::ops::Not>::Output as ValueType>::Type,
+            > {
+                std::ops::Not::not(v)
+            }
+        };
+    };
+}
+
+make_impls! {
+    #[kinds((int_local<'a, Width>), (bool<'a>))]
+    assert_not_impls! {}
+}
+
+macro_rules! assert_cast_to_bits_impls {
+    ([$($Lifetimes:tt)*][$($Bounds:tt)*] ($ty:ty),) => {
+        const _: () = {
+            fn _check_cast_to_bits_impl<$($Lifetimes)*$($Bounds)*>(v: $ty)
+            -> impl ValueType<
+                ValueCategory = <$ty as ValueType>::ValueCategory,
+                Type = <<Valueless<<$ty as ValueType>::Type> as CastToBits>::Output as ValueType>::Type,
+            > {
+                <$ty as CastToBits>::cast_to_bits(&v)
+            }
+        };
+    };
+}
+
+make_impls! {
+    #[kinds((uint<'a, Width>), (sint<'a, Width>), (bool<'a>))]
+    assert_cast_to_bits_impls! {}
+}
+
+macro_rules! assert_simple_bin_op_impls {
+    ([$($LLifetimes:tt)*][$($LBounds:tt)*] ($($L:tt)*), [$($RLifetimes:tt)*][$($RBounds:tt)*] ($($R:tt)*), !$Trait:ident::$f:ident) => {
+        #[expect(dead_code)]
+        const _: () = {
+            trait HasImpl {
+                fn check_impl(self);
+            }
+
+            trait NoImpl {
+                fn check_impl(&self) -> &'static dyn NoImpl;
+            }
+
+            impl<L, R> NoImpl for (L, R) {
+                fn check_impl(&self) -> &'static dyn NoImpl {
+                    unreachable!()
+                }
+            }
+
+            impl<L: std::ops::$Trait<R>, R> HasImpl for (L, R) {
+                fn check_impl(self) {}
+            }
+
+            fn check_simple_bin_op_no_impl<$($LLifetimes)* $($RLifetimes)* $($LBounds)* $($RBounds)*>(l: $($L)*, r: $($R)*) {
+                let _: &'static dyn NoImpl = (l, r).check_impl();
+            }
+        };
+    };
+    ([$($LLifetimes:tt)*][$($LBounds:tt)*] ($($L:tt)*), [$($RLifetimes:tt)*][$($RBounds:tt)*] (usize), Shl::shl) => {
+        const _: () = {
+            #[expect(dead_code)]
+            fn check_simple_bin_op_impl<$($LLifetimes)* $($RLifetimes)* $($LBounds)* $($RBounds)*>(l: $($L)*, r: usize)
+            -> impl ValueType<
+                ValueCategory = <($($L)*, usize) as ValueType>::ValueCategory,
+                Type = <<Valueless<<$($L)* as ValueType>::Type> as std::ops::Shl<usize>>::Output as ValueType>::Type,
+            > {
+                std::ops::Shl::shl(l, r)
+            }
+        };
+    };
+    ([$($LLifetimes:tt)*][$($LBounds:tt)*] ($($L:tt)*), [$($RLifetimes:tt)*][$($RBounds:tt)*] (usize), Shr::shr) => {
+        const _: () = {
+            #[expect(dead_code)]
+            fn check_simple_bin_op_impl<$($LLifetimes)* $($RLifetimes)* $($LBounds)* $($RBounds)*>(l: $($L)*, r: usize)
+            -> impl ValueType<
+                ValueCategory = <($($L)*, usize) as ValueType>::ValueCategory,
+                Type = <<Valueless<<$($L)* as ValueType>::Type> as std::ops::Shr<usize>>::Output as ValueType>::Type,
+            > {
+                std::ops::Shr::shr(l, r)
+            }
+        };
+    };
+    ([$($LLifetimes:tt)*][$($LBounds:tt)*] ($($L:tt)*), [$($RLifetimes:tt)*][$($RBounds:tt)*] ($($R:tt)*), $Trait:ident::$f:ident) => {
+        const _: () = {
+            #[expect(dead_code)]
+            fn check_simple_bin_op_impl<$($LLifetimes)* $($RLifetimes)* $($LBounds)* $($RBounds)*>(l: $($L)*, r: $($R)*)
+            -> impl ValueType<
+                ValueCategory = <($($L)*, $($R)*) as ValueType>::ValueCategory,
+                Type = <<Valueless<<$($L)* as ValueType>::Type> as std::ops::$Trait<Valueless<<$($R)* as ValueType>::Type>>>::Output as ValueType>::Type,
+            > {
+                std::ops::$Trait::$f(l, r)
+            }
+        };
+    };
+    ($LLifetimes:tt $LBounds:tt ($($L:tt)*), $RLifetimes:tt $RBounds:tt ($($R:tt)*), !$FirstTrait:ident::$first_f:ident, $($rest:tt)*) => {
+        assert_simple_bin_op_impls! {
+            $LLifetimes $LBounds ($($L)*), $RLifetimes $RBounds ($($R)*), !$FirstTrait::$first_f
+        }
+        assert_simple_bin_op_impls! {
+            $LLifetimes $LBounds ($($L)*), $RLifetimes $RBounds ($($R)*), $($rest)*
+        }
+    };
+    ($LLifetimes:tt $LBounds:tt ($($L:tt)*), $RLifetimes:tt $RBounds:tt ($($R:tt)*), $FirstTrait:ident::$first_f:ident, $($rest:tt)*) => {
+        assert_simple_bin_op_impls! {
+            $LLifetimes $LBounds ($($L)*), $RLifetimes $RBounds ($($R)*), $FirstTrait::$first_f
+        }
+        assert_simple_bin_op_impls! {
+            $LLifetimes $LBounds ($($L)*), $RLifetimes $RBounds ($($R)*), $($rest)*
+        }
+    };
+}
+
+make_impls! {
+    #[kinds((uint_local<'l, L>))]
+    #[kinds((uint<'r, R>))]
+    assert_simple_bin_op_impls! {Add::add, Sub::sub, Mul::mul, Div::div, Rem::rem, BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((uint<'l, L>))]
+    #[kinds((uint_local<'r, R>))]
+    assert_simple_bin_op_impls! {Add::add, Sub::sub, Mul::mul, Div::div, Rem::rem, BitAnd::bitand, BitOr::bitor, BitXor::bitxor, Shl::shl, Shr::shr}
+}
+
+make_impls! {
+    #[kinds((sint_local<'l, L>))]
+    #[kinds((sint<'r, R>))]
+    assert_simple_bin_op_impls! {Add::add, Sub::sub, Mul::mul, Div::div, Rem::rem, BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((sint<'l, L>))]
+    #[kinds((sint_local<'r, R>))]
+    assert_simple_bin_op_impls! {Add::add, Sub::sub, Mul::mul, Div::div, Rem::rem, BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((sint<'l, L>))]
+    #[kinds((uint_local<'r, R>))]
+    assert_simple_bin_op_impls! {Shl::shl, Shr::shr}
+}
+
+make_impls! {
+    #[kinds((uint_local<'l, L>))]
+    assert_simple_bin_op_impls! {[][] (usize), Shl::shl, Shr::shr}
+}
+
+make_impls! {
+    #[kinds((sint_local<'l, L>))]
+    assert_simple_bin_op_impls! {[][] (usize), Shl::shl, Shr::shr}
+}
+
+make_impls! {
+    #[kinds((bool_local<'l>))]
+    #[kinds((bool_local<'r>))]
+    assert_simple_bin_op_impls! {BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((bool<'l>))]
+    #[kinds((Valueless<Bool>))]
+    assert_simple_bin_op_impls! {BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((Valueless<Bool>))]
+    #[kinds((bool<'r>))]
+    assert_simple_bin_op_impls! {BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds((bool_at_most_sim_value<'l>))]
+    #[kinds((bool_at_most_sim_value<'r>))]
+    assert_simple_bin_op_impls! {BitAnd::bitand, BitOr::bitor, BitXor::bitxor}
+}
+
+// assert there are no impls of BitAnd/BitOr/BitXor between Expr<Bool> and Rust's bool,
+// since that helps avoid using `==`/`!=` in hdl boolean expressions, which doesn't do
+// what is usually wanted.
+make_impls! {
+    #[kinds((Expr<Bool>))]
+    #[kinds(bool)]
+    assert_simple_bin_op_impls! {!BitAnd::bitand, !BitOr::bitor, !BitXor::bitxor}
+}
+
+make_impls! {
+    #[kinds(bool)]
+    #[kinds((Expr<Bool>))]
+    assert_simple_bin_op_impls! {!BitAnd::bitand, !BitOr::bitor, !BitXor::bitxor}
+}

crates/fayalite/src/expr/target.rs

@@ -3,7 +3,7 @@
 use crate::{
     array::Array,
     bundle::{Bundle, BundleField},
-    expr::{Expr, Flow, ToExpr},
+    expr::{Expr, Flow, ToExpr, ValueType, value_category::ValueCategoryExpr},
     intern::{Intern, Interned},
     memory::{DynPortType, MemPort},
     module::{Instance, ModuleIO, TargetName},
@@ -196,9 +196,18 @@ macro_rules! impl_target_base {
             }
         }
 
-        impl ToExpr for $TargetBase {
+        impl ValueType for $TargetBase {
             type Type = CanonicalType;
+            type ValueCategory = ValueCategoryExpr;
 
+            fn ty(&self) -> Self::Type {
+                match self {
+                    $(Self::$Variant(v) => v.ty().canonical(),)*
+                }
+            }
+        }
+
+        impl ToExpr for $TargetBase {
             fn to_expr(&self) -> Expr<Self::Type> {
                 match self {
                     $(Self::$Variant(v) => Expr::canonical(v.to_expr()),)*

crates/fayalite/src/expr/value_category.rs

@@ -0,0 +1,378 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+use crate::{expr::ValueType, ty::Type};
+
+trait ValueCategorySealed {}
+
+#[expect(private_bounds)]
+pub trait ValueCategory:
+    ValueCategorySealed
+    + Copy
+    + Ord
+    + Default
+    + std::fmt::Debug
+    + std::hash::Hash
+    + 'static
+    + Send
+    + Sync
+{
+    type DispatchOutput<D: ValueCategoryDispatch<InputValueCategory = Self>>: ValueType<Type = D::Type, ValueCategory: ValueCategoryIsValueSimValueExprOrValueless>;
+    #[track_caller]
+    fn dispatch<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> Self::DispatchOutput<D>;
+    #[track_caller]
+    fn dispatch_enum<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> ValueCategoryDispatchOutputEnum<D>;
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default, Debug, Hash)]
+pub struct ValueCategoryValue;
+
+impl ValueCategorySealed for ValueCategoryValue {}
+
+impl ValueCategory for ValueCategoryValue {
+    type DispatchOutput<D: ValueCategoryDispatch<InputValueCategory = Self>> = D::Value;
+
+    #[track_caller]
+    fn dispatch<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> Self::DispatchOutput<D> {
+        dispatch.dispatch_value()
+    }
+
+    #[track_caller]
+    fn dispatch_enum<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> ValueCategoryDispatchOutputEnum<D> {
+        ValueCategoryDispatchOutputEnum::Value(dispatch.dispatch_value())
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default, Debug, Hash)]
+pub struct ValueCategorySimValue;
+
+impl ValueCategorySealed for ValueCategorySimValue {}
+
+impl ValueCategory for ValueCategorySimValue {
+    type DispatchOutput<D: ValueCategoryDispatch<InputValueCategory = Self>> = D::SimValue;
+
+    #[track_caller]
+    fn dispatch<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> Self::DispatchOutput<D> {
+        dispatch.dispatch_sim_value()
+    }
+
+    #[track_caller]
+    fn dispatch_enum<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> ValueCategoryDispatchOutputEnum<D> {
+        ValueCategoryDispatchOutputEnum::SimValue(dispatch.dispatch_sim_value())
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default, Debug, Hash)]
+pub struct ValueCategoryExpr;
+
+impl ValueCategorySealed for ValueCategoryExpr {}
+
+impl ValueCategory for ValueCategoryExpr {
+    type DispatchOutput<D: ValueCategoryDispatch<InputValueCategory = Self>> = D::Expr;
+
+    #[track_caller]
+    fn dispatch<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> Self::DispatchOutput<D> {
+        dispatch.dispatch_expr()
+    }
+
+    #[track_caller]
+    fn dispatch_enum<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> ValueCategoryDispatchOutputEnum<D> {
+        ValueCategoryDispatchOutputEnum::Expr(dispatch.dispatch_expr())
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default, Debug, Hash)]
+pub struct ValueCategoryValueless;
+
+impl ValueCategorySealed for ValueCategoryValueless {}
+
+impl ValueCategory for ValueCategoryValueless {
+    type DispatchOutput<D: ValueCategoryDispatch<InputValueCategory = Self>> = D::Valueless;
+
+    #[track_caller]
+    fn dispatch<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> Self::DispatchOutput<D> {
+        dispatch.dispatch_valueless()
+    }
+
+    #[track_caller]
+    fn dispatch_enum<D: ValueCategoryDispatch<InputValueCategory = Self>>(
+        dispatch: D,
+    ) -> ValueCategoryDispatchOutputEnum<D> {
+        ValueCategoryDispatchOutputEnum::Valueless(dispatch.dispatch_valueless())
+    }
+}
+
+pub trait ValueCategoryIsValue: ValueCategoryIsValueOrSimValue {}
+
+impl ValueCategoryIsValue for ValueCategoryValue {}
+
+pub trait ValueCategoryIsValueOrSimValue: ValueCategoryIsValueSimValueOrExpr {}
+
+impl ValueCategoryIsValueOrSimValue for ValueCategoryValue {}
+impl ValueCategoryIsValueOrSimValue for ValueCategorySimValue {}
+
+pub trait ValueCategoryIsValueSimValueOrExpr: ValueCategoryIsValueSimValueExprOrValueless {}
+
+impl ValueCategoryIsValueSimValueOrExpr for ValueCategoryValue {}
+impl ValueCategoryIsValueSimValueOrExpr for ValueCategorySimValue {}
+impl ValueCategoryIsValueSimValueOrExpr for ValueCategoryExpr {}
+
+pub trait ValueCategoryIsValueSimValueExprOrValueless: ValueCategory {}
+
+impl ValueCategoryIsValueSimValueExprOrValueless for ValueCategoryValue {}
+impl ValueCategoryIsValueSimValueExprOrValueless for ValueCategorySimValue {}
+impl ValueCategoryIsValueSimValueExprOrValueless for ValueCategoryExpr {}
+impl ValueCategoryIsValueSimValueExprOrValueless for ValueCategoryValueless {}
+
+pub trait ValueCategoryIsValueless: ValueCategoryIsExprOrValueless {}
+
+impl ValueCategoryIsValueless for ValueCategoryValueless {}
+
+pub trait ValueCategoryIsExprOrValueless: ValueCategoryIsValueSimValueExprOrValueless {}
+
+impl ValueCategoryIsExprOrValueless for ValueCategoryExpr {}
+impl ValueCategoryIsExprOrValueless for ValueCategoryValueless {}
+
+pub trait ValueCategoryIsSimValueExprOrValueless:
+    ValueCategoryIsValueSimValueExprOrValueless
+{
+}
+
+impl ValueCategoryIsSimValueExprOrValueless for ValueCategorySimValue {}
+impl ValueCategoryIsSimValueExprOrValueless for ValueCategoryExpr {}
+impl ValueCategoryIsSimValueExprOrValueless for ValueCategoryValueless {}
+
+trait ValueCategoryCommonSealed {}
+
+#[expect(private_bounds)]
+pub trait ValueCategoryCommon<
+    T: ValueCategoryCommonSealed
+        + Copy
+        + Ord
+        + Default
+        + std::fmt::Debug
+        + std::hash::Hash
+        + 'static
+        + Send
+        + Sync,
+>: ValueCategory
+{
+    type Common: ValueCategory;
+}
+
+macro_rules! impl_value_category_common {
+    ($($T:ident),* $(,)?) => {
+        impl_value_category_common!([$($T,)*]);
+    };
+    ([$($A:ident,)?]) => {};
+    ([$FirstT:ident, $($T:ident,)+]) => {
+        impl_value_category_common!([$($T,)*]);
+
+        impl<$FirstT: ValueCategory, $($T: ValueCategory),*> ValueCategoryCommonSealed for ($FirstT, $($T),*) {}
+
+        impl<This, $FirstT, $($T),*> ValueCategoryCommon<($FirstT, $($T),*)> for This
+        where
+            $FirstT: ValueCategory,
+            $($T: ValueCategory,)*
+            This: ValueCategoryCommon<($FirstT,), Common: ValueCategoryCommon<($($T,)*)>>,
+        {
+            type Common = <<This as ValueCategoryCommon<($FirstT,)>>::Common as ValueCategoryCommon<($($T,)*)>>::Common;
+        }
+    };
+}
+
+impl_value_category_common!(T11, T10, T9, T8, T7, T6, T5, T4, T3, T2, T1, T0);
+
+impl<T: ValueCategory> ValueCategoryCommonSealed for (T,) {}
+
+impl ValueCategoryCommonSealed for () {}
+
+impl<T: ValueCategory> ValueCategoryCommon<()> for T {
+    type Common = T;
+}
+
+impl<T: ValueCategoryIsValue> ValueCategoryCommon<(ValueCategoryValue,)> for T {
+    type Common = ValueCategoryValue;
+}
+
+impl<T: ValueCategoryIsValueOrSimValue> ValueCategoryCommon<(ValueCategorySimValue,)> for T {
+    type Common = ValueCategorySimValue;
+}
+
+impl<T: ValueCategoryIsValue> ValueCategoryCommon<(T,)> for ValueCategorySimValue {
+    type Common = ValueCategorySimValue;
+}
+
+impl<T: ValueCategoryIsValueSimValueOrExpr> ValueCategoryCommon<(ValueCategoryExpr,)> for T {
+    type Common = ValueCategoryExpr;
+}
+
+impl<T: ValueCategoryIsValueOrSimValue> ValueCategoryCommon<(T,)> for ValueCategoryExpr {
+    type Common = ValueCategoryExpr;
+}
+
+impl<T: ValueCategoryIsValueSimValueExprOrValueless> ValueCategoryCommon<(ValueCategoryValueless,)>
+    for T
+{
+    type Common = ValueCategoryValueless;
+}
+
+impl<T: ValueCategoryIsValueSimValueOrExpr> ValueCategoryCommon<(T,)> for ValueCategoryValueless {
+    type Common = ValueCategoryValueless;
+}
+
+pub trait ValueCategoryDispatch: Sized {
+    type Type: Type;
+    type InputValueCategory: ValueCategory;
+    type Value: ValueType<ValueCategory: ValueCategoryIsValueSimValueExprOrValueless, Type = Self::Type>;
+    type SimValue: ValueType<ValueCategory: ValueCategoryIsSimValueExprOrValueless, Type = Self::Type>;
+    type Expr: ValueType<ValueCategory: ValueCategoryIsExprOrValueless, Type = Self::Type>;
+    type Valueless: ValueType<ValueCategory: ValueCategoryIsValueless, Type = Self::Type>;
+    fn dispatch_value(self) -> Self::Value
+    where
+        Self: ValueCategoryDispatch<InputValueCategory = ValueCategoryValue>;
+    fn dispatch_sim_value(self) -> Self::SimValue
+    where
+        Self: ValueCategoryDispatch<InputValueCategory = ValueCategorySimValue>;
+    fn dispatch_expr(self) -> Self::Expr
+    where
+        Self: ValueCategoryDispatch<InputValueCategory = ValueCategoryExpr>;
+    fn dispatch_valueless(self) -> Self::Valueless
+    where
+        Self: ValueCategoryDispatch<InputValueCategory = ValueCategoryValueless>;
+    fn dispatch(self) -> <Self::InputValueCategory as ValueCategory>::DispatchOutput<Self> {
+        Self::InputValueCategory::dispatch(self)
+    }
+    fn dispatch_enum(self) -> ValueCategoryDispatchOutputEnum<Self> {
+        Self::InputValueCategory::dispatch_enum(self)
+    }
+}
+
+pub enum ValueCategoryDispatchOutputEnum<T: ValueCategoryDispatch> {
+    Value(T::Value),
+    SimValue(T::SimValue),
+    Expr(T::Expr),
+    Valueless(T::Valueless),
+}
+
+impl<T: ValueCategoryDispatch> ValueCategoryDispatchOutputEnum<T> {
+    pub fn try_into_value(self) -> Result<T::Value, Self> {
+        if let Self::Value(v) = self {
+            Ok(v)
+        } else {
+            Err(self)
+        }
+    }
+    pub fn try_into_sim_value(self) -> Result<T::SimValue, Self> {
+        if let Self::SimValue(v) = self {
+            Ok(v)
+        } else {
+            Err(self)
+        }
+    }
+    pub fn try_into_expr(self) -> Result<T::Expr, Self> {
+        if let Self::Expr(v) = self {
+            Ok(v)
+        } else {
+            Err(self)
+        }
+    }
+    pub fn try_into_valueless(self) -> Result<T::Valueless, Self> {
+        if let Self::Valueless(v) = self {
+            Ok(v)
+        } else {
+            Err(self)
+        }
+    }
+    #[track_caller]
+    #[cold]
+    fn unwrap_invalid(self, expected_kind: &'static str) -> ! {
+        match self {
+            Self::Value(_) => panic!("expected {expected_kind}, got Value"),
+            Self::SimValue(_) => panic!("expected {expected_kind}, got SimValue"),
+            Self::Expr(_) => panic!("expected {expected_kind}, got Expr"),
+            Self::Valueless(_) => panic!("expected {expected_kind}, got Valueless"),
+        }
+    }
+    #[track_caller]
+    pub fn into_value_unwrap(self) -> T::Value {
+        let Self::Value(v) = self else {
+            self.unwrap_invalid("Value");
+        };
+        v
+    }
+    #[track_caller]
+    pub fn into_sim_value_unwrap(self) -> T::SimValue {
+        let Self::SimValue(v) = self else {
+            self.unwrap_invalid("SimValue");
+        };
+        v
+    }
+    #[track_caller]
+    pub fn into_expr_unwrap(self) -> T::Expr {
+        let Self::Expr(v) = self else {
+            self.unwrap_invalid("Expr");
+        };
+        v
+    }
+    #[track_caller]
+    pub fn into_valueless_unwrap(self) -> T::Valueless {
+        let Self::Valueless(v) = self else {
+            self.unwrap_invalid("Valueless");
+        };
+        v
+    }
+    pub fn ty(&self) -> T::Type {
+        match self {
+            Self::Value(v) => v.ty(),
+            Self::SimValue(v) => v.ty(),
+            Self::Expr(v) => v.ty(),
+            Self::Valueless(v) => v.ty(),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    type Identity<T> = T;
+
+    macro_rules! check_categories {
+        ($($Categories:ident,)+) => {
+            check_categories!([] [$($Categories,)+]);
+        };
+        ([$($Categories:ident,)*] []) => {};
+        ([$($WeakerCategories:ident,)*] [$Category:ident, $($StrongerCategories:ident,)*]) => {
+            $(const _: $Category = Identity::<<$WeakerCategories as ValueCategoryCommon<($Category,)>>::Common> {};
+            const _: $Category = Identity::<<$Category as ValueCategoryCommon<($WeakerCategories,)>>::Common> {};)*
+            const _: $Category = Identity::<<$Category as ValueCategoryCommon<($Category,)>>::Common> {};
+            check_categories!([$($WeakerCategories,)* $Category,] [$($StrongerCategories,)*]);
+        };
+    }
+
+    check_categories!(
+        ValueCategoryValue,
+        ValueCategorySimValue,
+        ValueCategoryExpr,
+        ValueCategoryValueless,
+    );
+}

crates/fayalite/src/firrtl.rs

@@ -12,7 +12,7 @@ use crate::{
     clock::Clock,
     enum_::{Enum, EnumType, EnumVariant},
     expr::{
-        CastBitsTo, Expr, ExprEnum,
+        CastBitsTo, Expr, ExprEnum, ToExpr, ValueType,
         ops::{self, VariantAccess},
         target::{
             Target, TargetBase, TargetPathArrayElement, TargetPathBundleField, TargetPathElement,
@@ -877,7 +877,7 @@ impl<'a> Exporter<'a> {
         definitions: &RcDefinitions,
         const_ty: bool,
     ) -> Result<String> {
-        let from_ty = Expr::ty(value);
+        let from_ty = value.ty();
         let mut value = self.expr(Expr::canonical(value), definitions, const_ty)?;
         if from_ty.width().checked_add(1) == Some(to_ty.width())
             && !FromTy::Signed::VALUE
@@ -926,7 +926,7 @@ impl<'a> Exporter<'a> {
         definitions: &RcDefinitions,
         const_ty: bool,
     ) -> Result<String> {
-        let base_width = Expr::ty(base).width();
+        let base_width = base.ty().width();
         let base = self.expr(Expr::canonical(base), definitions, const_ty)?;
         if range.is_empty() {
             Ok(format!("tail({base}, {base_width})"))
@@ -1470,7 +1470,7 @@ impl<'a> Exporter<'a> {
             ExprEnum::SIntLiteral(literal) => Ok(self.sint_literal(&literal)),
             ExprEnum::BoolLiteral(literal) => Ok(self.bool_literal(literal)),
             ExprEnum::PhantomConst(ty) => self.expr(
-                UInt[0].zero().cast_bits_to(ty.canonical()),
+                UInt[0].zero().to_expr().cast_bits_to(ty.canonical()),
                 definitions,
                 const_ty,
             ),
@@ -1653,7 +1653,7 @@ impl<'a> Exporter<'a> {
                 let value_str = self.expr(expr.arg(), definitions, const_ty)?;
                 self.expr_cast_to_bits(
                     value_str,
-                    Expr::ty(expr.arg()),
+                    expr.arg().ty(),
                     definitions,
                     Indent {
                         indent_depth: &Cell::new(0),
@@ -1776,7 +1776,7 @@ impl<'a> Exporter<'a> {
                 let mut out = self.expr(Expr::canonical(expr.base()), definitions, const_ty)?;
                 let name = self
                     .type_state
-                    .get_bundle_field(Expr::ty(expr.base()), expr.field_name())?;
+                    .get_bundle_field(expr.base().ty(), expr.field_name())?;
                 write!(out, ".{name}").unwrap();
                 Ok(out)
             }
@@ -2101,12 +2101,12 @@ impl<'a> Exporter<'a> {
                     rhs,
                     source_location,
                 }) => {
-                    if Expr::ty(lhs) != Expr::ty(rhs) {
+                    if lhs.ty() != rhs.ty() {
                         writeln!(
                             body,
                             "{indent}; connect different types:\n{indent}; lhs: {:?}\n{indent}; rhs: {:?}",
-                            Expr::ty(lhs),
-                            Expr::ty(rhs),
+                            lhs.ty(),
+                            rhs.ty(),
                         )
                         .unwrap();
                     }
@@ -2200,7 +2200,7 @@ impl<'a> Exporter<'a> {
                         FileInfo::new(source_location),
                     )
                     .unwrap();
-                    let enum_ty = Expr::ty(expr);
+                    let enum_ty = expr.ty();
                     let match_arms_indent = indent.push();
                     for ((variant_index, variant), match_arm_block) in
                         enum_ty.variants().iter().enumerate().zip(blocks)

crates/fayalite/src/int.rs

@@ -4,16 +4,19 @@
 use crate::{
     array::ArrayType,
     expr::{
-        Expr, NotALiteralExpr, ToExpr, ToLiteralBits,
+        Expr, NotALiteralExpr, ToExpr, ToLiteralBits, ToSimValueInner, ToValueless, ValueType,
+        Valueless,
         target::{GetTarget, Target},
+        value_category::ValueCategoryValue,
     },
     hdl,
     intern::{Intern, Interned, Memoize},
     sim::value::{SimValue, ToSimValueWithType},
     source_location::SourceLocation,
     ty::{
-        CanonicalType, OpaqueSimValueSize, OpaqueSimValueSlice, OpaqueSimValueWriter,
-        OpaqueSimValueWritten, StaticType, Type, TypeProperties, impl_match_variant_as_self,
+        CanonicalType, FillInDefaultedGenerics, OpaqueSimValueSize, OpaqueSimValueSlice,
+        OpaqueSimValueWriter, OpaqueSimValueWritten, StaticType, Type, TypeProperties,
+        impl_match_variant_as_self,
     },
     util::{ConstBool, ConstUsize, GenericConstBool, GenericConstUsize, interned_bit, slice_range},
 };
@@ -31,7 +34,7 @@ use std::{
     num::NonZero,
     ops::{Index, Not, Range, RangeBounds, RangeInclusive},
     str::FromStr,
-    sync::Arc,
+    sync::{Arc, OnceLock},
 };
 
 mod uint_in_range;
@@ -60,8 +63,62 @@ mod sealed {
 pub const DYN_SIZE: usize = !0;
 pub type DynSize = ConstUsize<DYN_SIZE>;
 
+trait KnownSizeBaseSealed {}
+
+impl<const N: usize> KnownSizeBaseSealed for [(); N] {}
+
+#[expect(private_bounds)]
+pub trait KnownSizeBase: KnownSizeBaseSealed {}
+
+macro_rules! impl_known_size_base {
+    ($($size:literal),* $(,)?) => {
+        $(impl KnownSizeBase for [(); $size] {})*
+    };
+}
+
+#[rustfmt::skip]
+impl_known_size_base! {
+    0x000, 0x001, 0x002, 0x003, 0x004, 0x005, 0x006, 0x007, 0x008, 0x009, 0x00A, 0x00B, 0x00C, 0x00D, 0x00E, 0x00F,
+    0x010, 0x011, 0x012, 0x013, 0x014, 0x015, 0x016, 0x017, 0x018, 0x019, 0x01A, 0x01B, 0x01C, 0x01D, 0x01E, 0x01F,
+    0x020, 0x021, 0x022, 0x023, 0x024, 0x025, 0x026, 0x027, 0x028, 0x029, 0x02A, 0x02B, 0x02C, 0x02D, 0x02E, 0x02F,
+    0x030, 0x031, 0x032, 0x033, 0x034, 0x035, 0x036, 0x037, 0x038, 0x039, 0x03A, 0x03B, 0x03C, 0x03D, 0x03E, 0x03F,
+    0x040, 0x041, 0x042, 0x043, 0x044, 0x045, 0x046, 0x047, 0x048, 0x049, 0x04A, 0x04B, 0x04C, 0x04D, 0x04E, 0x04F,
+    0x050, 0x051, 0x052, 0x053, 0x054, 0x055, 0x056, 0x057, 0x058, 0x059, 0x05A, 0x05B, 0x05C, 0x05D, 0x05E, 0x05F,
+    0x060, 0x061, 0x062, 0x063, 0x064, 0x065, 0x066, 0x067, 0x068, 0x069, 0x06A, 0x06B, 0x06C, 0x06D, 0x06E, 0x06F,
+    0x070, 0x071, 0x072, 0x073, 0x074, 0x075, 0x076, 0x077, 0x078, 0x079, 0x07A, 0x07B, 0x07C, 0x07D, 0x07E, 0x07F,
+    0x080, 0x081, 0x082, 0x083, 0x084, 0x085, 0x086, 0x087, 0x088, 0x089, 0x08A, 0x08B, 0x08C, 0x08D, 0x08E, 0x08F,
+    0x090, 0x091, 0x092, 0x093, 0x094, 0x095, 0x096, 0x097, 0x098, 0x099, 0x09A, 0x09B, 0x09C, 0x09D, 0x09E, 0x09F,
+    0x0A0, 0x0A1, 0x0A2, 0x0A3, 0x0A4, 0x0A5, 0x0A6, 0x0A7, 0x0A8, 0x0A9, 0x0AA, 0x0AB, 0x0AC, 0x0AD, 0x0AE, 0x0AF,
+    0x0B0, 0x0B1, 0x0B2, 0x0B3, 0x0B4, 0x0B5, 0x0B6, 0x0B7, 0x0B8, 0x0B9, 0x0BA, 0x0BB, 0x0BC, 0x0BD, 0x0BE, 0x0BF,
+    0x0C0, 0x0C1, 0x0C2, 0x0C3, 0x0C4, 0x0C5, 0x0C6, 0x0C7, 0x0C8, 0x0C9, 0x0CA, 0x0CB, 0x0CC, 0x0CD, 0x0CE, 0x0CF,
+    0x0D0, 0x0D1, 0x0D2, 0x0D3, 0x0D4, 0x0D5, 0x0D6, 0x0D7, 0x0D8, 0x0D9, 0x0DA, 0x0DB, 0x0DC, 0x0DD, 0x0DE, 0x0DF,
+    0x0E0, 0x0E1, 0x0E2, 0x0E3, 0x0E4, 0x0E5, 0x0E6, 0x0E7, 0x0E8, 0x0E9, 0x0EA, 0x0EB, 0x0EC, 0x0ED, 0x0EE, 0x0EF,
+    0x0F0, 0x0F1, 0x0F2, 0x0F3, 0x0F4, 0x0F5, 0x0F6, 0x0F7, 0x0F8, 0x0F9, 0x0FA, 0x0FB, 0x0FC, 0x0FD, 0x0FE, 0x0FF,
+    0x100, 0x101, 0x102, 0x103, 0x104, 0x105, 0x106, 0x107, 0x108, 0x109, 0x10A, 0x10B, 0x10C, 0x10D, 0x10E, 0x10F,
+    0x110, 0x111, 0x112, 0x113, 0x114, 0x115, 0x116, 0x117, 0x118, 0x119, 0x11A, 0x11B, 0x11C, 0x11D, 0x11E, 0x11F,
+    0x120, 0x121, 0x122, 0x123, 0x124, 0x125, 0x126, 0x127, 0x128, 0x129, 0x12A, 0x12B, 0x12C, 0x12D, 0x12E, 0x12F,
+    0x130, 0x131, 0x132, 0x133, 0x134, 0x135, 0x136, 0x137, 0x138, 0x139, 0x13A, 0x13B, 0x13C, 0x13D, 0x13E, 0x13F,
+    0x140, 0x141, 0x142, 0x143, 0x144, 0x145, 0x146, 0x147, 0x148, 0x149, 0x14A, 0x14B, 0x14C, 0x14D, 0x14E, 0x14F,
+    0x150, 0x151, 0x152, 0x153, 0x154, 0x155, 0x156, 0x157, 0x158, 0x159, 0x15A, 0x15B, 0x15C, 0x15D, 0x15E, 0x15F,
+    0x160, 0x161, 0x162, 0x163, 0x164, 0x165, 0x166, 0x167, 0x168, 0x169, 0x16A, 0x16B, 0x16C, 0x16D, 0x16E, 0x16F,
+    0x170, 0x171, 0x172, 0x173, 0x174, 0x175, 0x176, 0x177, 0x178, 0x179, 0x17A, 0x17B, 0x17C, 0x17D, 0x17E, 0x17F,
+    0x180, 0x181, 0x182, 0x183, 0x184, 0x185, 0x186, 0x187, 0x188, 0x189, 0x18A, 0x18B, 0x18C, 0x18D, 0x18E, 0x18F,
+    0x190, 0x191, 0x192, 0x193, 0x194, 0x195, 0x196, 0x197, 0x198, 0x199, 0x19A, 0x19B, 0x19C, 0x19D, 0x19E, 0x19F,
+    0x1A0, 0x1A1, 0x1A2, 0x1A3, 0x1A4, 0x1A5, 0x1A6, 0x1A7, 0x1A8, 0x1A9, 0x1AA, 0x1AB, 0x1AC, 0x1AD, 0x1AE, 0x1AF,
+    0x1B0, 0x1B1, 0x1B2, 0x1B3, 0x1B4, 0x1B5, 0x1B6, 0x1B7, 0x1B8, 0x1B9, 0x1BA, 0x1BB, 0x1BC, 0x1BD, 0x1BE, 0x1BF,
+    0x1C0, 0x1C1, 0x1C2, 0x1C3, 0x1C4, 0x1C5, 0x1C6, 0x1C7, 0x1C8, 0x1C9, 0x1CA, 0x1CB, 0x1CC, 0x1CD, 0x1CE, 0x1CF,
+    0x1D0, 0x1D1, 0x1D2, 0x1D3, 0x1D4, 0x1D5, 0x1D6, 0x1D7, 0x1D8, 0x1D9, 0x1DA, 0x1DB, 0x1DC, 0x1DD, 0x1DE, 0x1DF,
+    0x1E0, 0x1E1, 0x1E2, 0x1E3, 0x1E4, 0x1E5, 0x1E6, 0x1E7, 0x1E8, 0x1E9, 0x1EA, 0x1EB, 0x1EC, 0x1ED, 0x1EE, 0x1EF,
+    0x1F0, 0x1F1, 0x1F2, 0x1F3, 0x1F4, 0x1F5, 0x1F6, 0x1F7, 0x1F8, 0x1F9, 0x1FA, 0x1FB, 0x1FC, 0x1FD, 0x1FE, 0x1FF,
+    0x200,
+}
+
 pub trait KnownSize:
-    GenericConstUsize + sealed::SizeTypeSealed + sealed::SizeSealed + Default
+    GenericConstUsize
+    + sealed::SizeTypeSealed
+    + sealed::SizeSealed
+    + Default
+    + FillInDefaultedGenerics<Type = Self>
 {
     const SIZE: Self;
     type ArrayMatch<Element: Type>: AsRef<[Expr<Element>]>
@@ -89,35 +146,15 @@ pub trait KnownSize:
         + ToSimValueWithType<ArrayType<Element, Self>>;
 }
 
-macro_rules! known_widths {
-    ([] $($bits:literal)+) => {
-        impl KnownSize for ConstUsize<{
-            let v = 0;
-            $(let v = v * 2 + $bits;)*
-            v
-        }> {
-            const SIZE: Self = Self;
-            type ArrayMatch<Element: Type> = [Expr<Element>; Self::VALUE];
-            type ArraySimValue<Element: Type> = [SimValue<Element>; Self::VALUE];
-        }
-    };
-    ([2 $($rest:tt)*] $($bits:literal)+) => {
-        known_widths!([$($rest)*] $($bits)* 0);
-        known_widths!([$($rest)*] $($bits)* 1);
-    };
-    ([2 $($rest:tt)*]) => {
-        known_widths!([$($rest)*] 0);
-        known_widths!([$($rest)*] 1);
-        impl KnownSize for ConstUsize<{2 $(* $rest)*}> {
-            const SIZE: Self = Self;
-            type ArrayMatch<Element: Type> = [Expr<Element>; Self::VALUE];
-            type ArraySimValue<Element: Type> = [SimValue<Element>; Self::VALUE];
-        }
-    };
+impl<const N: usize> KnownSize for ConstUsize<N>
+where
+    [(); N]: KnownSizeBase,
+{
+    const SIZE: Self = Self;
+    type ArrayMatch<Element: Type> = [Expr<Element>; N];
+    type ArraySimValue<Element: Type> = [SimValue<Element>; N];
 }
 
-known_widths!([2 2 2 2 2 2 2 2 2]);
-
 pub trait SizeType:
     sealed::SizeTypeSealed
     + Copy
@@ -129,6 +166,7 @@ pub trait SizeType:
     + 'static
     + Serialize
     + DeserializeOwned
+    + FillInDefaultedGenerics<Type = Self>
 {
     type Size: Size<SizeType = Self>;
 }
@@ -530,6 +568,23 @@ fn deserialize_int_value<'de, D: Deserializer<'de>>(
     })
 }
 
+macro_rules! impl_valueless_op_forward {
+    (
+        #[forward_to = $ForwardTrait:path]
+        impl<$($G:ident: $Bound:path),*> $TraitPath:ident$(::$TraitPathRest:ident)+<$($Rhs:ty)?> for $SelfTy:ty {
+            $($(type $Output:ident;)?
+            use $forward_fn:path as $fn:ident($self:ident $(, $rhs:ident)?);)?
+        }
+    ) => {
+        impl<$($G: $Bound),*> $TraitPath$(::$TraitPathRest)+<$($Rhs)?> for $SelfTy {
+            $($(type $Output = <$SelfTy as $ForwardTrait>::$Output;)?
+            fn $fn($self $(, $rhs: $Rhs)?) $(-> Self::$Output)? {
+                $forward_fn($self $(, $rhs)?)
+            })?
+        }
+    };
+}
+
 macro_rules! impl_int {
     ($pretty_name:ident, $name:ident, $generic_name:ident, $value:ident, $SIGNED:literal) => {
         #[derive(Copy, Clone, PartialEq, Eq, Hash)]
@@ -582,6 +637,176 @@ macro_rules! impl_int {
             }
         }
 
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::Add<Valueless<$name<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<$name>;
+
+            fn add(self, rhs: Valueless<$name<RhsWidth>>) -> Self::Output {
+                Valueless::new($name::new_dyn(
+                    self.ty()
+                        .width()
+                        .max(rhs.ty().width())
+                        .checked_add(1)
+                        .expect("width too big"),
+                ))
+            }
+        }
+
+        impl_valueless_op_forward! {
+            #[forward_to = std::ops::Add<Valueless<$name<RhsWidth>>>]
+            impl<LhsWidth: Size, RhsWidth: Size> std::ops::Sub<Valueless<$name<RhsWidth>>>
+                for Valueless<$name<LhsWidth>>
+            {
+                type Output;
+
+                use std::ops::Add::<Valueless<$name<RhsWidth>>>::add as sub(self, rhs);
+            }
+        }
+
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::BitOr<Valueless<$name<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<UInt>;
+
+            fn bitor(self, rhs: Valueless<$name<RhsWidth>>) -> Self::Output {
+                Valueless::new(UInt::new_dyn(self.ty().width().max(rhs.ty().width())))
+            }
+        }
+
+        impl_valueless_op_forward! {
+            #[forward_to = std::ops::BitOr<Valueless<$name<RhsWidth>>>]
+            impl<LhsWidth: Size, RhsWidth: Size> std::ops::BitAnd<Valueless<$name<RhsWidth>>>
+                for Valueless<$name<LhsWidth>>
+            {
+                type Output;
+
+                use std::ops::BitOr::<Valueless<$name<RhsWidth>>>::bitor as bitand(self, rhs);
+            }
+        }
+
+        impl_valueless_op_forward! {
+            #[forward_to = std::ops::BitOr<Valueless<$name<RhsWidth>>>]
+            impl<LhsWidth: Size, RhsWidth: Size> std::ops::BitXor<Valueless<$name<RhsWidth>>>
+                for Valueless<$name<LhsWidth>>
+            {
+                type Output;
+
+                use std::ops::BitOr::<Valueless<$name<RhsWidth>>>::bitor as bitxor(self, rhs);
+            }
+        }
+
+        impl<Width: Size> std::ops::Not for Valueless<$name<Width>> {
+            type Output = Valueless<UIntType<Width>>;
+
+            fn not(self) -> Self::Output {
+                Valueless::new(self.ty().as_same_width_uint())
+            }
+        }
+
+        impl<Width: Size> std::ops::Not for $value<Width> {
+            type Output = UIntValue<Width>;
+
+            fn not(mut self) -> Self::Output {
+                // modifies in-place despite using `Not::not`
+                let _ = Not::not(self.bits_mut());
+                UIntValue::new(self.into_bits())
+            }
+        }
+
+        impl<Width: Size> std::ops::Not for &'_ $value<Width> {
+            type Output = UIntValue<Width>;
+
+            fn not(self) -> Self::Output {
+                $value::not(self.clone())
+            }
+        }
+
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::Mul<Valueless<$name<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<$name>;
+
+            fn mul(self, rhs: Valueless<$name<RhsWidth>>) -> Self::Output {
+                Valueless::new($name::new_dyn(
+                    self.ty()
+                        .width()
+                        .checked_add(rhs.ty().width())
+                        .expect("width too big"),
+                ))
+            }
+        }
+
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::Rem<Valueless<$name<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<$name>;
+
+            fn rem(self, rhs: Valueless<$name<RhsWidth>>) -> Self::Output {
+                Valueless::new($name::new_dyn(self.ty().width().min(rhs.ty().width())))
+            }
+        }
+
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::Shl<Valueless<UIntType<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<$name>;
+
+            #[track_caller]
+            fn shl(self, rhs: Valueless<UIntType<RhsWidth>>) -> Self::Output {
+                let Some(pow2_rhs_width) = rhs
+                    .ty()
+                    .width()
+                    .try_into()
+                    .ok()
+                    .and_then(|v| 2usize.checked_pow(v))
+                else {
+                    panic!(
+                        "dynamic left-shift amount's bit-width is too big, try casting the shift \
+                        amount to a smaller bit-width before shifting"
+                    );
+                };
+                Valueless::new($name::new_dyn(
+                    (pow2_rhs_width - 1)
+                        .checked_add(self.ty().width())
+                        .expect("width too big"),
+                ))
+            }
+        }
+
+        impl<LhsWidth: Size, RhsWidth: Size> std::ops::Shr<Valueless<UIntType<RhsWidth>>>
+            for Valueless<$name<LhsWidth>>
+        {
+            type Output = Valueless<$name<LhsWidth>>;
+
+            fn shr(self, _rhs: Valueless<UIntType<RhsWidth>>) -> Self::Output {
+                self
+            }
+        }
+
+        impl<LhsWidth: Size> std::ops::Shl<usize> for Valueless<$name<LhsWidth>> {
+            type Output = Valueless<$name>;
+
+            fn shl(self, rhs: usize) -> Self::Output {
+                Valueless::new($name::new_dyn(
+                    self.ty().width().checked_add(rhs).expect("width too big"),
+                ))
+            }
+        }
+
+        impl<LhsWidth: Size> std::ops::Shr<usize> for Valueless<$name<LhsWidth>> {
+            type Output = Valueless<$name>;
+
+            fn shr(self, rhs: usize) -> Self::Output {
+                let width = self.ty().width().saturating_sub(rhs);
+                Valueless::new($name::new_dyn(if $SIGNED && width == 0 {
+                    1
+                } else {
+                    width
+                }))
+            }
+        }
+
         impl<Width: Size> sealed::BoolOrIntTypeSealed for $name<Width> {}
 
         impl<Width: Size> BoolOrIntType for $name<Width> {
@@ -843,6 +1068,12 @@ macro_rules! impl_int {
             }
         }
 
+        impl<'a, Width: Size> From<&'a $value<Width>> for BigInt {
+            fn from(v: &'a $value<Width>) -> BigInt {
+                v.to_bigint()
+            }
+        }
+
         impl<Width: Size> $value<Width> {
             pub fn width(&self) -> usize {
                 if let Some(retval) = Width::KNOWN_VALUE {
@@ -861,11 +1092,6 @@ macro_rules! impl_int {
             pub fn into_bits(self) -> Arc<BitVec> {
                 self.bits
             }
-            pub fn ty(&self) -> $name<Width> {
-                $name {
-                    width: Width::from_usize(self.width()),
-                }
-            }
             pub fn as_dyn_int(self) -> $value {
                 $value {
                     bits: self.bits,
@@ -878,6 +1104,38 @@ macro_rules! impl_int {
             pub fn bits_mut(&mut self) -> &mut BitSlice {
                 Arc::<BitVec>::make_mut(&mut self.bits)
             }
+            pub fn hdl_cmp<R: Size>(&self, other: &$value<R>) -> std::cmp::Ordering {
+                self.to_bigint().cmp(&other.to_bigint())
+            }
+        }
+
+        impl<Width: Size> ValueType for $value<Width> {
+            type Type = $name<Width>;
+            type ValueCategory = ValueCategoryValue;
+
+            fn ty(&self) -> Self::Type {
+                $name {
+                    width: Width::from_usize(self.width()),
+                }
+            }
+        }
+
+        impl<'a, Width: Size> ToSimValueInner<'a> for $value<Width> {
+            fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+                Cow::Borrowed(this)
+            }
+            fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+                Cow::Owned(this)
+            }
+        }
+
+        impl<'a, Width: Size> ToSimValueInner<'a> for &'a $value<Width> {
+            fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+                Cow::Borrowed(&**this)
+            }
+            fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+                Cow::Borrowed(this)
+            }
         }
 
         impl<Width: Size> ToLiteralBits for $value<Width> {
@@ -1015,11 +1273,58 @@ impl SInt {
     }
 }
 
-macro_rules! impl_prim_int {
+impl<LhsWidth: Size, RhsWidth: Size> std::ops::Div<Valueless<UIntType<RhsWidth>>>
+    for Valueless<UIntType<LhsWidth>>
+{
+    type Output = Self;
+
+    fn div(self, _rhs: Valueless<UIntType<RhsWidth>>) -> Self::Output {
+        self
+    }
+}
+
+impl<LhsWidth: Size, RhsWidth: Size> std::ops::Div<Valueless<SIntType<RhsWidth>>>
+    for Valueless<SIntType<LhsWidth>>
+{
+    type Output = Valueless<SInt>;
+
+    fn div(self, _rhs: Valueless<SIntType<RhsWidth>>) -> Self::Output {
+        Valueless::new(SInt::new_dyn(
+            self.ty().width().checked_add(1).expect("width too big"),
+        ))
+    }
+}
+
+impl<Width: Size> std::ops::Neg for Valueless<SIntType<Width>> {
+    type Output = Valueless<SInt>;
+    fn neg(self) -> Self::Output {
+        Valueless::new(SInt::new_dyn(
+            self.ty().width().checked_add(1).expect("width too big"),
+        ))
+    }
+}
+
+impl<Width: Size> std::ops::Neg for SIntValue<Width> {
+    type Output = SIntValue;
+    fn neg(self) -> Self::Output {
+        -&self
+    }
+}
+
+impl<Width: Size> std::ops::Neg for &'_ SIntValue<Width> {
+    type Output = SIntValue;
+    fn neg(self) -> Self::Output {
+        let ty = self.to_valueless().neg().ty();
+        ty.from_bigint_wrapping(&-self.to_bigint())
+    }
+}
+
+macro_rules! impl_prim_int_to_expr {
     (
         $(#[$meta:meta])*
         $prim_int:ident, $ty:ty
     ) => {
+        $(#[$meta])*
         impl From<$prim_int> for <$ty as BoolOrIntType>::Value {
             fn from(v: $prim_int) -> Self {
                 <$ty>::le_bytes_to_value_wrapping(
@@ -1028,15 +1333,32 @@ macro_rules! impl_prim_int {
                 )
             }
         }
+        $(#[$meta])*
         impl From<NonZero<$prim_int>> for <$ty as BoolOrIntType>::Value {
             fn from(v: NonZero<$prim_int>) -> Self {
                 v.get().into()
             }
         }
         $(#[$meta])*
-        impl ToExpr for $prim_int {
+        impl<'a> ToSimValueInner<'a> for $prim_int {
+            fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+                Self::into_sim_value_inner(*this)
+            }
+            fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+                Cow::Owned(this.into())
+            }
+        }
+        $(#[$meta])*
+        impl ValueType for $prim_int {
             type Type = $ty;
+            type ValueCategory = ValueCategoryValue;
 
+            fn ty(&self) -> Self::Type {
+                StaticType::TYPE
+            }
+        }
+        $(#[$meta])*
+        impl ToExpr for $prim_int {
             fn to_expr(&self) -> Expr<Self::Type> {
                 <$ty>::le_bytes_to_expr_wrapping(
                     &self.to_le_bytes(),
@@ -1045,9 +1367,25 @@ macro_rules! impl_prim_int {
             }
         }
         $(#[$meta])*
-        impl ToExpr for NonZero<$prim_int> {
+        impl<'a> ToSimValueInner<'a> for NonZero<$prim_int> {
+            fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+                Self::into_sim_value_inner(*this)
+            }
+            fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+                Cow::Owned(this.into())
+            }
+        }
+        $(#[$meta])*
+        impl ValueType for NonZero<$prim_int> {
             type Type = $ty;
+            type ValueCategory = ValueCategoryValue;
 
+            fn ty(&self) -> Self::Type {
+                StaticType::TYPE
+            }
+        }
+        $(#[$meta])*
+        impl ToExpr for NonZero<$prim_int> {
             fn to_expr(&self) -> Expr<Self::Type> {
                 self.get().to_expr()
             }
@@ -1055,28 +1393,208 @@ macro_rules! impl_prim_int {
     };
 }
 
-impl_prim_int!(u8, UInt<8>);
-impl_prim_int!(u16, UInt<16>);
-impl_prim_int!(u32, UInt<32>);
-impl_prim_int!(u64, UInt<64>);
-impl_prim_int!(u128, UInt<128>);
-impl_prim_int!(i8, SInt<8>);
-impl_prim_int!(i16, SInt<16>);
-impl_prim_int!(i32, SInt<32>);
-impl_prim_int!(i64, SInt<64>);
-impl_prim_int!(i128, SInt<128>);
+macro_rules! impl_for_all_prim_uints {
+    (
+        #[size =, $(rest:tt)*]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_uints!(
+            #[usize =, $($rest)*]
+            $m!()
+        );
+    };
+    (
+        #[size = size, $(rest:tt)*]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_uints!(
+            #[usize = usize, $($rest)*]
+            $m!()
+        );
+    };
+    (
+        #[usize = $($usize:ident)?, NonZero = $NonZero:ident]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_uints!(
+            #[usize = $($usize)?, NonZero = $NonZero, NonZero<usize> = $((NonZero<$usize>))?]
+            $m!()
+        );
+    };
+    (
+        #[usize = $($usize:ident)?, NonZero =]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_uints!(
+            #[usize = $($usize)?, NonZero =, NonZero<usize> =]
+            $m!()
+        );
+    };
+    (
+        #[usize = $($usize:ident)?, NonZero = $($NonZero:ident)?, NonZero<usize> = $(($($NonZeroUsize:tt)*))?]
+        $m:ident!()
+    ) => {
+        $m!(u8, UInt<8>);
+        $m!(u16, UInt<16>);
+        $m!(u32, UInt<32>);
+        $m!(u64, UInt<64>);
+        $m!(u128, UInt<128>);
+        $($m!($NonZero<u8>, UInt<8>);)?
+        $($m!($NonZero<u16>, UInt<16>);)?
+        $($m!($NonZero<u32>, UInt<32>);)?
+        $($m!($NonZero<u64>, UInt<64>);)?
+        $($m!($NonZero<u128>, UInt<128>);)?
+        $($m!(
+            /// for portability reasons, [`usize`] always translates to [`UInt<64>`][type@UInt]
+            $usize, UInt<64>
+        );)?
+        $($m!(
+            /// for portability reasons, [`usize`] always translates to [`UInt<64>`][type@UInt]
+            $($NonZeroUsize)*, UInt<64>
+        );)?
+    };
+}
 
-impl_prim_int!(
-    /// for portability reasons, [`usize`] always translates to [`UInt<64>`][type@UInt]
-    usize, UInt<64>
+macro_rules! impl_for_all_prim_sints {
+    (
+        #[size =, $(rest:tt)*]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_sints!(
+            #[isize =, $($rest)*]
+            $m!()
+        );
+    };
+    (
+        #[size = size, $(rest:tt)*]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_sints!(
+            #[isize = isize, $($rest)*]
+            $m!()
+        );
+    };
+    (
+        #[isize = $($isize:ident)?, NonZero = $NonZero:ident]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_sints!(
+            #[isize = $($isize)?, NonZero = $NonZero, NonZero<isize> = $((NonZero<$isize>))?]
+            $m!()
+        );
+    };
+    (
+        #[isize = $($isize:ident)?, NonZero =]
+        $m:ident!()
+    ) => {
+        impl_for_all_prim_sints!(
+            #[isize = $($isize)?, NonZero =, NonZero<isize> =]
+            $m!()
+        );
+    };
+    (
+        #[isize = $($isize:ident)?, NonZero = $($NonZero:ident)?, NonZero<isize> = $(($($NonZeroIsize:tt)*))?]
+        $m:ident!()
+    ) => {
+        $m!(i8, SInt<8>);
+        $m!(i16, SInt<16>);
+        $m!(i32, SInt<32>);
+        $m!(i64, SInt<64>);
+        $m!(i128, SInt<128>);
+        $($m!($NonZero<i8>, SInt<8>);)?
+        $($m!($NonZero<i16>, SInt<16>);)?
+        $($m!($NonZero<i32>, SInt<32>);)?
+        $($m!($NonZero<i64>, SInt<64>);)?
+        $($m!($NonZero<i128>, SInt<128>);)?
+        $($m!(
+            /// for portability reasons, [`isize`] always translates to [`SInt<64>`][type@SInt]
+            $isize, SInt<64>
+        );)?
+        $($m!(
+            /// for portability reasons, [`isize`] always translates to [`SInt<64>`][type@SInt]
+            $($NonZeroIsize)*, SInt<64>
+        );)?
+    };
+}
+
+impl_for_all_prim_uints!(
+    #[usize = usize, NonZero =]
+    impl_prim_int_to_expr!()
 );
 
-impl_prim_int!(
-    /// for portability reasons, [`isize`] always translates to [`SInt<64>`][type@SInt]
-    isize, SInt<64>
+impl_for_all_prim_sints!(
+    #[isize = isize, NonZero =]
+    impl_prim_int_to_expr!()
 );
 
-pub trait BoolOrIntType: Type + sealed::BoolOrIntTypeSealed {
+macro_rules! impl_prim_int_from_value {
+    ($prim_int:ident, UInt<$width:literal>) => {
+        impl_prim_int_from_value!($prim_int, UInt<$width>, UIntValue<ConstUsize<$width>>);
+    };
+    ($prim_int:ident, SInt<$width:literal>) => {
+        impl_prim_int_from_value!($prim_int, SInt<$width>, SIntValue<ConstUsize<$width>>);
+    };
+    ($prim_int:ident, $ty:ty, $value:ty) => {
+        impl From<$value> for $prim_int {
+            fn from(value: $value) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl<'a> From<&'a mut $value> for $prim_int {
+            fn from(value: &'a mut $value) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl From<SimValue<$ty>> for $prim_int {
+            fn from(value: SimValue<$ty>) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl<'a> From<&'a mut SimValue<$ty>> for $prim_int {
+            fn from(value: &'a mut SimValue<$ty>) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl<'a> From<&'a SimValue<$ty>> for $prim_int {
+            fn from(value: &'a SimValue<$ty>) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl<'a> From<&'a $value> for $prim_int {
+            fn from(value: &'a $value) -> Self {
+                value.as_int()
+            }
+        }
+
+        impl $value {
+            pub fn as_int(&self) -> $prim_int {
+                let mut le_bytes = (0 as $prim_int).to_le_bytes();
+                let bitslice = BitSlice::<u8, Lsb0>::from_slice_mut(&mut le_bytes);
+                bitslice.clone_from_bitslice(self.bits());
+                $prim_int::from_le_bytes(le_bytes)
+            }
+        }
+    };
+}
+
+impl_for_all_prim_uints!(
+    #[usize =, NonZero =]
+    impl_prim_int_from_value!()
+);
+
+impl_for_all_prim_sints!(
+    #[isize =, NonZero =]
+    impl_prim_int_from_value!()
+);
+
+pub trait BoolOrIntType:
+    Type<SimValue = <Self as BoolOrIntType>::Value> + sealed::BoolOrIntTypeSealed
+{
     type Width: Size;
     type Signed: GenericConstBool;
     type Value: Clone
@@ -1301,12 +1819,80 @@ impl StaticType for Bool {
     const MASK_TYPE_PROPERTIES: TypeProperties = Bool::TYPE_PROPERTIES;
 }
 
+impl From<bool> for UIntValue<ConstUsize<1>> {
+    fn from(value: bool) -> Self {
+        static VALUES: OnceLock<[UIntValue<ConstUsize<1>>; 2]> = OnceLock::new();
+        let values = VALUES
+            .get_or_init(|| std::array::from_fn(|i| UInt::<1>::new_static().from_int_wrapping(i)));
+        values[value as usize].clone()
+    }
+}
+
+impl From<bool> for SIntValue<ConstUsize<1>> {
+    fn from(value: bool) -> Self {
+        SIntValue::new(UIntValue::<ConstUsize<1>>::from(value).into_bits())
+    }
+}
+
+impl From<bool> for UIntValue {
+    fn from(value: bool) -> Self {
+        UIntValue::new(UIntValue::<ConstUsize<1>>::from(value).into_bits())
+    }
+}
+
+impl From<bool> for SIntValue {
+    fn from(value: bool) -> Self {
+        SIntValue::new(UIntValue::<ConstUsize<1>>::from(value).into_bits())
+    }
+}
+
 impl ToLiteralBits for bool {
     fn to_literal_bits(&self) -> Result<Interned<BitSlice>, NotALiteralExpr> {
         Ok(interned_bit(*self))
     }
 }
 
+impl<'a> ToSimValueInner<'a> for bool {
+    fn to_sim_value_inner(this: &Self) -> Cow<'_, <Self::Type as Type>::SimValue> {
+        Cow::Owned(*this)
+    }
+    fn into_sim_value_inner(this: Self) -> Cow<'a, <Self::Type as Type>::SimValue> {
+        Cow::Owned(this)
+    }
+}
+
+impl std::ops::Not for Valueless<Bool> {
+    type Output = Valueless<Bool>;
+
+    fn not(self) -> Self::Output {
+        self
+    }
+}
+
+impl std::ops::BitAnd for Valueless<Bool> {
+    type Output = Valueless<Bool>;
+
+    fn bitand(self, _rhs: Valueless<Bool>) -> Self::Output {
+        self
+    }
+}
+
+impl std::ops::BitOr for Valueless<Bool> {
+    type Output = Valueless<Bool>;
+
+    fn bitor(self, _rhs: Valueless<Bool>) -> Self::Output {
+        self
+    }
+}
+
+impl std::ops::BitXor for Valueless<Bool> {
+    type Output = Valueless<Bool>;
+
+    fn bitxor(self, _rhs: Valueless<Bool>) -> Self::Output {
+        self
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/fayalite/src/int/uint_in_range.rs

@@ -4,13 +4,13 @@
 use crate::{
     bundle::{Bundle, BundleField, BundleType, BundleTypePropertiesBuilder, NoBuilder},
     expr::{
-        CastBitsTo, CastTo, CastToBits, Expr, HdlPartialEq, HdlPartialOrd,
-        ops::{ExprCastTo, ExprPartialEq, ExprPartialOrd},
+        CastBitsTo, CastTo, CastToBits, CastToImpl, Expr, HdlPartialEq, HdlPartialEqImpl,
+        HdlPartialOrd, HdlPartialOrdImpl,
     },
-    int::{Bool, DynSize, KnownSize, Size, SizeType, UInt, UIntType},
+    int::{Bool, DynSize, KnownSize, Size, SizeType, UInt, UIntType, UIntValue},
     intern::{Intern, InternSlice, Interned},
     phantom_const::PhantomConst,
-    sim::value::{SimValue, SimValuePartialEq, ToSimValueWithType},
+    sim::value::{SimValue, ToSimValueWithType},
     source_location::SourceLocation,
     ty::{
         CanonicalType, OpaqueSimValueSlice, OpaqueSimValueWriter, OpaqueSimValueWritten,
@@ -22,7 +22,7 @@ use serde::{
     Deserialize, Deserializer, Serialize, Serializer,
     de::{Error, Visitor, value::UsizeDeserializer},
 };
-use std::{fmt, marker::PhantomData, ops::Index};
+use std::{borrow::Cow, fmt, marker::PhantomData, ops::Index};
 
 const UINT_IN_RANGE_TYPE_FIELD_NAMES: [&'static str; 2] = ["value", "range"];
 
@@ -135,30 +135,57 @@ impl ToSimValueWithType<UIntInRangeMaskType> for bool {
     }
 }
 
-impl ExprCastTo<Bool> for UIntInRangeMaskType {
-    fn cast_to(src: Expr<Self>, to_type: Bool) -> Expr<Bool> {
-        src.cast_to_bits().cast_to(to_type)
+impl CastToImpl<Bool> for UIntInRangeMaskType {
+    type ValueOutput = bool;
+
+    fn cast_value_to(
+        _this: Self,
+        value: Cow<'_, Self::SimValue>,
+        _to_type: Bool,
+    ) -> Self::ValueOutput {
+        *value
+    }
+
+    fn cast_expr_to(value: Expr<Self>, to_type: Bool) -> Expr<Bool> {
+        value.cast_to_bits().cast_to(to_type)
     }
 }
 
-impl ExprCastTo<UIntInRangeMaskType> for Bool {
-    fn cast_to(src: Expr<Self>, to_type: UIntInRangeMaskType) -> Expr<UIntInRangeMaskType> {
-        src.cast_to_static::<UInt<1>>().cast_bits_to(to_type)
+impl CastToImpl<UIntInRangeMaskType> for Bool {
+    type ValueOutput = SimValue<UIntInRangeMaskType>;
+
+    fn cast_value_to(
+        _this: Self,
+        value: Cow<'_, Self::SimValue>,
+        to_type: UIntInRangeMaskType,
+    ) -> Self::ValueOutput {
+        SimValue::from_value(to_type, *value)
+    }
+
+    fn cast_expr_to(value: Expr<Self>, to_type: UIntInRangeMaskType) -> Expr<UIntInRangeMaskType> {
+        value.cast_to_static::<UInt<1>>().cast_bits_to(to_type)
     }
 }
 
-impl ExprPartialEq<Self> for UIntInRangeMaskType {
-    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+impl HdlPartialEqImpl<Self> for UIntInRangeMaskType {
+    #[track_caller]
+    fn cmp_value_eq(
+        _lhs: Self,
+        lhs_value: Cow<'_, Self::SimValue>,
+        _rhs: Self,
+        rhs_value: Cow<'_, Self::SimValue>,
+    ) -> bool {
+        *lhs_value == *rhs_value
+    }
+
+    #[track_caller]
+    fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
         lhs.cast_to_bits().cmp_eq(rhs.cast_to_bits())
     }
-    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        lhs.cast_to_bits().cmp_ne(rhs.cast_to_bits())
-    }
-}
 
-impl SimValuePartialEq<Self> for UIntInRangeMaskType {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
+    #[track_caller]
+    fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        lhs.cast_to_bits().cmp_ne(rhs.cast_to_bits())
     }
 }
 
@@ -482,36 +509,64 @@ macro_rules! define_uint_in_range_type {
             }
         }
 
-        impl<Start: Size, End: Size, Width: Size> ExprCastTo<UIntType<Width>>
+        impl<Start: Size, End: Size, Width: Size> CastToImpl<UIntType<Width>>
             for $UIntInRangeType<Start, End>
         {
-            fn cast_to(src: Expr<Self>, to_type: UIntType<Width>) -> Expr<UIntType<Width>> {
-                src.cast_to_bits().cast_to(to_type)
+            type ValueOutput = UIntValue<Width>;
+
+            fn cast_value_to(
+                _this: Self,
+                value: Cow<'_, Self::SimValue>,
+                to_type: UIntType<Width>,
+            ) -> Self::ValueOutput {
+                value.cast_to(to_type)
+            }
+
+            fn cast_expr_to(value: Expr<Self>, to_type: UIntType<Width>) -> Expr<UIntType<Width>> {
+                value.cast_to_bits().cast_to(to_type)
             }
         }
 
-        impl<Start: Size, End: Size, Width: Size> ExprCastTo<$UIntInRangeType<Start, End>>
+        impl<Start: Size, End: Size, Width: Size> CastToImpl<$UIntInRangeType<Start, End>>
             for UIntType<Width>
         {
-            fn cast_to(
-                src: Expr<Self>,
+            type ValueOutput = SimValue<$UIntInRangeType<Start, End>>;
+
+            fn cast_value_to(
+                _this: Self,
+                value: Cow<'_, Self::SimValue>,
+                to_type: $UIntInRangeType<Start, End>,
+            ) -> Self::ValueOutput {
+                value.cast_to(to_type.value).cast_bits_to(to_type)
+            }
+
+            fn cast_expr_to(
+                value: Expr<Self>,
                 to_type: $UIntInRangeType<Start, End>,
             ) -> Expr<$UIntInRangeType<Start, End>> {
-                src.cast_to(to_type.value).cast_bits_to(to_type)
+                value.cast_to(to_type.value).cast_bits_to(to_type)
             }
         }
 
         impl<LhsStart: Size, LhsEnd: Size, RhsStart: Size, RhsEnd: Size>
-            ExprPartialEq<$UIntInRangeType<RhsStart, RhsEnd>>
+            HdlPartialEqImpl<$UIntInRangeType<RhsStart, RhsEnd>>
             for $UIntInRangeType<LhsStart, LhsEnd>
         {
-            fn cmp_eq(
+            fn cmp_value_eq(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<RhsStart, RhsEnd>,
+                rhs_value: Cow<'_, <$UIntInRangeType<RhsStart, RhsEnd> as Type>::SimValue>,
+            ) -> bool {
+                *lhs_value == *rhs_value
+            }
+            fn cmp_expr_eq(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_eq(rhs.cast_to_bits())
             }
-            fn cmp_ne(
+            fn cmp_expr_ne(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
@@ -520,28 +575,60 @@ macro_rules! define_uint_in_range_type {
         }
 
         impl<LhsStart: Size, LhsEnd: Size, RhsStart: Size, RhsEnd: Size>
-            ExprPartialOrd<$UIntInRangeType<RhsStart, RhsEnd>>
+            HdlPartialOrdImpl<$UIntInRangeType<RhsStart, RhsEnd>>
             for $UIntInRangeType<LhsStart, LhsEnd>
         {
-            fn cmp_lt(
+            fn cmp_value_lt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<RhsStart, RhsEnd>,
+                rhs_value: Cow<'_, <$UIntInRangeType<RhsStart, RhsEnd> as Type>::SimValue>,
+            ) -> bool {
+                PartialOrd::lt(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_le(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<RhsStart, RhsEnd>,
+                rhs_value: Cow<'_, <$UIntInRangeType<RhsStart, RhsEnd> as Type>::SimValue>,
+            ) -> bool {
+                PartialOrd::le(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_gt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<RhsStart, RhsEnd>,
+                rhs_value: Cow<'_, <$UIntInRangeType<RhsStart, RhsEnd> as Type>::SimValue>,
+            ) -> bool {
+                PartialOrd::gt(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_ge(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<RhsStart, RhsEnd>,
+                rhs_value: Cow<'_, <$UIntInRangeType<RhsStart, RhsEnd> as Type>::SimValue>,
+            ) -> bool {
+                PartialOrd::ge(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_expr_lt(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_lt(rhs.cast_to_bits())
             }
-            fn cmp_le(
+            fn cmp_expr_le(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_le(rhs.cast_to_bits())
             }
-            fn cmp_gt(
+            fn cmp_expr_gt(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_gt(rhs.cast_to_bits())
             }
-            fn cmp_ge(
+            fn cmp_expr_ge(
                 lhs: Expr<Self>,
                 rhs: Expr<$UIntInRangeType<RhsStart, RhsEnd>>,
             ) -> Expr<Bool> {
@@ -549,70 +636,138 @@ macro_rules! define_uint_in_range_type {
             }
         }
 
-        impl<LhsStart: Size, LhsEnd: Size, RhsStart: Size, RhsEnd: Size>
-            SimValuePartialEq<$UIntInRangeType<RhsStart, RhsEnd>>
-            for $UIntInRangeType<LhsStart, LhsEnd>
-        {
-            fn sim_value_eq(
-                this: &SimValue<Self>,
-                other: &SimValue<$UIntInRangeType<RhsStart, RhsEnd>>,
-            ) -> bool {
-                **this == **other
-            }
-        }
-
-        impl<Start: Size, End: Size, Width: Size> ExprPartialEq<UIntType<Width>>
+        impl<Start: Size, End: Size, Width: Size> HdlPartialEqImpl<UIntType<Width>>
             for $UIntInRangeType<Start, End>
         {
-            fn cmp_eq(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_value_eq(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: UIntType<Width>,
+                rhs_value: Cow<'_, UIntValue<Width>>,
+            ) -> bool {
+                HdlPartialEq::cmp_eq(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_eq(rhs)
             }
-            fn cmp_ne(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_ne(rhs)
             }
         }
 
-        impl<Start: Size, End: Size, Width: Size> ExprPartialEq<$UIntInRangeType<Start, End>>
+        impl<Start: Size, End: Size, Width: Size> HdlPartialEqImpl<$UIntInRangeType<Start, End>>
             for UIntType<Width>
         {
-            fn cmp_eq(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_value_eq(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<Start, End>,
+                rhs_value: Cow<'_, <$UIntInRangeType<Start, End> as Type>::SimValue>,
+            ) -> bool {
+                HdlPartialEq::cmp_eq(&*lhs_value, *rhs_value)
+            }
+            fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_eq(rhs.cast_to_bits())
             }
-            fn cmp_ne(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_ne(rhs.cast_to_bits())
             }
         }
 
-        impl<Start: Size, End: Size, Width: Size> ExprPartialOrd<UIntType<Width>>
+        impl<Start: Size, End: Size, Width: Size> HdlPartialOrdImpl<UIntType<Width>>
             for $UIntInRangeType<Start, End>
         {
-            fn cmp_lt(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_value_lt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: UIntType<Width>,
+                rhs_value: Cow<'_, UIntValue<Width>>,
+            ) -> bool {
+                HdlPartialOrd::cmp_lt(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_le(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: UIntType<Width>,
+                rhs_value: Cow<'_, UIntValue<Width>>,
+            ) -> bool {
+                HdlPartialOrd::cmp_le(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_gt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: UIntType<Width>,
+                rhs_value: Cow<'_, UIntValue<Width>>,
+            ) -> bool {
+                HdlPartialOrd::cmp_gt(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_value_ge(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: UIntType<Width>,
+                rhs_value: Cow<'_, UIntValue<Width>>,
+            ) -> bool {
+                HdlPartialOrd::cmp_ge(&*lhs_value, &*rhs_value)
+            }
+            fn cmp_expr_lt(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_lt(rhs)
             }
-            fn cmp_le(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_expr_le(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_le(rhs)
             }
-            fn cmp_gt(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_expr_gt(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_gt(rhs)
             }
-            fn cmp_ge(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
+            fn cmp_expr_ge(lhs: Expr<Self>, rhs: Expr<UIntType<Width>>) -> Expr<Bool> {
                 lhs.cast_to_bits().cmp_ge(rhs)
             }
         }
 
-        impl<Start: Size, End: Size, Width: Size> ExprPartialOrd<$UIntInRangeType<Start, End>>
+        impl<Start: Size, End: Size, Width: Size> HdlPartialOrdImpl<$UIntInRangeType<Start, End>>
             for UIntType<Width>
         {
-            fn cmp_lt(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_value_lt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<Start, End>,
+                rhs_value: Cow<'_, <$UIntInRangeType<Start, End> as Type>::SimValue>,
+            ) -> bool {
+                HdlPartialOrd::cmp_lt(&*lhs_value, *rhs_value)
+            }
+            fn cmp_value_le(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<Start, End>,
+                rhs_value: Cow<'_, <$UIntInRangeType<Start, End> as Type>::SimValue>,
+            ) -> bool {
+                HdlPartialOrd::cmp_le(&*lhs_value, *rhs_value)
+            }
+            fn cmp_value_gt(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<Start, End>,
+                rhs_value: Cow<'_, <$UIntInRangeType<Start, End> as Type>::SimValue>,
+            ) -> bool {
+                HdlPartialOrd::cmp_gt(&*lhs_value, *rhs_value)
+            }
+            fn cmp_value_ge(
+                _lhs: Self,
+                lhs_value: Cow<'_, Self::SimValue>,
+                _rhs: $UIntInRangeType<Start, End>,
+                rhs_value: Cow<'_, <$UIntInRangeType<Start, End> as Type>::SimValue>,
+            ) -> bool {
+                HdlPartialOrd::cmp_ge(&*lhs_value, *rhs_value)
+            }
+            fn cmp_expr_lt(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_lt(rhs.cast_to_bits())
             }
-            fn cmp_le(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_expr_le(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_le(rhs.cast_to_bits())
             }
-            fn cmp_gt(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_expr_gt(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_gt(rhs.cast_to_bits())
             }
-            fn cmp_ge(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
+            fn cmp_expr_ge(lhs: Expr<Self>, rhs: Expr<$UIntInRangeType<Start, End>>) -> Expr<Bool> {
                 lhs.cmp_ge(rhs.cast_to_bits())
             }
         }

crates/fayalite/src/memory.rs

@@ -7,7 +7,10 @@ use crate::{
     array::{Array, ArrayType},
     bundle::{Bundle, BundleType},
     clock::Clock,
-    expr::{Expr, Flow, ToExpr, ToLiteralBits, ops::BundleLiteral, repeat},
+    expr::{
+        Expr, Flow, ToExpr, ToLiteralBits, ValueType, ops::BundleLiteral, repeat,
+        value_category::ValueCategoryExpr,
+    },
     hdl,
     int::{Bool, DynSize, Size, UInt, UIntType},
     intern::{Intern, Interned},
@@ -366,10 +369,16 @@ impl<T: PortType> fmt::Debug for MemPort<T> {
     }
 }
 
-impl<T: PortType> MemPort<T> {
-    pub fn ty(&self) -> T::Port {
+impl<T: PortType> ValueType for MemPort<T> {
+    type Type = T::Port;
+    type ValueCategory = ValueCategoryExpr;
+
+    fn ty(&self) -> T::Port {
         T::port_ty(self)
     }
+}
+
+impl<T: PortType> MemPort<T> {
     pub fn source_location(&self) -> SourceLocation {
         self.source_location
     }
@@ -830,7 +839,7 @@ impl<Element: Type, Len: Size> MemBuilder<Element, Len> {
         depth: Option<usize>,
         initial_value: Expr<Array>,
     ) -> Interned<BitSlice> {
-        let initial_value_ty = Expr::ty(initial_value);
+        let initial_value_ty = initial_value.ty();
         assert_eq!(
             *mem_element_type,
             Element::from_canonical(initial_value_ty.element()),
@@ -1011,7 +1020,7 @@ impl<Element: Type, Len: Size> MemBuilder<Element, Len> {
             target.depth,
             initial_value,
         ));
-        target.depth = Some(Expr::ty(initial_value).len());
+        target.depth = Some(initial_value.ty().len());
     }
     #[track_caller]
     pub fn initial_value_bit_slice(&mut self, initial_value: Interned<BitSlice>) {

crates/fayalite/src/module.rs

@@ -8,12 +8,13 @@ use crate::{
     clock::{Clock, ClockDomain},
     enum_::{Enum, EnumMatchVariantsIter, EnumType},
     expr::{
-        Expr, Flow, ToExpr,
+        Expr, Flow, ToExpr, ValueType,
         ops::VariantAccess,
         target::{
             GetTarget, Target, TargetBase, TargetPathArrayElement, TargetPathBundleField,
             TargetPathElement,
         },
+        value_category::ValueCategoryExpr,
     },
     formal::FormalKind,
     int::{Bool, DynSize, Size},
@@ -205,7 +206,7 @@ impl StmtConnect {
             source_location,
         } = *self;
         assert!(
-            Expr::ty(lhs).can_connect(Expr::ty(rhs)),
+            lhs.ty().can_connect(rhs.ty()),
             "can't connect types that are not equivalent:\nlhs type:\n{lhs_orig_ty:?}\nrhs type:\n{rhs_orig_ty:?}\nat: {source_location}",
         );
         assert!(
@@ -219,14 +220,14 @@ impl StmtConnect {
         match Expr::flow(rhs) {
             Flow::Source | Flow::Duplex => {}
             Flow::Sink => assert!(
-                Expr::ty(rhs).is_passive(),
+                rhs.ty().is_passive(),
                 "can't connect from sink with non-passive type\nat: {source_location}"
             ),
         }
     }
     #[track_caller]
     fn assert_validity(&self) {
-        self.assert_validity_with_original_types(Expr::ty(self.lhs), Expr::ty(self.rhs));
+        self.assert_validity_with_original_types(self.lhs.ty(), self.rhs.ty());
     }
 }
 
@@ -331,7 +332,7 @@ impl Copy for StmtMatch {}
 impl StmtMatch {
     #[track_caller]
     fn assert_validity(&self) {
-        assert_eq!(Expr::ty(self.expr).variants().len(), self.blocks.len());
+        assert_eq!(self.expr.ty().variants().len(), self.blocks.len());
     }
 }
 
@@ -765,6 +766,15 @@ impl<T: BundleType> fmt::Debug for Instance<T> {
     }
 }
 
+impl<T: BundleType> ValueType for Instance<T> {
+    type Type = T;
+    type ValueCategory = ValueCategoryExpr;
+
+    fn ty(&self) -> T {
+        self.instantiated.io_ty()
+    }
+}
+
 impl<T: BundleType> Instance<T> {
     pub fn canonical(self) -> Instance<Bundle> {
         let Self {
@@ -828,9 +838,6 @@ impl<T: BundleType> Instance<T> {
     pub fn must_connect_to(&self) -> bool {
         true
     }
-    pub fn ty(&self) -> T {
-        self.instantiated.io_ty()
-    }
 }
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
@@ -2028,7 +2035,7 @@ impl<CD> RegBuilder<CD, (), ()> {
             init: _,
             ty: _,
         } = self;
-        let ty = Expr::ty(init);
+        let ty = init.ty();
         RegBuilder {
             name,
             source_location,
@@ -2597,7 +2604,7 @@ pub fn enum_match_variants_helper<T: EnumType>(
     ModuleBuilder::with(|m| {
         let mut impl_ = m.impl_.borrow_mut();
         let body = impl_.body.builder_normal_body();
-        let enum_ty = Expr::ty(base);
+        let enum_ty = base.ty();
         let outer_block: BlockId = m.block_stack.top();
         let blocks = Interned::from_iter(enum_ty.variants().iter().map(|_| body.new_block()));
         body.block(outer_block).stmts.push(
@@ -2649,7 +2656,7 @@ pub fn connect_any_with_loc<Lhs: ToExpr, Rhs: ToExpr>(
         rhs,
         source_location,
     };
-    connect.assert_validity_with_original_types(Expr::ty(lhs_orig), Expr::ty(rhs_orig));
+    connect.assert_validity_with_original_types(lhs_orig.ty(), rhs_orig.ty());
     ModuleBuilder::with(|m| {
         m.impl_
             .borrow_mut()
@@ -2764,7 +2771,7 @@ pub fn memory_with_init_and_loc<Element: Type, Len: Size>(
     source_location: SourceLocation,
 ) -> MemBuilder<Element, Len> {
     let initial_value = initial_value.to_expr();
-    let mut retval = memory_array_with_loc(name, Expr::ty(initial_value), source_location);
+    let mut retval = memory_array_with_loc(name, initial_value.ty(), source_location);
     retval.initial_value(initial_value);
     retval
 }
@@ -2807,6 +2814,15 @@ pub struct ModuleIO<T: Type> {
     source_location: SourceLocation,
 }
 
+impl<T: Type> ValueType for ModuleIO<T> {
+    type Type = T;
+    type ValueCategory = ValueCategoryExpr;
+
+    fn ty(&self) -> Self::Type {
+        self.ty
+    }
+}
+
 impl<T: Type> fmt::Debug for ModuleIO<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("ModuleIO")
@@ -2908,9 +2924,6 @@ impl<T: Type> ModuleIO<T> {
             unreachable!()
         }
     }
-    pub fn ty(&self) -> T {
-        self.ty
-    }
 }
 
 #[derive(PartialEq, Eq, Hash, Clone, Copy)]

crates/fayalite/src/module/transform/deduce_resets.rs

@@ -6,7 +6,7 @@ use crate::{
     bundle::{BundleField, BundleType},
     enum_::{EnumType, EnumVariant},
     expr::{
-        ExprEnum,
+        ExprEnum, ValueType,
         ops::{self, ArrayLiteral},
         target::{
             Target, TargetBase, TargetChild, TargetPathArrayElement, TargetPathBundleField,
@@ -521,7 +521,7 @@ impl State {
             Entry::Vacant(entry) => (
                 *entry.insert(Resets::with_new_nodes(
                     &mut self.reset_graph,
-                    Expr::ty(expr),
+                    expr.ty(),
                     source_location,
                 )),
                 true,
@@ -1020,7 +1020,7 @@ fn cast_bit_op<P: Pass, T: Type, A: Type>(
                 }
                 macro_rules! match_arg_ty {
                     ($($Variant:ident),*) => {
-                        *match Expr::ty(arg) {
+                        *match arg.ty() {
                             CanonicalType::Array(_)
                             | CanonicalType::Enum(_)
                             | CanonicalType::Bundle(_)
@@ -1660,7 +1660,8 @@ impl RunPassDispatch for AnyReg {
             let clock_domain = Expr::<Bundle>::from_canonical(
                 Expr::canonical(reg.clock_domain()).run_pass(pass_args)?.0,
             );
-            match Expr::ty(clock_domain)
+            match clock_domain
+                .ty()
                 .field_by_name("rst".intern())
                 .expect("ClockDomain has rst field")
                 .ty

crates/fayalite/src/module/transform/simplify_enums.rs

@@ -5,7 +5,7 @@ use crate::{
     bundle::{Bundle, BundleField, BundleType},
     enum_::{Enum, EnumType, EnumVariant},
     expr::{
-        CastBitsTo, CastTo, CastToBits, Expr, ExprEnum, HdlPartialEq, ToExpr,
+        CastBitsTo, CastTo, CastToBits, Expr, ExprEnum, HdlPartialEq, ToExpr, ValueType,
         ops::{self, EnumLiteral},
     },
     hdl,
@@ -528,7 +528,7 @@ fn connect_port(
     rhs: Expr<CanonicalType>,
     source_location: SourceLocation,
 ) {
-    if Expr::ty(lhs) == Expr::ty(rhs) {
+    if lhs.ty() == rhs.ty() {
         stmts.push(
             StmtConnect {
                 lhs,
@@ -539,7 +539,7 @@ fn connect_port(
         );
         return;
     }
-    match (Expr::ty(lhs), Expr::ty(rhs)) {
+    match (lhs.ty(), rhs.ty()) {
         (CanonicalType::Bundle(lhs_type), CanonicalType::UInt(_) | CanonicalType::Bool(_)) => {
             let lhs = Expr::<Bundle>::from_canonical(lhs);
             for field in lhs_type.fields() {
@@ -586,8 +586,8 @@ fn connect_port(
         | (CanonicalType::PhantomConst(_), _)
         | (CanonicalType::DynSimOnly(_), _) => unreachable!(
             "trying to connect memory ports:\n{:?}\n{:?}",
-            Expr::ty(lhs),
-            Expr::ty(rhs),
+            lhs.ty(),
+            rhs.ty(),
         ),
     }
 }
@@ -607,14 +607,17 @@ fn match_int_tag(
         };
     };
     let mut retval = StmtIf {
-        cond: int_tag_expr
-            .cmp_eq(Expr::ty(int_tag_expr).from_int_wrapping(next_to_last_variant_index)),
+        cond: int_tag_expr.cmp_eq(
+            int_tag_expr
+                .ty()
+                .from_int_wrapping(next_to_last_variant_index),
+        ),
         source_location,
         blocks: [next_to_last_block, last_block],
     };
     for (variant_index, block) in blocks_iter.rev() {
         retval = StmtIf {
-            cond: int_tag_expr.cmp_eq(Expr::ty(int_tag_expr).from_int_wrapping(variant_index)),
+            cond: int_tag_expr.cmp_eq(int_tag_expr.ty().from_int_wrapping(variant_index)),
             source_location,
             blocks: [
                 block,
@@ -657,7 +660,7 @@ impl Folder for State {
             ExprEnum::VariantAccess(op) => {
                 let folded_base_expr = Expr::canonical(op.base()).fold(self)?;
                 Ok(*Expr::expr_enum(self.handle_variant_access(
-                    Expr::ty(op.base()),
+                    op.base().ty(),
                     folded_base_expr,
                     op.variant_index(),
                 )?))
@@ -867,7 +870,7 @@ impl Folder for State {
             }) => {
                 let folded_expr = Expr::canonical(expr).fold(self)?;
                 let folded_blocks = blocks.fold(self)?;
-                self.handle_match(Expr::ty(expr), folded_expr, source_location, &folded_blocks)
+                self.handle_match(expr.ty(), folded_expr, source_location, &folded_blocks)
             }
             Stmt::Connect(StmtConnect {
                 lhs,
@@ -878,8 +881,8 @@ impl Folder for State {
                 let folded_rhs = rhs.fold(self)?;
                 let mut output_stmts = vec![];
                 self.handle_stmt_connect(
-                    Expr::ty(lhs),
-                    Expr::ty(rhs),
+                    lhs.ty(),
+                    rhs.ty(),
                     folded_lhs,
                     folded_rhs,
                     source_location,

crates/fayalite/src/module/transform/simplify_memories.rs

@@ -4,7 +4,7 @@ use crate::{
     annotations::TargetedAnnotation,
     array::Array,
     bundle::{Bundle, BundleType},
-    expr::{CastBitsTo, CastToBits, Expr, ExprEnum, ToExpr},
+    expr::{CastBitsTo, CastToBits, Expr, ExprEnum, ToExpr, ValueType},
     int::{Bool, SInt, Size, UInt},
     intern::{Intern, Interned},
     memory::{Mem, MemPort, PortType},
@@ -530,7 +530,7 @@ impl ModuleState {
             connect_read(
                 output_stmts,
                 wire_read,
-                Expr::<UInt>::from_canonical(port_read).cast_bits_to(Expr::ty(wire_read)),
+                Expr::<UInt>::from_canonical(port_read).cast_bits_to(wire_read.ty()),
             );
         };
         let connect_write_enum =

crates/fayalite/src/module/transform/visit.rs

@@ -11,7 +11,7 @@ use crate::{
     clock::Clock,
     enum_::{Enum, EnumType, EnumVariant},
     expr::{
-        Expr, ExprEnum, ops,
+        Expr, ExprEnum, ValueType, ops,
         target::{
             Target, TargetBase, TargetChild, TargetPathArrayElement, TargetPathBundleField,
             TargetPathDynArrayElement, TargetPathElement,

crates/fayalite/src/phantom_const.rs

@@ -2,13 +2,10 @@
 // See Notices.txt for copyright information
 
 use crate::{
-    expr::{
-        Expr, ToExpr,
-        ops::{ExprPartialEq, ExprPartialOrd},
-    },
+    expr::{Expr, HdlPartialEqImpl, HdlPartialOrdImpl, ToExpr, ValueType},
     int::Bool,
     intern::{Intern, Interned, InternedCompare, LazyInterned, LazyInternedTrait, Memoize},
-    sim::value::{SimValue, SimValuePartialEq, ToSimValue, ToSimValueWithType},
+    sim::value::{SimValue, ToSimValue, ToSimValueWithType},
     source_location::SourceLocation,
     ty::{
         CanonicalType, OpaqueSimValueSlice, OpaqueSimValueWriter, OpaqueSimValueWritten,
@@ -22,6 +19,7 @@ use serde::{
 };
 use std::{
     any::Any,
+    borrow::Cow,
     fmt,
     hash::{Hash, Hasher},
     marker::PhantomData,
@@ -372,50 +370,102 @@ impl<'de, T: ?Sized + PhantomConstValue> Deserialize<'de> for PhantomConst<T> {
     }
 }
 
-impl<T: ?Sized + PhantomConstValue> ExprPartialEq<Self> for PhantomConst<T> {
-    fn cmp_eq(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        true.to_expr()
-    }
-
-    fn cmp_ne(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        false.to_expr()
-    }
-}
-
-impl<T: ?Sized + PhantomConstValue> ExprPartialOrd<Self> for PhantomConst<T> {
-    fn cmp_lt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        false.to_expr()
-    }
-
-    fn cmp_le(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        true.to_expr()
-    }
-
-    fn cmp_gt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        false.to_expr()
-    }
-
-    fn cmp_ge(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
-        assert_eq!(Expr::ty(lhs), Expr::ty(rhs));
-        true.to_expr()
-    }
-}
-
-impl<T: ?Sized + PhantomConstValue> SimValuePartialEq<Self> for PhantomConst<T> {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        assert_eq!(SimValue::ty(this), SimValue::ty(other));
+impl<T: ?Sized + PhantomConstValue> HdlPartialEqImpl<Self> for PhantomConst<T> {
+    #[track_caller]
+    fn cmp_value_eq(
+        lhs: Self,
+        _lhs_value: Cow<'_, Self::SimValue>,
+        rhs: Self,
+        _rhs_value: Cow<'_, <Self as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs, rhs);
         true
     }
+
+    #[track_caller]
+    fn cmp_expr_eq(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        true.to_expr()
+    }
+
+    #[track_caller]
+    fn cmp_expr_ne(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        false.to_expr()
+    }
+}
+
+impl<T: ?Sized + PhantomConstValue> HdlPartialOrdImpl<Self> for PhantomConst<T> {
+    #[track_caller]
+    fn cmp_value_lt(
+        lhs: Self,
+        _lhs_value: Cow<'_, Self::SimValue>,
+        rhs: Self,
+        _rhs_value: Cow<'_, <Self as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs, rhs);
+        false
+    }
+
+    #[track_caller]
+    fn cmp_value_le(
+        lhs: Self,
+        _lhs_value: Cow<'_, Self::SimValue>,
+        rhs: Self,
+        _rhs_value: Cow<'_, <Self as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs, rhs);
+        true
+    }
+
+    #[track_caller]
+    fn cmp_value_gt(
+        lhs: Self,
+        _lhs_value: Cow<'_, Self::SimValue>,
+        rhs: Self,
+        _rhs_value: Cow<'_, <Self as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs, rhs);
+        false
+    }
+
+    #[track_caller]
+    fn cmp_value_ge(
+        lhs: Self,
+        _lhs_value: Cow<'_, Self::SimValue>,
+        rhs: Self,
+        _rhs_value: Cow<'_, <Self as Type>::SimValue>,
+    ) -> bool {
+        assert_eq!(lhs, rhs);
+        true
+    }
+
+    #[track_caller]
+    fn cmp_expr_lt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        false.to_expr()
+    }
+
+    #[track_caller]
+    fn cmp_expr_le(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        true.to_expr()
+    }
+
+    #[track_caller]
+    fn cmp_expr_gt(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        false.to_expr()
+    }
+
+    #[track_caller]
+    fn cmp_expr_ge(lhs: Expr<Self>, rhs: Expr<Self>) -> Expr<Bool> {
+        assert_eq!(lhs.ty(), rhs.ty());
+        true.to_expr()
+    }
 }
 
 impl<T: ?Sized + PhantomConstValue> ToSimValue for PhantomConst<T> {
-    type Type = PhantomConst<T>;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_value(*self, *self)
     }
@@ -479,7 +529,7 @@ impl_phantom_const_get! {
 impl_phantom_const_get! {
     impl PhantomConstGet<T> for Expr<PhantomConst<T>> {
         fn get(&self) -> _ {
-            PhantomConst::get(Expr::ty(*self))
+            PhantomConst::get(self.ty())
         }
     }
 }

crates/fayalite/src/platform.rs

@@ -3,7 +3,7 @@
 
 use crate::{
     bundle::{Bundle, BundleField, BundleType},
-    expr::{Expr, ExprEnum},
+    expr::{Expr, ExprEnum, ValueType},
     intern::{Intern, Interned},
     module::{Module, ModuleBuilder, ModuleIO, connect_with_loc, instance_with_loc, wire_with_loc},
     source_location::SourceLocation,
@@ -615,8 +615,8 @@ impl<T: Type> Peripheral<T> {
         };
         drop(state);
         let Self { ty, common } = self;
-        let instance_io_field = Expr::field(output, &common.id.name);
-        assert_eq!(ty, Expr::ty(instance_io_field));
+        let instance_io_field = Expr::field::<T>(output, &common.id.name);
+        assert_eq!(ty, instance_io_field.ty());
         Ok(UsedPeripheral {
             instance_io_field,
             common,
@@ -654,7 +654,7 @@ impl<T: Type> UsedPeripheral<T> {
             ref common,
         } = *self;
         PeripheralRef {
-            ty: Expr::ty(instance_io_field),
+            ty: instance_io_field.ty(),
             common,
         }
     }
@@ -915,7 +915,7 @@ impl<'a, T: Type> PeripheralRef<'a, T> {
         main_module_io_fields.push(BundleField {
             name: self.name(),
             flipped: self.is_input(),
-            ty: Expr::ty(canonical_wire),
+            ty: canonical_wire.ty(),
         });
         on_use_function(&mut **shared_state, self.canonical(), canonical_wire);
         drop(on_use_state);

crates/fayalite/src/prelude.rs

@@ -13,7 +13,7 @@ pub use crate::{
     enum_::{Enum, HdlNone, HdlOption, HdlSome},
     expr::{
         CastBitsTo, CastTo, CastToBits, Expr, HdlPartialEq, HdlPartialOrd, MakeUninitExpr,
-        ReduceBits, ToExpr, repeat,
+        ReduceBits, ToExpr, ValueType, repeat,
     },
     formal::{
         MakeFormalExpr, all_const, all_seq, any_const, any_seq, formal_global_clock, formal_reset,

crates/fayalite/src/reg.rs

@@ -2,7 +2,7 @@
 // See Notices.txt for copyright information
 use crate::{
     clock::ClockDomain,
-    expr::{Expr, Flow},
+    expr::{Expr, Flow, ValueType, value_category::ValueCategoryExpr},
     intern::Interned,
     module::{NameId, ScopedNameId},
     reset::{Reset, ResetType},
@@ -20,7 +20,16 @@ pub struct Reg<T: Type, R: ResetType = Reset> {
     init: Option<Expr<T>>,
 }
 
-impl<T: Type + fmt::Debug, R: ResetType> fmt::Debug for Reg<T, R> {
+impl<T: Type, R: ResetType> ValueType for Reg<T, R> {
+    type Type = T;
+    type ValueCategory = ValueCategoryExpr;
+
+    fn ty(&self) -> Self::Type {
+        self.ty
+    }
+}
+
+impl<T: Type, R: ResetType> fmt::Debug for Reg<T, R> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let Self {
             name,
@@ -68,7 +77,7 @@ impl<T: Type, R: ResetType> Reg<T, R> {
             "register type must be a storable type"
         );
         if let Some(init) = init {
-            assert_eq!(ty, Expr::ty(init), "register's type must match init type");
+            assert_eq!(ty, init.ty(), "register's type must match init type");
         }
         Self {
             name: scoped_name,
@@ -78,9 +87,6 @@ impl<T: Type, R: ResetType> Reg<T, R> {
             init,
         }
     }
-    pub fn ty(&self) -> T {
-        self.ty
-    }
     pub fn source_location(&self) -> SourceLocation {
         self.source_location
     }

crates/fayalite/src/reset.rs

@@ -2,13 +2,15 @@
 // See Notices.txt for copyright information
 use crate::{
     clock::Clock,
-    expr::{Expr, ToExpr, ops},
-    int::{Bool, SInt, UInt},
+    expr::{CastToImpl, Expr, ValueType},
+    int::{Bool, SInt, SIntValue, UInt, UIntValue},
+    sim::value::SimValue,
     source_location::SourceLocation,
     ty::{
         CanonicalType, OpaqueSimValueSize, OpaqueSimValueSlice, OpaqueSimValueWriter,
         OpaqueSimValueWritten, StaticType, Type, TypeProperties, impl_match_variant_as_self,
     },
+    util::ConstUsize,
 };
 use bitvec::{bits, order::Lsb0};
 
@@ -19,15 +21,15 @@ mod sealed {
 pub trait ResetType:
     StaticType<MaskType = Bool>
     + sealed::ResetTypeSealed
-    + ops::ExprCastTo<Bool>
-    + ops::ExprCastTo<Reset>
-    + ops::ExprCastTo<SyncReset>
-    + ops::ExprCastTo<AsyncReset>
-    + ops::ExprCastTo<Clock>
-    + ops::ExprCastTo<UInt<1>>
-    + ops::ExprCastTo<SInt<1>>
-    + ops::ExprCastTo<UInt>
-    + ops::ExprCastTo<SInt>
+    + CastToImpl<Bool, ValueOutput = bool>
+    + CastToImpl<Reset, ValueOutput = SimValue<Reset>>
+    + CastToImpl<SyncReset, ValueOutput = SimValue<SyncReset>>
+    + CastToImpl<AsyncReset, ValueOutput = SimValue<AsyncReset>>
+    + CastToImpl<Clock, ValueOutput = SimValue<Clock>>
+    + CastToImpl<UInt<1>, ValueOutput = UIntValue<ConstUsize<1>>>
+    + CastToImpl<SInt<1>, ValueOutput = SIntValue<ConstUsize<1>>>
+    + CastToImpl<UInt, ValueOutput = UIntValue>
+    + CastToImpl<SInt, ValueOutput = SIntValue>
 {
     fn dispatch<D: ResetTypeDispatch>(input: D::Input<Self>, dispatch: D) -> D::Output<Self>;
 }
@@ -132,29 +134,34 @@ macro_rules! reset_type {
         }
 
         pub trait $Trait {
-            fn $trait_fn(&self) -> Expr<$name>;
+            type Output: ValueType<Type = $name>;
+            fn $trait_fn(&self) -> Self::Output;
         }
 
         impl<T: ?Sized + $Trait> $Trait for &'_ T {
-            fn $trait_fn(&self) -> Expr<$name> {
+            type Output = T::Output;
+            fn $trait_fn(&self) -> Self::Output {
                 (**self).$trait_fn()
             }
         }
 
         impl<T: ?Sized + $Trait> $Trait for &'_ mut T {
-            fn $trait_fn(&self) -> Expr<$name> {
+            type Output = T::Output;
+            fn $trait_fn(&self) -> Self::Output {
                 (**self).$trait_fn()
             }
         }
 
         impl<T: ?Sized + $Trait> $Trait for Box<T> {
-            fn $trait_fn(&self) -> Expr<$name> {
+            type Output = T::Output;
+            fn $trait_fn(&self) -> Self::Output {
                 (**self).$trait_fn()
             }
         }
 
         $($impl_trait $Trait for Expr<$name> {
-            fn $trait_fn(&self) -> Expr<$name> {
+            type Output = Expr<$name>;
+            fn $trait_fn(&self) -> Self::Output {
                 *self
             }
         })?
@@ -171,13 +178,15 @@ reset_type!(
 );
 
 impl ToSyncReset for bool {
-    fn to_sync_reset(&self) -> Expr<SyncReset> {
-        self.to_expr().to_sync_reset()
+    type Output = SimValue<SyncReset>;
+    fn to_sync_reset(&self) -> Self::Output {
+        SimValue::from_value(SyncReset, *self)
     }
 }
 
 impl ToAsyncReset for bool {
-    fn to_async_reset(&self) -> Expr<AsyncReset> {
-        self.to_expr().to_async_reset()
+    type Output = SimValue<AsyncReset>;
+    fn to_async_reset(&self) -> Self::Output {
+        SimValue::from_value(AsyncReset, *self)
     }
 }

crates/fayalite/src/sim.rs

@@ -6,7 +6,7 @@
 use crate::{
     bundle::{BundleField, BundleType},
     expr::{
-        Flow, ToLiteralBits,
+        Flow,
         target::{
             GetTarget, Target, TargetPathArrayElement, TargetPathBundleField, TargetPathElement,
         },
@@ -47,7 +47,6 @@ use num_bigint::BigInt;
 use num_traits::{Signed, Zero};
 use std::{
     any::Any,
-    borrow::Cow,
     cell::{Cell, RefCell},
     collections::{BTreeMap, BTreeSet},
     fmt,
@@ -1504,9 +1503,10 @@ impl<I: BoolOrIntType> MaybeNeedsSettleFn<&'_ mut interpreter::State> for ReadBo
     fn call(self, state: &mut interpreter::State) -> Self::Output {
         let Self { compiled_value, io } = self;
         match compiled_value.range.len().as_single() {
-            Some(TypeLenSingle::SmallSlot) => Expr::ty(io)
+            Some(TypeLenSingle::SmallSlot) => io
+                .ty()
                 .value_from_int_wrapping(state.small_slots[compiled_value.range.small_slots.start]),
-            Some(TypeLenSingle::BigSlot) => Expr::ty(io).value_from_int_wrapping(
+            Some(TypeLenSingle::BigSlot) => io.ty().value_from_int_wrapping(
                 state.big_slots[compiled_value.range.big_slots.start].clone(),
             ),
             Some(TypeLenSingle::SimOnlySlot) | None => unreachable!(),
@@ -2889,7 +2889,7 @@ impl SimulationImpl {
                 },
             );
         }
-        let size = Expr::ty(io).size();
+        let size = io.ty().size();
         let mut opaque = OpaqueSimValue::with_capacity(size);
         opaque.rewrite_with(size, |mut writer| {
             SimulationImpl::read_write_sim_value_helper(
@@ -2922,7 +2922,7 @@ impl SimulationImpl {
             );
             writer.fill_cloned_from_slice(OpaqueSimValueSlice::empty())
         });
-        SimValue::from_opaque(Expr::ty(io), opaque)
+        SimValue::from_opaque(io.ty(), opaque)
     }
     /// doesn't modify `opaque`
     fn value_changed(
@@ -3006,7 +3006,7 @@ impl SimulationImpl {
             .get_module_mut(which_module)
             .write_helper(io, which_module);
         self.event_queue.add_event_for_now(EventKind::State);
-        assert_eq!(Expr::ty(io), SimValue::ty(value));
+        assert_eq!(io.ty(), value.ty());
         Self::read_write_sim_value_helper(
             &mut self.state,
             compiled_value,
@@ -3269,16 +3269,12 @@ macro_rules! impl_simulation_methods {
         pub $($async)? fn write_bool_or_int<I: BoolOrIntType>(
             &mut $self,
             io: Expr<I>,
-            value: impl ToExpr<Type = I>,
+            value: impl ToSimValueWithType<I>,
         ) {
-            let value = value.to_expr();
-            assert_eq!(Expr::ty(io), Expr::ty(value), "type mismatch");
-            let value = value
-                .to_literal_bits()
-                .expect("the value that is being written to an input must be a literal");
+            let value = value.to_sim_value_with_type(io.ty());
             $self.sim_impl.borrow_mut().write_bool_or_int(
                 io,
-                I::bits_to_value(Cow::Borrowed(&value)),
+                SimValue::into_value(value),
                 $which_module,
             );
         }
@@ -3343,7 +3339,7 @@ macro_rules! impl_simulation_methods {
         pub $($async)? fn write<IO: Type, V: value::ToSimValueWithType<IO>>(&mut $self, io: Expr<IO>, value: V) {
             $self.sim_impl.borrow_mut().write(
                 Expr::canonical(io),
-                &SimValue::into_canonical(value.into_sim_value_with_type(Expr::ty(io))),
+                &SimValue::into_canonical(value.into_sim_value_with_type(io.ty())),
                 $which_module,
             );
         }

crates/fayalite/src/sim/compiler.rs

@@ -7,7 +7,7 @@ use crate::{
     bundle::{BundleField, BundleType},
     enum_::{EnumType, EnumVariant},
     expr::{
-        ExprEnum, Flow, ops,
+        ExprEnum, Flow, ValueType, ops,
         target::{
             GetTarget, Target, TargetBase, TargetPathArrayElement, TargetPathBundleField,
             TargetPathElement,
@@ -1714,7 +1714,7 @@ impl MakeTraceDeclTarget {
     }
     fn ty(self) -> CanonicalType {
         match self {
-            MakeTraceDeclTarget::Expr(expr) => Expr::ty(expr),
+            MakeTraceDeclTarget::Expr(expr) => expr.ty(),
             MakeTraceDeclTarget::Memory { ty, .. } => ty,
         }
     }
@@ -2771,7 +2771,7 @@ impl Compiler {
         let retval = parts
             .into_iter()
             .map(|part| part.cast_to_bits())
-            .reduce(|accumulator, part| accumulator | (part << Expr::ty(accumulator).width))
+            .reduce(|accumulator, part| accumulator | (part << accumulator.ty().width))
             .unwrap_or_else(|| UInt[0].zero().to_expr());
         let retval = self.compile_expr(instantiated_module, Expr::canonical(retval));
         let retval = self
@@ -2783,7 +2783,7 @@ impl Compiler {
         instantiated_module: InstantiatedModule,
         expr: ops::CastToBits,
     ) -> CompiledValue<UInt> {
-        match Expr::ty(expr.arg()) {
+        match expr.arg().ty() {
             CanonicalType::UInt(_) => {
                 self.compile_cast_scalar_to_bits(instantiated_module, expr.arg(), |arg| arg)
             }
@@ -2949,7 +2949,7 @@ impl Compiler {
             return retval;
         }
         let mut cast_bit = |arg: Expr<CanonicalType>| {
-            let src_signed = match Expr::ty(arg) {
+            let src_signed = match arg.ty() {
                 CanonicalType::UInt(_) => false,
                 CanonicalType::SInt(_) => true,
                 CanonicalType::Bool(_) => false,
@@ -2963,7 +2963,7 @@ impl Compiler {
                 CanonicalType::PhantomConst(_) => unreachable!(),
                 CanonicalType::DynSimOnly(_) => unreachable!(),
             };
-            let dest_signed = match Expr::ty(expr) {
+            let dest_signed = match expr.ty() {
                 CanonicalType::UInt(_) => false,
                 CanonicalType::SInt(_) => true,
                 CanonicalType::Bool(_) => false,
@@ -2977,22 +2977,23 @@ impl Compiler {
                 CanonicalType::PhantomConst(_) => unreachable!(),
                 CanonicalType::DynSimOnly(_) => unreachable!(),
             };
-            self.simple_nary_big_expr(instantiated_module, Expr::ty(expr), [arg], |dest, [src]| {
-                match (src_signed, dest_signed) {
-                    (false, false) | (true, true) => {
-                        vec![Insn::Copy { dest, src }]
-                    }
-                    (false, true) => vec![Insn::CastToSInt {
-                        dest,
-                        src,
-                        dest_width: 1,
-                    }],
-                    (true, false) => vec![Insn::CastToUInt {
-                        dest,
-                        src,
-                        dest_width: 1,
-                    }],
+            self.simple_nary_big_expr(instantiated_module, expr.ty(), [arg], |dest, [src]| match (
+                src_signed,
+                dest_signed,
+            ) {
+                (false, false) | (true, true) => {
+                    vec![Insn::Copy { dest, src }]
                 }
+                (false, true) => vec![Insn::CastToSInt {
+                    dest,
+                    src,
+                    dest_width: 1,
+                }],
+                (true, false) => vec![Insn::CastToUInt {
+                    dest,
+                    src,
+                    dest_width: 1,
+                }],
             })
             .into()
         };
@@ -3032,21 +3033,13 @@ impl Compiler {
                 })
                 .into(),
             ExprEnum::PhantomConst(_) => self
-                .compile_aggregate_literal(instantiated_module, Expr::ty(expr), Interned::default())
+                .compile_aggregate_literal(instantiated_module, expr.ty(), Interned::default())
                 .into(),
             ExprEnum::BundleLiteral(literal) => self
-                .compile_aggregate_literal(
-                    instantiated_module,
-                    Expr::ty(expr),
-                    literal.field_values(),
-                )
+                .compile_aggregate_literal(instantiated_module, expr.ty(), literal.field_values())
                 .into(),
             ExprEnum::ArrayLiteral(literal) => self
-                .compile_aggregate_literal(
-                    instantiated_module,
-                    Expr::ty(expr),
-                    literal.element_values(),
-                )
+                .compile_aggregate_literal(instantiated_module, expr.ty(), literal.element_values())
                 .into(),
             ExprEnum::EnumLiteral(expr) => {
                 let enum_bits_ty = UInt[expr.ty().type_properties().bit_width];
@@ -3074,13 +3067,13 @@ impl Compiler {
             ExprEnum::NotU(expr) => self
                 .simple_nary_big_expr(
                     instantiated_module,
-                    Expr::ty(expr.arg()).canonical(),
+                    expr.arg().ty().canonical(),
                     [Expr::canonical(expr.arg())],
                     |dest, [src]| {
                         vec![Insn::NotU {
                             dest,
                             src,
-                            width: Expr::ty(expr.arg()).width(),
+                            width: expr.arg().ty().width(),
                         }]
                     },
                 )
@@ -3088,7 +3081,7 @@ impl Compiler {
             ExprEnum::NotS(expr) => self
                 .simple_nary_big_expr(
                     instantiated_module,
-                    Expr::ty(expr.arg()).canonical(),
+                    expr.arg().ty().canonical(),
                     [Expr::canonical(expr.arg())],
                     |dest, [src]| vec![Insn::NotS { dest, src }],
                 )
@@ -3096,7 +3089,7 @@ impl Compiler {
             ExprEnum::NotB(expr) => self
                 .simple_nary_big_expr(
                     instantiated_module,
-                    Expr::ty(expr.arg()).canonical(),
+                    expr.arg().ty().canonical(),
                     [Expr::canonical(expr.arg())],
                     |dest, [src]| {
                         vec![Insn::NotU {
@@ -3600,12 +3593,12 @@ impl Compiler {
                 .map_ty(Bundle::from_canonical)
                 .field_by_index(expr.field_index()),
             ExprEnum::VariantAccess(variant_access) => {
-                let start = Expr::ty(variant_access.base()).discriminant_bit_width();
-                let len = Expr::ty(expr).bit_width();
+                let start = variant_access.base().ty().discriminant_bit_width();
+                let len = expr.ty().bit_width();
                 self.compile_expr(
                     instantiated_module,
                     variant_access.base().cast_to_bits()[start..start + len]
-                        .cast_bits_to(Expr::ty(expr)),
+                        .cast_bits_to(expr.ty()),
                 )
             }
             ExprEnum::ArrayIndex(expr) => self
@@ -3627,45 +3620,39 @@ impl Compiler {
                     .map_ty(Array::from_canonical)
                     .element_dyn(index_slot)
             }
-            ExprEnum::ReduceBitAndU(expr) => if Expr::ty(expr.arg()).width() == 0 {
+            ExprEnum::ReduceBitAndU(expr) => if expr.arg().ty().width() == 0 {
                 self.compile_expr(instantiated_module, Expr::canonical(true.to_expr()))
             } else {
                 self.compile_expr(
                     instantiated_module,
-                    Expr::canonical(
-                        expr.arg()
-                            .cmp_eq(Expr::ty(expr.arg()).from_int_wrapping(-1)),
-                    ),
+                    Expr::canonical(expr.arg().cmp_eq(expr.arg().ty().from_int_wrapping(-1))),
                 )
             }
             .into(),
-            ExprEnum::ReduceBitAndS(expr) => if Expr::ty(expr.arg()).width() == 0 {
+            ExprEnum::ReduceBitAndS(expr) => if expr.arg().ty().width() == 0 {
                 self.compile_expr(instantiated_module, Expr::canonical(true.to_expr()))
             } else {
                 self.compile_expr(
                     instantiated_module,
-                    Expr::canonical(
-                        expr.arg()
-                            .cmp_eq(Expr::ty(expr.arg()).from_int_wrapping(-1)),
-                    ),
+                    Expr::canonical(expr.arg().cmp_eq(expr.arg().ty().from_int_wrapping(-1))),
                 )
             }
             .into(),
-            ExprEnum::ReduceBitOrU(expr) => if Expr::ty(expr.arg()).width() == 0 {
+            ExprEnum::ReduceBitOrU(expr) => if expr.arg().ty().width() == 0 {
                 self.compile_expr(instantiated_module, Expr::canonical(false.to_expr()))
             } else {
                 self.compile_expr(
                     instantiated_module,
-                    Expr::canonical(expr.arg().cmp_ne(Expr::ty(expr.arg()).from_int_wrapping(0))),
+                    Expr::canonical(expr.arg().cmp_ne(expr.arg().ty().from_int_wrapping(0))),
                 )
             }
             .into(),
-            ExprEnum::ReduceBitOrS(expr) => if Expr::ty(expr.arg()).width() == 0 {
+            ExprEnum::ReduceBitOrS(expr) => if expr.arg().ty().width() == 0 {
                 self.compile_expr(instantiated_module, Expr::canonical(false.to_expr()))
             } else {
                 self.compile_expr(
                     instantiated_module,
-                    Expr::canonical(expr.arg().cmp_ne(Expr::ty(expr.arg()).from_int_wrapping(0))),
+                    Expr::canonical(expr.arg().cmp_ne(expr.arg().ty().from_int_wrapping(0))),
                 )
             }
             .into(),
@@ -3678,7 +3665,7 @@ impl Compiler {
                         vec![Insn::ReduceBitXor {
                             dest,
                             src,
-                            input_width: Expr::ty(expr.arg()).width(),
+                            input_width: expr.arg().ty().width(),
                         }]
                     },
                 )
@@ -3692,7 +3679,7 @@ impl Compiler {
                         vec![Insn::ReduceBitXor {
                             dest,
                             src,
-                            input_width: Expr::ty(expr.arg()).width(),
+                            input_width: expr.arg().ty().width(),
                         }]
                     },
                 )
@@ -3790,8 +3777,8 @@ impl Compiler {
         mut rhs: Expr<CanonicalType>,
         source_location: SourceLocation,
     ) {
-        if Expr::ty(lhs) != Expr::ty(rhs) || !Expr::ty(lhs).is_passive() {
-            match Expr::ty(lhs) {
+        if lhs.ty() != rhs.ty() || !lhs.ty().is_passive() {
+            match lhs.ty() {
                 CanonicalType::UInt(lhs_ty) => {
                     rhs = Expr::canonical(Expr::<UInt>::from_canonical(rhs).cast_to(lhs_ty));
                 }
@@ -3800,7 +3787,7 @@ impl Compiler {
                 }
                 CanonicalType::Bool(_) => unreachable!(),
                 CanonicalType::Array(lhs_ty) => {
-                    let CanonicalType::Array(rhs_ty) = Expr::ty(rhs) else {
+                    let CanonicalType::Array(rhs_ty) = rhs.ty() else {
                         unreachable!();
                     };
                     assert_eq!(lhs_ty.len(), rhs_ty.len());
@@ -3820,13 +3807,13 @@ impl Compiler {
                     return;
                 }
                 CanonicalType::Enum(lhs_ty) => {
-                    let CanonicalType::Enum(rhs_ty) = Expr::ty(rhs) else {
+                    let CanonicalType::Enum(rhs_ty) = rhs.ty() else {
                         unreachable!();
                     };
                     todo!("handle connect with different enum types");
                 }
                 CanonicalType::Bundle(lhs_ty) => {
-                    let CanonicalType::Bundle(rhs_ty) = Expr::ty(rhs) else {
+                    let CanonicalType::Bundle(rhs_ty) = rhs.ty() else {
                         unreachable!();
                     };
                     assert_eq!(lhs_ty.fields().len(), rhs_ty.fields().len());

crates/fayalite/src/sim/interpreter.rs

@@ -2,6 +2,7 @@
 // See Notices.txt for copyright information
 
 use crate::{
+    expr::ValueType,
     int::{BoolOrIntType, SInt, UInt},
     intern::{Intern, Interned, Memoize},
     sim::interpreter::parts::{

crates/fayalite/src/sim/value.rs

@@ -6,7 +6,10 @@ use crate::{
     bundle::{Bundle, BundleType},
     clock::Clock,
     enum_::{Enum, EnumType},
-    expr::{CastBitsTo, Expr, ToExpr},
+    expr::{
+        CastBitsTo, Expr, HdlPartialEq, HdlPartialEqImpl, HdlPartialOrd, ToExpr, ValueType,
+        value_category::{ValueCategorySimValue, ValueCategoryValue},
+    },
     int::{Bool, IntType, KnownSize, SInt, SIntType, SIntValue, Size, UInt, UIntType, UIntValue},
     reset::{AsyncReset, Reset, SyncReset},
     source_location::SourceLocation,
@@ -23,10 +26,11 @@ use bitvec::{slice::BitSlice, vec::BitVec};
 use hashbrown::hash_map::Entry;
 use serde::{Deserialize, Deserializer, Serialize, Serializer, de::Error as _, ser::Error as _};
 use std::{
-    borrow::Cow,
+    borrow::{Borrow, BorrowMut, Cow},
     fmt::{self, Write},
     hash::{BuildHasher, Hash, Hasher, RandomState},
-    ops::{Deref, DerefMut},
+    num::NonZero,
+    ops::{Deref, DerefMut, Index, IndexMut},
     sync::{Arc, Mutex},
 };
 
@@ -136,7 +140,7 @@ impl<T: Type<SimValue: Serialize> + Serialize> Serialize for SimValue<T> {
         S: Serializer,
     {
         SerdeSimValue {
-            ty: SimValue::ty(self),
+            ty: self.ty(),
             value: std::borrow::Cow::Borrowed(&*self),
         }
         .serialize(serializer)
@@ -157,7 +161,22 @@ pub struct SimValue<T: Type> {
     inner: AlternatingCell<SimValueInner<T>>,
 }
 
-impl<T: Type + Clone> Clone for SimValue<T> {
+impl<T: Type> ValueType for SimValue<T> {
+    type Type = T;
+    type ValueCategory = ValueCategorySimValue;
+
+    fn ty(&self) -> Self::Type {
+        self.inner.share().ty
+    }
+}
+
+impl<T: Type<SimValue: fmt::Display>> fmt::Display for SimValue<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        T::SimValue::fmt(self, f)
+    }
+}
+
+impl<T: Type> Clone for SimValue<T> {
     fn clone(&self) -> Self {
         Self {
             inner: AlternatingCell::new_unique(self.inner.share().clone()),
@@ -212,9 +231,6 @@ impl<T: Type> SimValue<T> {
             inner: AlternatingCell::new_unique(inner),
         }
     }
-    pub fn ty(this: &Self) -> T {
-        this.inner.share().ty
-    }
     pub fn into_opaque(this: Self) -> OpaqueSimValue {
         this.inner.into_inner().into_opaque()
     }
@@ -253,7 +269,7 @@ impl<T: Type> SimValue<T> {
         SimValue::from_opaque(ty.canonical(), opaque)
     }
     pub fn canonical(this: &Self) -> SimValue<CanonicalType> {
-        SimValue::from_opaque(Self::ty(this).canonical(), Self::opaque(this).clone())
+        SimValue::from_opaque(this.ty().canonical(), Self::opaque(this).clone())
     }
     #[track_caller]
     pub fn from_dyn_int(v: SimValue<T::Dyn>) -> Self
@@ -274,7 +290,7 @@ impl<T: Type> SimValue<T> {
     where
         T: IntType,
     {
-        SimValue::from_opaque(Self::ty(this).as_dyn_int(), Self::opaque(&this).clone())
+        SimValue::from_opaque(this.ty().as_dyn_int(), Self::opaque(&this).clone())
     }
     #[track_caller]
     pub fn from_bundle(v: SimValue<Bundle>) -> Self
@@ -296,7 +312,7 @@ impl<T: Type> SimValue<T> {
         T: BundleType,
     {
         SimValue::from_opaque(
-            Bundle::from_canonical(Self::ty(this).canonical()),
+            Bundle::from_canonical(this.ty().canonical()),
             Self::opaque(&this).clone(),
         )
     }
@@ -320,7 +336,7 @@ impl<T: Type> SimValue<T> {
         T: EnumType,
     {
         SimValue::from_opaque(
-            Enum::from_canonical(Self::ty(this).canonical()),
+            Enum::from_canonical(this.ty().canonical()),
             Self::opaque(&this).clone(),
         )
     }
@@ -342,17 +358,11 @@ impl<T: Type> DerefMut for SimValue<T> {
 
 impl<T: Type> fmt::Debug for SimValue<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let inner = self.inner.share();
-        f.debug_struct("SimValue")
-            .field("ty", &inner.ty)
-            .field("value", &inner.value)
-            .finish()
+        T::SimValue::fmt(&**self, f)
     }
 }
 
 impl<T: Type> ToExpr for SimValue<T> {
-    type Type = T;
-
     #[track_caller]
     fn to_expr(&self) -> Expr<Self::Type> {
         let inner = self.inner.share();
@@ -360,67 +370,297 @@ impl<T: Type> ToExpr for SimValue<T> {
             inner.sim_only_values_len, 0,
             "can't convert sim-only values to Expr"
         );
-        inner.opaque.bits().cast_bits_to(inner.ty)
+        inner.opaque.bits().to_expr().cast_bits_to(inner.ty)
     }
 }
 
-pub trait SimValuePartialEq<T: Type = Self>: Type {
-    #[track_caller]
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<T>) -> bool;
+impl<T: Type, Len: Size, I> Index<I> for SimValue<ArrayType<T, Len>>
+where
+    [SimValue<T>]: Index<I>,
+{
+    type Output = <[SimValue<T>] as Index<I>>::Output;
+
+    fn index(&self, index: I) -> &Self::Output {
+        (**self).borrow().index(index)
+    }
 }
 
-impl<T: SimValuePartialEq<U>, U: Type> PartialEq<SimValue<U>> for SimValue<T> {
+impl<T: Type, Len: Size, I> IndexMut<I> for SimValue<ArrayType<T, Len>>
+where
+    [SimValue<T>]: IndexMut<I>,
+{
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        (**self).borrow_mut().index_mut(index)
+    }
+}
+
+impl<T: Type, Len: Size> SimValue<ArrayType<T, Len>> {
+    pub fn iter(&self) -> std::slice::Iter<'_, SimValue<T>> {
+        (**self).borrow().iter()
+    }
+    pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, SimValue<T>> {
+        (**self).borrow_mut().iter_mut()
+    }
+}
+
+impl<T: Type, Len: Size> IntoIterator for SimValue<ArrayType<T, Len>> {
+    type Item = SimValue<T>;
+    type IntoIter = std::vec::IntoIter<SimValue<T>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Vec::into_iter(Self::into_value(self).into())
+    }
+}
+
+impl<'a, T: Type, Len: Size> IntoIterator for &'a SimValue<ArrayType<T, Len>> {
+    type Item = &'a SimValue<T>;
+    type IntoIter = std::slice::Iter<'a, SimValue<T>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, T: Type, Len: Size> IntoIterator for &'a mut SimValue<ArrayType<T, Len>> {
+    type Item = &'a mut SimValue<T>;
+    type IntoIter = std::slice::IterMut<'a, SimValue<T>>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+impl<T: Type, Len: Size> AsRef<[SimValue<T>]> for SimValue<ArrayType<T, Len>> {
+    fn as_ref(&self) -> &[SimValue<T>] {
+        (**self).as_ref()
+    }
+}
+
+impl<T: Type, Len: Size> AsMut<[SimValue<T>]> for SimValue<ArrayType<T, Len>> {
+    fn as_mut(&mut self) -> &mut [SimValue<T>] {
+        (**self).as_mut()
+    }
+}
+
+impl<T: Type, U: Type> PartialEq<SimValue<U>> for SimValue<T>
+where
+    Self: for<'a> HdlPartialEq<&'a SimValue<U>, Output = SimValue<Bool>>,
+{
     #[track_caller]
     fn eq(&self, other: &SimValue<U>) -> bool {
-        T::sim_value_eq(self, other)
+        *self.cmp_eq(other)
+    }
+    #[track_caller]
+    fn ne(&self, other: &SimValue<U>) -> bool {
+        *self.cmp_ne(other)
     }
 }
 
-impl<Width: Size> SimValuePartialEq<Self> for UIntType<Width> {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
+pub trait SimValueEq: Type
+where
+    for<'a> SimValue<Self>: HdlPartialEq<&'a SimValue<Self>, Output = SimValue<Bool>>,
+{
+}
+
+impl<T: SimValueEq> Eq for SimValue<T> where
+    for<'a> SimValue<T>: HdlPartialEq<&'a SimValue<T>, Output = SimValue<Bool>>
+{
+}
+
+impl<T: Type, U: Type> PartialOrd<SimValue<U>> for SimValue<T>
+where
+    Self: for<'a> HdlPartialOrd<&'a SimValue<U>, Output = SimValue<Bool>>,
+{
+    #[track_caller]
+    fn partial_cmp(&self, other: &SimValue<U>) -> Option<std::cmp::Ordering> {
+        if *self.cmp_eq(other) {
+            Some(std::cmp::Ordering::Equal)
+        } else if *self.cmp_lt(other) {
+            Some(std::cmp::Ordering::Less)
+        } else if *self.cmp_gt(other) {
+            Some(std::cmp::Ordering::Greater)
+        } else {
+            None
+        }
+    }
+
+    #[track_caller]
+    fn lt(&self, other: &SimValue<U>) -> bool {
+        *self.cmp_lt(other)
+    }
+
+    #[track_caller]
+    fn le(&self, other: &SimValue<U>) -> bool {
+        *self.cmp_le(other)
+    }
+
+    #[track_caller]
+    fn gt(&self, other: &SimValue<U>) -> bool {
+        *self.cmp_gt(other)
+    }
+
+    #[track_caller]
+    fn ge(&self, other: &SimValue<U>) -> bool {
+        *self.cmp_ge(other)
     }
 }
 
-impl<Width: Size> SimValuePartialEq<Self> for SIntType<Width> {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
+pub trait SimValueOrd: SimValueEq
+where
+    for<'a> SimValue<Self>: HdlPartialOrd<&'a SimValue<Self>, Output = SimValue<Bool>>,
+{
+}
+
+impl<T: SimValueOrd> Ord for SimValue<T>
+where
+    for<'a> SimValue<T>: HdlPartialOrd<&'a SimValue<T>, Output = SimValue<Bool>>,
+{
+    #[track_caller]
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        if *self.cmp_eq(other) {
+            std::cmp::Ordering::Equal
+        } else if *self.cmp_lt(other) {
+            std::cmp::Ordering::Less
+        } else {
+            std::cmp::Ordering::Greater
+        }
     }
 }
 
-impl SimValuePartialEq<Bool> for Bool {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Bool>) -> bool {
-        **this == **other
+impl<Width: Size> SimValueEq for UIntType<Width> {}
+
+impl<Width: Size> SimValueOrd for UIntType<Width> {}
+
+impl<Width: Size> SimValueEq for SIntType<Width> {}
+
+impl<Width: Size> SimValueOrd for SIntType<Width> {}
+
+macro_rules! impl_sim_value_cmp_as_bool {
+    ($ty:ident) => {
+        impl SimValueEq for $ty {}
+
+        impl SimValueOrd for $ty {}
+    };
+}
+
+impl_sim_value_cmp_as_bool!(Bool);
+impl_sim_value_cmp_as_bool!(Clock);
+impl_sim_value_cmp_as_bool!(Reset);
+impl_sim_value_cmp_as_bool!(SyncReset);
+impl_sim_value_cmp_as_bool!(AsyncReset);
+
+#[doc(hidden)]
+pub mod match_sim_value {
+    use crate::{
+        sim::value::{SimValue, ToSimValue},
+        ty::Type,
+    };
+
+    #[doc(hidden)]
+    pub struct MatchSimValueHelper<T>(Option<T>);
+
+    impl<T> MatchSimValueHelper<T> {
+        pub fn new(v: T) -> Self {
+            Self(Some(v))
+        }
+    }
+
+    #[doc(hidden)]
+    pub trait MatchSimValue {
+        type MatchValue;
+
+        /// use `self` so it comes first in the method resolution order
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue
+        where
+            Self: Sized;
+    }
+
+    impl<T: Type> MatchSimValue for MatchSimValueHelper<SimValue<T>> {
+        type MatchValue = T::SimValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            SimValue::into_value(self.0.expect("should be Some"))
+        }
+    }
+
+    impl<'a, T: Type> MatchSimValue for MatchSimValueHelper<&'a SimValue<T>> {
+        type MatchValue = &'a T::SimValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            SimValue::value(self.0.expect("should be Some"))
+        }
+    }
+
+    impl<'a, T: Type> MatchSimValue for MatchSimValueHelper<&'a mut SimValue<T>> {
+        type MatchValue = &'a mut T::SimValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            SimValue::value_mut(self.0.expect("should be Some"))
+        }
+    }
+
+    impl<'a, T> MatchSimValue for MatchSimValueHelper<&'_ &'a T>
+    where
+        MatchSimValueHelper<&'a T>: MatchSimValue,
+    {
+        type MatchValue = <MatchSimValueHelper<&'a T> as MatchSimValue>::MatchValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            MatchSimValue::__fayalite_match_sim_value(MatchSimValueHelper(self.0.map(|v| *v)))
+        }
+    }
+
+    impl<'a, T> MatchSimValue for MatchSimValueHelper<&'_ mut &'a T>
+    where
+        MatchSimValueHelper<&'a T>: MatchSimValue,
+    {
+        type MatchValue = <MatchSimValueHelper<&'a T> as MatchSimValue>::MatchValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            MatchSimValue::__fayalite_match_sim_value(MatchSimValueHelper(self.0.map(|v| *v)))
+        }
+    }
+
+    impl<'a, T> MatchSimValue for MatchSimValueHelper<&'a &'_ mut T>
+    where
+        MatchSimValueHelper<&'a T>: MatchSimValue,
+    {
+        type MatchValue = <MatchSimValueHelper<&'a T> as MatchSimValue>::MatchValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            MatchSimValue::__fayalite_match_sim_value(MatchSimValueHelper(self.0.map(|v| &**v)))
+        }
+    }
+
+    impl<'a, T> MatchSimValue for MatchSimValueHelper<&'a mut &'_ mut T>
+    where
+        MatchSimValueHelper<&'a mut T>: MatchSimValue,
+    {
+        type MatchValue = <MatchSimValueHelper<&'a mut T> as MatchSimValue>::MatchValue;
+
+        fn __fayalite_match_sim_value(self) -> Self::MatchValue {
+            MatchSimValue::__fayalite_match_sim_value(MatchSimValueHelper(self.0.map(|v| &mut **v)))
+        }
+    }
+
+    #[doc(hidden)]
+    pub trait MatchSimValueFallback {
+        type MatchValue;
+
+        /// use `&mut self` so it comes later in the method resolution order than MatchSimValue
+        fn __fayalite_match_sim_value(&mut self) -> Self::MatchValue;
+    }
+
+    impl<T: ToSimValue> MatchSimValueFallback for MatchSimValueHelper<T> {
+        type MatchValue = <T::Type as Type>::SimValue;
+
+        fn __fayalite_match_sim_value(&mut self) -> Self::MatchValue {
+            SimValue::into_value(self.0.take().expect("should be Some").into_sim_value())
+        }
     }
 }
 
-impl SimValuePartialEq for Clock {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
-    }
-}
-
-impl SimValuePartialEq for Reset {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
-    }
-}
-
-impl SimValuePartialEq for SyncReset {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
-    }
-}
-
-impl SimValuePartialEq for AsyncReset {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
-    }
-}
-
-pub trait ToSimValue: ToSimValueWithType<<Self as ToSimValue>::Type> {
-    type Type: Type;
-
+pub trait ToSimValue: ToSimValueWithType<<Self as ValueType>::Type> + ValueType {
     #[track_caller]
     fn to_sim_value(&self) -> SimValue<Self::Type>;
     #[track_caller]
@@ -462,31 +702,31 @@ pub trait ToSimValueWithType<T: Type> {
 
 macro_rules! forward_to_sim_value_with_type {
     ([$($generics:tt)*] $ty:ty) => {
-        impl<$($generics)*> ToSimValueWithType<<Self as ToSimValue>::Type> for $ty {
-            fn to_sim_value_with_type(&self, ty: <Self as ToSimValue>::Type) -> SimValue<<Self as ToSimValue>::Type> {
+        impl<$($generics)*> ToSimValueWithType<<Self as ValueType>::Type> for $ty {
+            fn to_sim_value_with_type(&self, ty: <Self as ValueType>::Type) -> SimValue<<Self as ValueType>::Type> {
                 let retval = Self::to_sim_value(self);
-                assert_eq!(SimValue::ty(&retval), ty);
+                assert_eq!(retval.ty(), ty);
                 retval
             }
             #[track_caller]
-            fn into_sim_value_with_type(self, ty: <Self as ToSimValue>::Type) -> SimValue<<Self as ToSimValue>::Type>
+            fn into_sim_value_with_type(self, ty: <Self as ValueType>::Type) -> SimValue<<Self as ValueType>::Type>
             where
                 Self: Sized,
             {
                 let retval = Self::into_sim_value(self);
-                assert_eq!(SimValue::ty(&retval), ty);
+                assert_eq!(retval.ty(), ty);
                 retval
             }
             #[track_caller]
-            fn arc_into_sim_value_with_type(self: Arc<Self>, ty: <Self as ToSimValue>::Type) -> SimValue<<Self as ToSimValue>::Type> {
+            fn arc_into_sim_value_with_type(self: Arc<Self>, ty: <Self as ValueType>::Type) -> SimValue<<Self as ValueType>::Type> {
                 let retval = Self::arc_into_sim_value(self);
-                assert_eq!(SimValue::ty(&retval), ty);
+                assert_eq!(retval.ty(), ty);
                 retval
             }
             #[track_caller]
-            fn arc_to_sim_value_with_type(self: &Arc<Self>, ty: <Self as ToSimValue>::Type) -> SimValue<<Self as ToSimValue>::Type> {
+            fn arc_to_sim_value_with_type(self: &Arc<Self>, ty: <Self as ValueType>::Type) -> SimValue<<Self as ValueType>::Type> {
                 let retval = Self::arc_to_sim_value(self);
-                assert_eq!(SimValue::ty(&retval), ty);
+                assert_eq!(retval.ty(), ty);
                 retval
             }
         }
@@ -494,7 +734,6 @@ macro_rules! forward_to_sim_value_with_type {
 }
 
 impl<T: Type> ToSimValue for SimValue<T> {
-    type Type = T;
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         self.clone()
     }
@@ -550,9 +789,7 @@ impl<T: Type> ToSimValueWithType<T> for BitSlice {
     }
 }
 
-impl<This: ?Sized + ToSimValue> ToSimValue for &'_ This {
-    type Type = This::Type;
-
+impl<'a, This: ?Sized + ToSimValue> ToSimValue for &'a This {
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         This::to_sim_value(self)
     }
@@ -565,8 +802,6 @@ impl<This: ?Sized + ToSimValueWithType<T>, T: Type> ToSimValueWithType<T> for &'
 }
 
 impl<This: ?Sized + ToSimValue> ToSimValue for &'_ mut This {
-    type Type = This::Type;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         This::to_sim_value(self)
     }
@@ -579,8 +814,6 @@ impl<This: ?Sized + ToSimValueWithType<T>, T: Type> ToSimValueWithType<T> for &'
 }
 
 impl<This: ?Sized + ToSimValue> ToSimValue for Arc<This> {
-    type Type = This::Type;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         This::arc_to_sim_value(self)
     }
@@ -601,7 +834,6 @@ impl<This: ?Sized + ToSimValueWithType<T>, T: Type> ToSimValueWithType<T> for Ar
 impl<This: ?Sized + ToSimValue + Send + Sync + 'static> ToSimValue
     for crate::intern::Interned<This>
 {
-    type Type = This::Type;
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         This::to_sim_value(self)
     }
@@ -616,8 +848,6 @@ impl<This: ?Sized + ToSimValueWithType<T> + Send + Sync + 'static, T: Type> ToSi
 }
 
 impl<This: ToSimValue> ToSimValue for Box<This> {
-    type Type = This::Type;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         This::to_sim_value(self)
     }
@@ -660,8 +890,6 @@ impl<Element: ToSimValueWithType<T>, T: Type> ToSimValueWithType<Array<T>> for [
 }
 
 impl<Element: ToSimValue<Type: StaticType>> ToSimValue for [Element] {
-    type Type = Array<Element::Type>;
-
     #[track_caller]
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_array_elements(ArrayType::new_dyn(StaticType::TYPE, self.len()), self)
@@ -697,8 +925,6 @@ impl<Element: ToSimValue<Type: StaticType>, const N: usize> ToSimValue for [Elem
 where
     ConstUsize<N>: KnownSize,
 {
-    type Type = Array<Element::Type, N>;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_array_elements(StaticType::TYPE, self)
     }
@@ -752,8 +978,6 @@ impl<Element: ToSimValueWithType<T>, T: Type> ToSimValueWithType<Array<T>> for V
 }
 
 impl<Element: ToSimValue<Type: StaticType>> ToSimValue for Vec<Element> {
-    type Type = Array<Element::Type>;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_array_elements(ArrayType::new_dyn(StaticType::TYPE, self.len()), self)
     }
@@ -794,8 +1018,6 @@ impl<Element: ToSimValueWithType<T>, T: Type> ToSimValueWithType<Array<T>> for B
 }
 
 impl<Element: ToSimValue<Type: StaticType>> ToSimValue for Box<[Element]> {
-    type Type = Array<Element::Type>;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_array_elements(ArrayType::new_dyn(StaticType::TYPE, self.len()), self)
     }
@@ -825,11 +1047,10 @@ impl<Element: ToSimValueWithType<CanonicalType>> ToSimValueWithType<CanonicalTyp
 }
 
 impl<T: Type> ToSimValue for Expr<T> {
-    type Type = T;
     #[track_caller]
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_bitslice(
-            Expr::ty(*self),
+            self.ty(),
             &crate::expr::ToLiteralBits::to_literal_bits(self)
                 .expect("must be a literal expression"),
         )
@@ -849,8 +1070,6 @@ macro_rules! impl_to_sim_value_for_bool_like {
 }
 
 impl ToSimValue for bool {
-    type Type = Bool;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_value(Bool, *self)
     }
@@ -888,10 +1107,8 @@ impl ToSimValueWithType<CanonicalType> for bool {
 }
 
 macro_rules! impl_to_sim_value_for_primitive_int {
-    ($prim:ident) => {
+    ($prim:ty) => {
         impl ToSimValue for $prim {
-            type Type = <$prim as ToExpr>::Type;
-
             #[track_caller]
             fn to_sim_value(
                 &self,
@@ -902,15 +1119,15 @@ macro_rules! impl_to_sim_value_for_primitive_int {
 
         forward_to_sim_value_with_type!([] $prim);
 
-        impl ToSimValueWithType<<<$prim as ToExpr>::Type as IntType>::Dyn> for $prim {
+        impl ToSimValueWithType<<<$prim as ValueType>::Type as IntType>::Dyn> for $prim {
             #[track_caller]
             fn to_sim_value_with_type(
                 &self,
-                ty: <<$prim as ToExpr>::Type as IntType>::Dyn,
-            ) -> SimValue<<<$prim as ToExpr>::Type as IntType>::Dyn> {
+                ty: <<$prim as ValueType>::Type as IntType>::Dyn,
+            ) -> SimValue<<<$prim as ValueType>::Type as IntType>::Dyn> {
                 SimValue::from_value(
                     ty,
-                    <<$prim as ToExpr>::Type as Type>::SimValue::from(*self).as_dyn_int(),
+                    <<$prim as ValueType>::Type as Type>::SimValue::from(*self).as_dyn_int(),
                 )
             }
         }
@@ -918,7 +1135,7 @@ macro_rules! impl_to_sim_value_for_primitive_int {
         impl ToSimValueWithType<CanonicalType> for $prim {
             #[track_caller]
             fn to_sim_value_with_type(&self, ty: CanonicalType) -> SimValue<CanonicalType> {
-                let ty: <<$prim as ToExpr>::Type as IntType>::Dyn = Type::from_canonical(ty);
+                let ty: <<$prim as ValueType>::Type as IntType>::Dyn = Type::from_canonical(ty);
                 SimValue::into_canonical(self.to_sim_value_with_type(ty))
             }
         }
@@ -937,12 +1154,22 @@ impl_to_sim_value_for_primitive_int!(i32);
 impl_to_sim_value_for_primitive_int!(i64);
 impl_to_sim_value_for_primitive_int!(i128);
 impl_to_sim_value_for_primitive_int!(isize);
+impl_to_sim_value_for_primitive_int!(NonZero<u8>);
+impl_to_sim_value_for_primitive_int!(NonZero<u16>);
+impl_to_sim_value_for_primitive_int!(NonZero<u32>);
+impl_to_sim_value_for_primitive_int!(NonZero<u64>);
+impl_to_sim_value_for_primitive_int!(NonZero<u128>);
+impl_to_sim_value_for_primitive_int!(NonZero<usize>);
+impl_to_sim_value_for_primitive_int!(NonZero<i8>);
+impl_to_sim_value_for_primitive_int!(NonZero<i16>);
+impl_to_sim_value_for_primitive_int!(NonZero<i32>);
+impl_to_sim_value_for_primitive_int!(NonZero<i64>);
+impl_to_sim_value_for_primitive_int!(NonZero<i128>);
+impl_to_sim_value_for_primitive_int!(NonZero<isize>);
 
 macro_rules! impl_to_sim_value_for_int_value {
     ($IntValue:ident, $Int:ident, $IntType:ident) => {
         impl<Width: Size> ToSimValue for $IntValue<Width> {
-            type Type = $IntType<Width>;
-
             fn to_sim_value(&self) -> SimValue<Self::Type> {
                 SimValue::from_value(self.ty(), self.clone())
             }
@@ -1303,8 +1530,6 @@ impl<T: SimOnlyValueTrait> ToSimValueWithType<SimOnly<T>> for SimOnlyValue<T> {
 }
 
 impl ToSimValue for DynSimOnlyValue {
-    type Type = DynSimOnly;
-
     fn to_sim_value(&self) -> SimValue<Self::Type> {
         SimValue::from_value(self.ty(), self.clone())
     }
@@ -1314,29 +1539,58 @@ impl ToSimValue for DynSimOnlyValue {
     }
 }
 
-impl<T: SimOnlyValueTrait> ToSimValue for SimOnlyValue<T> {
+impl<T: SimOnlyValueTrait> ValueType for SimOnlyValue<T> {
     type Type = SimOnly<T>;
+    type ValueCategory = ValueCategoryValue;
 
+    fn ty(&self) -> Self::Type {
+        SimOnly::new()
+    }
+}
+
+impl<T: SimOnlyValueTrait> ToSimValue for SimOnlyValue<T> {
     fn to_sim_value(&self) -> SimValue<Self::Type> {
-        SimValue::from_value(Default::default(), self.clone())
+        SimValue::from_value(self.ty(), self.clone())
     }
 
     fn into_sim_value(self) -> SimValue<Self::Type> {
-        SimValue::from_value(Default::default(), self)
+        SimValue::from_value(self.ty(), self)
     }
 }
 
-impl SimValuePartialEq for DynSimOnly {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<Self>) -> bool {
-        **this == **other
+impl HdlPartialEqImpl<Self> for DynSimOnly {
+    #[track_caller]
+    fn cmp_value_eq(
+        _lhs: Self,
+        lhs_value: Cow<'_, Self::SimValue>,
+        _rhs: Self,
+        rhs_value: Cow<'_, Self::SimValue>,
+    ) -> bool {
+        *lhs_value == *rhs_value
+    }
+
+    #[track_caller]
+    fn cmp_expr_eq(_lhs: Expr<Self>, _rhs: Expr<Self>) -> Expr<Bool> {
+        panic!("can't compare Expr<DynSimOnly>");
     }
 }
 
-impl<T: SimOnlyValueTrait + PartialEq<U>, U: SimOnlyValueTrait> SimValuePartialEq<SimOnly<U>>
-    for SimOnly<T>
+impl<L: SimOnlyValueTrait + PartialEq<R>, R: SimOnlyValueTrait> HdlPartialEqImpl<SimOnly<R>>
+    for SimOnly<L>
 {
-    fn sim_value_eq(this: &SimValue<Self>, other: &SimValue<SimOnly<U>>) -> bool {
-        ***this == ***other
+    #[track_caller]
+    fn cmp_value_eq(
+        _lhs: Self,
+        lhs_value: Cow<'_, Self::SimValue>,
+        _rhs: SimOnly<R>,
+        rhs_value: Cow<'_, <SimOnly<R> as Type>::SimValue>,
+    ) -> bool {
+        **lhs_value == **rhs_value
+    }
+
+    #[track_caller]
+    fn cmp_expr_eq(_lhs: Expr<Self>, _rhs: Expr<SimOnly<R>>) -> Expr<Bool> {
+        panic!("can't compare Expr<SimOnly<_>>");
     }
 }
 

crates/fayalite/src/sim/value/sim_only_value_unsafe.rs

@@ -3,6 +3,7 @@
 
 //! `unsafe` parts of [`DynSimOnlyValue`]
 
+use crate::expr::{ValueType, value_category::ValueCategoryValue};
 use serde::{Serialize, de::DeserializeOwned};
 use std::{
     any::{self, TypeId},
@@ -295,10 +296,16 @@ impl<T: SimOnlyValueTrait> From<SimOnlyValue<T>> for DynSimOnlyValue {
     }
 }
 
-impl DynSimOnlyValue {
-    pub fn ty(&self) -> DynSimOnly {
+impl ValueType for DynSimOnlyValue {
+    type Type = DynSimOnly;
+    type ValueCategory = ValueCategoryValue;
+
+    fn ty(&self) -> Self::Type {
         self.0.ty()
     }
+}
+
+impl DynSimOnlyValue {
     pub fn type_id(&self) -> TypeId {
         self.0.type_id_dyn()
     }

crates/fayalite/src/ty.rs

@@ -11,7 +11,7 @@ use crate::{
     intern::{Intern, Interned},
     phantom_const::PhantomConst,
     reset::{AsyncReset, Reset, SyncReset},
-    sim::value::{DynSimOnlyValue, DynSimOnly, SimValue, ToSimValueWithType},
+    sim::value::{DynSimOnly, DynSimOnlyValue, SimValue, ToSimValueWithType},
     source_location::SourceLocation,
     util::{ConstUsize, slice_range, try_slice_range},
 };

crates/fayalite/src/util/ready_valid.rs

@@ -25,7 +25,7 @@ impl<T: Type> ReadyValid<T> {
     #[hdl]
     pub fn firing_data(expr: impl ToExpr<Type = Self>) -> Expr<HdlOption<T>> {
         let expr = expr.to_expr();
-        let option_ty = Expr::ty(expr).data;
+        let option_ty = expr.ty().data;
         #[hdl]
         let firing_data = wire(option_ty);
         connect(firing_data, option_ty.HdlNone());
@@ -42,7 +42,7 @@ impl<T: Type> ReadyValid<T> {
     ) -> Expr<ReadyValid<R>> {
         let data = HdlOption::map(expr.data, f);
         #[hdl]
-        let mapped = wire(ReadyValid[Expr::ty(data).HdlSome]);
+        let mapped = wire(ReadyValid[data.ty().HdlSome]);
         connect(mapped.data, data);
         connect(expr.ready, mapped.ready);
         mapped
@@ -81,7 +81,7 @@ pub fn queue<T: Type>(
     let count: UInt = m.output(count_ty);
 
     #[hdl]
-    let inp_index_reg = reg_builder().clock_domain(cd).reset(0.cast_to(index_ty));
+    let inp_index_reg: UInt = reg_builder().clock_domain(cd).reset(0.cast_to(index_ty));
     #[hdl]
     let out_index_reg = reg_builder().clock_domain(cd).reset(0.cast_to(index_ty));
     #[hdl]

crates/fayalite/src/wire.rs

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: LGPL-3.0-or-later
 // See Notices.txt for copyright information
 use crate::{
-    expr::{Expr, Flow, ToExpr},
+    expr::{Expr, Flow, ToExpr, ValueType, value_category::ValueCategoryExpr},
     intern::Interned,
     module::{IncompleteDeclaration, NameId, ScopedNameId, StmtDeclaration, StmtWire},
     source_location::SourceLocation,
@@ -16,7 +16,16 @@ pub struct Wire<T: Type> {
     ty: T,
 }
 
-impl<T: Type + fmt::Debug> fmt::Debug for Wire<T> {
+impl<T: Type> ValueType for Wire<T> {
+    type Type = T;
+    type ValueCategory = ValueCategoryExpr;
+
+    fn ty(&self) -> Self::Type {
+        self.ty
+    }
+}
+
+impl<T: Type> fmt::Debug for Wire<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "Wire({:?}: ", self.name)?;
         self.ty.fmt(f)?;
@@ -49,9 +58,6 @@ impl<T: Type> Wire<T> {
             ty: T::from_canonical(ty),
         }
     }
-    pub fn ty(&self) -> T {
-        self.ty
-    }
     pub fn new_unchecked(
         scoped_name: ScopedNameId,
         source_location: SourceLocation,

crates/fayalite/tests/module.rs

@@ -215,7 +215,7 @@ where
     let o: Array<T, N> = m.output();
     let bytes = v.to_string().as_bytes().to_expr();
     #[hdl]
-    let o2: Array<UInt<8>> = m.output(Expr::ty(bytes));
+    let o2: Array<UInt<8>> = m.output(bytes.ty());
     connect(
         o,
         #[hdl]
@@ -1176,7 +1176,7 @@ pub fn check_memory_init() {
     let waddr2: UInt<4> = m.input();
     #[hdl]
     let wdata2: UInt<31> = m.input();
-    let mem_init2 = Vec::from_iter((0..0x10u32).map(|i| (i * i * i).cast_to_static()));
+    let mem_init2 = Vec::from_iter((0..0x10u32).map(|i| (i * i * i).cast_to_static::<UInt<31>>()));
     #[hdl]
     let mut mem2 = memory_with_init(mem_init2);
     let read_port2 = mem2.new_read_port();
@@ -1784,7 +1784,7 @@ pub fn check_memory_of_bundle_of_arrays() {
                 [(i * i).wrapping_mul(2), (i * i).wrapping_mul(3)],
                 [(i * i).wrapping_mul(i), i * 2],
             ],
-            i.cast_to_static(),
+            i.cast_to_static::<UInt<2>>(),
         )
     }));
     #[hdl]
@@ -1954,9 +1954,9 @@ pub fn check_memory_of_array_of_bundle() {
     let clk: Clock = m.input();
     let mem_init = Vec::from_iter((0..0x10u8).map(|i| {
         [
-            (i, i.cast_to_static()),
-            ((i * i), (i / 2).cast_to_static()),
-            ((i * i).wrapping_mul(i), (i / 4).cast_to_static()),
+            (i, i.cast_to_static::<SInt<1>>()),
+            ((i * i), (i / 2).cast_to_static::<SInt<1>>()),
+            ((i * i).wrapping_mul(i), (i / 4).cast_to_static::<SInt<1>>()),
         ]
     }));
     #[hdl]
@@ -2269,7 +2269,8 @@ pub fn check_memory_of_bundle() {
     let wmask: (Bool, Bool) = m.input();
     #[hdl]
     let clk: Clock = m.input();
-    let mem_init = Vec::from_iter((0..0x10u8).map(|i| (i ^ 3, (i ^ (i / 2)).cast_to_static())));
+    let mem_init =
+        Vec::from_iter((0..0x10u8).map(|i| (i ^ 3, (i ^ (i / 2)).cast_to_static::<SInt<1>>())));
     #[hdl]
     let mut mem = memory_with_init(mem_init);
     let read_port = mem.new_read_port();

crates/fayalite/tests/sim.rs

@@ -86,7 +86,7 @@ pub fn mod1() {
     #[hdl]
     let child = instance(mod1_child());
     #[hdl]
-    let o: mod1_child = m.output(Expr::ty(child));
+    let o: mod1_child = m.output(child.ty());
     connect(o, child);
 }
 
@@ -506,10 +506,10 @@ fn test_enums() {
             data_out: _,
             b_out: _,
             b2_out: _,
-        } = expected;
-        sim.write(sim.io().en, &en);
-        sim.write(sim.io().which_in, &which_in);
-        sim.write(sim.io().data_in, &data_in);
+        } = &expected;
+        sim.write(sim.io().en, en);
+        sim.write(sim.io().which_in, which_in);
+        sim.write(sim.io().data_in, data_in);
         let io = #[hdl(sim)]
         IO::<_> {
             en,
@@ -528,7 +528,7 @@ fn test_enums() {
         );
         // make sure matching on SimValue<SomeEnum> works
         #[hdl(sim)]
-        match io.b_out {
+        match &io.b_out {
             HdlNone => println!("io.b_out is HdlNone"),
             HdlSome(v) => println!("io.b_out is HdlSome(({:?}, {:?}))", *v.0, *v.1),
         }
@@ -706,13 +706,13 @@ fn test_memories() {
             w_en,
             w_data,
             w_mask,
-        } = expected;
-        sim.write(sim.io().r.addr, &r_addr);
-        sim.write(sim.io().r.en, &r_en);
-        sim.write(sim.io().w.addr, &w_addr);
-        sim.write(sim.io().w.en, &w_en);
-        sim.write(sim.io().w.data, &w_data);
-        sim.write(sim.io().w.mask, &w_mask);
+        } = &expected;
+        sim.write(sim.io().r.addr, r_addr);
+        sim.write(sim.io().r.en, r_en);
+        sim.write(sim.io().w.addr, w_addr);
+        sim.write(sim.io().w.en, w_en);
+        sim.write(sim.io().w.data, w_data);
+        sim.write(sim.io().w.mask, w_mask);
         let io = #[hdl(sim)]
         IO {
             r_addr,
@@ -979,10 +979,10 @@ fn test_memories2() {
         },
     ) in io_cycles.into_iter().enumerate()
     {
-        sim.write_bool_or_int(sim.io().rw.addr, addr.cast_to_static());
+        sim.write_bool_or_int(sim.io().rw.addr, addr.cast_to_static::<UInt<3>>());
         sim.write_bool(sim.io().rw.en, en);
         sim.write_bool(sim.io().rw.wmode, wmode);
-        sim.write_bool_or_int(sim.io().rw.wdata, wdata.cast_to_static());
+        sim.write_bool_or_int(sim.io().rw.wdata, wdata.cast_to_static::<UInt<2>>());
         sim.write_bool(sim.io().rw.wmask, wmask);
         sim.advance_time(SimDuration::from_nanos(250));
         sim.write_clock(sim.io().rw.clk, true);
@@ -1195,9 +1195,9 @@ fn test_memories3() {
                 w_data: [0; 8],
                 w_mask: [false; 8],
             });
-            sim.write_bool_or_int(sim.io().r.addr, r_addr.cast_to_static());
+            sim.write_bool_or_int(sim.io().r.addr, r_addr.cast_to_static::<UInt<3>>());
             sim.write_bool(sim.io().r.en, r_en);
-            sim.write_bool_or_int(sim.io().w.addr, w_addr.cast_to_static());
+            sim.write_bool_or_int(sim.io().w.addr, w_addr.cast_to_static::<UInt<3>>());
             sim.write_bool(sim.io().w.en, w_en);
             for (i, v) in w_data.into_iter().enumerate() {
                 sim.write_bool_or_int(sim.io().w.data[i], v);
@@ -1505,7 +1505,7 @@ fn test_many_memories() {
             w_en,
             w_data,
             w_mask,
-        } = expected;
+        } = &expected;
         for (((r, w), w_data), w_mask) in sim
             .io()
             .r
@@ -1514,10 +1514,10 @@ fn test_many_memories() {
             .zip(w_data.iter())
             .zip(w_mask.iter())
         {
-            sim.write(r.addr, &r_addr);
-            sim.write(r.en, &r_en);
-            sim.write(w.addr, &w_addr);
-            sim.write(w.en, &w_en);
+            sim.write(r.addr, r_addr);
+            sim.write(r.en, r_en);
+            sim.write(w.addr, w_addr);
+            sim.write(w.en, w_en);
             sim.write(w.data, w_data);
             sim.write(w.mask, w_mask);
         }

crates/fayalite/tests/sim/expected/connect_const_reset.txt

@@ -21,7 +21,7 @@ Simulation {
                             },
                             SlotDebugData {
                                 name: "",
-                                ty: Bool,
+                                ty: UInt<1>,
                             },
                             SlotDebugData {
                                 name: "",
@@ -51,12 +51,12 @@ Simulation {
             insns: [
                 // at: module-XXXXXXXXXX.rs:1:1
                 0: Const {
-                    dest: StatePartIndex<BigSlots>(2), // (0x1) SlotDebugData { name: "", ty: Bool },
+                    dest: StatePartIndex<BigSlots>(2), // (0x1) SlotDebugData { name: "", ty: UInt<1> },
                     value: 0x1,
                 },
                 1: Copy {
                     dest: StatePartIndex<BigSlots>(3), // (0x1) SlotDebugData { name: "", ty: AsyncReset },
-                    src: StatePartIndex<BigSlots>(2), // (0x1) SlotDebugData { name: "", ty: Bool },
+                    src: StatePartIndex<BigSlots>(2), // (0x1) SlotDebugData { name: "", ty: UInt<1> },
                 },
                 // at: module-XXXXXXXXXX.rs:4:1
                 2: Copy {

crates/fayalite/tests/sim/expected/phantom_const.txt

@@ -30,7 +30,7 @@ Simulation {
                         ..
                     },
                     big_slots: StatePartLayout<BigSlots> {
-                        len: 7,
+                        len: 8,
                         debug_data: [
                             SlotDebugData {
                                 name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.addr",
@@ -54,12 +54,16 @@ Simulation {
                             },
                             SlotDebugData {
                                 name: "",
-                                ty: Bool,
+                                ty: UInt<1>,
                             },
                             SlotDebugData {
                                 name: "",
                                 ty: Clock,
                             },
+                            SlotDebugData {
+                                name: "",
+                                ty: Bool,
+                            },
                         ],
                         ..
                     },
@@ -90,78 +94,83 @@ Simulation {
             insns: [
                 // at: module-XXXXXXXXXX.rs:1:1
                 0: Const {
-                    dest: StatePartIndex<BigSlots>(5), // (0x0) SlotDebugData { name: "", ty: Bool },
+                    dest: StatePartIndex<BigSlots>(7), // (0x0) SlotDebugData { name: "", ty: Bool },
                     value: 0x0,
                 },
+                // at: module-XXXXXXXXXX.rs:7:1
                 1: Copy {
+                    dest: StatePartIndex<BigSlots>(1), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.en", ty: Bool },
+                    src: StatePartIndex<BigSlots>(7), // (0x0) SlotDebugData { name: "", ty: Bool },
+                },
+                // at: module-XXXXXXXXXX.rs:1:1
+                2: Const {
+                    dest: StatePartIndex<BigSlots>(5), // (0x0) SlotDebugData { name: "", ty: UInt<1> },
+                    value: 0x0,
+                },
+                3: Copy {
                     dest: StatePartIndex<BigSlots>(6), // (0x0) SlotDebugData { name: "", ty: Clock },
-                    src: StatePartIndex<BigSlots>(5), // (0x0) SlotDebugData { name: "", ty: Bool },
+                    src: StatePartIndex<BigSlots>(5), // (0x0) SlotDebugData { name: "", ty: UInt<1> },
                 },
                 // at: module-XXXXXXXXXX.rs:6:1
-                2: Copy {
+                4: Copy {
                     dest: StatePartIndex<BigSlots>(2), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.clk", ty: Clock },
                     src: StatePartIndex<BigSlots>(6), // (0x0) SlotDebugData { name: "", ty: Clock },
                 },
-                // at: module-XXXXXXXXXX.rs:7:1
-                3: Copy {
-                    dest: StatePartIndex<BigSlots>(1), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.en", ty: Bool },
-                    src: StatePartIndex<BigSlots>(5), // (0x0) SlotDebugData { name: "", ty: Bool },
-                },
                 // at: module-XXXXXXXXXX.rs:1:1
-                4: Const {
+                5: Const {
                     dest: StatePartIndex<BigSlots>(3), // (0x0) SlotDebugData { name: "", ty: UInt<8> },
                     value: 0x0,
                 },
-                5: CastToUInt {
+                6: CastToUInt {
                     dest: StatePartIndex<BigSlots>(4), // (0x0) SlotDebugData { name: "", ty: UInt<0> },
                     src: StatePartIndex<BigSlots>(3), // (0x0) SlotDebugData { name: "", ty: UInt<8> },
                     dest_width: 0,
                 },
                 // at: module-XXXXXXXXXX.rs:5:1
-                6: Copy {
+                7: Copy {
                     dest: StatePartIndex<BigSlots>(0), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.addr", ty: UInt<0> },
                     src: StatePartIndex<BigSlots>(4), // (0x0) SlotDebugData { name: "", ty: UInt<0> },
                 },
                 // at: module-XXXXXXXXXX.rs:3:1
-                7: CastBigToArrayIndex {
+                8: CastBigToArrayIndex {
                     dest: StatePartIndex<SmallSlots>(4), // (0x0 0) SlotDebugData { name: "", ty: UInt<0> },
                     src: StatePartIndex<BigSlots>(0), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.addr", ty: UInt<0> },
                 },
-                8: IsNonZeroDestIsSmall {
+                9: IsNonZeroDestIsSmall {
                     dest: StatePartIndex<SmallSlots>(3), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                     src: StatePartIndex<BigSlots>(1), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.en", ty: Bool },
                 },
-                9: BranchIfSmallZero {
-                    target: 11,
+                10: BranchIfSmallZero {
+                    target: 12,
                     value: StatePartIndex<SmallSlots>(3), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                 },
-                10: Branch {
-                    target: 11,
+                11: Branch {
+                    target: 12,
                 },
-                11: IsNonZeroDestIsSmall {
+                12: IsNonZeroDestIsSmall {
                     dest: StatePartIndex<SmallSlots>(2), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                     src: StatePartIndex<BigSlots>(2), // (0x0) SlotDebugData { name: "InstantiatedModule(phantom_const: phantom_const).phantom_const::mem::r0.clk", ty: Clock },
                 },
-                12: AndSmall {
+                13: AndSmall {
                     dest: StatePartIndex<SmallSlots>(1), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                     lhs: StatePartIndex<SmallSlots>(2), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                     rhs: StatePartIndex<SmallSlots>(0), // (0x1 1) SlotDebugData { name: "", ty: Bool },
                 },
-                13: BranchIfSmallZero {
-                    target: 14,
+                14: BranchIfSmallZero {
+                    target: 15,
                     value: StatePartIndex<SmallSlots>(1), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                 },
-                14: XorSmallImmediate {
+                15: XorSmallImmediate {
                     dest: StatePartIndex<SmallSlots>(0), // (0x1 1) SlotDebugData { name: "", ty: Bool },
                     lhs: StatePartIndex<SmallSlots>(2), // (0x0 0) SlotDebugData { name: "", ty: Bool },
                     rhs: 0x1,
                 },
                 // at: module-XXXXXXXXXX.rs:1:1
-                15: Return,
+                16: Return,
             ],
             ..
         },
-        pc: 15,
+        pc: 16,
         memory_write_log: [],
         memories: StatePart {
             value: [
@@ -192,6 +201,7 @@ Simulation {
                 0,
                 0,
                 0,
+                0,
             ],
         },
         sim_only_slots: StatePart {

crates/fayalite/tests/sim/expected/ripple_counter.txt

@@ -162,7 +162,7 @@ Simulation {
                             },
                             SlotDebugData {
                                 name: "",
-                                ty: Bool,
+                                ty: UInt<1>,
                             },
                             SlotDebugData {
                                 name: "",
@@ -429,12 +429,12 @@ Simulation {
                 },
                 // at: module-XXXXXXXXXX.rs:1:1
                 26: Const {
-                    dest: StatePartIndex<BigSlots>(28), // (0x0) SlotDebugData { name: "", ty: Bool },
+                    dest: StatePartIndex<BigSlots>(28), // (0x0) SlotDebugData { name: "", ty: UInt<1> },
                     value: 0x0,
                 },
                 27: Copy {
                     dest: StatePartIndex<BigSlots>(29), // (0x0) SlotDebugData { name: "", ty: SyncReset },
-                    src: StatePartIndex<BigSlots>(28), // (0x0) SlotDebugData { name: "", ty: Bool },
+                    src: StatePartIndex<BigSlots>(28), // (0x0) SlotDebugData { name: "", ty: UInt<1> },
                 },
                 28: Copy {
                     dest: StatePartIndex<BigSlots>(26), // (0x1) SlotDebugData { name: ".clk", ty: Clock },

crates/fayalite/tests/ui/simvalue_is_not_internable.stderr

@@ -4,14 +4,14 @@ error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between thr
 11 | fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
    |                          ^^^^^^^^^^^^^^^^^^^^^^ `Cell<util::alternating_cell::State>` cannot be shared between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
    = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -28,13 +28,13 @@ error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between th
 11 | fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
    |                          ^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -51,7 +51,7 @@ error[E0277]: `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'sta
 11 | fn f(v: SimValue<()>) -> Interned<SimValue<()>> {
    |                          ^^^^^^^^^^^^^^^^^^^^^^ `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>` cannot be sent between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
 note: required because it appears within the type `DynSimOnlyValue`
   --> src/sim/value/sim_only_value_unsafe.rs
    |
@@ -92,7 +92,7 @@ note: required because it appears within the type `util::alternating_cell::Alter
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -103,29 +103,15 @@ note: required by a bound in `fayalite::intern::Interned`
    | pub struct Interned<T: ?Sized + 'static + Send + Sync> {
    |                                           ^^^^ required by this bound in `Interned`
 
-error[E0277]: the trait bound `SimValue<()>: Intern` is not satisfied
+error[E0277]: the trait bound `fayalite::prelude::SimValue<()>: Intern` is not satisfied
   --> tests/ui/simvalue_is_not_internable.rs:12:26
    |
 12 |     Intern::intern_sized(v)
-   |     -------------------- ^ the trait `Hash` is not implemented for `SimValue<()>`
+   |     -------------------- ^ the trait `Hash` is not implemented for `fayalite::prelude::SimValue<()>`
    |     |
    |     required by a bound introduced by this call
    |
-   = note: required for `SimValue<()>` to implement `Intern`
-help: consider dereferencing here
-   |
-12 |     Intern::intern_sized(*v)
-   |                          +
-
-error[E0277]: the trait bound `SimValue<()>: Intern` is not satisfied
-  --> tests/ui/simvalue_is_not_internable.rs:12:26
-   |
-12 |     Intern::intern_sized(v)
-   |     -------------------- ^ the trait `std::cmp::Eq` is not implemented for `SimValue<()>`
-   |     |
-   |     required by a bound introduced by this call
-   |
-   = note: required for `SimValue<()>` to implement `Intern`
+   = note: required for `fayalite::prelude::SimValue<()>` to implement `Intern`
 help: consider dereferencing here
    |
 12 |     Intern::intern_sized(*v)
@@ -139,14 +125,14 @@ error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between thr
    |     |
    |     required by a bound introduced by this call
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
    = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -172,13 +158,13 @@ error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between th
    |     |
    |     required by a bound introduced by this call
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -204,7 +190,7 @@ error[E0277]: `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'sta
    |     |
    |     required by a bound introduced by this call
    |
-   = help: within `SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
 note: required because it appears within the type `DynSimOnlyValue`
   --> src/sim/value/sim_only_value_unsafe.rs
    |
@@ -245,7 +231,7 @@ note: required because it appears within the type `util::alternating_cell::Alter
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -269,14 +255,14 @@ error[E0277]: `Cell<util::alternating_cell::State>` cannot be shared between thr
 12 |     Intern::intern_sized(v)
    |     ^^^^^^^^^^^^^^^^^^^^^^^ `Cell<util::alternating_cell::State>` cannot be shared between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `Cell<util::alternating_cell::State>`
    = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -293,13 +279,13 @@ error[E0277]: `UnsafeCell<value::SimValueInner<()>>` cannot be shared between th
 12 |     Intern::intern_sized(v)
    |     ^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<value::SimValueInner<()>>` cannot be shared between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Sync` is not implemented for `UnsafeCell<value::SimValueInner<()>>`
 note: required because it appears within the type `util::alternating_cell::AlternatingCell<value::SimValueInner<()>>`
   --> src/util/alternating_cell.rs
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {
@@ -316,7 +302,7 @@ error[E0277]: `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'sta
 12 |     Intern::intern_sized(v)
    |     ^^^^^^^^^^^^^^^^^^^^^^^ `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>` cannot be sent between threads safely
    |
-   = help: within `SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
+   = help: within `fayalite::prelude::SimValue<()>`, the trait `Send` is not implemented for `Rc<(dyn value::sim_only_value_unsafe::DynSimOnlyValueTrait + 'static)>`
 note: required because it appears within the type `DynSimOnlyValue`
   --> src/sim/value/sim_only_value_unsafe.rs
    |
@@ -357,7 +343,7 @@ note: required because it appears within the type `util::alternating_cell::Alter
    |
    | pub(crate) struct AlternatingCell<T: ?Sized> {
    |                   ^^^^^^^^^^^^^^^
-note: required because it appears within the type `SimValue<()>`
+note: required because it appears within the type `fayalite::prelude::SimValue<()>`
   --> src/sim/value.rs
    |
    | pub struct SimValue<T: Type> {

rocq-demo/rocq_hdl.v

@@ -0,0 +1,171 @@
+(*  SPDX-License-Identifier: LGPL-3.0-or-later
+    See Notices.txt for copyright information *)
+
+(*  This file demonstrates converting simple HDL designs into Rocq, as well
+    as proofs by induction that parallels those of formal verification in
+    Symbiyosys with the "smtbmc" engine in the "prove" mode. *)
+
+(*  Models a simple register, feeding back to itself. We prove that,
+    when initialized to zero, it stays always at zero. *)
+Module simple_register.
+
+  (*  State record. Contains only one boolean variable, which we call "a" *)
+  Record S := { a: bool }.
+  (*  The above automatically defines an accessor function "a: S->bool", so
+      we can write "a s" to get the value of "a" in state "s". *)
+
+  (*  Defines an "initial" predicate, so "initial s" means
+      "s is an initial state". In our case, the value of "a"
+      in the initial state is zero (false) *)
+  Definition initial (s: S) :=
+    a s = false.
+  (*  As an example, we construct a state where "a" is indeed false,
+      and prove it is an initial state. The syntax for instantiating
+      such a record is "{| a := false |}". *)
+  Example test_initial: initial {| a := false |}.
+  Proof. reflexivity. Qed.
+
+  (*  Defines an "assert" predicate, so "assert s" means "assertions
+      hold in state s" or equivalently "state s is valid". In our case,
+      valid states correspond to those where "a" is false. *)
+  Definition assert (s: S) :=
+    a s = false.
+
+  (*  The following proof by induction follows the article "Temporal
+      Induction by Incremental SAT Solving",
+      https://doi.org/10.1016/S1571-0661(05)82542-3 *)
+  (*  Proves the base case, with one step: the initial state is a
+      valid state. *)
+  Theorem base1: forall s0, initial s0 -> assert s0.
+  Proof. trivial. Qed.
+
+  (*  Defines a "transition" predicate, so "t s1 s2" means:
+      "s2 can be reached in one step from s1". In our case,
+      the value of "a" in s2 is the same as in s1. *)
+  Definition t (s1 s2 : S) :=
+    a s2 = a s1.
+
+  (*  Induction principle: for all transitions from a valid state,
+      we reach a valid state. *)
+  Theorem induct1:
+    forall s0 s1, assert s0 -> t s0 s1 -> assert s1.
+  Proof.
+    unfold t,  assert.
+    intros s0 s1 A T.
+    transitivity (a s0).
+    apply T. apply A.
+  Qed.
+  (*  Here we have proven the base case and the inductive case, so we
+      declare success. However, we may want to formalize it from first
+      principles, something like "All reacheable states from an initial
+      state are valid", and use the above theorems to prove it (TODO). *)
+
+  (*  Example: all states reacheable in one step from the initial state
+      are valid. *)
+  Example one_step_valid:
+    forall s0 s1, initial s0 -> t s0 s1 -> assert s1.
+  Proof.
+    unfold initial, t, assert.
+    intros s0 s1 I T.
+    transitivity (a s0).
+    apply T. apply I.
+  Qed.
+  (*  Same as above, but we prove using only the induction theorems. *)
+  Example one_step_valid':
+    forall s0 s1, initial s0 -> t s0 s1 -> assert s1.
+  Proof.
+    apply induct1.
+  Qed.
+End simple_register.
+
+(*  The same circuit as above, but with an additional output register.
+    The output is asserted to be always false, but no such restriction
+    is made on the inner register, a "hidden" state. It creates a
+    difficulty for induction: there are unreacheable valid states that
+    leads to invalid states. A two step induction solves the problem. *)
+Module hidden_state.
+  (*  Demonstrate state with several (two) variables. *)
+  Record S :=
+  { a: bool
+  ; b: bool
+  }.
+  (*  Both registers start at zero (false). *)
+  Definition initial (s: S) :=
+    a s = false /\ b s = false.
+  (*  Just b is constrained to be zero (false) *)
+  Definition assert (s: S) :=
+    b s = false.
+  (*  "a" keeps its previous value, "b" copies "a". *)
+  Definition t (s1 s2 : S) :=
+    a s2 = a s1 /\ b s2 = a s1.
+  (*  Base case in one step. *)
+  Theorem base1:
+    forall s0,
+    initial s0 -> assert s0.
+  Proof.
+    unfold initial, assert.
+    intros s0 [_ H].
+    apply H.
+  Qed.
+  (*  Try proving the inductive case in one step. *)
+  Theorem induct1:
+    forall s0 s1,
+    assert s0 -> t s0 s1 -> assert s1.
+  Proof.
+    unfold t, assert.
+    intros s0 s1 A T.
+    destruct T as [_ Tb].
+    transitivity (a s0). apply Tb.
+  Abort.
+  (*  Ops, we reach a dead-end. Maybe it's not provable after all?
+      Try proving its negation by finding a counter-example. *)
+  Theorem not_induct1:
+    not (forall s0 s1,
+    assert s0 -> t s0 s1 -> assert s1).
+  Proof.
+    unfold not, assert, t.
+    intros H.
+    specialize H with (s0 := {|a := true; b := false|}).
+    simpl in H.
+    specialize H with (s1 := {|a := true; b := true|}).
+    simpl in H.
+    discriminate H. reflexivity. auto.
+  Qed.
+  (*  Indeed, a valid state where "a" is one (true) leads to
+      an invalid state. Try one more step. *)
+  Theorem base2:
+    forall s0 s1,
+    initial s0 -> assert s0 -> t s0 s1 -> assert s1.
+  Proof.
+    intros s0 s1 [Ia _] _ [_ Tb].
+    unfold assert.
+    transitivity (a s0). apply Tb.
+    apply Ia.
+  Qed.
+  Theorem induct2:
+    forall s0 s1 s2,
+    assert s0 -> t s0 s1 -> assert s1 -> t s1 s2 -> assert s2.
+  Proof.
+    intros s0 s1 s2 A0 [T0a T0b] A1 [T1a T1b].
+    unfold assert in *.
+    transitivity (a s1). apply T1b.
+    transitivity (a s0). apply T0a.
+    transitivity (b s1). symmetry. apply T0b.
+    apply A1.
+  Qed.
+  (* Success! Two steps indeed work. *)
+
+  (* Example: all states reacheable in two steps are valid *)
+  Example two_steps_valid:
+    forall s0 s1 s2,
+    initial s0 -> t s0 s1 -> t s1 s2 -> assert s2.
+  Proof.
+    intros s0 s1 s2.
+    intros Hi T01.
+    apply induct2 with (s0 := s0).
+    - apply base1. apply Hi.
+    - apply T01.
+    - apply base2 with (s0 := s0).
+      apply Hi. apply base1. apply Hi. apply T01.
+  Qed.
+End hidden_state.

scripts/check-copyright.sh

@@ -32,6 +32,7 @@ POUND_HEADER=('^"# SPDX-License-Identifier: LGPL-3.0-or-later"$' '^"# See Notice
 SLASH_HEADER=('^"// SPDX-License-Identifier: LGPL-3.0-or-later"$' '^"// See Notices.txt for copyright information"$')
 MD_HEADER=('^"<!--"$' '^"SPDX-License-Identifier: LGPL-3.0-or-later"$' '^"See Notices.txt for copyright information"$')
 JSON_HEADER=('^"{"$' '^"    \"license_header\": ["$' '^"        \"SPDX-License-Identifier: LGPL-3.0-or-later\","$' '^"        \"See Notices.txt for copyright information\""')
+ROCQ_HEADER=('^"(*  SPDX-License-Identifier: LGPL-3.0-or-later"$' '^"   See Notices.txt for copyright information *)"$')
 
 function main()
 {
@@ -64,6 +65,9 @@ function main()
         *.json)
             check_file "$file" "${JSON_HEADER[@]}"
             ;;
+        *.v)
+            check_file "$file" "${ROCQ_HEADER[@]}"
+            ;;
         *)
             fail_file "$file" 0 "unimplemented file kind -- you need to add it to $0"
             ;;