add array-ext to externally exposed functions to enable interpolants with arrays to be usable in feedback loops with Z3. Addresses one issue raised in #292

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/api_array.cpp

@@ -187,7 +187,8 @@ extern "C" {
     MK_BINARY(Z3_mk_set_difference, mk_c(c)->get_array_fid(), OP_SET_DIFFERENCE, SKIP);
     MK_UNARY(Z3_mk_set_complement, mk_c(c)->get_array_fid(), OP_SET_COMPLEMENT, SKIP);
     MK_BINARY(Z3_mk_set_subset, mk_c(c)->get_array_fid(), OP_SET_SUBSET, SKIP);
-    
+    MK_BINARY(Z3_mk_array_ext, mk_c(c)->get_array_fid(), OP_ARRAY_EXT, SKIP);
+
     Z3_ast Z3_mk_set_member(Z3_context c, Z3_ast elem, Z3_ast set) {
         return Z3_mk_select(c, set, elem);
     }

src/api/api_ast.cpp

@@ -1012,6 +1012,7 @@ extern "C" {
             case OP_SET_COMPLEMENT: return Z3_OP_SET_COMPLEMENT;
             case OP_SET_SUBSET: return Z3_OP_SET_SUBSET;
             case OP_AS_ARRAY: return Z3_OP_AS_ARRAY;
+            case OP_ARRAY_EXT: return Z3_OP_ARRAY_EXT;
             default:
                 UNREACHABLE();
                 return Z3_OP_UNINTERPRETED;

src/api/dotnet/Context.cs

@@ -2122,6 +2122,21 @@ namespace Microsoft.Z3
             CheckContextMatch(array);
             return Expr.Create(this, Native.Z3_mk_array_default(nCtx, array.NativeObject));
         }
+
+        /// <summary>
+        /// Create Extentionality index. Two arrays are equal if and only if they are equal on the index returned by MkArrayExt.
+        /// </summary>
+        public Expr MkArrayExt(ArrayExpr arg1, ArrayExpr arg2)
+        {
+            Contract.Requires(arg1 != null);
+            Contract.Requires(arg2 != null);
+            Contract.Ensures(Contract.Result<Expr>() != null);
+
+            CheckContextMatch(arg1);
+            CheckContextMatch(arg2);
+            return Expr.Create(this, Native.Z3_mk_array_ext(nCtx, arg1.NativeObject, arg2.NativeObject));
+        }
+
         #endregion
 
         #region Sets
@@ -2268,6 +2283,7 @@ namespace Microsoft.Z3
             CheckContextMatch(arg2);
             return (BoolExpr) Expr.Create(this, Native.Z3_mk_set_subset(nCtx, arg1.NativeObject, arg2.NativeObject));
         }
+
         #endregion
 
         #region Pseudo-Boolean constraints

src/api/java/Context.java

@@ -1717,6 +1717,17 @@ public class Context extends IDisposable
                 Native.mkArrayDefault(nCtx(), array.getNativeObject()));
     }
 
+    /**
+     * Create Extentionality index. Two arrays are equal if and only if they are equal on the index returned by MkArrayExt.
+     **/
+    public Expr mkArrayExt(ArrayExpr arg1, ArrayExpr arg2)
+    {
+	checkContextMatch(arg1);
+	checkContextMatch(arg2);
+	return Expr.create(this, Native.mkArrayExt(nCtx(), arg1.getNativeObject(), arg2.getNativeObject()));
+    }
+
+
     /**
      * Create a set type.
      **/

src/api/python/z3.py

@@ -4143,6 +4143,13 @@ def K(dom, v):
         v = _py2expr(v, ctx)
     return ArrayRef(Z3_mk_const_array(ctx.ref(), dom.ast, v.as_ast()), ctx)
 
+def Ext(a, b):
+    """Return extensionality index for arrays.
+    """
+    if __debug__:
+	_z3_assert(is_array(a) and is_array(b))
+    return _to_expr_ref(Z3_mk_array_ext(ctx.ref(), a.as_ast(), b.as_ast()));
+
 def is_select(a):
     """Return `True` if `a` is a Z3 array select application.
     

src/api/python/z3printer.py

@@ -31,7 +31,7 @@ _z3_op_to_str = {
     Z3_OP_BASHR : '>>', Z3_OP_BSHL : '<<', Z3_OP_BLSHR : 'LShR', 
     Z3_OP_CONCAT : 'Concat', Z3_OP_EXTRACT : 'Extract', Z3_OP_BV2INT : 'BV2Int',
     Z3_OP_ARRAY_MAP : 'Map', Z3_OP_SELECT : 'Select', Z3_OP_STORE : 'Store', 
-    Z3_OP_CONST_ARRAY : 'K',
+    Z3_OP_CONST_ARRAY : 'K', Z3_OP_ARRAY_EXT : 'Ext', 
     Z3_OP_PB_AT_MOST : 'AtMost', Z3_OP_PB_LE : 'PbLe', Z3_OP_PB_GE : 'PbGe'
     }
 

src/api/z3_api.h

@@ -322,6 +322,9 @@ typedef enum
    - Z3_OP_AS_ARRAY An array value that behaves as the function graph of the
                     function passed as parameter.
 
+   - Z3_OP_ARRAY_EXT Array extensionality function. It takes two arrays as arguments and produces an index, such that the arrays
+                    are different if they are different on the index.
+
    - Z3_OP_BNUM Bit-vector numeral.
 
    - Z3_OP_BIT1 One bit bit-vector.
@@ -1033,6 +1036,7 @@ typedef enum {
     Z3_OP_SET_COMPLEMENT,
     Z3_OP_SET_SUBSET,
     Z3_OP_AS_ARRAY,
+    Z3_OP_ARRAY_EXT,
 
     // Bit-vectors
     Z3_OP_BNUM = 0x400,
@@ -3260,6 +3264,17 @@ END_MLAPI_EXCLUDE
     Z3_ast Z3_API Z3_mk_set_subset(Z3_context c, Z3_ast arg1, Z3_ast arg2);
     /*@}*/
 
+    /**
+       \brief Create array extensionality index given two arrays with the same sort. 
+              The meaning is given by the axiom:
+              (=> (= (select A (array-ext A B)) (select B (array-ext A B))) (= A B))
+
+       def_API('Z3_mk_array_ext', AST, (_in(CONTEXT), _in(AST), _in(AST)))
+    */
+
+    Z3_ast Z3_API Z3_mk_array_ext(Z3_context c, Z3_ast arg1, Z3_ast arg2);
+    /*@}*/
+
     /**
        @name Numerals
     */