fix #1828, add self-contained utility to extract arithmetical values for use in theory_seq and theory_str and other theories that access current values assigned to numeric variables

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

src/smt/smt_arith_value.h

@@ -0,0 +1,37 @@
+
+/*++
+Copyright (c) 2018 Microsoft Corporation
+
+Module Name:
+
+    smt_arith_value.h
+
+Abstract:
+
+    Utility to extract arithmetic values from context.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2018-12-08.
+
+Revision History:
+
+--*/
+#pragma once;
+
+#include "ast/arith_decl_plugin.h"
+#include "smt/smt_context.h"
+
+
+namespace smt {
+    class arith_value {
+        context& m_ctx;        
+        ast_manager& m;
+        arith_util a;
+    public:
+        arith_value(context& ctx);
+        bool get_lo(expr* e, rational& lo, bool& strict);
+        bool get_up(expr* e, rational& up, bool& strict);
+        bool get_value(expr* e, rational& value);
+    };
+};