3 files changed, 23 insertions, 5 deletions
diff --git a/include/klee/Expr.h b/include/klee/Expr.h
index 69ed60a1..3473784b 100644
--- a/include/klee/Expr.h
+++ b/include/klee/Expr.h
@@ -330,14 +330,14 @@ public:
   static ref<Expr> fromMemory(void *address, Width w);
   void toMemory(void *address);
 
-  static ref<Expr> alloc(uint64_t v, Width w) {
+  static ref<ConstantExpr> alloc(uint64_t v, Width w) {
     // constructs an "optimized" ConstantExpr
-    ref<Expr> r(new ConstantExpr(v, w));
+    ref<ConstantExpr> r(new ConstantExpr(v, w));
     r->computeHash();
     return r;
   }
   
-  static ref<Expr> create(uint64_t v, Width w) {
+  static ref<ConstantExpr> create(uint64_t v, Width w) {
     assert(v == bits64::truncateToNBits(v, w) &&
            "invalid constant");
     return alloc(v, w);
diff --git a/lib/Expr/Parser.cpp b/lib/Expr/Parser.cpp
index 3bbe3334..1808ca7b 100644
--- a/lib/Expr/Parser.cpp
+++ b/lib/Expr/Parser.cpp
@@ -49,8 +49,26 @@ namespace {
     }
   };
   
+  class ExprResult {
+    bool IsValid;
+    ExprHandle Value;
+
+  public:
+    ExprResult() : IsValid(false) {}
+    ExprResult(ExprHandle _Value) : IsValid(true), Value(_Value) {}
+    ExprResult(ref<ConstantExpr> _Value) : IsValid(true), Value(_Value.get()) {}
+    ExprResult(bool _IsValid, ExprHandle _Value) : IsValid(_IsValid), Value(_Value) {}
+
+    bool isValid() { 
+      return IsValid; 
+    }
+    ExprHandle get() { 
+      assert(IsValid && "get() on invalid ParseResult!");
+      return Value; 
+    }
+  };
+
   typedef ParseResult<Decl*> DeclResult;
-  typedef ParseResult<ExprHandle> ExprResult;
   typedef ParseResult<Expr::Width> TypeResult;
   typedef ParseResult<VersionHandle> VersionResult;
 
diff --git a/unittests/Expr/ExprTest.cpp b/unittests/Expr/ExprTest.cpp
index a5e5d5d7..7b37973a 100644
--- a/unittests/Expr/ExprTest.cpp
+++ b/unittests/Expr/ExprTest.cpp
@@ -22,7 +22,7 @@ ref<Expr> getConstant(int value, Expr::Width width) {
 }
 
 TEST(ExprTest, BasicConstruction) {
-  EXPECT_EQ(ConstantExpr::alloc(0, 32),
+  EXPECT_EQ(ref<Expr>(ConstantExpr::alloc(0, 32)),
             SubExpr::create(ConstantExpr::alloc(10, 32),
                             ConstantExpr::alloc(10, 32)));
 }