1 files changed, 7 insertions, 1 deletions
diff --git a/var.h b/var.h
index 5fc09fa..75653de 100644
--- a/var.h
+++ b/var.h
@@ -56,8 +56,14 @@ class Var : public Evaluable {
 
   virtual string DebugString() const = 0;
 
+  bool ReadOnly() const { return readonly_; }
+  void SetReadOnly() { readonly_ = true; }
+
  protected:
   Var();
+
+ private:
+  bool readonly_;
 };
 
 class SimpleVar : public Var {
@@ -177,7 +183,7 @@ class Vars : public unordered_map<Symbol, Var*> {
 
   Var* Lookup(Symbol name) const;
 
-  void Assign(Symbol name, Var* v);
+  void Assign(Symbol name, Var* v, bool* readonly);
 
   static void add_used_env_vars(Symbol v);