1 files changed, 10 insertions, 1 deletions
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 6912e22887fd..1a9862c29533 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -14,8 +14,9 @@ class Hash;
 class EvalState;
 struct Env;
 struct Value;
+struct Attr;
 
-typedef std::map<Symbol, Value> Bindings;
+typedef std::map<Symbol, Attr> Bindings;
 
 
 typedef enum {
@@ -111,6 +112,14 @@ struct Env
 };
 
 
+struct Attr
+{
+    Value value;
+    Pos * pos;
+    Attr() : pos(&noPos) { };
+};
+
+
 static inline void mkInt(Value & v, int n)
 {
     v.type = tInt;