Make Env self-describing

If the Env denotes a 'with', then values[0] may be an Expr* cast to a
Value*. For code that generically traverses Values/Envs, it's useful
to know this.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 8594a2707d9a..3725e45dad9b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -35,8 +35,8 @@ struct Env
 {
     Env * up;
     unsigned short size; // used by ‘valueSize’
-    unsigned short prevWith:15; // nr of levels up to next `with' environment
-    unsigned short haveWithAttrs:1;
+    unsigned short prevWith:14; // nr of levels up to next `with' environment
+    enum { Plain = 0, HasWithExpr, HasWithAttrs } type:2;
     Value * values[0];
 };