Cure an assert failure by gathering the right set of free variables

[ghc-hetmet.git] / compiler / coreSyn / CoreSubst.lhs

diff --git a/compiler/coreSyn/CoreSubst.lhs b/compiler/coreSyn/CoreSubst.lhs
index f1f02d9..3fe4800 100644 (file)
--- a/compiler/coreSyn/CoreSubst.lhs
+++ b/compiler/coreSyn/CoreSubst.lhs
@@ -227,10 +227,10 @@ lookupTvSubst (Subst _ _ tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v
 --   No left-right shadowing
 --   ie the substitution for   (\x \y. e) a1 a2
 --      so neither x nor y scope over a1 a2
-mkOpenSubst :: [(Var,CoreArg)] -> Subst
-mkOpenSubst pairs = Subst (mkInScopeSet (exprsFreeVars (map snd pairs)))
-                         (mkVarEnv [(id,e)  | (id, e) <- pairs, isId id])
-                         (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
+mkOpenSubst :: InScopeSet -> [(Var,CoreArg)] -> Subst
+mkOpenSubst in_scope pairs = Subst in_scope
+                                  (mkVarEnv [(id,e)  | (id, e) <- pairs, isId id])
+                                  (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
 
 ------------------------------
 isInScope :: Var -> Subst -> Bool