[project @ 2002-11-19 09:37:08 by simonpj]

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

diff --git a/ghc/compiler/coreSyn/Subst.lhs b/ghc/compiler/coreSyn/Subst.lhs
index 17586a1..e2aded0 100644 (file)
--- a/ghc/compiler/coreSyn/Subst.lhs
+++ b/ghc/compiler/coreSyn/Subst.lhs
@@ -373,13 +373,21 @@ type TyVarSubst = Subst   -- TyVarSubst are expected to have range elements
 -- it'll never be evaluated
 mkTyVarSubst :: [TyVar] -> [Type] -> Subst
 mkTyVarSubst tyvars tys = Subst (mkInScopeSet (tyVarsOfTypes tys)) 
-                               (zip_ty_env tyvars tys emptySubstEnv)
+                               (zipTyEnv tyvars tys)
 
 -- mkTopTyVarSubst is called when doing top-level substitutions.
 -- Here we expect that the free vars of the range of the
 -- substitution will be empty.
 mkTopTyVarSubst :: [TyVar] -> [Type] -> Subst
-mkTopTyVarSubst tyvars tys = Subst emptyInScopeSet (zip_ty_env tyvars tys emptySubstEnv)
+mkTopTyVarSubst tyvars tys = Subst emptyInScopeSet (zipTyEnv tyvars tys)
+
+zipTyEnv tyvars tys
+#ifdef DEBUG
+  | length tyvars /= length tys
+  = pprTrace "mkTopTyVarSubst" (ppr tyvars $$ ppr tys) emptySubstEnv
+  | otherwise
+#endif
+  = zip_ty_env tyvars tys emptySubstEnv
 
 zip_ty_env []       []       env = env
 zip_ty_env (tv:tvs) (ty:tys) env = zip_ty_env tvs tys (extendSubstEnv env tv (DoneTy ty))