X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcGadt.lhs;h=48b2b0623cd6455cba11c982be5e06cdc096cdfe;hb=9e5f0a0f6848dd8234a83d8ff514365aa4717eea;hp=6650bde180e336969190515205bd553a767ab608;hpb=7fc749a43b4b6b85d234fa95d4928648259584f4;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcGadt.lhs b/compiler/typecheck/TcGadt.lhs
index 6650bde..48b2b06 100644
--- a/compiler/typecheck/TcGadt.lhs
+++ b/compiler/typecheck/TcGadt.lhs
@@ -39,11 +39,8 @@ import Maybes
 import Control.Monad
 import Outputable
 import TcType
-
-#ifdef DEBUG
 import Unique
 import UniqFM
-#endif
 \end{code}
 
 
@@ -240,11 +237,15 @@ fixTvCoEnv in_scope env
       -- then use transitivity with the original coercion
 
 -----------------------------
+-- XXX Can we do this more nicely, by exploiting laziness?
+-- Or avoid needing it in the first place?
 fixTvSubstEnv :: InScopeSet -> TvSubstEnv -> TvSubstEnv
-fixTvSubstEnv in_scope env
-  = fixpt 
+fixTvSubstEnv in_scope env = f env
   where
-    fixpt = mapVarEnv (substTy (mkTvSubst in_scope fixpt)) env
+    f e = let e' = mapUFM (substTy (mkTvSubst in_scope e)) e
+          in if and $ eltsUFM $ intersectUFM_C tcEqType e e'
+             then e
+             else f e'
 
 ----------------------------
 tryToBind :: TyVarSet -> TyVar -> BindFlag
@@ -261,7 +262,6 @@ tryToBind tv_set tv | tv `elemVarSet` tv_set = BindMe
 %************************************************************************
 
 \begin{code}
-#ifdef DEBUG
 badReftElts :: InternalReft -> [(Unique, (Coercion,Type))]
 -- Return the BAD elements of the refinement
 -- Should be empty; used in asserions only
@@ -274,7 +274,6 @@ badReftElts env
 		     | otherwise = False
 	where
 	  (ty1,ty2) = coercionKind co
-#endif
 
 emptyInternalReft :: InternalReft
 emptyInternalReft = emptyVarEnv