X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcGadt.lhs;h=48b2b0623cd6455cba11c982be5e06cdc096cdfe;hb=0843c0bdc66008008d38eff07c90437ed56d9ca1;hp=b3156ed747a9643ec097da4e7dcc99e630e4974f;hpb=727fae32ea0b6ca6ebdf1b3137649813e4d7ac3d;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcGadt.lhs b/compiler/typecheck/TcGadt.lhs
index b3156ed..48b2b06 100644
--- a/compiler/typecheck/TcGadt.lhs
+++ b/compiler/typecheck/TcGadt.lhs
@@ -40,7 +40,7 @@ import Control.Monad
 import Outputable
 import TcType
 import Unique
-import LazyUniqFM
+import UniqFM
 \end{code}
 
 
@@ -237,11 +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