X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;ds=sidebyside;f=compiler%2Ftypecheck%2FTcTyFuns.lhs;h=c91ac63e19b917770fdad042cdcbb1c0c27fa531;hb=03b468c46b2a12a51400a6d5f5aa37524b5b998b;hp=0130aa6c4ebd984cff9d64ebfb7e48f10a2179ea;hpb=421819753b3eb4940a26e578ef0e4c5cd31761fa;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcTyFuns.lhs b/compiler/typecheck/TcTyFuns.lhs
index 0130aa6..c91ac63 100644
--- a/compiler/typecheck/TcTyFuns.lhs
+++ b/compiler/typecheck/TcTyFuns.lhs
@@ -526,7 +526,12 @@ swapInst i@(EqInst {})
 		-- we should swap!
 	      go ty1 ty2@(TyConApp tyCon _) 
 					| isOpenSynTyCon tyCon
-					= do { wg_co <- eitherEqInst i
+					= actual_swap ty1 ty2
+	      go ty1@(TyConApp _ _) ty2@(TyVarTy _)
+					= actual_swap ty1 ty2
+	      go _ _			= return (i,False)
+
+	      actual_swap ty1 ty2 = do { wg_co <- eitherEqInst i
 						          -- old_co := sym new_co
 						          (\old_covar ->
 							   do { new_cotv <- newMetaTyVar TauTv (mkCoKind ty2 ty1)
@@ -539,7 +544,6 @@ swapInst i@(EqInst {})
 					     ; new_inst <- mkEqInst (EqPred ty2 ty1) wg_co
 					     ; return (new_inst,True)
 					     }
-	      go _ _			= return (i,False)
 
 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 decompInsts :: [Inst] -> TcM ([Inst],Bool)