X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=cc50e50d732837f6d30763423dc6f151deb867e6;hb=2423c249f5ca7785d0ec89eb33e72662da7561c1;hp=2e3b80ba7e356008476191881a40f513de80dba1;hpb=1166c7d62f3fa9acd2084c90df6585cbbf868ceb;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 2e3b80b..cc50e50 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -400,6 +400,9 @@ refineEnvironment :: Refinement -> TcM a -> TcM a
 -- I don't think I have to refine the set of global type variables in scope
 -- Reason: the refinement never increases that set
 refineEnvironment reft thing_inside
+  | isEmptyRefinement reft		-- Common case
+  = thing_inside
+  | otherwise
   = do	{ env <- getLclEnv
 	; let le' = mapNameEnv refine (tcl_env env)
  	; setLclEnv (env {tcl_env = le'}) thing_inside }