Use implication constraints to improve type inference

[ghc-hetmet.git] / compiler / typecheck / TcEnv.lhs

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index 2e3b80b..cc50e50 100644 (file)
--- 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 }