Change type of TcGadt.refineType, plus consequences

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

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index c638c04..2e3b80b 100644 (file)
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -405,11 +405,13 @@ refineEnvironment reft thing_inside
        ; setLclEnv (env {tcl_env = le'}) thing_inside }
   where
     refine elt@(ATcId { tct_co = Just co, tct_type = ty })
-                         = let (co', ty') = refineType reft ty
-                           in elt { tct_co = Just (co' <.> co), tct_type = ty' }
-    refine (ATyVar tv ty) = ATyVar tv (snd (refineType reft ty))
-                               -- Ignore the coercion that refineType returns
-    refine elt           = elt
+       | Just (co', ty') <- refineType reft ty
+       = elt { tct_co = Just (WpCo co' <.> co), tct_type = ty' }
+    refine (ATyVar tv ty) 
+       | Just (_, ty') <- refineType reft ty
+       = ATyVar tv ty' -- Ignore the coercion that refineType returns
+
+    refine elt = elt   -- Common case
 \end{code}
 
 %************************************************************************