Better error message for unsolvable equalities

diff --git a/compiler/typecheck/TcTyFuns.lhs b/compiler/typecheck/TcTyFuns.lhs
index 141afb1..39cee90 100644 (file)
--- a/compiler/typecheck/TcTyFuns.lhs
+++ b/compiler/typecheck/TcTyFuns.lhs
@@ -591,10 +591,11 @@ decompInst i@(EqInst {})
       | con1 /= con2 && not (isOpenSynTyCon con1 || isOpenSynTyCon con2)
         -- not matching data constructors (of any flavour) are bad news
       = do { env0 <- tcInitTidyEnv
-           ; let (env1, tidy_ty1)  =  tidyOpenType env0 ty1
-                 (env2, tidy_ty2)  =  tidyOpenType env1 ty2
-                 extra                  = sep [ppr tidy_ty1, char '~', ppr tidy_ty2]
-                 msg            = ptext SLIT("Couldn't match expected type against inferred type")
+           ; let (env1, tidy_ty1) = tidyOpenType env0 ty1
+                 (env2, tidy_ty2) = tidyOpenType env1 ty2
+                 extra                   = sep [ppr tidy_ty1, char '~', ppr tidy_ty2]
+                 msg             = 
+                   ptext SLIT("Unsolvable equality constraint:")
            ; failWithTcM (env2, hang msg 2 extra)
            }
       where