Improve error message (part of Trac #1606)

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

diff --git a/compiler/typecheck/TcMatches.lhs b/compiler/typecheck/TcMatches.lhs
index 68e1398..485aacb 100644 (file)
--- a/compiler/typecheck/TcMatches.lhs
+++ b/compiler/typecheck/TcMatches.lhs
@@ -153,7 +153,7 @@ tcMatch ctxt pat_tys rhs_ty match
   = wrapLocM (tc_match ctxt pat_tys rhs_ty) match
   where
     tc_match ctxt pat_tys rhs_ty match@(Match pats maybe_rhs_sig grhss)
-      = addErrCtxt (matchCtxt (mc_what ctxt) match)    $       
+      = add_match_ctxt match $
         do { (pats', grhss') <- tcLamPats pats pat_tys rhs_ty $
                                tc_grhss ctxt maybe_rhs_sig grhss
           ; return (Match pats' Nothing grhss') }
@@ -167,6 +167,13 @@ tcMatch ctxt pat_tys rhs_ty match
                        <+> ppr res_sig)
           ; tcGRHSs ctxt grhss (co, rhs_ty) }
 
+       -- For (\x -> e), tcExpr has already said "In the expresssion \x->e"
+       -- so we don't want to add "In the lambda abstraction \x->e"
+    add_match_ctxt match thing_inside
+       = case mc_what ctxt of
+           LambdaExpr -> thing_inside
+           m_ctxt     -> addErrCtxt (matchCtxt m_ctxt match) thing_inside
+
 -------------
 tcGRHSs :: TcMatchCtxt -> GRHSs Name -> (Refinement, BoxyRhoType) 
        -> TcM (GRHSs TcId)