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 d9146d9..485aacb 100644 (file)
--- a/compiler/typecheck/TcMatches.lhs
+++ b/compiler/typecheck/TcMatches.lhs
@@ -1,7 +1,9 @@
 %
+% (c) The University of Glasgow 2006
 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
-\section[TcMatches]{Typecheck some @Matches@}
+
+TcMatches: Typecheck some @Matches@
 
 \begin{code}
 module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
@@ -14,36 +16,24 @@ module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda,
 
 import {-# SOURCE #-}  TcExpr( tcSyntaxOp, tcInferRho, tcMonoExpr, tcPolyExpr )
 
-import HsSyn           ( HsExpr(..), LHsExpr, MatchGroup(..),
-                         Match(..), LMatch, GRHSs(..), GRHS(..), 
-                         Stmt(..), LStmt, HsMatchContext(..),
-                         HsStmtContext(..), 
-                         pprMatch, isIrrefutableHsPat, mkHsWrap,
-                         mkLHsWrap, pprMatchContext, pprStmtContext,  
-                         noSyntaxExpr, matchGroupArity, pprMatches,
-                         HsWrapper )
-
+import HsSyn
 import TcRnMonad
-import TcGadt          ( Refinement, emptyRefinement, refineResType )
-import Inst            ( newMethodFromName )
-import TcEnv           ( TcId, tcLookupLocalIds, tcLookupId, tcExtendIdEnv )
-import TcPat           ( tcLamPats, tcLamPat )
-import TcMType         ( newFlexiTyVarTy, newFlexiTyVarTys ) 
-import TcType          ( TcType, TcRhoType, 
-                         BoxySigmaType, BoxyRhoType, 
-                         mkFunTys, mkFunTy, mkAppTy, mkTyConApp,
-                         liftedTypeKind )
-import TcBinds         ( tcLocalBinds )
-import TcUnify         ( boxySplitAppTy, boxySplitTyConApp, boxySplitListTy,
-                         subFunTys, tcSubExp, withBox )
-import TcSimplify      ( bindInstsOfLocalFuns )
-import Name            ( Name )
-import TysWiredIn      ( stringTy, boolTy, parrTyCon, listTyCon, mkListTy, mkPArrTy )
-import PrelNames       ( bindMName, returnMName, mfixName, thenMName, failMName )
-import Id              ( idType, mkLocalId )
-import TyCon           ( TyCon )
+import TcGadt
+import Inst
+import TcEnv
+import TcPat
+import TcMType
+import TcType
+import TcBinds
+import TcUnify
+import TcSimplify
+import Name
+import TysWiredIn
+import PrelNames
+import Id
+import TyCon
 import Outputable
-import SrcLoc          ( Located(..), getLoc )
+import SrcLoc
 \end{code}
 
 %************************************************************************
@@ -163,7 +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') }
@@ -177,6 +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)