[project @ 2001-05-03 09:01:50 by simonpj]

Improve error message

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index 9b478e0..d4dd386 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -13,7 +13,7 @@ import CmdLineOpts    ( DynFlag(..), dopt )
 
 import HsSyn           ( HsDecl(..), InstDecl(..), TyClDecl(..), HsType(..),
                          MonoBinds(..), HsExpr(..),  HsLit(..), Sig(..), 
-                         andMonoBindList, collectMonoBinders, isClassDecl
+                         andMonoBindList, collectMonoBinders, isClassDecl, toHsType
                        )
 import RnHsSyn         ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl, 
                          RenamedMonoBinds, RenamedTyClDecl, RenamedHsType, 
@@ -512,8 +512,9 @@ tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
 tcInstDecl2 (InstInfo { iDFunId = dfun_id, 
                        iBinds = monobinds, iPrags = uprags })
   =     -- Prime error recovery
-    recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds))  $
-    tcAddSrcLoc (getSrcLoc dfun_id)                       $
+    recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds))      $
+    tcAddSrcLoc (getSrcLoc dfun_id)                            $
+    tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id)))    $
 
        -- Instantiate the instance decl with tc-style type variables
     tcInstType (idType dfun_id)                `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->