[project @ 1996-07-25 20:43:49 by partain]

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

diff --git a/ghc/compiler/typecheck/TcInstDcls.lhs b/ghc/compiler/typecheck/TcInstDcls.lhs
index e12fb7a..5194f9e 100644 (file)
--- a/ghc/compiler/typecheck/TcInstDcls.lhs
+++ b/ghc/compiler/typecheck/TcInstDcls.lhs
@@ -61,7 +61,7 @@ import CmdLineOpts    ( opt_GlasgowExts, opt_CompilingGhcInternals,
 import Class           ( GenClass, GenClassOp, 
                          isCcallishClass, classBigSig,
                          classOps, classOpLocalType,
-                         classOpTagByString
+                         classOpTagByString_maybe
                          )
 import Id              ( GenId, idType, isDefaultMethodId_maybe )
 import ListSetOps      ( minusList )
@@ -80,7 +80,7 @@ import Type           ( GenType(..), SYN_IE(ThetaType), mkTyVarTys,
                          splitSigmaTy, splitAppTy, isTyVarTy, matchTy, mkSigmaTy,
                          getTyCon_maybe, maybeBoxedPrimType, splitRhoTy, eqTy
                        )
-import TyVar           ( GenTyVar, GenTyVarSet(..), mkTyVarSet, unionTyVarSets )
+import TyVar           ( GenTyVar, SYN_IE(GenTyVarSet), mkTyVarSet, unionTyVarSets )
 import TysWiredIn      ( stringTy )
 import Unique          ( Unique )
 import Util            ( zipEqual, panic )
@@ -602,10 +602,13 @@ processInstBinds1 clas avail_insts method_ids mbind
 
     -- Make a method id for the method
     let
-       tag       = classOpTagByString clas occ
-       method_id = method_ids !! (tag-1)
-       method_ty = tcIdType method_id
+       maybe_tag  = classOpTagByString_maybe clas occ
+       (Just tag) = maybe_tag
+       method_id  = method_ids !! (tag-1)
+       method_ty  = tcIdType method_id
     in
+    -- check that the method mentioned is actually in the class:
+    checkMaybeTc maybe_tag (instMethodNotInClassErr occ clas) `thenTc_`
 
     tcInstTcType method_ty             `thenNF_Tc` \ (method_tyvars, method_rho) ->
     let
@@ -921,6 +924,10 @@ omitDefaultMethodWarn clas_op clas_name inst_ty sty
           ppr sty clas_op, ppStr "in instance",
           ppPStr clas_name, pprParendGenType sty inst_ty]
 
+instMethodNotInClassErr occ clas sty
+  = ppHang (ppStr "Instance mentions a method not in the class")
+        4 (ppBesides [ppStr "class `", ppr sty clas, ppStr "' method `",
+                      ppPStr occ, ppStr "'"])
 
 patMonoBindsCtxt pbind sty
   = ppHang (ppStr "In a pattern binding:")