[project @ 2003-10-13 14:54:37 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcHsType.lhs b/ghc/compiler/typecheck/TcHsType.lhs
index 3be9d31..9a73ff3 100644 (file)
--- a/ghc/compiler/typecheck/TcHsType.lhs
+++ b/ghc/compiler/typecheck/TcHsType.lhs
@@ -34,7 +34,7 @@ import TcEnv          ( tcExtendTyVarEnv, tcExtendTyVarKindEnv,
                        )
 import TcMType         ( newKindVar, tcInstType, newMutTyVar,
                          zonkTcType, zonkTcKindToKind,
-                         checkValidType, UserTypeCtxt(..), pprUserTypeCtxt
+                         checkValidType, UserTypeCtxt(..), pprHsSigCtxt
                        )
 import TcUnify         ( unifyKind, unifyFunKind, unifyTypeKind )
 import TcType          ( Type, PredType(..), ThetaType, TyVarDetails(..),
@@ -152,7 +152,7 @@ the TyCon being defined.
 tcHsSigType :: UserTypeCtxt -> RenamedHsType -> TcM Type
   -- Do kind checking, and hoist for-alls to the top
 tcHsSigType ctxt hs_ty 
-  = addErrCtxt (checkHsTypeCtxt ctxt hs_ty) $
+  = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
     do { kinded_ty <- kcTypeType hs_ty
        ; ty <- tcHsKindedType kinded_ty
        ; checkValidType ctxt ty        
@@ -164,11 +164,6 @@ tcHsPred pred
   = do { (kinded_pred,_) <- kc_pred pred       -- kc_pred rather than kcHsPred
                                                -- to avoid the partial application check
        ; dsHsPred kinded_pred }
-
-
-checkHsTypeCtxt ctxt hs_ty
-  = vcat [ptext SLIT("In the type signature:") <+> ppr hs_ty,
-         ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
 \end{code}
 
        These functions are used during knot-tying in
@@ -642,12 +637,19 @@ tcAddScopedTyVars sig_tys thing_inside
        -- Zonk the mutable kinds and bring the tyvars into scope
        -- Rather like tcTyVarBndrs, except that it brings *mutable* 
        -- tyvars into scope, not immutable ones
+       --
+       -- Furthermore, the tyvars are PatSigTvs, which means that we get better
+       -- error messages when type variables escape:
+       --      Inferred type is less polymorphic than expected
+       --      Quantified type variable `t' escapes
+       --      It is mentioned in the environment:
+       --      t is bound by the pattern type signature at tcfail103.hs:6
     mapM zonk kinded_tvs       `thenM` \ tyvars ->
     tcExtendTyVarEnv tyvars thing_inside
 
   where
     zonk (KindedTyVar name kind) = zonkTcKindToKind kind       `thenM` \ kind' ->
-                                  newMutTyVar name kind' VanillaTv 
+                                  newMutTyVar name kind' PatSigTv
     zonk (UserTyVar name) = pprTrace "BAD: Un-kinded tyvar" (ppr name) $
                            returnM (mkTyVar name liftedTypeKind)
 \end{code}