+
+-----------------------
+misMatchMsg :: TcType -> TcType -> TcM (TidyEnv, SDoc)
+-- Generate the message when two types fail to match,
+-- going to some trouble to make it helpful.
+-- The argument order is: actual type, expected type
+misMatchMsg ty_act ty_exp
+ = do { env0 <- tcInitTidyEnv
+ ; (env1, pp_exp, extra_exp) <- ppr_ty env0 ty_exp ty_act
+ ; (env2, pp_act, extra_act) <- ppr_ty env1 ty_act ty_exp
+ ; return (env2,
+ sep [sep [ptext SLIT("Couldn't match expected type") <+> pp_exp,
+ nest 7 $
+ ptext SLIT("against inferred type") <+> pp_act],
+ nest 2 (extra_exp $$ extra_act)]) }
+
+ppr_ty :: TidyEnv -> TcType -> TcType -> TcM (TidyEnv, SDoc, SDoc)
+ppr_ty env ty other_ty
+ = do { ty' <- zonkTcType ty
+ ; let (env1, tidy_ty) = tidyOpenType env ty'
+ ; (env2, extra) <- ppr_extra env1 tidy_ty other_ty
+ ; return (env2, quotes (ppr tidy_ty), extra) }
+
+-- (ppr_extra env ty other_ty) shows extra info about 'ty'
+ppr_extra env (TyVarTy tv) other_ty
+ | isSkolemTyVar tv || isSigTyVar tv
+ = return (env1, pprSkolTvBinding tv1)
+ where
+ (env1, tv1) = tidySkolemTyVar env tv
+
+ppr_extra env (TyConApp tc1 _) (TyConApp tc2 _)
+ | getOccName tc1 == getOccName tc2
+ = -- This case helps with messages that would otherwise say
+ -- Could not match 'T' does not match 'M.T'
+ -- which is not helpful
+ do { this_mod <- getModule
+ ; return (env, quotes (ppr tc1) <+> ptext SLIT("is defined") <+> mk_mod this_mod) }
+ where
+ tc_mod = nameModule (getName tc1)
+ tc_pkg = modulePackageId tc_mod
+ tc2_pkg = modulePackageId (nameModule (getName tc2))
+ mk_mod this_mod
+ | tc_mod == this_mod = ptext SLIT("in this module")
+
+ | not home_pkg && tc2_pkg /= tc_pkg = pp_pkg
+ -- Suppress the module name if (a) it's from another package
+ -- (b) other_ty isn't from that same package
+
+ | otherwise = ptext SLIT("in module") <+> quotes (ppr tc_mod) <+> pp_pkg
+ where
+ home_pkg = tc_pkg == modulePackageId this_mod
+ pp_pkg | home_pkg = empty
+ | otherwise = ptext SLIT("in package") <+> quotes (ppr tc_pkg)
+
+ppr_extra env ty other_ty = return (env, empty) -- Normal case