X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcUnify.lhs;h=c13cff66fae6e871c7629c506004889d41c1ee5e;hb=5f553f0c0508cb09b75f78e6c2ac1baa4c01b6aa;hp=04a804d0ae197787f3b012ebe70b1fa13406c047;hpb=ac41c500b3769f005eeeaf964170a78c79135196;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcUnify.lhs b/ghc/compiler/typecheck/TcUnify.lhs index 04a804d..c13cff6 100644 --- a/ghc/compiler/typecheck/TcUnify.lhs +++ b/ghc/compiler/typecheck/TcUnify.lhs @@ -12,6 +12,7 @@ module TcUnify ( -- Various unifications unifyTauTy, unifyTauTyList, unifyTauTyLists, unifyKind, unifyKinds, unifyFunKind, + checkExpectedKind, -------------------------------- -- Holes @@ -28,9 +29,9 @@ module TcUnify ( import HsSyn ( HsExpr(..) ) -import TcHsSyn ( mkHsLet, +import TcHsSyn ( mkHsLet, mkHsDictLam, ExprCoFn, idCoercion, isIdCoercion, mkCoercion, (<.>), (<$>) ) -import TypeRep ( Type(..), PredType(..), TyNote(..), typeCon, openKindCon, isSuperKind ) +import TypeRep ( Type(..), PredType(..), TyNote(..) ) import TcRnMonad -- TcType, amongst others import TcType ( TcKind, TcType, TcSigmaType, TcRhoType, TcTyVar, TcTauType, @@ -42,12 +43,16 @@ import TcType ( TcKind, TcType, TcSigmaType, TcRhoType, TcTyVar, TcTauType, typeKind, tcSplitFunTy_maybe, mkForAllTys, isSkolemTyVar, isUserTyVar, tidyOpenType, tidyOpenTypes, tidyOpenTyVar, tidyOpenTyVars, - eqKind, openTypeKind, liftedTypeKind, isTypeKind, mkArrowKind, - hasMoreBoxityInfo, allDistinctTyVars, pprType, pprKind ) + allDistinctTyVars, pprType ) +import Kind ( Kind(..), SimpleKind, KindVar, isArgTypeKind, + openTypeKind, liftedTypeKind, mkArrowKind, + isOpenTypeKind, argTypeKind, isLiftedTypeKind, isUnliftedTypeKind, + isSubKind, pprKind, splitKindFunTys ) import Inst ( newDicts, instToId, tcInstCall ) import TcMType ( getTcTyVar, putTcTyVar, tcInstType, newKindVar, - newTyVarTy, newTyVarTys, newOpenTypeKind, - zonkTcType, zonkTcTyVars, zonkTcTyVarsAndFV ) + newTyVarTy, newTyVarTys, zonkTcKind, + zonkTcType, zonkTcTyVars, zonkTcTyVarsAndFV, + readKindVar,writeKindVar ) import TcSimplify ( tcSimplifyCheck ) import TysWiredIn ( listTyCon, parrTyCon, tupleTyCon ) import TcEnv ( tcGetGlobalTyVars, findGlobals ) @@ -58,6 +63,7 @@ import VarSet ( emptyVarSet, unitVarSet, unionVarSet, elemVarSet, varSetElems ) import VarEnv import Name ( isSystemName ) import ErrUtils ( Message ) +import SrcLoc ( noLoc ) import BasicTypes ( Boxity, Arity, isBoxed ) import Util ( equalLength, lengthExceeds, notNull ) import Outputable @@ -84,14 +90,22 @@ readExpectedType :: Expected ty -> TcM ty readExpectedType (Infer hole) = readMutVar hole readExpectedType (Check ty) = returnM ty -zapExpectedType :: Expected TcType -> TcM TcTauType +zapExpectedType :: Expected TcType -> Kind -> TcM TcTauType -- In the inference case, ensure we have a monotype -zapExpectedType (Infer hole) - = do { ty <- newTyVarTy openTypeKind ; +-- (including an unboxed tuple) +zapExpectedType (Infer hole) kind + = do { ty <- newTyVarTy kind ; writeMutVar hole ty ; return ty } -zapExpectedType (Check ty) = return ty +zapExpectedType (Check ty) kind + | typeKind ty `isSubKind` kind = return ty + | otherwise = do { ty1 <- newTyVarTy kind + ; unifyTauTy ty1 ty + ; return ty } + -- The unify is to ensure that 'ty' has the desired kind + -- For example, in (case e of r -> b) we push an OpenTypeKind + -- type variable zapExpectedTo :: Expected TcType -> TcTauType -> TcM () zapExpectedTo (Infer hole) ty2 = writeMutVar hole ty2 @@ -100,7 +114,7 @@ zapExpectedTo (Check ty1) ty2 = unifyTauTy ty1 ty2 zapExpectedBranches :: [a] -> Expected TcType -> TcM (Expected TcType) -- Zap the expected type to a monotype if there is more than one branch zapExpectedBranches branches exp_ty - | lengthExceeds branches 1 = zapExpectedType exp_ty `thenM` \ exp_ty' -> + | lengthExceeds branches 1 = zapExpectedType exp_ty openTypeKind `thenM` \ exp_ty' -> return (Check exp_ty') | otherwise = returnM exp_ty @@ -176,7 +190,7 @@ unifyFunTy ty Nothing -> unify_fun_ty_help ty unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification - = newTyVarTy openTypeKind `thenM` \ arg -> + = newTyVarTy argTypeKind `thenM` \ arg -> newTyVarTy openTypeKind `thenM` \ res -> unifyTauTy ty (mkFunTy arg res) `thenM_` returnM (arg,res) @@ -255,7 +269,8 @@ new_tuple_ty boxity arity where tup_tc = tupleTyCon boxity arity kind | isBoxed boxity = liftedTypeKind - | otherwise = openTypeKind + | otherwise = argTypeKind -- Components of an unboxed tuple + -- can be unboxed, but not unboxed tuples \end{code} @@ -441,7 +456,7 @@ tcSub_fun exp_arg exp_res act_arg act_res | otherwise = mkCoercion co_fn co_fn e = DictLam [arg_id] - (co_fn_res <$> (HsApp e (co_fn_arg <$> (HsVar arg_id)))) + (noLoc (co_fn_res <$> (HsApp (noLoc e) (noLoc (co_fn_arg <$> HsVar arg_id))))) -- Slight hack; using a "DictLam" to get an ordinary simple lambda -- HsVar arg_id :: HsExpr exp_arg -- co_fn_arg $it :: HsExpr act_arg @@ -460,7 +475,7 @@ imitateFun tv ty checkM (not (isSkolemTyVar tv)) (failWithTcM (unifyWithSigErr tv ty)) `thenM_` - newTyVarTy openTypeKind `thenM` \ arg -> + newTyVarTy argTypeKind `thenM` \ arg -> newTyVarTy openTypeKind `thenM` \ res -> putTcTyVar tv (mkFunTy arg res) `thenM_` returnM (arg,res) @@ -521,7 +536,7 @@ tcGen expected_ty extra_tvs thing_inside -- We expect expected_ty to be a forall -- It's a bit out of place here, but using AbsBind involves inventing -- a couple of new names which seems worse. dict_ids = map instToId dicts - co_fn e = TyLam zonked_tvs (DictLam dict_ids (mkHsLet inst_binds e)) + co_fn e = TyLam zonked_tvs (mkHsDictLam dict_ids (mkHsLet inst_binds (noLoc e))) in returnM (mkCoercion co_fn, result) where @@ -629,12 +644,6 @@ uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2) | con1 == con2 && equalLength tys1 tys2 = unifyTauTyLists tys1 tys2 - | con1 == openKindCon - -- When we are doing kind checking, we might match a kind '?' - -- against a kind '*' or '#'. Notably, CCallable :: ? -> *, and - -- (CCallable Int) and (CCallable Int#) are both OK - = unifyTypeKind ps_ty2 - -- Applications need a bit of care! -- They can match FunTy and TyConApp, so use splitAppTy_maybe -- NB: we've already dealt with type variables and Notes, @@ -736,42 +745,46 @@ uVar swapped tv1 ps_ty2 ty2 case maybe_ty1 of Just ty1 | swapped -> uTys ps_ty2 ty2 ty1 ty1 -- Swap back | otherwise -> uTys ty1 ty1 ps_ty2 ty2 -- Same order - other -> uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2 + other -> uUnboundVar swapped tv1 ps_ty2 ty2 -- Expand synonyms; ignore FTVs -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy n2 ty2) - = uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2 +uUnboundVar swapped tv1 ps_ty2 (NoteTy n2 ty2) + = uUnboundVar swapped tv1 ps_ty2 ty2 -- The both-type-variable case -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2) +uUnboundVar swapped tv1 ps_ty2 ty2@(TyVarTy tv2) -- Same type variable => no-op | tv1 == tv2 = returnM () -- Distinct type variables - -- ASSERT maybe_ty1 /= Just | otherwise = getTcTyVar tv2 `thenM` \ maybe_ty2 -> case maybe_ty2 of - Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2' + Just ty2' -> uUnboundVar swapped tv1 ty2' ty2' Nothing | update_tv2 + -- It should always be the case that either k1 <: k2 or k2 <: k1 + -- Reason: a type variable never gets the kinds (#) or # - -> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) ) + -> ASSERT2( k1 `isSubKind` k2, (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) ) putTcTyVar tv2 (TyVarTy tv1) `thenM_` returnM () - | otherwise - -> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) ) + | otherwise + -> ASSERT2( k2 `isSubKind` k1, (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) ) putTcTyVar tv1 ps_ty2 `thenM_` returnM () where k1 = tyVarKind tv1 k2 = tyVarKind tv2 - update_tv2 = (k2 `eqKind` openTypeKind) || (not (k1 `eqKind` openTypeKind) && nicer_to_update_tv2) - -- Try to get rid of open type variables as soon as poss + update_tv2 = k1 `isSubKind` k2 && (k1 /= k2 || nicer_to_update_tv2) + -- Update the variable with least kind info + -- See notes on type inference in Kind.lhs + -- The "nicer to" part only applies if the two kinds are the same, + -- so we can choose which to do. nicer_to_update_tv2 = isUserTyVar tv1 -- Don't unify a signature type variable if poss @@ -779,7 +792,7 @@ uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2) -- Try to update sys-y type variables in preference to sig-y ones -- Second one isn't a type variable -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2 +uUnboundVar swapped tv1 ps_ty2 non_var_ty2 = -- Check that tv1 isn't a type-signature type variable checkM (not (isSkolemTyVar tv1)) (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenM_` @@ -802,7 +815,7 @@ checkKinds swapped tv1 ty2 -- We're about to unify a type variable tv1 with a non-tyvar-type ty2. -- ty2 has been zonked at this stage, which ensures that -- its kind has as much boxity information visible as possible. - | tk2 `hasMoreBoxityInfo` tk1 = returnM () + | tk2 `isSubKind` tk1 = returnM () | otherwise -- Either the kinds aren't compatible @@ -810,7 +823,7 @@ checkKinds swapped tv1 ty2 -- or we are unifying a lifted type variable with an -- unlifted type: e.g. (id 3#) is illegal = addErrCtxtM (unifyKindCtxt swapped tv1 ty2) $ - unifyMisMatch k1 k2 + unifyKindMisMatch k1 k2 where (k1,k2) | swapped = (tk2,tk1) @@ -891,61 +904,133 @@ okToUnifyWith tv ty Just p `and` m = Just p \end{code} + %************************************************************************ %* * -\subsection{Kind unification} + Kind unification %* * %************************************************************************ +Unifying kinds is much, much simpler than unifying types. + \begin{code} unifyKind :: TcKind -- Expected -> TcKind -- Actual -> TcM () -unifyKind k1 k2 = uTys k1 k1 k2 k2 +unifyKind LiftedTypeKind LiftedTypeKind = returnM () +unifyKind UnliftedTypeKind UnliftedTypeKind = returnM () + +unifyKind OpenTypeKind k2 | isOpenTypeKind k2 = returnM () +unifyKind ArgTypeKind k2 | isArgTypeKind k2 = returnM () + -- Respect sub-kinding + +unifyKind (FunKind a1 r1) (FunKind a2 r2) + = do { unifyKind a2 a1; unifyKind r1 r2 } + -- Notice the flip in the argument, + -- so that the sub-kinding works right + +unifyKind (KindVar kv1) k2 = uKVar False kv1 k2 +unifyKind k1 (KindVar kv2) = uKVar True kv2 k1 +unifyKind k1 k2 = unifyKindMisMatch k1 k2 unifyKinds :: [TcKind] -> [TcKind] -> TcM () unifyKinds [] [] = returnM () unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenM_` unifyKinds ks1 ks2 -unifyKinds _ _ = panic "unifyKinds: length mis-match" -\end{code} - -\begin{code} -unifyTypeKind :: TcKind -> TcM () --- Ensures that the argument kind is a liftedTypeKind or unliftedTypeKind --- If it's a kind variable, make it (Type bx), for a fresh boxity variable bx - -unifyTypeKind ty@(TyVarTy tyvar) - = getTcTyVar tyvar `thenM` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyTypeKind ty' - Nothing -> newOpenTypeKind `thenM` \ kind -> - putTcTyVar tyvar kind `thenM_` - returnM () - -unifyTypeKind ty - | isTypeKind ty = returnM () - | otherwise -- Failure - = zonkTcType ty `thenM` \ ty1 -> - failWithTc (ptext SLIT("Type expected but") <+> quotes (ppr ty1) <+> ptext SLIT("found")) +unifyKinds _ _ = panic "unifyKinds: length mis-match" + +---------------- +uKVar :: Bool -> KindVar -> TcKind -> TcM () +uKVar swapped kv1 k2 + = do { mb_k1 <- readKindVar kv1 + ; case mb_k1 of + Nothing -> uUnboundKVar swapped kv1 k2 + Just k1 | swapped -> unifyKind k2 k1 + | otherwise -> unifyKind k1 k2 } + +---------------- +uUnboundKVar :: Bool -> KindVar -> TcKind -> TcM () +uUnboundKVar swapped kv1 k2@(KindVar kv2) + | kv1 == kv2 = returnM () + | otherwise -- Distinct kind variables + = do { mb_k2 <- readKindVar kv2 + ; case mb_k2 of + Just k2 -> uUnboundKVar swapped kv1 k2 + Nothing -> writeKindVar kv1 k2 } + +uUnboundKVar swapped kv1 non_var_k2 + = do { k2' <- zonkTcKind non_var_k2 + ; kindOccurCheck kv1 k2' + ; k2'' <- kindSimpleKind swapped k2' + -- KindVars must be bound only to simple kinds + -- Polarities: (kindSimpleKind True ?) succeeds + -- returning *, corresponding to unifying + -- expected: ? + -- actual: kind-ver + ; writeKindVar kv1 k2'' } + +---------------- +kindOccurCheck kv1 k2 -- k2 is zonked + = checkTc (not_in k2) (kindOccurCheckErr kv1 k2) + where + not_in (KindVar kv2) = kv1 /= kv2 + not_in (FunKind a2 r2) = not_in a2 && not_in r2 + not_in other = True + +kindSimpleKind :: Bool -> Kind -> TcM SimpleKind +-- (kindSimpleKind True k) returns a simple kind sk such that sk <: k +-- If the flag is False, it requires k <: sk +-- E.g. kindSimpleKind False ?? = * +-- What about (kv -> *) :=: ?? -> * +kindSimpleKind orig_swapped orig_kind + = go orig_swapped orig_kind + where + go sw (FunKind k1 k2) = do { k1' <- go (not sw) k1 + ; k2' <- go sw k2 + ; return (FunKind k1' k2') } + go True OpenTypeKind = return liftedTypeKind + go True ArgTypeKind = return liftedTypeKind + go sw LiftedTypeKind = return liftedTypeKind + go sw k@(KindVar _) = return k -- KindVars are always simple + go swapped kind = failWithTc (ptext SLIT("Unexpected kind unification failure:") + <+> ppr orig_swapped <+> ppr orig_kind) + -- I think this can't actually happen + +-- T v = MkT v v must be a type +-- T v w = MkT (v -> w) v must not be an umboxed tuple + +---------------- +kindOccurCheckErr tyvar ty + = hang (ptext SLIT("Occurs check: cannot construct the infinite kind:")) + 2 (sep [ppr tyvar, char '=', ppr ty]) + +unifyKindMisMatch ty1 ty2 + = zonkTcKind ty1 `thenM` \ ty1' -> + zonkTcKind ty2 `thenM` \ ty2' -> + let + msg = hang (ptext SLIT("Couldn't match kind")) + 2 (sep [quotes (ppr ty1'), + ptext SLIT("against"), + quotes (ppr ty2')]) + in + failWithTc msg \end{code} \begin{code} unifyFunKind :: TcKind -> TcM (Maybe (TcKind, TcKind)) -- Like unifyFunTy, but does not fail; instead just returns Nothing -unifyFunKind (TyVarTy tyvar) - = getTcTyVar tyvar `thenM` \ maybe_ty -> - case maybe_ty of +unifyFunKind (KindVar kvar) + = readKindVar kvar `thenM` \ maybe_kind -> + case maybe_kind of Just fun_kind -> unifyFunKind fun_kind - Nothing -> newKindVar `thenM` \ arg_kind -> - newKindVar `thenM` \ res_kind -> - putTcTyVar tyvar (mkArrowKind arg_kind res_kind) `thenM_` - returnM (Just (arg_kind,res_kind)) + Nothing -> do { arg_kind <- newKindVar + ; res_kind <- newKindVar + ; writeKindVar kvar (mkArrowKind arg_kind res_kind) + ; returnM (Just (arg_kind,res_kind)) } -unifyFunKind (FunTy arg_kind res_kind) = returnM (Just (arg_kind,res_kind)) -unifyFunKind (NoteTy _ ty) = unifyFunKind ty -unifyFunKind other = returnM Nothing +unifyFunKind (FunKind arg_kind res_kind) = returnM (Just (arg_kind,res_kind)) +unifyFunKind other = returnM Nothing \end{code} %************************************************************************ @@ -964,7 +1049,7 @@ unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred returnM (err ty1' ty2') where err ty1 ty2 = (env1, - nest 4 + nest 2 (vcat [ text "Expected" <+> text s <> colon <+> ppr tidy_ty1, text "Inferred" <+> text s <> colon <+> ppr tidy_ty2 @@ -973,44 +1058,42 @@ unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred (env1, [tidy_ty1,tidy_ty2]) = tidyOpenTypes tidy_env [ty1,ty2] unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 inferred - -- tv1 is zonked already - = zonkTcType ty2 `thenM` \ ty2' -> - returnM (err ty2') + -- tv1 and ty2 are zonked already + = returnM msg where - err ty2 = (env2, ptext SLIT("When matching types") <+> - sep [quotes pp_expected, ptext SLIT("and"), quotes pp_actual]) - where - (pp_expected, pp_actual) | swapped = (pp2, pp1) - | otherwise = (pp1, pp2) - (env1, tv1') = tidyOpenTyVar tidy_env tv1 - (env2, ty2') = tidyOpenType env1 ty2 - pp1 = ppr tv1' - pp2 = ppr ty2' + msg = (env2, ptext SLIT("When matching types") <+> + sep [quotes pp_expected <+> ptext SLIT("and"), quotes pp_actual]) + + (pp_expected, pp_actual) | swapped = (pp2, pp1) + | otherwise = (pp1, pp2) + (env1, tv1') = tidyOpenTyVar tidy_env tv1 + (env2, ty2') = tidyOpenType env1 ty2 + pp1 = ppr tv1' <+> dcolon <+> ppr (tyVarKind tv1) + pp2 = ppr ty2' <+> dcolon <+> ppr (typeKind ty2) unifyMisMatch ty1 ty2 = zonkTcType ty1 `thenM` \ ty1' -> zonkTcType ty2 `thenM` \ ty2' -> let (env, [tidy_ty1, tidy_ty2]) = tidyOpenTypes emptyTidyEnv [ty1',ty2'] - ppr | isSuperKind (typeKind ty1) = pprKind - | otherwise = pprType msg = hang (ptext SLIT("Couldn't match")) - 4 (sep [quotes (ppr tidy_ty1), + 2 (sep [quotes (ppr tidy_ty1), ptext SLIT("against"), quotes (ppr tidy_ty2)]) in failWithTcM (env, msg) + unifyWithSigErr tyvar ty = (env2, hang (ptext SLIT("Cannot unify the type-signature variable") <+> quotes (ppr tidy_tyvar)) - 4 (ptext SLIT("with the type") <+> quotes (ppr tidy_ty))) + 2 (ptext SLIT("with the type") <+> quotes (ppr tidy_ty))) where (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar (env2, tidy_ty) = tidyOpenType env1 ty unifyCheck problem tyvar ty = (env2, hang msg - 4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty])) + 2 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty])) where (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar (env2, tidy_ty) = tidyOpenType env1 ty @@ -1021,6 +1104,64 @@ unifyCheck problem tyvar ty \end{code} +%************************************************************************ +%* * + Checking kinds +%* * +%************************************************************************ + +--------------------------- +-- We would like to get a decent error message from +-- (a) Under-applied type constructors +-- f :: (Maybe, Maybe) +-- (b) Over-applied type constructors +-- f :: Int x -> Int x +-- + +\begin{code} +checkExpectedKind :: Outputable a => a -> TcKind -> TcKind -> TcM () +-- A fancy wrapper for 'unifyKind', which tries +-- to give decent error messages. +checkExpectedKind ty act_kind exp_kind + | act_kind `isSubKind` exp_kind -- Short cut for a very common case + = returnM () + | otherwise + = tryTc (unifyKind exp_kind act_kind) `thenM` \ (errs, mb_r) -> + case mb_r of { + Just _ -> returnM () ; -- Unification succeeded + Nothing -> + + -- So there's definitely an error + -- Now to find out what sort + zonkTcKind exp_kind `thenM` \ exp_kind -> + zonkTcKind act_kind `thenM` \ act_kind -> + + let (exp_as, _) = splitKindFunTys exp_kind + (act_as, _) = splitKindFunTys act_kind + n_exp_as = length exp_as + n_act_as = length act_as + + err | n_exp_as < n_act_as -- E.g. [Maybe] + = quotes (ppr ty) <+> ptext SLIT("is not applied to enough type arguments") + + -- Now n_exp_as >= n_act_as. In the next two cases, + -- n_exp_as == 0, and hence so is n_act_as + | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind + = ptext SLIT("Expecting a lifted type, but") <+> quotes (ppr ty) + <+> ptext SLIT("is unlifted") + + | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind + = ptext SLIT("Expecting an unlifted type, but") <+> quotes (ppr ty) + <+> ptext SLIT("is lifted") + + | otherwise -- E.g. Monad [Int] + = sep [ ptext SLIT("Expecting kind") <+> quotes (pprKind exp_kind) <> comma, + ptext SLIT("but") <+> quotes (ppr ty) <+> + ptext SLIT("has kind") <+> quotes (pprKind act_kind)] + in + failWithTc (ptext SLIT("Kind error:") <+> err) + } +\end{code} %************************************************************************ %* * @@ -1125,7 +1266,7 @@ check_sig_tyvars extra_tvs sig_tvs (env2, emptyVarEnv, []) (tidy_tvs `zip` tidy_tys) `thenM` \ (env3, _, msgs) -> - failWithTcM (env3, main_msg $$ nest 4 (vcat msgs)) + failWithTcM (env3, main_msg $$ nest 2 (vcat msgs)) where (env1, tidy_tvs) = tidyOpenTyVars emptyTidyEnv sig_tvs (env2, tidy_tys) = tidyOpenTypes env1 sig_tys @@ -1200,7 +1341,7 @@ sigCtxt id sig_tvs sig_theta sig_tau tidy_env ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau ] msg = vcat [ptext SLIT("When trying to generalise the type inferred for") <+> quotes (ppr id), - nest 4 sub_msg] + nest 2 sub_msg] in returnM (env3, msg) \end{code}