X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcUnify.lhs;h=395df1e7a43cab6a923638911d345b3c7dbf975e;hb=8e67f5502e2e316245806ee3735a2f41a844b611;hp=a026827894d5a84411f5635ca0f020282e357161;hpb=1c3601593186639f1086bc402582ff56fd3fe9f8;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcUnify.lhs b/ghc/compiler/typecheck/TcUnify.lhs index a026827..395df1e 100644 --- a/ghc/compiler/typecheck/TcUnify.lhs +++ b/ghc/compiler/typecheck/TcUnify.lhs @@ -1,89 +1,613 @@ % % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % -\section[Unify]{Unifier} - -The unifier is now squarely in the typechecker monad (because of the -updatable substitution). +\section{Type subsumption and unification} \begin{code} -module TcUnify ( unifyTauTy, unifyTauTyList, unifyTauTyLists, - unifyFunTy, unifyListTy, unifyTupleTy, - unifyKind, unifyKinds, unifyOpenTypeKind - ) where +module TcUnify ( + -- Full-blown subsumption + tcSubPat, tcSubExp, tcGen, + checkSigTyVars, checkSigTyVarsWrt, bleatEscapedTvs, sigCtxt, + + -- Various unifications + unifyTauTy, unifyTauTyList, unifyTheta, + unifyKind, unifyKinds, unifyFunKind, + checkExpectedKind, + + -------------------------------- + -- Holes + Expected(..), tcInfer, readExpectedType, + zapExpectedType, zapExpectedTo, zapExpectedBranches, + subFunTys, unifyFunTys, + zapToListTy, unifyListTy, + zapToTyConApp, unifyTyConApp, + unifyAppTy + ) where #include "HsVersions.h" --- friends: -import TcMonad -import TypeRep ( Type(..), PredType(..) ) -- friend -import Type ( funTyCon, Kind, unboxedTypeKind, boxedTypeKind, openTypeKind, - superBoxity, typeCon, openKindCon, hasMoreBoxityInfo, - tyVarsOfType, typeKind, - mkTyVarTy, mkFunTy, splitFunTy_maybe, splitTyConApp_maybe, - isNotUsgTy, splitAppTy_maybe, mkTyConApp, - tidyOpenType, tidyOpenTypes, tidyTyVar - ) -import TyCon ( TyCon, isTupleTyCon, tupleTyConBoxity, tyConArity ) -import Name ( hasBetterProv ) -import Var ( TyVar, tyVarKind, varName, isSigTyVar ) -import VarSet ( varSetElems ) -import TcType ( TcType, TcTauType, TcTyVar, TcKind, newBoxityVar, - newTyVarTy, newTyVarTys, tcGetTyVar, tcPutTyVar, zonkTcType - ) - --- others: -import BasicTypes ( Arity, Boxity, isBoxed ) -import TysWiredIn ( listTyCon, mkListTy, mkTupleTy ) +-- gaw 2004 +import HsSyn ( HsExpr(..) , MatchGroup(..), hsLMatchPats ) +import TcHsSyn ( mkHsLet, mkHsDictLam, + ExprCoFn, idCoercion, isIdCoercion, mkCoercion, (<.>), (<$>) ) +import TypeRep ( Type(..), PredType(..), TyNote(..) ) + +import TcRnMonad -- TcType, amongst others +import TcType ( TcKind, TcType, TcSigmaType, TcRhoType, TcTyVar, TcTauType, + TcTyVarSet, TcThetaType, Expected(..), + SkolemInfo( GenSkol ), MetaDetails(..), + pprSkolemTyVar, isTauTy, isSigmaTy, mkFunTys, mkTyConApp, + tcSplitAppTy_maybe, tcSplitTyConApp_maybe, + tyVarsOfType, mkPhiTy, mkTyVarTy, mkPredTy, + typeKind, tcSplitFunTy_maybe, mkForAllTys, mkAppTy, + tidyOpenType, tidyOpenTypes, tidyOpenTyVar, tidyOpenTyVars, + pprType, tidySkolemTyVar, isSkolemTyVar ) +import Kind ( Kind(..), SimpleKind, KindVar, isArgTypeKind, + openTypeKind, liftedTypeKind, mkArrowKind, kindFunResult, + isOpenTypeKind, argTypeKind, isLiftedTypeKind, isUnliftedTypeKind, + isSubKind, pprKind, splitKindFunTys ) +import Inst ( newDicts, instToId, tcInstCall ) +import TcMType ( condLookupTcTyVar, LookupTyVarResult(..), + putMetaTyVar, tcSkolType, newKindVar, tcInstTyVars, newMetaTyVar, + newTyFlexiVarTy, zonkTcKind, zonkType, zonkTcType, zonkTcTyVarsAndFV, + readKindVar, writeKindVar ) +import TcSimplify ( tcSimplifyCheck ) +import TcEnv ( tcGetGlobalTyVars, findGlobals ) +import TyCon ( TyCon, tyConArity, tyConTyVars ) +import TysWiredIn ( listTyCon ) +import Id ( Id, mkSysLocal ) +import Var ( Var, varName, tyVarKind ) +import VarSet ( emptyVarSet, unitVarSet, unionVarSet, elemVarSet, varSetElems ) +import VarEnv +import Name ( isSystemName, mkSysTvName ) +import ErrUtils ( Message ) +import SrcLoc ( noLoc ) +import BasicTypes ( Arity ) +import Util ( notNull, equalLength ) import Outputable \end{code} +Notes on holes +~~~~~~~~~~~~~~ +* A hole is always filled in with an ordinary type, not another hole. %************************************************************************ %* * -\subsection{The Kind variants} +\subsection{'hole' type variables} %* * %************************************************************************ \begin{code} -unifyKind :: TcKind -- Expected - -> TcKind -- Actual - -> TcM () -unifyKind k1 k2 - = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $ - uTys k1 k1 k2 k2 +newHole = newMutVar (error "Empty hole in typechecker") + +tcInfer :: (Expected ty -> TcM a) -> TcM (a,ty) +tcInfer tc_infer + = do { hole <- newHole + ; res <- tc_infer (Infer hole) + ; res_ty <- readMutVar hole + ; return (res, res_ty) } + +readExpectedType :: Expected ty -> TcM ty +readExpectedType (Infer hole) = readMutVar hole +readExpectedType (Check ty) = returnM ty + +zapExpectedType :: Expected TcType -> Kind -> TcM TcTauType +-- In the inference case, ensure we have a monotype +-- (including an unboxed tuple) +zapExpectedType (Infer hole) kind + = do { ty <- newTyFlexiVarTy kind ; + writeMutVar hole ty ; + return ty } + +zapExpectedType (Check ty) kind + | typeKind ty `isSubKind` kind = return ty + | otherwise = do { ty1 <- newTyFlexiVarTy 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 + +zapExpectedBranches :: MatchGroup id -> Expected TcRhoType -> TcM (Expected TcRhoType) +-- If there is more than one branch in a case expression, +-- and exp_ty is a 'hole', all branches must be types, not type schemes, +-- otherwise the order in which we check them would affect the result. +zapExpectedBranches (MatchGroup [match] _) exp_ty + = return exp_ty -- One branch +zapExpectedBranches matches (Check ty) + = return (Check ty) +zapExpectedBranches matches (Infer hole) + = do { -- Many branches, and inference mode, + -- so switch to checking mode with a monotype + ty <- newTyFlexiVarTy openTypeKind + ; writeMutVar hole ty + ; return (Check ty) } + +zapExpectedTo :: Expected TcType -> TcTauType -> TcM () +zapExpectedTo (Check ty1) ty2 = unifyTauTy ty1 ty2 +zapExpectedTo (Infer hole) ty2 = do { ty2' <- zonkTcType ty2; writeMutVar hole ty2' } + -- See Note [Zonk return type] + +instance Outputable ty => Outputable (Expected ty) where + ppr (Check ty) = ptext SLIT("Expected type") <+> ppr ty + ppr (Infer hole) = ptext SLIT("Inferring type") +\end{code} -unifyKinds :: [TcKind] -> [TcKind] -> TcM () -unifyKinds [] [] = returnTc () -unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_` - unifyKinds ks1 ks2 -unifyKinds _ _ = panic "unifyKinds: length mis-match" + +%************************************************************************ +%* * +\subsection[Unify-fun]{@unifyFunTy@} +%* * +%************************************************************************ + +@subFunTy@ and @unifyFunTy@ is used to avoid the fruitless +creation of type variables. + +* subFunTy is used when we might be faced with a "hole" type variable, + in which case we should create two new holes. + +* unifyFunTy is used when we expect to encounter only "ordinary" + type variables, so we should create new ordinary type variables + +\begin{code} +subFunTys :: MatchGroup name + -> Expected TcRhoType -- Fail if ty isn't a function type + -> ([Expected TcRhoType] -> Expected TcRhoType -> TcM a) + -> TcM a + +subFunTys (MatchGroup (match:null_matches) _) (Infer hole) thing_inside + = -- This is the interesting case + ASSERT( null null_matches ) + do { pat_holes <- mapM (\ _ -> newHole) (hsLMatchPats match) + ; res_hole <- newHole + + -- Do the business + ; res <- thing_inside (map Infer pat_holes) (Infer res_hole) + + -- Extract the answers + ; arg_tys <- mapM readMutVar pat_holes + ; res_ty <- readMutVar res_hole + + -- Write the answer into the incoming hole + ; writeMutVar hole (mkFunTys arg_tys res_ty) + + -- And return the answer + ; return res } + +subFunTys (MatchGroup (match:matches) _) (Check ty) thing_inside + = ASSERT( all ((== length (hsLMatchPats match)) . length . hsLMatchPats) matches ) + -- Assertion just checks that all the matches have the same number of pats + do { (pat_tys, res_ty) <- unifyFunTys (length (hsLMatchPats match)) ty + ; thing_inside (map Check pat_tys) (Check res_ty) } + +unifyFunTys :: Arity -> TcRhoType -> TcM ([TcSigmaType], TcRhoType) +-- Fail if ty isn't a function type, otherwise return arg and result types +-- The result types are guaranteed wobbly if the argument is wobbly +-- +-- Does not allocate unnecessary meta variables: if the input already is +-- a function, we just take it apart. Not only is this efficient, it's important +-- for (a) higher rank: the argument might be of form +-- (forall a. ty) -> other +-- If allocated (fresh-meta-var1 -> fresh-meta-var2) and unified, we'd +-- blow up with the meta var meets the forall +-- +-- (b) GADTs: if the argument is not wobbly we do not want the result to be + +unifyFunTys arity ty = unify_fun_ty True arity ty + +unify_fun_ty use_refinement arity ty + | arity == 0 + = do { res_ty <- wobblify use_refinement ty + ; return ([], ty) } + +unify_fun_ty use_refinement arity (NoteTy _ ty) + = unify_fun_ty use_refinement arity ty + +unify_fun_ty use_refinement arity ty@(TyVarTy tv) + = do { details <- condLookupTcTyVar use_refinement tv + ; case details of + IndirectTv use' ty' -> unify_fun_ty use' arity ty' + other -> unify_fun_help arity ty + } + +unify_fun_ty use_refinement arity ty + = case tcSplitFunTy_maybe ty of + Just (arg,res) -> do { arg' <- wobblify use_refinement arg + ; (args', res') <- unify_fun_ty use_refinement (arity-1) res + ; return (arg':args', res') } + + Nothing -> unify_fun_help arity ty + -- Usually an error, but ty could be (a Int Bool), which can match + +unify_fun_help :: Arity -> TcRhoType -> TcM ([TcSigmaType], TcRhoType) +unify_fun_help arity ty + = do { args <- mappM newTyFlexiVarTy (replicate arity argTypeKind) + ; res <- newTyFlexiVarTy openTypeKind + ; unifyTauTy ty (mkFunTys args res) + ; return (args, res) } \end{code} \begin{code} -unifyOpenTypeKind :: TcKind -> TcM () --- Ensures that the argument kind is of the form (Type bx) --- for some boxity bx - -unifyOpenTypeKind ty@(TyVarTy tyvar) - = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyOpenTypeKind ty' - other -> unify_open_kind_help ty - -unifyOpenTypeKind ty - = case splitTyConApp_maybe ty of - Just (tycon, [_]) | tycon == typeCon -> returnTc () - other -> unify_open_kind_help ty - -unify_open_kind_help ty -- Revert to ordinary unification - = newBoxityVar `thenNF_Tc` \ boxity -> - unifyKind ty (mkTyConApp typeCon [boxity]) +---------------------- +zapToTyConApp :: TyCon -- T :: k1 -> ... -> kn -> * + -> Expected TcSigmaType -- Expected type (T a b c) + -> TcM [TcType] -- Element types, a b c + -- Insists that the Expected type is not a forall-type + +zapToTyConApp tc (Check ty) + = unifyTyConApp tc ty -- NB: fails for a forall-type +zapToTyConApp tc (Infer hole) + = do { (tc_app, elt_tys) <- newTyConApp tc + ; writeMutVar hole tc_app + ; return elt_tys } + +zapToListTy :: Expected TcType -> TcM TcType -- Special case for lists +zapToListTy exp_ty = do { [elt_ty] <- zapToTyConApp listTyCon exp_ty + ; return elt_ty } + +---------------------- +unifyTyConApp :: TyCon -> TcType -> TcM [TcType] +unifyTyConApp tc ty = unify_tc_app True tc ty + -- Add a boolean flag to remember whether to use + -- the type refinement or not + +unifyListTy :: TcType -> TcM TcType -- Special case for lists +unifyListTy exp_ty = do { [elt_ty] <- unifyTyConApp listTyCon exp_ty + ; return elt_ty } + +---------- +unify_tc_app use_refinement tc (NoteTy _ ty) + = unify_tc_app use_refinement tc ty + +unify_tc_app use_refinement tc ty@(TyVarTy tyvar) + = do { details <- condLookupTcTyVar use_refinement tyvar + ; case details of + IndirectTv use' ty' -> unify_tc_app use' tc ty' + other -> unify_tc_app_help tc ty + } + +unify_tc_app use_refinement tc ty + | Just (tycon, arg_tys) <- tcSplitTyConApp_maybe ty, + tycon == tc + = ASSERT( tyConArity tycon == length arg_tys ) -- ty::* + mapM (wobblify use_refinement) arg_tys + +unify_tc_app use_refinement tc ty = unify_tc_app_help tc ty + +---------- +unify_tc_app_help tc ty -- Revert to ordinary unification + = do { (tc_app, arg_tys) <- newTyConApp tc + ; if not (isTauTy ty) then -- Can happen if we call zapToTyConApp tc (forall a. ty) + unifyMisMatch ty tc_app + else do + { unifyTauTy ty tc_app + ; returnM arg_tys } } + + +---------------------- +unifyAppTy :: TcType -- Expected type function: m + -> TcType -- Type to split: m a + -> TcM TcType -- Type arg: a +unifyAppTy tc ty = unify_app_ty True tc ty + +unify_app_ty use tc (NoteTy _ ty) = unify_app_ty use tc ty + +unify_app_ty use tc ty@(TyVarTy tyvar) + = do { details <- condLookupTcTyVar use tyvar + ; case details of + IndirectTv use' ty' -> unify_app_ty use' tc ty' + other -> unify_app_ty_help tc ty + } + +unify_app_ty use tc ty + | Just (fun_ty, arg_ty) <- tcSplitAppTy_maybe ty + = do { unifyTauTy tc fun_ty + ; wobblify use arg_ty } + + | otherwise = unify_app_ty_help tc ty + +unify_app_ty_help tc ty -- Revert to ordinary unification + = do { arg_ty <- newTyFlexiVarTy (kindFunResult (typeKind tc)) + ; unifyTauTy (mkAppTy tc arg_ty) ty + ; return arg_ty } + + +---------------------- +wobblify :: Bool -- True <=> don't wobblify + -> TcTauType + -> TcM TcTauType +-- Return a wobbly type. At the moment we do that by +-- allocating a fresh meta type variable. +wobblify True ty = return ty +wobblify False ty = do { uniq <- newUnique + ; tv <- newMetaTyVar (mkSysTvName uniq FSLIT("w")) + (typeKind ty) + (Indirect ty) + ; return (mkTyVarTy tv) } + +---------------------- +newTyConApp :: TyCon -> TcM (TcTauType, [TcTauType]) +newTyConApp tc = do { (tvs, args, _) <- tcInstTyVars (tyConTyVars tc) + ; return (mkTyConApp tc args, args) } +\end{code} + + +%************************************************************************ +%* * +\subsection{Subsumption} +%* * +%************************************************************************ + +All the tcSub calls have the form + + tcSub expected_ty offered_ty +which checks + offered_ty <= expected_ty + +That is, that a value of type offered_ty is acceptable in +a place expecting a value of type expected_ty. + +It returns a coercion function + co_fn :: offered_ty -> expected_ty +which takes an HsExpr of type offered_ty into one of type +expected_ty. + +\begin{code} +----------------------- +-- tcSubExp is used for expressions +tcSubExp :: Expected TcRhoType -> TcRhoType -> TcM ExprCoFn + +tcSubExp (Infer hole) offered_ty + = do { offered' <- zonkTcType offered_ty + -- Note [Zonk return type] + -- zonk to take advantage of the current GADT type refinement. + -- If we don't we get spurious "existential type variable escapes": + -- case (x::Maybe a) of + -- Just b (y::b) -> y + -- We need the refinement [b->a] to be applied to the result type + ; writeMutVar hole offered' + ; return idCoercion } + +tcSubExp (Check expected_ty) offered_ty + = tcSub expected_ty offered_ty + +----------------------- +-- tcSubPat is used for patterns +tcSubPat :: TcSigmaType -- Pattern type signature + -> Expected TcSigmaType -- Type from context + -> TcM () +-- In patterns we insist on an exact match; hence no CoFn returned +-- See Note [Pattern coercions] in TcPat +-- However, we can't call unify directly, because both types might be +-- polymorphic; hence the call to tcSub, followed by a check for +-- the identity coercion + +tcSubPat sig_ty (Infer hole) + = do { sig_ty' <- zonkTcType sig_ty + ; writeMutVar hole sig_ty' -- See notes with tcSubExp above + ; return () } + +tcSubPat sig_ty (Check exp_ty) + = do { co_fn <- tcSub sig_ty exp_ty + + ; if isIdCoercion co_fn then + return () + else + unifyMisMatch sig_ty exp_ty } +\end{code} + + + +%************************************************************************ +%* * + tcSub: main subsumption-check code +%* * +%************************************************************************ + +No holes expected now. Add some error-check context info. + +\begin{code} +----------------- +tcSub :: TcSigmaType -> TcSigmaType -> TcM ExprCoFn -- Locally used only + -- tcSub exp act checks that + -- act <= exp +tcSub expected_ty actual_ty + = traceTc (text "tcSub" <+> details) `thenM_` + addErrCtxtM (unifyCtxt "type" expected_ty actual_ty) + (tc_sub expected_ty expected_ty actual_ty actual_ty) + where + details = vcat [text "Expected:" <+> ppr expected_ty, + text "Actual: " <+> ppr actual_ty] + +----------------- +tc_sub :: TcSigmaType -- expected_ty, before expanding synonyms + -> TcSigmaType -- ..and after + -> TcSigmaType -- actual_ty, before + -> TcSigmaType -- ..and after + -> TcM ExprCoFn + +----------------------------------- +-- Expand synonyms +tc_sub exp_sty (NoteTy _ exp_ty) act_sty act_ty = tc_sub exp_sty exp_ty act_sty act_ty +tc_sub exp_sty exp_ty act_sty (NoteTy _ act_ty) = tc_sub exp_sty exp_ty act_sty act_ty + +----------------------------------- +-- Generalisation case +-- actual_ty: d:Eq b => b->b +-- expected_ty: forall a. Ord a => a->a +-- co_fn e /\a. \d2:Ord a. let d = eqFromOrd d2 in e + +-- It is essential to do this *before* the specialisation case +-- Example: f :: (Eq a => a->a) -> ... +-- g :: Ord b => b->b +-- Consider f g ! + +tc_sub exp_sty expected_ty act_sty actual_ty + | isSigmaTy expected_ty + = tcGen expected_ty (tyVarsOfType actual_ty) ( + -- It's really important to check for escape wrt the free vars of + -- both expected_ty *and* actual_ty + \ body_exp_ty -> tc_sub body_exp_ty body_exp_ty act_sty actual_ty + ) `thenM` \ (gen_fn, co_fn) -> + returnM (gen_fn <.> co_fn) + +----------------------------------- +-- Specialisation case: +-- actual_ty: forall a. Ord a => a->a +-- expected_ty: Int -> Int +-- co_fn e = e Int dOrdInt + +tc_sub exp_sty expected_ty act_sty actual_ty + | isSigmaTy actual_ty + = tcInstCall InstSigOrigin actual_ty `thenM` \ (inst_fn, _, body_ty) -> + tc_sub exp_sty expected_ty body_ty body_ty `thenM` \ co_fn -> + returnM (co_fn <.> inst_fn) + +----------------------------------- +-- Function case + +tc_sub _ (FunTy exp_arg exp_res) _ (FunTy act_arg act_res) + = tcSub_fun exp_arg exp_res act_arg act_res + +----------------------------------- +-- Type variable meets function: imitate +-- +-- NB 1: we can't just unify the type variable with the type +-- because the type might not be a tau-type, and we aren't +-- allowed to instantiate an ordinary type variable with +-- a sigma-type +-- +-- NB 2: can we short-cut to an error case? +-- when the arg/res is not a tau-type? +-- NO! e.g. f :: ((forall a. a->a) -> Int) -> Int +-- then x = (f,f) +-- is perfectly fine, because we can instantiate f's type to a monotype +-- +-- However, we get can get jolly unhelpful error messages. +-- e.g. foo = id runST +-- +-- Inferred type is less polymorphic than expected +-- Quantified type variable `s' escapes +-- Expected type: ST s a -> t +-- Inferred type: (forall s1. ST s1 a) -> a +-- In the first argument of `id', namely `runST' +-- In a right-hand side of function `foo': id runST +-- +-- I'm not quite sure what to do about this! + +tc_sub exp_sty exp_ty@(FunTy exp_arg exp_res) _ act_ty + = do { ([act_arg], act_res) <- unifyFunTys 1 act_ty + ; tcSub_fun exp_arg exp_res act_arg act_res } + +tc_sub _ exp_ty act_sty act_ty@(FunTy act_arg act_res) + = do { ([exp_arg], exp_res) <- unifyFunTys 1 exp_ty + ; tcSub_fun exp_arg exp_res act_arg act_res } + +----------------------------------- +-- Unification case +-- If none of the above match, we revert to the plain unifier +tc_sub exp_sty expected_ty act_sty actual_ty + = uTys True exp_sty expected_ty True act_sty actual_ty `thenM_` + returnM idCoercion +\end{code} + +\begin{code} +tcSub_fun exp_arg exp_res act_arg act_res + = tc_sub act_arg act_arg exp_arg exp_arg `thenM` \ co_fn_arg -> + tc_sub exp_res exp_res act_res act_res `thenM` \ co_fn_res -> + newUnique `thenM` \ uniq -> + let + -- co_fn_arg :: HsExpr exp_arg -> HsExpr act_arg + -- co_fn_res :: HsExpr act_res -> HsExpr exp_res + -- co_fn :: HsExpr (act_arg -> act_res) -> HsExpr (exp_arg -> exp_res) + arg_id = mkSysLocal FSLIT("sub") uniq exp_arg + coercion | isIdCoercion co_fn_arg, + isIdCoercion co_fn_res = idCoercion + | otherwise = mkCoercion co_fn + + co_fn e = DictLam [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 + -- HsApp e $it :: HsExpr act_res + -- co_fn_res $it :: HsExpr exp_res + in + returnM coercion \end{code} %************************************************************************ %* * +\subsection{Generalisation} +%* * +%************************************************************************ + +\begin{code} +tcGen :: TcSigmaType -- expected_ty + -> TcTyVarSet -- Extra tyvars that the universally + -- quantified tyvars of expected_ty + -- must not be unified + -> (TcRhoType -> TcM result) -- spec_ty + -> TcM (ExprCoFn, result) + -- The expression has type: spec_ty -> expected_ty + +tcGen expected_ty extra_tvs thing_inside -- We expect expected_ty to be a forall-type + -- If not, the call is a no-op + = do { -- We want the GenSkol info in the skolemised type variables to + -- mention the *instantiated* tyvar names, so that we get a + -- good error message "Rigid variable 'a' is bound by (forall a. a->a)" + -- Hence the tiresome but innocuous fixM + ((forall_tvs, theta, rho_ty), skol_info) <- fixM (\ ~(_, skol_info) -> + do { (forall_tvs, theta, rho_ty) <- tcSkolType skol_info expected_ty + ; span <- getSrcSpanM + ; let skol_info = GenSkol forall_tvs (mkPhiTy theta rho_ty) span + ; return ((forall_tvs, theta, rho_ty), skol_info) }) + +#ifdef DEBUG + ; traceTc (text "tcGen" <+> vcat [text "extra_tvs" <+> ppr extra_tvs, + text "expected_ty" <+> ppr expected_ty, + text "inst ty" <+> ppr forall_tvs <+> ppr theta <+> ppr rho_ty, + text "free_tvs" <+> ppr free_tvs, + text "forall_tvs" <+> ppr forall_tvs]) +#endif + + -- Type-check the arg and unify with poly type + ; (result, lie) <- getLIE (thing_inside rho_ty) + + -- Check that the "forall_tvs" havn't been constrained + -- The interesting bit here is that we must include the free variables + -- of the expected_ty. Here's an example: + -- runST (newVar True) + -- Here, if we don't make a check, we'll get a type (ST s (MutVar s Bool)) + -- for (newVar True), with s fresh. Then we unify with the runST's arg type + -- forall s'. ST s' a. That unifies s' with s, and a with MutVar s Bool. + -- So now s' isn't unconstrained because it's linked to a. + -- Conclusion: include the free vars of the expected_ty in the + -- list of "free vars" for the signature check. + + ; dicts <- newDicts (SigOrigin skol_info) theta + ; inst_binds <- tcSimplifyCheck sig_msg forall_tvs dicts lie + + ; checkSigTyVarsWrt free_tvs forall_tvs + ; traceTc (text "tcGen:done") + + ; let + -- This HsLet binds any Insts which came out of the simplification. + -- 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 forall_tvs (mkHsDictLam dict_ids (mkHsLet inst_binds (noLoc e))) + ; returnM (mkCoercion co_fn, result) } + where + free_tvs = tyVarsOfType expected_ty `unionVarSet` extra_tvs + sig_msg = ptext SLIT("expected type of an expression") +\end{code} + + + +%************************************************************************ +%* * \subsection[Unify-exported]{Exported unification functions} %* * %************************************************************************ @@ -96,8 +620,18 @@ Unify two @TauType@s. Dead straightforward. \begin{code} unifyTauTy :: TcTauType -> TcTauType -> TcM () unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred - = tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $ - uTys ty1 ty1 ty2 ty2 + = -- The unifier should only ever see tau-types + -- (no quantification whatsoever) + ASSERT2( isTauTy ty1, ppr ty1 ) + ASSERT2( isTauTy ty2, ppr ty2 ) + addErrCtxtM (unifyCtxt "type" ty1 ty2) $ + uTys True ty1 ty1 True ty2 ty2 + +unifyTheta :: TcThetaType -> TcThetaType -> TcM () +unifyTheta theta1 theta2 + = do { checkTc (equalLength theta1 theta2) + (ptext SLIT("Contexts differ in length")) + ; unifyTauTyLists True (map mkPredTy theta1) True (map mkPredTy theta2) } \end{code} @unifyTauTyList@ unifies corresponding elements of two lists of @@ -106,11 +640,17 @@ of equal length. We charge down the list explicitly so that we can complain if their lengths differ. \begin{code} -unifyTauTyLists :: [TcTauType] -> [TcTauType] -> TcM () -unifyTauTyLists [] [] = returnTc () -unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_` - unifyTauTyLists tys1 tys2 -unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!" +unifyTauTyLists :: Bool -> -- Allow refinements on tys1 + [TcTauType] -> + Bool -> -- Allow refinements on tys2 + [TcTauType] -> TcM () +-- Precondition: lists must be same length +-- Having the caller check gives better error messages +-- Actually the caller neve does need to check; see Note [Tycon app] +unifyTauTyLists r1 [] r2 [] = returnM () +unifyTauTyLists r1 (ty1:tys1) r2 (ty2:tys2) = uTys r1 ty1 ty1 r2 ty2 ty2 `thenM_` + unifyTauTyLists r1 tys1 r2 tys2 +unifyTauTyLists r1 ty1s r2 ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!" \end{code} @unifyTauTyList@ takes a single list of @TauType@s and unifies them @@ -119,9 +659,9 @@ lists, when all the elts should be of the same type. \begin{code} unifyTauTyList :: [TcTauType] -> TcM () -unifyTauTyList [] = returnTc () -unifyTauTyList [ty] = returnTc () -unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenTc_` +unifyTauTyList [] = returnM () +unifyTauTyList [ty] = returnM () +unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenM_` unifyTauTyList tys \end{code} @@ -140,58 +680,54 @@ de-synonym'd version. This way we get better error messages. We call the first one \tr{ps_ty1}, \tr{ps_ty2} for ``possible synomym''. \begin{code} -uTys :: TcTauType -> TcTauType -- Error reporting ty1 and real ty1 +uTys :: Bool -- Allow refinements to ty1 + -> TcTauType -> TcTauType -- Error reporting ty1 and real ty1 -- ty1 is the *expected* type - + -> Bool -- Allow refinements to ty2 -> TcTauType -> TcTauType -- Error reporting ty2 and real ty2 -- ty2 is the *actual* type -> TcM () -- Always expand synonyms (see notes at end) - -- (this also throws away FTVs and usage annots) -uTys ps_ty1 (NoteTy _ ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2 -uTys ps_ty1 ty1 ps_ty2 (NoteTy _ ty2) = uTys ps_ty1 ty1 ps_ty2 ty2 + -- (this also throws away FTVs) +uTys r1 ps_ty1 (NoteTy n1 ty1) r2 ps_ty2 ty2 = uTys r1 ps_ty1 ty1 r2 ps_ty2 ty2 +uTys r1 ps_ty1 ty1 r2 ps_ty2 (NoteTy n2 ty2) = uTys r1 ps_ty1 ty1 r2 ps_ty2 ty2 -- Variables; go for uVar -uTys ps_ty1 (TyVarTy tyvar1) ps_ty2 ty2 = uVar False tyvar1 ps_ty2 ty2 -uTys ps_ty1 ty1 ps_ty2 (TyVarTy tyvar2) = uVar True tyvar2 ps_ty1 ty1 +uTys r1 ps_ty1 (TyVarTy tyvar1) r2 ps_ty2 ty2 = uVar False r1 tyvar1 r2 ps_ty2 ty2 +uTys r1 ps_ty1 ty1 r2 ps_ty2 (TyVarTy tyvar2) = uVar True r2 tyvar2 r1 ps_ty1 ty1 -- "True" means args swapped -- Predicates -uTys _ (PredTy (IParam n1 t1)) _ (PredTy (IParam n2 t2)) - | n1 == n2 = uTys t1 t1 t2 t2 -uTys _ (PredTy (Class c1 tys1)) _ (PredTy (Class c2 tys2)) - | c1 == c2 = unifyTauTyLists tys1 tys2 +uTys r1 _ (PredTy (IParam n1 t1)) r2 _ (PredTy (IParam n2 t2)) + | n1 == n2 = uTys r1 t1 t1 r2 t2 t2 +uTys r1 _ (PredTy (ClassP c1 tys1)) r2 _ (PredTy (ClassP c2 tys2)) + | c1 == c2 = unifyTauTyLists r1 tys1 r2 tys2 + -- Guaranteed equal lengths because the kinds check -- Functions; just check the two parts -uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2) - = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2 +uTys r1 _ (FunTy fun1 arg1) r2 _ (FunTy fun2 arg2) + = uTys r1 fun1 fun1 r2 fun2 fun2 `thenM_` uTys r1 arg1 arg1 r2 arg2 arg2 -- Type constructors must match -uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2) - | con1 == con2 && length tys1 == length 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 - = unifyOpenTypeKind ps_ty2 +uTys r1 ps_ty1 (TyConApp con1 tys1) r2 ps_ty2 (TyConApp con2 tys2) + | con1 == con2 = unifyTauTyLists r1 tys1 r2 tys2 + -- See Note [TyCon app] -- 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, -- so if one type is an App the other one jolly well better be too -uTys ps_ty1 (AppTy s1 t1) ps_ty2 ty2 - = case splitAppTy_maybe ty2 of - Just (s2,t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2 +uTys r1 ps_ty1 (AppTy s1 t1) r2 ps_ty2 ty2 + = case tcSplitAppTy_maybe ty2 of + Just (s2,t2) -> uTys r1 s1 s1 r2 s2 s2 `thenM_` uTys r1 t1 t1 r2 t2 t2 Nothing -> unifyMisMatch ps_ty1 ps_ty2 -- Now the same, but the other way round -- Don't swap the types, because the error messages get worse -uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2) - = case splitAppTy_maybe ty1 of - Just (s1,t1) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2 +uTys r1 ps_ty1 ty1 r2 ps_ty2 (AppTy s2 t2) + = case tcSplitAppTy_maybe ty1 of + Just (s1,t1) -> uTys r1 s1 s1 r2 s2 s2 `thenM_` uTys r1 t1 t1 r2 t2 t2 Nothing -> unifyMisMatch ps_ty1 ps_ty2 -- Not expecting for-alls in unification @@ -199,23 +735,34 @@ uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2) -- than a panic message! -- Anything else fails -uTys ps_ty1 ty1 ps_ty2 ty2 = unifyMisMatch ps_ty1 ps_ty2 +uTys r1 ps_ty1 ty1 r2 ps_ty2 ty2 = unifyMisMatch ps_ty1 ps_ty2 \end{code} +Note [Tycon app] +~~~~~~~~~~~~~~~~ +When we find two TyConApps, the argument lists are guaranteed equal +length. Reason: intially the kinds of the two types to be unified is +the same. The only way it can become not the same is when unifying two +AppTys (f1 a1):=:(f2 a2). In that case there can't be a TyConApp in +the f1,f2 (because it'd absorb the app). If we unify f1:=:f2 first, +which we do, that ensures that f1,f2 have the same kind; and that +means a1,a2 have the same kind. And now the argument repeats. + + Notes on synonyms ~~~~~~~~~~~~~~~~~ If you are tempted to make a short cut on synonyms, as in this pseudocode... \begin{verbatim} -uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2) - = if (con1 == con2) then - -- Good news! Same synonym constructors, so we can shortcut - -- by unifying their arguments and ignoring their expansions. - unifyTauTypeLists args1 args2 - else - -- Never mind. Just expand them and try again - uTys ty1 ty2 +-- NO uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2) +-- NO = if (con1 == con2) then +-- NO -- Good news! Same synonym constructors, so we can shortcut +-- NO -- by unifying their arguments and ignoring their expansions. +-- NO unifyTauTypeLists args1 args2 +-- NO else +-- NO -- Never mind. Just expand them and try again +-- NO uTys ty1 ty2 \end{verbatim} then THINK AGAIN. Here is the whole story, as detected and reported @@ -268,113 +815,111 @@ back into @uTys@ if it turns out that the variable is already bound. \begin{code} uVar :: Bool -- False => tyvar is the "expected" -- True => ty is the "expected" thing + -> Bool -- True, allow refinements to tv1, False don't -> TcTyVar + -> Bool -- Allow refinements to ty2? -> TcTauType -> TcTauType -- printing and real versions -> TcM () -uVar swapped tv1 ps_ty2 ty2 - = tcGetTyVar tv1 `thenNF_Tc` \ maybe_ty1 -> - 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 - - -- Expand synonyms; ignore FTVs; ignore usage annots -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy _ ty2) - = uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2 - - - -- The both-type-variable case -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2) - +uVar swapped r1 tv1 r2 ps_ty2 ty2 + = traceTc (text "uVar" <+> ppr swapped <+> ppr tv1 <+> (ppr ps_ty2 $$ ppr ty2)) `thenM_` + condLookupTcTyVar r1 tv1 `thenM` \ details -> + case details of + IndirectTv r1' ty1 | swapped -> uTys r2 ps_ty2 ty2 r1' ty1 ty1 -- Swap back + | otherwise -> uTys r1' ty1 ty1 r2 ps_ty2 ty2 -- Same order + FlexiTv -> uFlexiVar swapped tv1 r2 ps_ty2 ty2 + RigidTv -> uRigidVar swapped tv1 r2 ps_ty2 ty2 + + -- Expand synonyms; ignore FTVs +uFlexiVar :: Bool -> TcTyVar -> + Bool -> -- Allow refinements to ty2 + TcTauType -> TcTauType -> TcM () +-- Invariant: tv1 is Flexi +uFlexiVar swapped tv1 r2 ps_ty2 (NoteTy n2 ty2) + = uFlexiVar swapped tv1 r2 ps_ty2 ty2 + +uFlexiVar swapped tv1 r2 ps_ty2 ty2@(TyVarTy tv2) -- Same type variable => no-op | tv1 == tv2 - = returnTc () + = returnM () -- Distinct type variables - -- ASSERT maybe_ty1 /= Just | otherwise - = tcGetTyVar tv2 `thenNF_Tc` \ maybe_ty2 -> - case maybe_ty2 of - Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2' - - Nothing | tv1_dominates_tv2 - - -> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) ) - tcPutTyVar tv2 (TyVarTy tv1) `thenNF_Tc_` - returnTc () - | otherwise - - -> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) ) - (ASSERT( isNotUsgTy ps_ty2 ) - tcPutTyVar tv1 ps_ty2 `thenNF_Tc_` - returnTc ()) + = condLookupTcTyVar r2 tv2 `thenM` \ details -> + case details of + IndirectTv b ty2' -> uFlexiVar swapped tv1 b ty2' ty2' + FlexiTv | update_tv2 -> putMetaTyVar tv2 (TyVarTy tv1) + | otherwise -> updateFlexi swapped tv1 ty2 + RigidTv -> updateFlexi swapped tv1 ty2 + -- Note that updateFlexi does a sub-kind check + -- We might unify (a b) with (c d) where b::*->* and d::*; this should fail where k1 = tyVarKind tv1 k2 = tyVarKind tv2 - tv1_dominates_tv2 = isSigTyVar tv1 - -- Don't unify a signature type variable if poss - || k2 == openTypeKind - -- Try to get rid of open type variables as soon as poss - || varName tv1 `hasBetterProv` varName tv2 - -- Try to update sys-y type variables in preference to sig-y ones + 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 = isSystemName (varName tv2) + -- Try to update sys-y type variables in preference to sig-y ones + + -- First one is flexi, second one isn't a type variable +uFlexiVar swapped tv1 r2 ps_ty2 non_var_ty2 + = -- Do the occurs check, and check that we are not + -- unifying a type variable with a polytype + -- Returns a zonked type ready for the update + do { ty2 <- checkValue tv1 r2 ps_ty2 non_var_ty2 + ; updateFlexi swapped tv1 ty2 } + +-- Ready to update tv1, which is flexi; occurs check is done +updateFlexi swapped tv1 ty2 + = do { checkKinds swapped tv1 ty2 + ; putMetaTyVar tv1 ty2 } + + +uRigidVar :: Bool -> TcTyVar + -> Bool -> -- Allow refinements to ty2 + TcTauType -> TcTauType -> TcM () +-- Invariant: tv1 is Rigid +uRigidVar swapped tv1 r2 ps_ty2 (NoteTy n2 ty2) + = uRigidVar swapped tv1 r2 ps_ty2 ty2 - -- Second one isn't a type variable -uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2 - = checkKinds swapped tv1 non_var_ty2 `thenTc_` - occur_check non_var_ty2 `thenTc_` - ASSERT( isNotUsgTy ps_ty2 ) - checkTcM (not (isSigTyVar tv1)) - (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenTc_` - - warnTc (not (typeKind non_var_ty2 `hasMoreBoxityInfo` tyVarKind tv1)) - ((ppr tv1 <+> ppr (tyVarKind tv1)) $$ - (ppr non_var_ty2 <+> ppr (typeKind non_var_ty2))) `thenNF_Tc_` - - tcPutTyVar tv1 non_var_ty2 `thenNF_Tc_` - -- This used to say "ps_ty2" instead of "non_var_ty2" - - -- But that led to an infinite loop in the type checker! - -- Consider - -- type A a = () - -- - -- f :: (A a -> a -> ()) -> () - -- f = \ _ -> () - -- - -- x :: () - -- x = f (\ x p -> p x) - -- - -- Here, we try to match "t" with "A t", and succeed - -- because the unifier looks through synonyms. The occurs - -- check doesn't kick in because we are "really" binding "t" to "()", - -- but we *actually* bind "t" to "A t" if we store ps_ty2. - -- That leads the typechecker into an infinite loop later. - - returnTc () - where - occur_check ty = mapTc occur_check_tv (varSetElems (tyVarsOfType ty)) `thenTc_` - returnTc () + -- The both-type-variable case +uRigidVar swapped tv1 r2 ps_ty2 ty2@(TyVarTy tv2) + -- Same type variable => no-op + | tv1 == tv2 + = returnM () - occur_check_tv tv2 - | tv1 == tv2 -- Same tyvar; fail - = zonkTcType ps_ty2 `thenNF_Tc` \ zonked_ty2 -> - failWithTcM (unifyOccurCheck tv1 zonked_ty2) + -- Distinct type variables + | otherwise + = condLookupTcTyVar r2 tv2 `thenM` \ details -> + case details of + IndirectTv b ty2' -> uRigidVar swapped tv1 b ty2' ty2' + FlexiTv -> updateFlexi swapped tv2 (TyVarTy tv1) + RigidTv -> unifyMisMatch (TyVarTy tv1) (TyVarTy tv2) - | otherwise -- A different tyvar - = tcGetTyVar tv2 `thenNF_Tc` \ maybe_ty2 -> - case maybe_ty2 of - Just ty2' -> occur_check ty2' - other -> returnTc () + -- Second one isn't a type variable +uRigidVar swapped tv1 r2 ps_ty2 non_var_ty2 + = unifyMisMatch (TyVarTy tv1) ps_ty2 +\end{code} +\begin{code} checkKinds swapped tv1 ty2 -- We're about to unify a type variable tv1 with a non-tyvar-type ty2. --- We need to check that we don't unify a boxed type variable with an --- unboxed type: e.g. (id 3#) is illegal - | tk1 == boxedTypeKind && tk2 == unboxedTypeKind - = tcAddErrCtxtM (unifyKindCtxt swapped tv1 ty2) $ - unifyMisMatch k1 k2 +-- ty2 has been zonked at this stage, which ensures that +-- its kind has as much boxity information visible as possible. + | tk2 `isSubKind` tk1 = returnM () + | otherwise - = returnTc () + -- Either the kinds aren't compatible + -- (can happen if we unify (a b) with (c d)) + -- or we are unifying a lifted type variable with an + -- unlifted type: e.g. (id 3#) is illegal + = addErrCtxtM (unifyKindCtxt swapped tv1 ty2) $ + unifyKindMisMatch k1 k2 + where (k1,k2) | swapped = (tk2,tk1) | otherwise = (tk1,tk2) @@ -382,84 +927,210 @@ checkKinds swapped tv1 ty2 tk2 = typeKind ty2 \end{code} +\begin{code} +checkValue tv1 r2 ps_ty2 non_var_ty2 +-- Do the occurs check, and check that we are not +-- unifying a type variable with a polytype +-- Return the type to update the type variable with, or fail + +-- Basically we want to update tv1 := ps_ty2 +-- because ps_ty2 has type-synonym info, which improves later error messages +-- +-- But consider +-- type A a = () +-- +-- f :: (A a -> a -> ()) -> () +-- f = \ _ -> () +-- +-- x :: () +-- x = f (\ x p -> p x) +-- +-- In the application (p x), we try to match "t" with "A t". If we go +-- ahead and bind t to A t (= ps_ty2), we'll lead the type checker into +-- an infinite loop later. +-- But we should not reject the program, because A t = (). +-- Rather, we should bind t to () (= non_var_ty2). +-- +-- That's why we have this two-state occurs-check + = zonk_tc_type r2 ps_ty2 `thenM` \ ps_ty2' -> + case okToUnifyWith tv1 ps_ty2' of { + Nothing -> returnM ps_ty2' ; -- Success + other -> + + zonk_tc_type r2 non_var_ty2 `thenM` \ non_var_ty2' -> + case okToUnifyWith tv1 non_var_ty2' of + Nothing -> -- This branch rarely succeeds, except in strange cases + -- like that in the example above + returnM non_var_ty2' + + Just problem -> failWithTcM (unifyCheck problem tv1 ps_ty2') + } + where + zonk_tc_type refine ty + = zonkType (\tv -> return (TyVarTy tv)) refine ty + -- We may already be inside a wobbly type t2, and + -- should take that into account here + +data Problem = OccurCheck | NotMonoType + +okToUnifyWith :: TcTyVar -> TcType -> Maybe Problem +-- (okToUnifyWith tv ty) checks whether it's ok to unify +-- tv :=: ty +-- Nothing => ok +-- Just p => not ok, problem p + +okToUnifyWith tv ty + = ok ty + where + ok (TyVarTy tv') | tv == tv' = Just OccurCheck + | otherwise = Nothing + ok (AppTy t1 t2) = ok t1 `and` ok t2 + ok (FunTy t1 t2) = ok t1 `and` ok t2 + ok (TyConApp _ ts) = oks ts + ok (ForAllTy _ _) = Just NotMonoType + ok (PredTy st) = ok_st st + ok (NoteTy (FTVNote _) t) = ok t + ok (NoteTy (SynNote t1) t2) = ok t1 `and` ok t2 + -- Type variables may be free in t1 but not t2 + -- A forall may be in t2 but not t1 + + oks ts = foldr (and . ok) Nothing ts + + ok_st (ClassP _ ts) = oks ts + ok_st (IParam _ t) = ok t + + Nothing `and` m = m + Just p `and` m = Just p +\end{code} + %************************************************************************ %* * -\subsection[Unify-fun]{@unifyFunTy@} + Kind unification %* * %************************************************************************ -@unifyFunTy@ is used to avoid the fruitless creation of type variables. +Unifying kinds is much, much simpler than unifying types. \begin{code} -unifyFunTy :: TcType -- Fail if ty isn't a function type - -> TcM (TcType, TcType) -- otherwise return arg and result types - -unifyFunTy ty@(TyVarTy tyvar) - = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyFunTy ty' - other -> unify_fun_ty_help ty - -unifyFunTy ty - = case splitFunTy_maybe ty of - Just arg_and_res -> returnTc arg_and_res - Nothing -> unify_fun_ty_help ty - -unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification - = newTyVarTy openTypeKind `thenNF_Tc` \ arg -> - newTyVarTy openTypeKind `thenNF_Tc` \ res -> - unifyTauTy ty (mkFunTy arg res) `thenTc_` - returnTc (arg,res) -\end{code} +unifyKind :: TcKind -- Expected + -> TcKind -- Actual + -> TcM () +unifyKind LiftedTypeKind LiftedTypeKind = returnM () +unifyKind UnliftedTypeKind UnliftedTypeKind = returnM () -\begin{code} -unifyListTy :: TcType -- expected list type - -> TcM TcType -- list element type - -unifyListTy ty@(TyVarTy tyvar) - = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyListTy ty' - other -> unify_list_ty_help ty - -unifyListTy ty - = case splitTyConApp_maybe ty of - Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty - other -> unify_list_ty_help ty - -unify_list_ty_help ty -- Revert to ordinary unification - = newTyVarTy boxedTypeKind `thenNF_Tc` \ elt_ty -> - unifyTauTy ty (mkListTy elt_ty) `thenTc_` - returnTc elt_ty -\end{code} +unifyKind OpenTypeKind k2 | isOpenTypeKind k2 = returnM () +unifyKind ArgTypeKind k2 | isArgTypeKind k2 = returnM () + -- Respect sub-kinding -\begin{code} -unifyTupleTy :: Boxity -> Arity -> TcType -> TcM [TcType] -unifyTupleTy boxity arity ty@(TyVarTy tyvar) - = tcGetTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyTupleTy boxity arity ty' - other -> unify_tuple_ty_help boxity arity ty - -unifyTupleTy boxity arity ty - = case splitTyConApp_maybe ty of - Just (tycon, arg_tys) - | isTupleTyCon tycon - && tyConArity tycon == arity - && tupleTyConBoxity tycon == boxity - -> returnTc arg_tys - other -> unify_tuple_ty_help boxity arity ty - -unify_tuple_ty_help boxity arity ty - = newTyVarTys arity kind `thenNF_Tc` \ arg_tys -> - unifyTauTy ty (mkTupleTy boxity arity arg_tys) `thenTc_` - returnTc arg_tys +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" + +---------------- +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 - kind | isBoxed boxity = boxedTypeKind - | otherwise = openTypeKind + 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 (KindVar kvar) + = readKindVar kvar `thenM` \ maybe_kind -> + case maybe_kind of + Just fun_kind -> unifyFunKind fun_kind + Nothing -> do { arg_kind <- newKindVar + ; res_kind <- newKindVar + ; writeKindVar kvar (mkArrowKind arg_kind res_kind) + ; returnM (Just (arg_kind,res_kind)) } + +unifyFunKind (FunKind arg_kind res_kind) = returnM (Just (arg_kind,res_kind)) +unifyFunKind other = returnM Nothing +\end{code} %************************************************************************ %* * @@ -472,12 +1143,12 @@ Errors \begin{code} unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred - = zonkTcType ty1 `thenNF_Tc` \ ty1' -> - zonkTcType ty2 `thenNF_Tc` \ ty2' -> - returnNF_Tc (err ty1' ty2') + = zonkTcType ty1 `thenM` \ ty1' -> + zonkTcType ty2 `thenM` \ ty2' -> + 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 @@ -486,44 +1157,233 @@ 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 `thenNF_Tc` \ ty2' -> - returnNF_Tc (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') = tidyTyVar tidy_env tv1 - (env2, ty2') = tidyOpenType env1 ty2 - pp1 = ppr tv1' - pp2 = ppr ty2' + msg = (env2, ptext SLIT("When matching the kinds of") <+> + 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 `thenNF_Tc` \ ty1' -> - zonkTcType ty2 `thenNF_Tc` \ ty2' -> - let - (env, [tidy_ty1, tidy_ty2]) = tidyOpenTypes emptyTidyEnv [ty1',ty2'] - msg = hang (ptext SLIT("Couldn't match")) - 4 (sep [quotes (ppr tidy_ty1), - ptext SLIT("against"), - quotes (ppr tidy_ty2)]) + = do { (env1, pp1, extra1) <- ppr_ty emptyTidyEnv ty1 + ; (env2, pp2, extra2) <- ppr_ty env1 ty2 + ; let msg = sep [sep [ptext SLIT("Couldn't match") <+> pp1, nest 7 (ptext SLIT("against") <+> pp2)], + nest 2 extra1, nest 2 extra2] in - failWithTcM (env, msg) + failWithTcM (env2, msg) } + +ppr_ty :: TidyEnv -> TcType -> TcM (TidyEnv, SDoc, SDoc) +ppr_ty env ty + = do { ty' <- zonkTcType ty + ; let (env1,tidy_ty) = tidyOpenType env ty' + simple_result = (env1, quotes (ppr tidy_ty), empty) + ; case tidy_ty of + TyVarTy tv + | isSkolemTyVar tv -> return (env2, pp_rigid tv', + pprSkolemTyVar tv') + | otherwise -> return simple_result + where + (env2, tv') = tidySkolemTyVar env1 tv + other -> return simple_result } + where + pp_rigid tv = ptext SLIT("the rigid variable") <+> quotes (ppr tv) -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))) +unifyCheck problem tyvar ty + = (env2, hang msg + 2 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty])) where - (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar - (env2, tidy_ty) = tidyOpenType env1 ty + (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar + (env2, tidy_ty) = tidyOpenType env1 ty + + msg = case problem of + OccurCheck -> ptext SLIT("Occurs check: cannot construct the infinite type:") + NotMonoType -> ptext SLIT("Cannot unify a type variable with a type scheme:") +\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} + +%************************************************************************ +%* * +\subsection{Checking signature type variables} +%* * +%************************************************************************ + +@checkSigTyVars@ checks that a set of universally quantified type varaibles +are not mentioned in the environment. In particular: + + (a) Not mentioned in the type of a variable in the envt + eg the signature for f in this: + + g x = ... where + f :: a->[a] + f y = [x,y] + + Here, f is forced to be monorphic by the free occurence of x. + + (d) Not (unified with another type variable that is) in scope. + eg f x :: (r->r) = (\y->y) :: forall a. a->r + when checking the expression type signature, we find that + even though there is nothing in scope whose type mentions r, + nevertheless the type signature for the expression isn't right. + + Another example is in a class or instance declaration: + class C a where + op :: forall b. a -> b + op x = x + Here, b gets unified with a -unifyOccurCheck tyvar ty - = (env2, hang (ptext SLIT("Occurs check: cannot construct the infinite type:")) - 4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty])) +Before doing this, the substitution is applied to the signature type variable. + +\begin{code} +checkSigTyVars :: [TcTyVar] -> TcM () +checkSigTyVars sig_tvs = check_sig_tyvars emptyVarSet sig_tvs + +checkSigTyVarsWrt :: TcTyVarSet -> [TcTyVar] -> TcM () +checkSigTyVarsWrt extra_tvs sig_tvs + = zonkTcTyVarsAndFV (varSetElems extra_tvs) `thenM` \ extra_tvs' -> + check_sig_tyvars extra_tvs' sig_tvs + +check_sig_tyvars + :: TcTyVarSet -- Global type variables. The universally quantified + -- tyvars should not mention any of these + -- Guaranteed already zonked. + -> [TcTyVar] -- Universally-quantified type variables in the signature + -- Guaranteed to be skolems + -> TcM () +check_sig_tyvars extra_tvs [] + = returnM () +check_sig_tyvars extra_tvs sig_tvs + = ASSERT( all isSkolemTyVar sig_tvs ) + do { gbl_tvs <- tcGetGlobalTyVars + ; traceTc (text "check_sig_tyvars" <+> (vcat [text "sig_tys" <+> ppr sig_tvs, + text "gbl_tvs" <+> ppr gbl_tvs, + text "extra_tvs" <+> ppr extra_tvs])) + + ; let env_tvs = gbl_tvs `unionVarSet` extra_tvs + ; ifM (any (`elemVarSet` env_tvs) sig_tvs) + (bleatEscapedTvs env_tvs sig_tvs sig_tvs) + } + +bleatEscapedTvs :: TcTyVarSet -- The global tvs + -> [TcTyVar] -- The possibly-escaping type variables + -> [TcTyVar] -- The zonked versions thereof + -> TcM () +-- Complain about escaping type variables +-- We pass a list of type variables, at least one of which +-- escapes. The first list contains the original signature type variable, +-- while the second contains the type variable it is unified to (usually itself) +bleatEscapedTvs globals sig_tvs zonked_tvs + = do { (env3, msgs) <- foldlM check (env2, []) (tidy_tvs `zip` tidy_zonked_tvs) + ; failWithTcM (env3, main_msg $$ nest 2 (vcat msgs)) } + where + (env1, tidy_tvs) = tidyOpenTyVars emptyTidyEnv sig_tvs + (env2, tidy_zonked_tvs) = tidyOpenTyVars env1 zonked_tvs + + main_msg = ptext SLIT("Inferred type is less polymorphic than expected") + + check (tidy_env, msgs) (sig_tv, zonked_tv) + | not (zonked_tv `elemVarSet` globals) = return (tidy_env, msgs) + | otherwise + = do { (tidy_env1, globs) <- findGlobals (unitVarSet zonked_tv) tidy_env + ; returnM (tidy_env1, escape_msg sig_tv zonked_tv globs : msgs) } + +----------------------- +escape_msg sig_tv zonked_tv globs + | notNull globs + = vcat [sep [msg, ptext SLIT("is mentioned in the environment:")], + nest 2 (vcat globs)] + | otherwise + = msg <+> ptext SLIT("escapes") + -- Sigh. It's really hard to give a good error message + -- all the time. One bad case is an existential pattern match. + -- We rely on the "When..." context to help. where - (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar - (env2, tidy_ty) = tidyOpenType env1 ty + msg = ptext SLIT("Quantified type variable") <+> quotes (ppr sig_tv) <+> is_bound_to + is_bound_to + | sig_tv == zonked_tv = empty + | otherwise = ptext SLIT("is unified with") <+> quotes (ppr zonked_tv) <+> ptext SLIT("which") \end{code} +These two context are used with checkSigTyVars + +\begin{code} +sigCtxt :: Id -> [TcTyVar] -> TcThetaType -> TcTauType + -> TidyEnv -> TcM (TidyEnv, Message) +sigCtxt id sig_tvs sig_theta sig_tau tidy_env + = zonkTcType sig_tau `thenM` \ actual_tau -> + let + (env1, tidy_sig_tvs) = tidyOpenTyVars tidy_env sig_tvs + (env2, tidy_sig_rho) = tidyOpenType env1 (mkPhiTy sig_theta sig_tau) + (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau + sub_msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tvs tidy_sig_rho), + 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 2 sub_msg] + in + returnM (env3, msg) +\end{code}