2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section{Monadic type operations}
6 This module contains monadic operations over types that contain mutable type variables
10 TcTyVar, TcKind, TcType, TcTauType, TcThetaType, TcTyVarSet,
12 --------------------------------
13 -- Creating new mutable type variables
14 newTyVar, newHoleTyVarTy,
15 newTyVarTy, -- Kind -> NF_TcM TcType
16 newTyVarTys, -- Int -> Kind -> NF_TcM [TcType]
17 newKindVar, newKindVars, newBoxityVar,
18 putTcTyVar, getTcTyVar,
20 --------------------------------
22 tcInstTyVar, tcInstTyVars,
23 tcInstSigTyVars, tcInstType, tcInstSigType,
26 --------------------------------
27 -- Checking type validity
28 Rank, UserTypeCtxt(..), checkValidType, pprUserTypeCtxt,
29 SourceTyCtxt(..), checkValidTheta,
30 checkValidInstHead, instTypeErr, checkAmbiguity,
32 --------------------------------
34 zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV,
35 zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType,
36 zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv,
40 #include "HsVersions.h"
44 import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation
47 import TcType ( TcType, TcThetaType, TcTauType, TcPredType,
48 TcTyVarSet, TcKind, TcTyVar, TyVarDetails(..),
50 tcSplitRhoTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe,
51 tcSplitTyConApp_maybe, tcSplitForAllTys,
52 tcIsTyVarTy, tcSplitSigmaTy,
53 isUnLiftedType, isIPPred,
55 mkAppTy, mkTyVarTy, mkTyVarTys,
56 tyVarsOfPred, getClassPredTys_maybe,
58 liftedTypeKind, openTypeKind, defaultKind, superKind,
59 superBoxity, liftedBoxity, typeKind,
60 tyVarsOfType, tyVarsOfTypes,
61 eqKind, isTypeKind, isAnyTypeKind,
63 isFFIArgumentTy, isFFIImportResultTy
65 import qualified Type ( splitFunTys )
66 import Subst ( Subst, mkTopTyVarSubst, substTy )
67 import Class ( Class, classArity, className )
68 import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon,
69 tyConArity, tyConName, tyConKind )
70 import PrimRep ( PrimRep(VoidRep) )
71 import Var ( TyVar, tyVarKind, tyVarName, isTyVar, mkTyVar, isMutTyVar )
74 import TcMonad -- TcType, amongst others
75 import TysWiredIn ( voidTy, listTyCon, tupleTyCon )
76 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
77 import ForeignCall ( Safety(..) )
78 import FunDeps ( grow )
79 import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred )
80 import Name ( Name, NamedThing(..), setNameUnique, mkSysLocalName,
81 mkLocalName, mkDerivedTyConOcc
84 import BasicTypes ( Boxity(Boxed) )
85 import CmdLineOpts ( dopt, DynFlag(..) )
86 import Unique ( Uniquable(..) )
87 import SrcLoc ( noSrcLoc )
88 import Util ( nOfThem, isSingleton, equalLength )
89 import ListSetOps ( removeDups )
94 %************************************************************************
96 \subsection{New type variables}
98 %************************************************************************
101 newTyVar :: Kind -> NF_TcM TcTyVar
103 = tcGetUnique `thenNF_Tc` \ uniq ->
104 tcNewMutTyVar (mkSysLocalName uniq FSLIT("t")) kind VanillaTv
106 newTyVarTy :: Kind -> NF_TcM TcType
108 = newTyVar kind `thenNF_Tc` \ tc_tyvar ->
109 returnNF_Tc (TyVarTy tc_tyvar)
111 newHoleTyVarTy :: NF_TcM TcType
112 = tcGetUnique `thenNF_Tc` \ uniq ->
113 tcNewMutTyVar (mkSysLocalName uniq FSLIT("h")) openTypeKind HoleTv `thenNF_Tc` \ tv ->
114 returnNF_Tc (TyVarTy tv)
116 newTyVarTys :: Int -> Kind -> NF_TcM [TcType]
117 newTyVarTys n kind = mapNF_Tc newTyVarTy (nOfThem n kind)
119 newKindVar :: NF_TcM TcKind
121 = tcGetUnique `thenNF_Tc` \ uniq ->
122 tcNewMutTyVar (mkSysLocalName uniq FSLIT("k")) superKind VanillaTv `thenNF_Tc` \ kv ->
123 returnNF_Tc (TyVarTy kv)
125 newKindVars :: Int -> NF_TcM [TcKind]
126 newKindVars n = mapNF_Tc (\ _ -> newKindVar) (nOfThem n ())
128 newBoxityVar :: NF_TcM TcKind
130 = tcGetUnique `thenNF_Tc` \ uniq ->
131 tcNewMutTyVar (mkSysLocalName uniq FSLIT("bx")) superBoxity VanillaTv `thenNF_Tc` \ kv ->
132 returnNF_Tc (TyVarTy kv)
136 %************************************************************************
138 \subsection{Type instantiation}
140 %************************************************************************
142 I don't understand why this is needed
143 An old comments says "No need for tcSplitForAllTyM because a type
144 variable can't be instantiated to a for-all type"
145 But the same is true of rho types!
148 tcSplitRhoTyM :: TcType -> NF_TcM (TcThetaType, TcType)
152 -- A type variable is never instantiated to a dictionary type,
153 -- so we don't need to do a tcReadVar on the "arg".
154 go syn_t (FunTy arg res) ts = case tcSplitPredTy_maybe arg of
155 Just pair -> go res res (pair:ts)
156 Nothing -> returnNF_Tc (reverse ts, syn_t)
157 go syn_t (NoteTy n t) ts = go syn_t t ts
158 go syn_t (TyVarTy tv) ts = getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
160 Just ty | not (tcIsTyVarTy ty) -> go syn_t ty ts
161 other -> returnNF_Tc (reverse ts, syn_t)
162 go syn_t t ts = returnNF_Tc (reverse ts, syn_t)
166 %************************************************************************
168 \subsection{Type instantiation}
170 %************************************************************************
172 Instantiating a bunch of type variables
175 tcInstTyVars :: [TyVar]
176 -> NF_TcM ([TcTyVar], [TcType], Subst)
179 = mapNF_Tc tcInstTyVar tyvars `thenNF_Tc` \ tc_tyvars ->
181 tys = mkTyVarTys tc_tyvars
183 returnNF_Tc (tc_tyvars, tys, mkTopTyVarSubst tyvars tys)
184 -- Since the tyvars are freshly made,
185 -- they cannot possibly be captured by
186 -- any existing for-alls. Hence mkTopTyVarSubst
189 = tcGetUnique `thenNF_Tc` \ uniq ->
191 name = setNameUnique (tyVarName tyvar) uniq
192 -- Note that we don't change the print-name
193 -- This won't confuse the type checker but there's a chance
194 -- that two different tyvars will print the same way
195 -- in an error message. -dppr-debug will show up the difference
196 -- Better watch out for this. If worst comes to worst, just
197 -- use mkSysLocalName.
199 tcNewMutTyVar name (tyVarKind tyvar) VanillaTv
201 tcInstSigTyVars :: TyVarDetails -> [TyVar] -> NF_TcM [TcTyVar]
202 tcInstSigTyVars details tyvars -- Very similar to tcInstTyVar
203 = tcGetUniques `thenNF_Tc` \ uniqs ->
204 listTc [ ASSERT( not (kind `eqKind` openTypeKind) ) -- Shouldn't happen
205 tcNewMutTyVar name kind details
206 | (tyvar, uniq) <- tyvars `zip` uniqs,
207 let name = setNameUnique (tyVarName tyvar) uniq,
208 let kind = tyVarKind tyvar
212 @tcInstType@ instantiates the outer-level for-alls of a TcType with
213 fresh type variables, splits off the dictionary part, and returns the results.
216 tcInstType :: TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType)
218 = case tcSplitForAllTys ty of
219 ([], rho) -> -- There may be overloading but no type variables;
220 -- (?x :: Int) => Int -> Int
222 (theta, tau) = tcSplitRhoTy rho -- Used to be tcSplitRhoTyM
224 returnNF_Tc ([], theta, tau)
226 (tyvars, rho) -> tcInstTyVars tyvars `thenNF_Tc` \ (tyvars', _, tenv) ->
228 (theta, tau) = tcSplitRhoTy (substTy tenv rho) -- Used to be tcSplitRhoTyM
230 returnNF_Tc (tyvars', theta, tau)
233 tcInstSigType :: TyVarDetails -> Type -> NF_TcM ([TcTyVar], TcThetaType, TcType)
234 -- Very similar to tcInstSigType, but uses signature type variables
235 -- Also, somewhat arbitrarily, don't deal with the monomorphic case so efficiently
236 tcInstSigType tv_details poly_ty
238 (tyvars, rho) = tcSplitForAllTys poly_ty
240 tcInstSigTyVars tv_details tyvars `thenNF_Tc` \ tyvars' ->
241 -- Make *signature* type variables
244 tyvar_tys' = mkTyVarTys tyvars'
245 rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho
246 -- mkTopTyVarSubst because the tyvars' are fresh
248 (theta', tau') = tcSplitRhoTy rho'
249 -- This splitRhoTy tries hard to make sure that tau' is a type synonym
250 -- wherever possible, which can improve interface files.
252 returnNF_Tc (tyvars', theta', tau')
257 %************************************************************************
259 \subsection{Putting and getting mutable type variables}
261 %************************************************************************
264 putTcTyVar :: TcTyVar -> TcType -> NF_TcM TcType
265 getTcTyVar :: TcTyVar -> NF_TcM (Maybe TcType)
272 | not (isMutTyVar tyvar)
273 = pprTrace "putTcTyVar" (ppr tyvar) $
277 = ASSERT( isMutTyVar tyvar )
278 tcWriteMutTyVar tyvar (Just ty) `thenNF_Tc_`
282 Getting is more interesting. The easy thing to do is just to read, thus:
285 getTcTyVar tyvar = tcReadMutTyVar tyvar
288 But it's more fun to short out indirections on the way: If this
289 version returns a TyVar, then that TyVar is unbound. If it returns
290 any other type, then there might be bound TyVars embedded inside it.
292 We return Nothing iff the original box was unbound.
296 | not (isMutTyVar tyvar)
297 = pprTrace "getTcTyVar" (ppr tyvar) $
298 returnNF_Tc (Just (mkTyVarTy tyvar))
301 = ASSERT2( isMutTyVar tyvar, ppr tyvar )
302 tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
304 Just ty -> short_out ty `thenNF_Tc` \ ty' ->
305 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
306 returnNF_Tc (Just ty')
308 Nothing -> returnNF_Tc Nothing
310 short_out :: TcType -> NF_TcM TcType
311 short_out ty@(TyVarTy tyvar)
312 | not (isMutTyVar tyvar)
316 = tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
318 Just ty' -> short_out ty' `thenNF_Tc` \ ty' ->
319 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
322 other -> returnNF_Tc ty
324 short_out other_ty = returnNF_Tc other_ty
328 %************************************************************************
330 \subsection{Zonking -- the exernal interfaces}
332 %************************************************************************
334 ----------------- Type variables
337 zonkTcTyVars :: [TcTyVar] -> NF_TcM [TcType]
338 zonkTcTyVars tyvars = mapNF_Tc zonkTcTyVar tyvars
340 zonkTcTyVarsAndFV :: [TcTyVar] -> NF_TcM TcTyVarSet
341 zonkTcTyVarsAndFV tyvars = mapNF_Tc zonkTcTyVar tyvars `thenNF_Tc` \ tys ->
342 returnNF_Tc (tyVarsOfTypes tys)
344 zonkTcTyVar :: TcTyVar -> NF_TcM TcType
345 zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar
348 ----------------- Types
351 zonkTcType :: TcType -> NF_TcM TcType
352 zonkTcType ty = zonkType (\ tv -> returnNF_Tc (TyVarTy tv)) ty
354 zonkTcTypes :: [TcType] -> NF_TcM [TcType]
355 zonkTcTypes tys = mapNF_Tc zonkTcType tys
357 zonkTcClassConstraints cts = mapNF_Tc zonk cts
358 where zonk (clas, tys)
359 = zonkTcTypes tys `thenNF_Tc` \ new_tys ->
360 returnNF_Tc (clas, new_tys)
362 zonkTcThetaType :: TcThetaType -> NF_TcM TcThetaType
363 zonkTcThetaType theta = mapNF_Tc zonkTcPredType theta
365 zonkTcPredType :: TcPredType -> NF_TcM TcPredType
366 zonkTcPredType (ClassP c ts)
367 = zonkTcTypes ts `thenNF_Tc` \ new_ts ->
368 returnNF_Tc (ClassP c new_ts)
369 zonkTcPredType (IParam n t)
370 = zonkTcType t `thenNF_Tc` \ new_t ->
371 returnNF_Tc (IParam n new_t)
374 ------------------- These ...ToType, ...ToKind versions
375 are used at the end of type checking
378 zonkKindEnv :: [(Name, TcKind)] -> NF_TcM [(Name, Kind)]
380 = mapNF_Tc zonk_it pairs
382 zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenNF_Tc` \ kind ->
383 returnNF_Tc (name, kind)
385 -- When zonking a kind, we want to
386 -- zonk a *kind* variable to (Type *)
387 -- zonk a *boxity* variable to *
388 zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind
389 | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity
390 | otherwise = pprPanic "zonkKindEnv" (ppr kv)
392 zonkTcTypeToType :: TcType -> NF_TcM Type
393 zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty
395 -- Zonk a mutable but unbound type variable to an arbitrary type
396 -- We know it's unbound even though we don't carry an environment,
397 -- because at the binding site for a type variable we bind the
398 -- mutable tyvar to a fresh immutable one. So the mutable store
399 -- plays the role of an environment. If we come across a mutable
400 -- type variable that isn't so bound, it must be completely free.
401 zonk_unbound_tyvar tv = putTcTyVar tv (mkArbitraryType tv)
404 -- When the type checker finds a type variable with no binding,
405 -- which means it can be instantiated with an arbitrary type, it
406 -- usually instantiates it to Void. Eg.
410 -- length Void (Nil Void)
412 -- But in really obscure programs, the type variable might have
413 -- a kind other than *, so we need to invent a suitably-kinded type.
417 -- List for kind *->*
418 -- Tuple for kind *->...*->*
420 -- which deals with most cases. (Previously, it only dealt with
423 -- In the other cases, it just makes up a TyCon with a suitable
424 -- kind. If this gets into an interface file, anyone reading that
425 -- file won't understand it. This is fixable (by making the client
426 -- of the interface file make up a TyCon too) but it is tiresome and
427 -- never happens, so I am leaving it
429 mkArbitraryType :: TcTyVar -> Type
430 -- Make up an arbitrary type whose kind is the same as the tyvar.
431 -- We'll use this to instantiate the (unbound) tyvar.
433 | isAnyTypeKind kind = voidTy -- The vastly common case
434 | otherwise = TyConApp tycon []
437 (args,res) = Type.splitFunTys kind -- Kinds are simple; use Type.splitFunTys
439 tycon | kind `eqKind` tyConKind listTyCon -- *->*
440 = listTyCon -- No tuples this size
442 | all isTypeKind args && isTypeKind res
443 = tupleTyCon Boxed (length args) -- *-> ... ->*->*
446 = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $
447 mkPrimTyCon tc_name kind 0 [] VoidRep
448 -- Same name as the tyvar, apart from making it start with a colon (sigh)
449 -- I dread to think what will happen if this gets out into an
450 -- interface file. Catastrophe likely. Major sigh.
452 tc_name = mkLocalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
454 -- zonkTcTyVarToTyVar is applied to the *binding* occurrence
455 -- of a type variable, at the *end* of type checking. It changes
456 -- the *mutable* type variable into an *immutable* one.
458 -- It does this by making an immutable version of tv and binds tv to it.
459 -- Now any bound occurences of the original type variable will get
460 -- zonked to the immutable version.
462 zonkTcTyVarToTyVar :: TcTyVar -> NF_TcM TyVar
463 zonkTcTyVarToTyVar tv
465 -- Make an immutable version, defaulting
466 -- the kind to lifted if necessary
467 immut_tv = mkTyVar (tyVarName tv) (defaultKind (tyVarKind tv))
468 immut_tv_ty = mkTyVarTy immut_tv
470 zap tv = putTcTyVar tv immut_tv_ty
471 -- Bind the mutable version to the immutable one
473 -- If the type variable is mutable, then bind it to immut_tv_ty
474 -- so that all other occurrences of the tyvar will get zapped too
475 zonkTyVar zap tv `thenNF_Tc` \ ty2 ->
477 WARN( not (immut_tv_ty `tcEqType` ty2), ppr tv $$ ppr immut_tv $$ ppr ty2 )
483 %************************************************************************
485 \subsection{Zonking -- the main work-horses: zonkType, zonkTyVar}
487 %* For internal use only! *
489 %************************************************************************
492 -- zonkType is used for Kinds as well
494 -- For unbound, mutable tyvars, zonkType uses the function given to it
495 -- For tyvars bound at a for-all, zonkType zonks them to an immutable
496 -- type variable and zonks the kind too
498 zonkType :: (TcTyVar -> NF_TcM Type) -- What to do with unbound mutable type variables
499 -- see zonkTcType, and zonkTcTypeToType
502 zonkType unbound_var_fn ty
505 go (TyConApp tycon tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
506 returnNF_Tc (TyConApp tycon tys')
508 go (NoteTy (SynNote ty1) ty2) = go ty1 `thenNF_Tc` \ ty1' ->
509 go ty2 `thenNF_Tc` \ ty2' ->
510 returnNF_Tc (NoteTy (SynNote ty1') ty2')
512 go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard free-tyvar annotations
514 go (SourceTy p) = go_pred p `thenNF_Tc` \ p' ->
515 returnNF_Tc (SourceTy p')
517 go (FunTy arg res) = go arg `thenNF_Tc` \ arg' ->
518 go res `thenNF_Tc` \ res' ->
519 returnNF_Tc (FunTy arg' res')
521 go (AppTy fun arg) = go fun `thenNF_Tc` \ fun' ->
522 go arg `thenNF_Tc` \ arg' ->
523 returnNF_Tc (mkAppTy fun' arg')
525 -- The two interesting cases!
526 go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar
528 go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenNF_Tc` \ tyvar' ->
529 go ty `thenNF_Tc` \ ty' ->
530 returnNF_Tc (ForAllTy tyvar' ty')
532 go_pred (ClassP c tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
533 returnNF_Tc (ClassP c tys')
534 go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
535 returnNF_Tc (NType tc tys')
536 go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
537 returnNF_Tc (IParam n ty')
539 zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable
540 -> TcTyVar -> NF_TcM TcType
541 zonkTyVar unbound_var_fn tyvar
542 | not (isMutTyVar tyvar) -- Not a mutable tyvar. This can happen when
543 -- zonking a forall type, when the bound type variable
544 -- needn't be mutable
545 = ASSERT( isTyVar tyvar ) -- Should not be any immutable kind vars
546 returnNF_Tc (TyVarTy tyvar)
549 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
551 Nothing -> unbound_var_fn tyvar -- Mutable and unbound
552 Just other_ty -> zonkType unbound_var_fn other_ty -- Bound
557 %************************************************************************
559 \subsection{Checking a user type}
561 %************************************************************************
563 When dealing with a user-written type, we first translate it from an HsType
564 to a Type, performing kind checking, and then check various things that should
565 be true about it. We don't want to perform these checks at the same time
566 as the initial translation because (a) they are unnecessary for interface-file
567 types and (b) when checking a mutually recursive group of type and class decls,
568 we can't "look" at the tycons/classes yet. Also, the checks are are rather
569 diverse, and used to really mess up the other code.
571 One thing we check for is 'rank'.
573 Rank 0: monotypes (no foralls)
574 Rank 1: foralls at the front only, Rank 0 inside
575 Rank 2: foralls at the front, Rank 1 on left of fn arrow,
577 basic ::= tyvar | T basic ... basic
579 r2 ::= forall tvs. cxt => r2a
580 r2a ::= r1 -> r2a | basic
581 r1 ::= forall tvs. cxt => r0
582 r0 ::= r0 -> r0 | basic
584 Another thing is to check that type synonyms are saturated.
585 This might not necessarily show up in kind checking.
587 data T k = MkT (k Int)
593 = FunSigCtxt Name -- Function type signature
594 | ExprSigCtxt -- Expression type signature
595 | ConArgCtxt Name -- Data constructor argument
596 | TySynCtxt Name -- RHS of a type synonym decl
597 | GenPatCtxt -- Pattern in generic decl
598 -- f{| a+b |} (Inl x) = ...
599 | PatSigCtxt -- Type sig in pattern
601 | ResSigCtxt -- Result type sig
603 | ForSigCtxt Name -- Foreign inport or export signature
604 | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE
606 -- Notes re TySynCtxt
607 -- We allow type synonyms that aren't types; e.g. type List = []
609 -- If the RHS mentions tyvars that aren't in scope, we'll
610 -- quantify over them:
611 -- e.g. type T = a->a
612 -- will become type T = forall a. a->a
614 -- With gla-exts that's right, but for H98 we should complain.
617 pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n)
618 pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature")
619 pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c)
620 pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c)
621 pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition")
622 pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature")
623 pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature")
624 pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n)
625 pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n)
629 checkValidType :: UserTypeCtxt -> Type -> TcM ()
630 -- Checks that the type is valid for the given context
631 checkValidType ctxt ty
632 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
634 rank | gla_exts = Arbitrary
636 = case ctxt of -- Haskell 98
640 TySynCtxt _ -> Rank 0
641 ExprSigCtxt -> Rank 1
642 FunSigCtxt _ -> Rank 1
643 ConArgCtxt _ -> Rank 1 -- We are given the type of the entire
644 -- constructor, hence rank 1
645 ForSigCtxt _ -> Rank 1
646 RuleSigCtxt _ -> Rank 1
648 actual_kind = typeKind ty
650 actual_kind_is_lifted = actual_kind `eqKind` liftedTypeKind
652 kind_ok = case ctxt of
653 TySynCtxt _ -> True -- Any kind will do
654 GenPatCtxt -> actual_kind_is_lifted
655 ForSigCtxt _ -> actual_kind_is_lifted
656 other -> isTypeKind actual_kind
658 ubx_tup | not gla_exts = UT_NotOk
659 | otherwise = case ctxt of
662 -- Unboxed tuples ok in function results,
663 -- but for type synonyms we allow them even at
666 tcAddErrCtxt (checkTypeCtxt ctxt ty) $
668 -- Check that the thing has kind Type, and is lifted if necessary
669 checkTc kind_ok (kindErr actual_kind) `thenTc_`
671 -- Check the internal validity of the type itself
672 check_poly_type rank ubx_tup ty
675 checkTypeCtxt ctxt ty
676 = vcat [ptext SLIT("In the type:") <+> ppr_ty ty,
677 ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
679 -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
680 -- something strange like {Eq k} -> k -> k, because there is no
681 -- ForAll at the top of the type. Since this is going to the user
682 -- we want it to look like a proper Haskell type even then; hence the hack
684 -- This shows up in the complaint about
686 -- op :: Eq a => a -> a
687 ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
690 (forall_tvs, theta, tau) = tcSplitSigmaTy ty
695 data Rank = Rank Int | Arbitrary
697 decRank :: Rank -> Rank
698 decRank Arbitrary = Arbitrary
699 decRank (Rank n) = Rank (n-1)
701 ----------------------------------------
702 data UbxTupFlag = UT_Ok | UT_NotOk
703 -- The "Ok" version means "ok if -fglasgow-exts is on"
705 ----------------------------------------
706 check_poly_type :: Rank -> UbxTupFlag -> Type -> TcM ()
707 check_poly_type (Rank 0) ubx_tup ty
708 = check_tau_type (Rank 0) ubx_tup ty
710 check_poly_type rank ubx_tup ty
712 (tvs, theta, tau) = tcSplitSigmaTy ty
714 check_valid_theta SigmaCtxt theta `thenTc_`
715 check_tau_type (decRank rank) ubx_tup tau `thenTc_`
716 checkFreeness tvs theta `thenTc_`
717 checkAmbiguity tvs theta (tyVarsOfType tau)
719 ----------------------------------------
720 check_arg_type :: Type -> TcM ()
721 -- The sort of type that can instantiate a type variable,
722 -- or be the argument of a type constructor.
723 -- Not an unboxed tuple, not a forall.
724 -- Other unboxed types are very occasionally allowed as type
725 -- arguments depending on the kind of the type constructor
727 -- For example, we want to reject things like:
729 -- instance Ord a => Ord (forall s. T s a)
731 -- g :: T s (forall b.b)
733 -- NB: unboxed tuples can have polymorphic or unboxed args.
734 -- This happens in the workers for functions returning
735 -- product types with polymorphic components.
736 -- But not in user code.
737 -- Anyway, they are dealt with by a special case in check_tau_type
740 = check_tau_type (Rank 0) UT_NotOk ty `thenTc_`
741 checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty)
743 ----------------------------------------
744 check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM ()
745 -- Rank is allowed rank for function args
746 -- No foralls otherwise
748 check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty)
749 check_tau_type rank ubx_tup (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags ->
750 check_source_ty dflags TypeCtxt sty
751 check_tau_type rank ubx_tup (TyVarTy _) = returnTc ()
752 check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty)
753 = check_poly_type rank UT_NotOk arg_ty `thenTc_`
754 check_tau_type rank UT_Ok res_ty
756 check_tau_type rank ubx_tup (AppTy ty1 ty2)
757 = check_arg_type ty1 `thenTc_` check_arg_type ty2
759 check_tau_type rank ubx_tup (NoteTy note ty)
760 = check_tau_type rank ubx_tup ty
761 -- Synonym notes are built only when the synonym is
762 -- saturated (see Type.mkSynTy)
763 -- Not checking the 'note' part allows us to instantiate a synonym
764 -- defn with a for-all type, but that seems OK too
766 check_tau_type rank ubx_tup ty@(TyConApp tc tys)
768 = -- NB: Type.mkSynTy builds a TyConApp (not a NoteTy) for an unsaturated
769 -- synonym application, leaving it to checkValidType (i.e. right here
771 checkTc syn_arity_ok arity_msg `thenTc_`
772 mapTc_ check_arg_type tys
774 | isUnboxedTupleTyCon tc
775 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
776 checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenTc_`
777 mapTc_ (check_tau_type (Rank 0) UT_Ok) tys
778 -- Args are allowed to be unlifted, or
779 -- more unboxed tuples, so can't use check_arg_ty
782 = mapTc_ check_arg_type tys
785 ubx_tup_ok gla_exts = case ubx_tup of { UT_Ok -> gla_exts; other -> False }
787 syn_arity_ok = tc_arity <= n_args
788 -- It's OK to have an *over-applied* type synonym
789 -- data Tree a b = ...
790 -- type Foo a = Tree [a]
791 -- f :: Foo a b -> ...
793 tc_arity = tyConArity tc
795 arity_msg = arityErr "Type synonym" (tyConName tc) tc_arity n_args
796 ubx_tup_msg = ubxArgTyErr ty
798 ----------------------------------------
799 forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty
800 unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty
801 ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty
802 kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind
808 is ambiguous if P contains generic variables
809 (i.e. one of the Vs) that are not mentioned in tau
811 However, we need to take account of functional dependencies
812 when we speak of 'mentioned in tau'. Example:
813 class C a b | a -> b where ...
815 forall x y. (C x y) => x
816 is not ambiguous because x is mentioned and x determines y
818 NB; the ambiguity check is only used for *user* types, not for types
819 coming from inteface files. The latter can legitimately have
820 ambiguous types. Example
822 class S a where s :: a -> (Int,Int)
823 instance S Char where s _ = (1,1)
824 f:: S a => [a] -> Int -> (Int,Int)
825 f (_::[a]) x = (a*x,b)
826 where (a,b) = s (undefined::a)
828 Here the worker for f gets the type
829 fw :: forall a. S a => Int -> (# Int, Int #)
831 If the list of tv_names is empty, we have a monotype, and then we
832 don't need to check for ambiguity either, because the test can't fail
836 checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM ()
837 checkAmbiguity forall_tyvars theta tau_tyvars
838 = mapTc_ complain (filter is_ambig theta)
840 complain pred = addErrTc (ambigErr pred)
841 extended_tau_vars = grow theta tau_tyvars
842 is_ambig pred = any ambig_var (varSetElems (tyVarsOfPred pred))
844 ambig_var ct_var = (ct_var `elem` forall_tyvars) &&
845 not (ct_var `elemVarSet` extended_tau_vars)
847 is_free ct_var = not (ct_var `elem` forall_tyvars)
850 = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
851 nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
852 ptext SLIT("must be reachable from the type after the '=>'"))]
855 In addition, GHC insists that at least one type variable
856 in each constraint is in V. So we disallow a type like
857 forall a. Eq b => b -> b
858 even in a scope where b is in scope.
861 checkFreeness forall_tyvars theta
862 = mapTc_ complain (filter is_free theta)
864 is_free pred = not (isIPPred pred)
865 && not (any bound_var (varSetElems (tyVarsOfPred pred)))
866 bound_var ct_var = ct_var `elem` forall_tyvars
867 complain pred = addErrTc (freeErr pred)
870 = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
871 ptext SLIT("are already in scope"),
872 nest 4 (ptext SLIT("At least one must be universally quantified here"))
877 %************************************************************************
879 \subsection{Checking a theta or source type}
881 %************************************************************************
885 = ClassSCCtxt Name -- Superclasses of clas
886 | SigmaCtxt -- Context of a normal for-all type
887 | DataTyCtxt Name -- Context of a data decl
888 | TypeCtxt -- Source type in an ordinary type
889 | InstThetaCtxt -- Context of an instance decl
890 | InstHeadCtxt -- Head of an instance decl
892 pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
893 pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type")
894 pprSourceTyCtxt (DataTyCtxt tc) = ptext SLIT("the context of the data type declaration for") <+> quotes (ppr tc)
895 pprSourceTyCtxt InstThetaCtxt = ptext SLIT("the context of an instance declaration")
896 pprSourceTyCtxt InstHeadCtxt = ptext SLIT("the head of an instance declaration")
897 pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type")
901 checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM ()
902 checkValidTheta ctxt theta
903 = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta)
905 -------------------------
906 check_valid_theta ctxt []
908 check_valid_theta ctxt theta
909 = getDOptsTc `thenNF_Tc` \ dflags ->
910 warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_`
911 mapTc_ (check_source_ty dflags ctxt) theta
913 (_,dups) = removeDups tcCmpPred theta
915 -------------------------
916 check_source_ty dflags ctxt pred@(ClassP cls tys)
917 = -- Class predicates are valid in all contexts
918 mapTc_ check_arg_type tys `thenTc_`
919 checkTc (arity == n_tys) arity_err `thenTc_`
920 checkTc (all tyvar_head tys || arby_preds_ok)
921 (predTyVarErr pred $$ how_to_allow)
924 class_name = className cls
925 arity = classArity cls
927 arity_err = arityErr "Class" class_name arity n_tys
929 arby_preds_ok = case ctxt of
930 InstHeadCtxt -> True -- We check for instance-head formation
931 -- in checkValidInstHead
932 InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags
933 other -> dopt Opt_GlasgowExts dflags
935 how_to_allow = case ctxt of
936 InstHeadCtxt -> empty -- Should not happen
937 InstThetaCtxt -> parens undecidableMsg
938 other -> parens (ptext SLIT("Use -fglasgow-exts to permit this"))
940 check_source_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty
941 -- Implicit parameters only allows in type
942 -- signatures; not in instance decls, superclasses etc
943 -- The reason for not allowing implicit params in instances is a bit subtle
944 -- If we allowed instance (?x::Int, Eq a) => Foo [a] where ...
945 -- then when we saw (e :: (?x::Int) => t) it would be unclear how to
946 -- discharge all the potential usas of the ?x in e. For example, a
947 -- constraint Foo [Int] might come out of e,and applying the
948 -- instance decl would show up two uses of ?x.
950 check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys
953 check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty)
955 -------------------------
956 tyvar_head ty -- Haskell 98 allows predicates of form
957 | tcIsTyVarTy ty = True -- C (a ty1 .. tyn)
958 | otherwise -- where a is a type variable
959 = case tcSplitAppTy_maybe ty of
960 Just (ty, _) -> tyvar_head ty
965 badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty
966 predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred
967 dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
969 checkThetaCtxt ctxt theta
970 = vcat [ptext SLIT("In the context:") <+> pprTheta theta,
971 ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
975 %************************************************************************
977 \subsection{Checking for a decent instance head type}
979 %************************************************************************
981 @checkValidInstHead@ checks the type {\em and} its syntactic constraints:
982 it must normally look like: @instance Foo (Tycon a b c ...) ...@
984 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
985 flag is on, or (2)~the instance is imported (they must have been
986 compiled elsewhere). In these cases, we let them go through anyway.
988 We can also have instances for functions: @instance Foo (a -> b) ...@.
991 checkValidInstHead :: Type -> TcM (Class, [TcType])
993 checkValidInstHead ty -- Should be a source type
994 = case tcSplitPredTy_maybe ty of {
995 Nothing -> failWithTc (instTypeErr (ppr ty) empty) ;
998 case getClassPredTys_maybe pred of {
999 Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ;
1002 getDOptsTc `thenNF_Tc` \ dflags ->
1003 mapTc_ check_arg_type tys `thenTc_`
1004 check_inst_head dflags clas tys `thenTc_`
1005 returnTc (clas, tys)
1008 check_inst_head dflags clas tys
1010 -- A user declaration of a CCallable/CReturnable instance
1011 -- must be for a "boxed primitive" type.
1012 (clas `hasKey` cCallableClassKey
1013 && not (ccallable_type first_ty))
1014 || (clas `hasKey` cReturnableClassKey
1015 && not (creturnable_type first_ty))
1016 = failWithTc (nonBoxedPrimCCallErr clas first_ty)
1018 -- If GlasgowExts then check at least one isn't a type variable
1019 | dopt Opt_GlasgowExts dflags
1020 = check_tyvars dflags clas tys
1022 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
1024 Just (tycon, arg_tys) <- tcSplitTyConApp_maybe first_ty,
1025 not (isSynTyCon tycon), -- ...but not a synonym
1026 all tcIsTyVarTy arg_tys, -- Applied to type variables
1027 equalLength (varSetElems (tyVarsOfTypes arg_tys)) arg_tys
1028 -- This last condition checks that all the type variables are distinct
1032 = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg)
1035 (first_ty : _) = tys
1037 ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty
1038 creturnable_type ty = isFFIImportResultTy dflags ty
1040 head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
1041 text "where T is not a synonym, and a,b,c are distinct type variables")
1043 check_tyvars dflags clas tys
1044 -- Check that at least one isn't a type variable
1045 -- unless -fallow-undecideable-instances
1046 | dopt Opt_AllowUndecidableInstances dflags = returnTc ()
1047 | not (all tcIsTyVarTy tys) = returnTc ()
1048 | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg)
1050 msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")
1053 undecidableMsg = ptext SLIT("Use -fallow-undecidable-instances to permit this")
1057 instTypeErr pp_ty msg
1058 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty,
1061 nonBoxedPrimCCallErr clas inst_ty
1062 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
1063 4 (pprClassPred clas [inst_ty])