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, tcInstType,
24 --------------------------------
25 -- Checking type validity
26 Rank, UserTypeCtxt(..), checkValidType, pprUserTypeCtxt,
27 SourceTyCtxt(..), checkValidTheta,
28 checkValidInstHead, instTypeErr, checkAmbiguity,
30 --------------------------------
32 zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV,
33 zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType,
34 zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv,
38 #include "HsVersions.h"
42 import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation
45 import TcType ( TcType, TcThetaType, TcTauType, TcPredType,
46 TcTyVarSet, TcKind, TcTyVar, TyVarDetails(..),
48 tcSplitRhoTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe,
49 tcSplitTyConApp_maybe, tcSplitForAllTys,
50 tcIsTyVarTy, tcSplitSigmaTy,
51 isUnLiftedType, isIPPred,
53 mkAppTy, mkTyVarTy, mkTyVarTys,
54 tyVarsOfPred, getClassPredTys_maybe,
56 liftedTypeKind, openTypeKind, defaultKind, superKind,
57 superBoxity, liftedBoxity, typeKind,
58 tyVarsOfType, tyVarsOfTypes,
59 eqKind, isTypeKind, isAnyTypeKind,
61 isFFIArgumentTy, isFFIImportResultTy
63 import qualified Type ( splitFunTys )
64 import Subst ( Subst, mkTopTyVarSubst, substTy )
65 import Class ( Class, classArity, className )
66 import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon,
67 tyConArity, tyConName, tyConKind )
68 import PrimRep ( PrimRep(VoidRep) )
69 import Var ( TyVar, tyVarKind, tyVarName, isTyVar, mkTyVar, isMutTyVar )
72 import TcMonad -- TcType, amongst others
73 import TysWiredIn ( voidTy, listTyCon, tupleTyCon )
74 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
75 import ForeignCall ( Safety(..) )
76 import FunDeps ( grow )
77 import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred )
78 import Name ( Name, NamedThing(..), setNameUnique, mkSysLocalName,
79 mkLocalName, mkDerivedTyConOcc
82 import BasicTypes ( Boxity(Boxed) )
83 import CmdLineOpts ( dopt, DynFlag(..) )
84 import Unique ( Uniquable(..) )
85 import SrcLoc ( noSrcLoc )
86 import Util ( nOfThem, isSingleton, equalLength )
87 import ListSetOps ( removeDups )
92 %************************************************************************
94 \subsection{New type variables}
96 %************************************************************************
99 newTyVar :: Kind -> NF_TcM TcTyVar
101 = tcGetUnique `thenNF_Tc` \ uniq ->
102 tcNewMutTyVar (mkSysLocalName uniq FSLIT("t")) kind VanillaTv
104 newTyVarTy :: Kind -> NF_TcM TcType
106 = newTyVar kind `thenNF_Tc` \ tc_tyvar ->
107 returnNF_Tc (TyVarTy tc_tyvar)
109 newHoleTyVarTy :: NF_TcM TcType
110 = tcGetUnique `thenNF_Tc` \ uniq ->
111 tcNewMutTyVar (mkSysLocalName uniq FSLIT("h")) openTypeKind HoleTv `thenNF_Tc` \ tv ->
112 returnNF_Tc (TyVarTy tv)
114 newTyVarTys :: Int -> Kind -> NF_TcM [TcType]
115 newTyVarTys n kind = mapNF_Tc newTyVarTy (nOfThem n kind)
117 newKindVar :: NF_TcM TcKind
119 = tcGetUnique `thenNF_Tc` \ uniq ->
120 tcNewMutTyVar (mkSysLocalName uniq FSLIT("k")) superKind VanillaTv `thenNF_Tc` \ kv ->
121 returnNF_Tc (TyVarTy kv)
123 newKindVars :: Int -> NF_TcM [TcKind]
124 newKindVars n = mapNF_Tc (\ _ -> newKindVar) (nOfThem n ())
126 newBoxityVar :: NF_TcM TcKind
128 = tcGetUnique `thenNF_Tc` \ uniq ->
129 tcNewMutTyVar (mkSysLocalName uniq FSLIT("bx")) superBoxity VanillaTv `thenNF_Tc` \ kv ->
130 returnNF_Tc (TyVarTy kv)
134 %************************************************************************
136 \subsection{Type instantiation}
138 %************************************************************************
140 Instantiating a bunch of type variables
143 tcInstTyVars :: TyVarDetails -> [TyVar]
144 -> NF_TcM ([TcTyVar], [TcType], Subst)
146 tcInstTyVars tv_details tyvars
147 = mapNF_Tc (tcInstTyVar tv_details) tyvars `thenNF_Tc` \ tc_tyvars ->
149 tys = mkTyVarTys tc_tyvars
151 returnNF_Tc (tc_tyvars, tys, mkTopTyVarSubst tyvars tys)
152 -- Since the tyvars are freshly made,
153 -- they cannot possibly be captured by
154 -- any existing for-alls. Hence mkTopTyVarSubst
156 tcInstTyVar tv_details tyvar
157 = tcGetUnique `thenNF_Tc` \ uniq ->
159 name = setNameUnique (tyVarName tyvar) uniq
160 -- Note that we don't change the print-name
161 -- This won't confuse the type checker but there's a chance
162 -- that two different tyvars will print the same way
163 -- in an error message. -dppr-debug will show up the difference
164 -- Better watch out for this. If worst comes to worst, just
165 -- use mkSysLocalName.
167 tcNewMutTyVar name (tyVarKind tyvar) tv_details
169 tcInstType :: TyVarDetails -> TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType)
170 -- tcInstType instantiates the outer-level for-alls of a TcType with
171 -- fresh (mutable) type variables, splits off the dictionary part,
172 -- and returns the pieces.
173 tcInstType tv_details ty
174 = case tcSplitForAllTys ty of
175 ([], rho) -> -- There may be overloading despite no type variables;
176 -- (?x :: Int) => Int -> Int
178 (theta, tau) = tcSplitRhoTy rho
180 returnNF_Tc ([], theta, tau)
182 (tyvars, rho) -> tcInstTyVars tv_details tyvars `thenNF_Tc` \ (tyvars', _, tenv) ->
184 (theta, tau) = tcSplitRhoTy (substTy tenv rho)
186 returnNF_Tc (tyvars', theta, tau)
190 %************************************************************************
192 \subsection{Putting and getting mutable type variables}
194 %************************************************************************
197 putTcTyVar :: TcTyVar -> TcType -> NF_TcM TcType
198 getTcTyVar :: TcTyVar -> NF_TcM (Maybe TcType)
205 | not (isMutTyVar tyvar)
206 = pprTrace "putTcTyVar" (ppr tyvar) $
210 = ASSERT( isMutTyVar tyvar )
211 tcWriteMutTyVar tyvar (Just ty) `thenNF_Tc_`
215 Getting is more interesting. The easy thing to do is just to read, thus:
218 getTcTyVar tyvar = tcReadMutTyVar tyvar
221 But it's more fun to short out indirections on the way: If this
222 version returns a TyVar, then that TyVar is unbound. If it returns
223 any other type, then there might be bound TyVars embedded inside it.
225 We return Nothing iff the original box was unbound.
229 | not (isMutTyVar tyvar)
230 = pprTrace "getTcTyVar" (ppr tyvar) $
231 returnNF_Tc (Just (mkTyVarTy tyvar))
234 = ASSERT2( isMutTyVar tyvar, ppr tyvar )
235 tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
237 Just ty -> short_out ty `thenNF_Tc` \ ty' ->
238 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
239 returnNF_Tc (Just ty')
241 Nothing -> returnNF_Tc Nothing
243 short_out :: TcType -> NF_TcM TcType
244 short_out ty@(TyVarTy tyvar)
245 | not (isMutTyVar tyvar)
249 = tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
251 Just ty' -> short_out ty' `thenNF_Tc` \ ty' ->
252 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
255 other -> returnNF_Tc ty
257 short_out other_ty = returnNF_Tc other_ty
261 %************************************************************************
263 \subsection{Zonking -- the exernal interfaces}
265 %************************************************************************
267 ----------------- Type variables
270 zonkTcTyVars :: [TcTyVar] -> NF_TcM [TcType]
271 zonkTcTyVars tyvars = mapNF_Tc zonkTcTyVar tyvars
273 zonkTcTyVarsAndFV :: [TcTyVar] -> NF_TcM TcTyVarSet
274 zonkTcTyVarsAndFV tyvars = mapNF_Tc zonkTcTyVar tyvars `thenNF_Tc` \ tys ->
275 returnNF_Tc (tyVarsOfTypes tys)
277 zonkTcTyVar :: TcTyVar -> NF_TcM TcType
278 zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar
281 ----------------- Types
284 zonkTcType :: TcType -> NF_TcM TcType
285 zonkTcType ty = zonkType (\ tv -> returnNF_Tc (TyVarTy tv)) ty
287 zonkTcTypes :: [TcType] -> NF_TcM [TcType]
288 zonkTcTypes tys = mapNF_Tc zonkTcType tys
290 zonkTcClassConstraints cts = mapNF_Tc zonk cts
291 where zonk (clas, tys)
292 = zonkTcTypes tys `thenNF_Tc` \ new_tys ->
293 returnNF_Tc (clas, new_tys)
295 zonkTcThetaType :: TcThetaType -> NF_TcM TcThetaType
296 zonkTcThetaType theta = mapNF_Tc zonkTcPredType theta
298 zonkTcPredType :: TcPredType -> NF_TcM TcPredType
299 zonkTcPredType (ClassP c ts)
300 = zonkTcTypes ts `thenNF_Tc` \ new_ts ->
301 returnNF_Tc (ClassP c new_ts)
302 zonkTcPredType (IParam n t)
303 = zonkTcType t `thenNF_Tc` \ new_t ->
304 returnNF_Tc (IParam n new_t)
307 ------------------- These ...ToType, ...ToKind versions
308 are used at the end of type checking
311 zonkKindEnv :: [(Name, TcKind)] -> NF_TcM [(Name, Kind)]
313 = mapNF_Tc zonk_it pairs
315 zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenNF_Tc` \ kind ->
316 returnNF_Tc (name, kind)
318 -- When zonking a kind, we want to
319 -- zonk a *kind* variable to (Type *)
320 -- zonk a *boxity* variable to *
321 zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind
322 | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity
323 | otherwise = pprPanic "zonkKindEnv" (ppr kv)
325 zonkTcTypeToType :: TcType -> NF_TcM Type
326 zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty
328 -- Zonk a mutable but unbound type variable to an arbitrary type
329 -- We know it's unbound even though we don't carry an environment,
330 -- because at the binding site for a type variable we bind the
331 -- mutable tyvar to a fresh immutable one. So the mutable store
332 -- plays the role of an environment. If we come across a mutable
333 -- type variable that isn't so bound, it must be completely free.
334 zonk_unbound_tyvar tv = putTcTyVar tv (mkArbitraryType tv)
337 -- When the type checker finds a type variable with no binding,
338 -- which means it can be instantiated with an arbitrary type, it
339 -- usually instantiates it to Void. Eg.
343 -- length Void (Nil Void)
345 -- But in really obscure programs, the type variable might have
346 -- a kind other than *, so we need to invent a suitably-kinded type.
350 -- List for kind *->*
351 -- Tuple for kind *->...*->*
353 -- which deals with most cases. (Previously, it only dealt with
356 -- In the other cases, it just makes up a TyCon with a suitable
357 -- kind. If this gets into an interface file, anyone reading that
358 -- file won't understand it. This is fixable (by making the client
359 -- of the interface file make up a TyCon too) but it is tiresome and
360 -- never happens, so I am leaving it
362 mkArbitraryType :: TcTyVar -> Type
363 -- Make up an arbitrary type whose kind is the same as the tyvar.
364 -- We'll use this to instantiate the (unbound) tyvar.
366 | isAnyTypeKind kind = voidTy -- The vastly common case
367 | otherwise = TyConApp tycon []
370 (args,res) = Type.splitFunTys kind -- Kinds are simple; use Type.splitFunTys
372 tycon | kind `eqKind` tyConKind listTyCon -- *->*
373 = listTyCon -- No tuples this size
375 | all isTypeKind args && isTypeKind res
376 = tupleTyCon Boxed (length args) -- *-> ... ->*->*
379 = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $
380 mkPrimTyCon tc_name kind 0 [] VoidRep
381 -- Same name as the tyvar, apart from making it start with a colon (sigh)
382 -- I dread to think what will happen if this gets out into an
383 -- interface file. Catastrophe likely. Major sigh.
385 tc_name = mkLocalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
387 -- zonkTcTyVarToTyVar is applied to the *binding* occurrence
388 -- of a type variable, at the *end* of type checking. It changes
389 -- the *mutable* type variable into an *immutable* one.
391 -- It does this by making an immutable version of tv and binds tv to it.
392 -- Now any bound occurences of the original type variable will get
393 -- zonked to the immutable version.
395 zonkTcTyVarToTyVar :: TcTyVar -> NF_TcM TyVar
396 zonkTcTyVarToTyVar tv
398 -- Make an immutable version, defaulting
399 -- the kind to lifted if necessary
400 immut_tv = mkTyVar (tyVarName tv) (defaultKind (tyVarKind tv))
401 immut_tv_ty = mkTyVarTy immut_tv
403 zap tv = putTcTyVar tv immut_tv_ty
404 -- Bind the mutable version to the immutable one
406 -- If the type variable is mutable, then bind it to immut_tv_ty
407 -- so that all other occurrences of the tyvar will get zapped too
408 zonkTyVar zap tv `thenNF_Tc` \ ty2 ->
410 WARN( not (immut_tv_ty `tcEqType` ty2), ppr tv $$ ppr immut_tv $$ ppr ty2 )
416 %************************************************************************
418 \subsection{Zonking -- the main work-horses: zonkType, zonkTyVar}
420 %* For internal use only! *
422 %************************************************************************
425 -- zonkType is used for Kinds as well
427 -- For unbound, mutable tyvars, zonkType uses the function given to it
428 -- For tyvars bound at a for-all, zonkType zonks them to an immutable
429 -- type variable and zonks the kind too
431 zonkType :: (TcTyVar -> NF_TcM Type) -- What to do with unbound mutable type variables
432 -- see zonkTcType, and zonkTcTypeToType
435 zonkType unbound_var_fn ty
438 go (TyConApp tycon tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
439 returnNF_Tc (TyConApp tycon tys')
441 go (NoteTy (SynNote ty1) ty2) = go ty1 `thenNF_Tc` \ ty1' ->
442 go ty2 `thenNF_Tc` \ ty2' ->
443 returnNF_Tc (NoteTy (SynNote ty1') ty2')
445 go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard free-tyvar annotations
447 go (SourceTy p) = go_pred p `thenNF_Tc` \ p' ->
448 returnNF_Tc (SourceTy p')
450 go (FunTy arg res) = go arg `thenNF_Tc` \ arg' ->
451 go res `thenNF_Tc` \ res' ->
452 returnNF_Tc (FunTy arg' res')
454 go (AppTy fun arg) = go fun `thenNF_Tc` \ fun' ->
455 go arg `thenNF_Tc` \ arg' ->
456 returnNF_Tc (mkAppTy fun' arg')
457 -- NB the mkAppTy; we might have instantiated a
458 -- type variable to a type constructor, so we need
459 -- to pull the TyConApp to the top.
461 -- The two interesting cases!
462 go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar
464 go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenNF_Tc` \ tyvar' ->
465 go ty `thenNF_Tc` \ ty' ->
466 returnNF_Tc (ForAllTy tyvar' ty')
468 go_pred (ClassP c tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
469 returnNF_Tc (ClassP c tys')
470 go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
471 returnNF_Tc (NType tc tys')
472 go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
473 returnNF_Tc (IParam n ty')
475 zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable
476 -> TcTyVar -> NF_TcM TcType
477 zonkTyVar unbound_var_fn tyvar
478 | not (isMutTyVar tyvar) -- Not a mutable tyvar. This can happen when
479 -- zonking a forall type, when the bound type variable
480 -- needn't be mutable
481 = ASSERT( isTyVar tyvar ) -- Should not be any immutable kind vars
482 returnNF_Tc (TyVarTy tyvar)
485 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
487 Nothing -> unbound_var_fn tyvar -- Mutable and unbound
488 Just other_ty -> zonkType unbound_var_fn other_ty -- Bound
493 %************************************************************************
495 \subsection{Checking a user type}
497 %************************************************************************
499 When dealing with a user-written type, we first translate it from an HsType
500 to a Type, performing kind checking, and then check various things that should
501 be true about it. We don't want to perform these checks at the same time
502 as the initial translation because (a) they are unnecessary for interface-file
503 types and (b) when checking a mutually recursive group of type and class decls,
504 we can't "look" at the tycons/classes yet. Also, the checks are are rather
505 diverse, and used to really mess up the other code.
507 One thing we check for is 'rank'.
509 Rank 0: monotypes (no foralls)
510 Rank 1: foralls at the front only, Rank 0 inside
511 Rank 2: foralls at the front, Rank 1 on left of fn arrow,
513 basic ::= tyvar | T basic ... basic
515 r2 ::= forall tvs. cxt => r2a
516 r2a ::= r1 -> r2a | basic
517 r1 ::= forall tvs. cxt => r0
518 r0 ::= r0 -> r0 | basic
520 Another thing is to check that type synonyms are saturated.
521 This might not necessarily show up in kind checking.
523 data T k = MkT (k Int)
529 = FunSigCtxt Name -- Function type signature
530 | ExprSigCtxt -- Expression type signature
531 | ConArgCtxt Name -- Data constructor argument
532 | TySynCtxt Name -- RHS of a type synonym decl
533 | GenPatCtxt -- Pattern in generic decl
534 -- f{| a+b |} (Inl x) = ...
535 | PatSigCtxt -- Type sig in pattern
537 | ResSigCtxt -- Result type sig
539 | ForSigCtxt Name -- Foreign inport or export signature
540 | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE
542 -- Notes re TySynCtxt
543 -- We allow type synonyms that aren't types; e.g. type List = []
545 -- If the RHS mentions tyvars that aren't in scope, we'll
546 -- quantify over them:
547 -- e.g. type T = a->a
548 -- will become type T = forall a. a->a
550 -- With gla-exts that's right, but for H98 we should complain.
553 pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n)
554 pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature")
555 pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c)
556 pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c)
557 pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition")
558 pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature")
559 pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature")
560 pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n)
561 pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n)
565 checkValidType :: UserTypeCtxt -> Type -> TcM ()
566 -- Checks that the type is valid for the given context
567 checkValidType ctxt ty
568 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
570 rank | gla_exts = Arbitrary
572 = case ctxt of -- Haskell 98
576 TySynCtxt _ -> Rank 0
577 ExprSigCtxt -> Rank 1
578 FunSigCtxt _ -> Rank 1
579 ConArgCtxt _ -> Rank 1 -- We are given the type of the entire
580 -- constructor, hence rank 1
581 ForSigCtxt _ -> Rank 1
582 RuleSigCtxt _ -> Rank 1
584 actual_kind = typeKind ty
586 actual_kind_is_lifted = actual_kind `eqKind` liftedTypeKind
588 kind_ok = case ctxt of
589 TySynCtxt _ -> True -- Any kind will do
590 GenPatCtxt -> actual_kind_is_lifted
591 ForSigCtxt _ -> actual_kind_is_lifted
592 other -> isTypeKind actual_kind
594 ubx_tup | not gla_exts = UT_NotOk
595 | otherwise = case ctxt of
598 -- Unboxed tuples ok in function results,
599 -- but for type synonyms we allow them even at
602 tcAddErrCtxt (checkTypeCtxt ctxt ty) $
604 -- Check that the thing has kind Type, and is lifted if necessary
605 checkTc kind_ok (kindErr actual_kind) `thenTc_`
607 -- Check the internal validity of the type itself
608 check_poly_type rank ubx_tup ty
611 checkTypeCtxt ctxt ty
612 = vcat [ptext SLIT("In the type:") <+> ppr_ty ty,
613 ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
615 -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
616 -- something strange like {Eq k} -> k -> k, because there is no
617 -- ForAll at the top of the type. Since this is going to the user
618 -- we want it to look like a proper Haskell type even then; hence the hack
620 -- This shows up in the complaint about
622 -- op :: Eq a => a -> a
623 ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
626 (forall_tvs, theta, tau) = tcSplitSigmaTy ty
631 data Rank = Rank Int | Arbitrary
633 decRank :: Rank -> Rank
634 decRank Arbitrary = Arbitrary
635 decRank (Rank n) = Rank (n-1)
637 ----------------------------------------
638 data UbxTupFlag = UT_Ok | UT_NotOk
639 -- The "Ok" version means "ok if -fglasgow-exts is on"
641 ----------------------------------------
642 check_poly_type :: Rank -> UbxTupFlag -> Type -> TcM ()
643 check_poly_type (Rank 0) ubx_tup ty
644 = check_tau_type (Rank 0) ubx_tup ty
646 check_poly_type rank ubx_tup ty
648 (tvs, theta, tau) = tcSplitSigmaTy ty
650 check_valid_theta SigmaCtxt theta `thenTc_`
651 check_tau_type (decRank rank) ubx_tup tau `thenTc_`
652 checkFreeness tvs theta `thenTc_`
653 checkAmbiguity tvs theta (tyVarsOfType tau)
655 ----------------------------------------
656 check_arg_type :: Type -> TcM ()
657 -- The sort of type that can instantiate a type variable,
658 -- or be the argument of a type constructor.
659 -- Not an unboxed tuple, not a forall.
660 -- Other unboxed types are very occasionally allowed as type
661 -- arguments depending on the kind of the type constructor
663 -- For example, we want to reject things like:
665 -- instance Ord a => Ord (forall s. T s a)
667 -- g :: T s (forall b.b)
669 -- NB: unboxed tuples can have polymorphic or unboxed args.
670 -- This happens in the workers for functions returning
671 -- product types with polymorphic components.
672 -- But not in user code.
673 -- Anyway, they are dealt with by a special case in check_tau_type
676 = check_tau_type (Rank 0) UT_NotOk ty `thenTc_`
677 checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty)
679 ----------------------------------------
680 check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM ()
681 -- Rank is allowed rank for function args
682 -- No foralls otherwise
684 check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty)
685 check_tau_type rank ubx_tup (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags ->
686 check_source_ty dflags TypeCtxt sty
687 check_tau_type rank ubx_tup (TyVarTy _) = returnTc ()
688 check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty)
689 = check_poly_type rank UT_NotOk arg_ty `thenTc_`
690 check_tau_type rank UT_Ok res_ty
692 check_tau_type rank ubx_tup (AppTy ty1 ty2)
693 = check_arg_type ty1 `thenTc_` check_arg_type ty2
695 check_tau_type rank ubx_tup (NoteTy note ty)
696 = check_tau_type rank ubx_tup ty
697 -- Synonym notes are built only when the synonym is
698 -- saturated (see Type.mkSynTy)
699 -- Not checking the 'note' part allows us to instantiate a synonym
700 -- defn with a for-all type, or with a partially-applied type synonym,
701 -- but that seems OK too
703 check_tau_type rank ubx_tup ty@(TyConApp tc tys)
705 = -- NB: Type.mkSynTy builds a TyConApp (not a NoteTy) for an unsaturated
706 -- synonym application, leaving it to checkValidType (i.e. right here
708 checkTc syn_arity_ok arity_msg `thenTc_`
709 mapTc_ check_arg_type tys
711 | isUnboxedTupleTyCon tc
712 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
713 checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenTc_`
714 mapTc_ (check_tau_type (Rank 0) UT_Ok) tys
715 -- Args are allowed to be unlifted, or
716 -- more unboxed tuples, so can't use check_arg_ty
719 = mapTc_ check_arg_type tys
722 ubx_tup_ok gla_exts = case ubx_tup of { UT_Ok -> gla_exts; other -> False }
724 syn_arity_ok = tc_arity <= n_args
725 -- It's OK to have an *over-applied* type synonym
726 -- data Tree a b = ...
727 -- type Foo a = Tree [a]
728 -- f :: Foo a b -> ...
730 tc_arity = tyConArity tc
732 arity_msg = arityErr "Type synonym" (tyConName tc) tc_arity n_args
733 ubx_tup_msg = ubxArgTyErr ty
735 ----------------------------------------
736 forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty
737 unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty
738 ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty
739 kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind
745 is ambiguous if P contains generic variables
746 (i.e. one of the Vs) that are not mentioned in tau
748 However, we need to take account of functional dependencies
749 when we speak of 'mentioned in tau'. Example:
750 class C a b | a -> b where ...
752 forall x y. (C x y) => x
753 is not ambiguous because x is mentioned and x determines y
755 NB; the ambiguity check is only used for *user* types, not for types
756 coming from inteface files. The latter can legitimately have
757 ambiguous types. Example
759 class S a where s :: a -> (Int,Int)
760 instance S Char where s _ = (1,1)
761 f:: S a => [a] -> Int -> (Int,Int)
762 f (_::[a]) x = (a*x,b)
763 where (a,b) = s (undefined::a)
765 Here the worker for f gets the type
766 fw :: forall a. S a => Int -> (# Int, Int #)
768 If the list of tv_names is empty, we have a monotype, and then we
769 don't need to check for ambiguity either, because the test can't fail
773 checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM ()
774 checkAmbiguity forall_tyvars theta tau_tyvars
775 = mapTc_ complain (filter is_ambig theta)
777 complain pred = addErrTc (ambigErr pred)
778 extended_tau_vars = grow theta tau_tyvars
779 is_ambig pred = any ambig_var (varSetElems (tyVarsOfPred pred))
781 ambig_var ct_var = (ct_var `elem` forall_tyvars) &&
782 not (ct_var `elemVarSet` extended_tau_vars)
784 is_free ct_var = not (ct_var `elem` forall_tyvars)
787 = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
788 nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
789 ptext SLIT("must be reachable from the type after the '=>'"))]
792 In addition, GHC insists that at least one type variable
793 in each constraint is in V. So we disallow a type like
794 forall a. Eq b => b -> b
795 even in a scope where b is in scope.
798 checkFreeness forall_tyvars theta
799 = mapTc_ complain (filter is_free theta)
801 is_free pred = not (isIPPred pred)
802 && not (any bound_var (varSetElems (tyVarsOfPred pred)))
803 bound_var ct_var = ct_var `elem` forall_tyvars
804 complain pred = addErrTc (freeErr pred)
807 = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
808 ptext SLIT("are already in scope"),
809 nest 4 (ptext SLIT("At least one must be universally quantified here"))
814 %************************************************************************
816 \subsection{Checking a theta or source type}
818 %************************************************************************
822 = ClassSCCtxt Name -- Superclasses of clas
823 | SigmaCtxt -- Context of a normal for-all type
824 | DataTyCtxt Name -- Context of a data decl
825 | TypeCtxt -- Source type in an ordinary type
826 | InstThetaCtxt -- Context of an instance decl
827 | InstHeadCtxt -- Head of an instance decl
829 pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
830 pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type")
831 pprSourceTyCtxt (DataTyCtxt tc) = ptext SLIT("the context of the data type declaration for") <+> quotes (ppr tc)
832 pprSourceTyCtxt InstThetaCtxt = ptext SLIT("the context of an instance declaration")
833 pprSourceTyCtxt InstHeadCtxt = ptext SLIT("the head of an instance declaration")
834 pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type")
838 checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM ()
839 checkValidTheta ctxt theta
840 = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta)
842 -------------------------
843 check_valid_theta ctxt []
845 check_valid_theta ctxt theta
846 = getDOptsTc `thenNF_Tc` \ dflags ->
847 warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_`
848 mapTc_ (check_source_ty dflags ctxt) theta
850 (_,dups) = removeDups tcCmpPred theta
852 -------------------------
853 check_source_ty dflags ctxt pred@(ClassP cls tys)
854 = -- Class predicates are valid in all contexts
855 mapTc_ check_arg_type tys `thenTc_`
856 checkTc (arity == n_tys) arity_err `thenTc_`
857 checkTc (all tyvar_head tys || arby_preds_ok)
858 (predTyVarErr pred $$ how_to_allow)
861 class_name = className cls
862 arity = classArity cls
864 arity_err = arityErr "Class" class_name arity n_tys
866 arby_preds_ok = case ctxt of
867 InstHeadCtxt -> True -- We check for instance-head formation
868 -- in checkValidInstHead
869 InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags
870 other -> dopt Opt_GlasgowExts dflags
872 how_to_allow = case ctxt of
873 InstHeadCtxt -> empty -- Should not happen
874 InstThetaCtxt -> parens undecidableMsg
875 other -> parens (ptext SLIT("Use -fglasgow-exts to permit this"))
877 check_source_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty
878 -- Implicit parameters only allows in type
879 -- signatures; not in instance decls, superclasses etc
880 -- The reason for not allowing implicit params in instances is a bit subtle
881 -- If we allowed instance (?x::Int, Eq a) => Foo [a] where ...
882 -- then when we saw (e :: (?x::Int) => t) it would be unclear how to
883 -- discharge all the potential usas of the ?x in e. For example, a
884 -- constraint Foo [Int] might come out of e,and applying the
885 -- instance decl would show up two uses of ?x.
887 check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys
890 check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty)
892 -------------------------
893 tyvar_head ty -- Haskell 98 allows predicates of form
894 | tcIsTyVarTy ty = True -- C (a ty1 .. tyn)
895 | otherwise -- where a is a type variable
896 = case tcSplitAppTy_maybe ty of
897 Just (ty, _) -> tyvar_head ty
902 badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty
903 predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred
904 dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
906 checkThetaCtxt ctxt theta
907 = vcat [ptext SLIT("In the context:") <+> pprTheta theta,
908 ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
912 %************************************************************************
914 \subsection{Checking for a decent instance head type}
916 %************************************************************************
918 @checkValidInstHead@ checks the type {\em and} its syntactic constraints:
919 it must normally look like: @instance Foo (Tycon a b c ...) ...@
921 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
922 flag is on, or (2)~the instance is imported (they must have been
923 compiled elsewhere). In these cases, we let them go through anyway.
925 We can also have instances for functions: @instance Foo (a -> b) ...@.
928 checkValidInstHead :: Type -> TcM (Class, [TcType])
930 checkValidInstHead ty -- Should be a source type
931 = case tcSplitPredTy_maybe ty of {
932 Nothing -> failWithTc (instTypeErr (ppr ty) empty) ;
935 case getClassPredTys_maybe pred of {
936 Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ;
939 getDOptsTc `thenNF_Tc` \ dflags ->
940 mapTc_ check_arg_type tys `thenTc_`
941 check_inst_head dflags clas tys `thenTc_`
945 check_inst_head dflags clas tys
947 -- A user declaration of a CCallable/CReturnable instance
948 -- must be for a "boxed primitive" type.
949 (clas `hasKey` cCallableClassKey
950 && not (ccallable_type first_ty))
951 || (clas `hasKey` cReturnableClassKey
952 && not (creturnable_type first_ty))
953 = failWithTc (nonBoxedPrimCCallErr clas first_ty)
955 -- If GlasgowExts then check at least one isn't a type variable
956 | dopt Opt_GlasgowExts dflags
957 = check_tyvars dflags clas tys
959 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
961 Just (tycon, arg_tys) <- tcSplitTyConApp_maybe first_ty,
962 not (isSynTyCon tycon), -- ...but not a synonym
963 all tcIsTyVarTy arg_tys, -- Applied to type variables
964 equalLength (varSetElems (tyVarsOfTypes arg_tys)) arg_tys
965 -- This last condition checks that all the type variables are distinct
969 = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg)
974 ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty
975 creturnable_type ty = isFFIImportResultTy dflags ty
977 head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
978 text "where T is not a synonym, and a,b,c are distinct type variables")
980 check_tyvars dflags clas tys
981 -- Check that at least one isn't a type variable
982 -- unless -fallow-undecideable-instances
983 | dopt Opt_AllowUndecidableInstances dflags = returnTc ()
984 | not (all tcIsTyVarTy tys) = returnTc ()
985 | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg)
987 msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")
990 undecidableMsg = ptext SLIT("Use -fallow-undecidable-instances to permit this")
994 instTypeErr pp_ty msg
995 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty,
998 nonBoxedPrimCCallErr clas inst_ty
999 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
1000 4 (pprClassPred clas [inst_ty])