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')
458 -- The two interesting cases!
459 go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar
461 go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenNF_Tc` \ tyvar' ->
462 go ty `thenNF_Tc` \ ty' ->
463 returnNF_Tc (ForAllTy tyvar' ty')
465 go_pred (ClassP c tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
466 returnNF_Tc (ClassP c tys')
467 go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
468 returnNF_Tc (NType tc tys')
469 go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
470 returnNF_Tc (IParam n ty')
472 zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable
473 -> TcTyVar -> NF_TcM TcType
474 zonkTyVar unbound_var_fn tyvar
475 | not (isMutTyVar tyvar) -- Not a mutable tyvar. This can happen when
476 -- zonking a forall type, when the bound type variable
477 -- needn't be mutable
478 = ASSERT( isTyVar tyvar ) -- Should not be any immutable kind vars
479 returnNF_Tc (TyVarTy tyvar)
482 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
484 Nothing -> unbound_var_fn tyvar -- Mutable and unbound
485 Just other_ty -> zonkType unbound_var_fn other_ty -- Bound
490 %************************************************************************
492 \subsection{Checking a user type}
494 %************************************************************************
496 When dealing with a user-written type, we first translate it from an HsType
497 to a Type, performing kind checking, and then check various things that should
498 be true about it. We don't want to perform these checks at the same time
499 as the initial translation because (a) they are unnecessary for interface-file
500 types and (b) when checking a mutually recursive group of type and class decls,
501 we can't "look" at the tycons/classes yet. Also, the checks are are rather
502 diverse, and used to really mess up the other code.
504 One thing we check for is 'rank'.
506 Rank 0: monotypes (no foralls)
507 Rank 1: foralls at the front only, Rank 0 inside
508 Rank 2: foralls at the front, Rank 1 on left of fn arrow,
510 basic ::= tyvar | T basic ... basic
512 r2 ::= forall tvs. cxt => r2a
513 r2a ::= r1 -> r2a | basic
514 r1 ::= forall tvs. cxt => r0
515 r0 ::= r0 -> r0 | basic
517 Another thing is to check that type synonyms are saturated.
518 This might not necessarily show up in kind checking.
520 data T k = MkT (k Int)
526 = FunSigCtxt Name -- Function type signature
527 | ExprSigCtxt -- Expression type signature
528 | ConArgCtxt Name -- Data constructor argument
529 | TySynCtxt Name -- RHS of a type synonym decl
530 | GenPatCtxt -- Pattern in generic decl
531 -- f{| a+b |} (Inl x) = ...
532 | PatSigCtxt -- Type sig in pattern
534 | ResSigCtxt -- Result type sig
536 | ForSigCtxt Name -- Foreign inport or export signature
537 | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE
539 -- Notes re TySynCtxt
540 -- We allow type synonyms that aren't types; e.g. type List = []
542 -- If the RHS mentions tyvars that aren't in scope, we'll
543 -- quantify over them:
544 -- e.g. type T = a->a
545 -- will become type T = forall a. a->a
547 -- With gla-exts that's right, but for H98 we should complain.
550 pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n)
551 pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature")
552 pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c)
553 pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c)
554 pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition")
555 pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature")
556 pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature")
557 pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n)
558 pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n)
562 checkValidType :: UserTypeCtxt -> Type -> TcM ()
563 -- Checks that the type is valid for the given context
564 checkValidType ctxt ty
565 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
567 rank | gla_exts = Arbitrary
569 = case ctxt of -- Haskell 98
573 TySynCtxt _ -> Rank 0
574 ExprSigCtxt -> Rank 1
575 FunSigCtxt _ -> Rank 1
576 ConArgCtxt _ -> Rank 1 -- We are given the type of the entire
577 -- constructor, hence rank 1
578 ForSigCtxt _ -> Rank 1
579 RuleSigCtxt _ -> Rank 1
581 actual_kind = typeKind ty
583 actual_kind_is_lifted = actual_kind `eqKind` liftedTypeKind
585 kind_ok = case ctxt of
586 TySynCtxt _ -> True -- Any kind will do
587 GenPatCtxt -> actual_kind_is_lifted
588 ForSigCtxt _ -> actual_kind_is_lifted
589 other -> isTypeKind actual_kind
591 ubx_tup | not gla_exts = UT_NotOk
592 | otherwise = case ctxt of
595 -- Unboxed tuples ok in function results,
596 -- but for type synonyms we allow them even at
599 tcAddErrCtxt (checkTypeCtxt ctxt ty) $
601 -- Check that the thing has kind Type, and is lifted if necessary
602 checkTc kind_ok (kindErr actual_kind) `thenTc_`
604 -- Check the internal validity of the type itself
605 check_poly_type rank ubx_tup ty
608 checkTypeCtxt ctxt ty
609 = vcat [ptext SLIT("In the type:") <+> ppr_ty ty,
610 ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
612 -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
613 -- something strange like {Eq k} -> k -> k, because there is no
614 -- ForAll at the top of the type. Since this is going to the user
615 -- we want it to look like a proper Haskell type even then; hence the hack
617 -- This shows up in the complaint about
619 -- op :: Eq a => a -> a
620 ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
623 (forall_tvs, theta, tau) = tcSplitSigmaTy ty
628 data Rank = Rank Int | Arbitrary
630 decRank :: Rank -> Rank
631 decRank Arbitrary = Arbitrary
632 decRank (Rank n) = Rank (n-1)
634 ----------------------------------------
635 data UbxTupFlag = UT_Ok | UT_NotOk
636 -- The "Ok" version means "ok if -fglasgow-exts is on"
638 ----------------------------------------
639 check_poly_type :: Rank -> UbxTupFlag -> Type -> TcM ()
640 check_poly_type (Rank 0) ubx_tup ty
641 = check_tau_type (Rank 0) ubx_tup ty
643 check_poly_type rank ubx_tup ty
645 (tvs, theta, tau) = tcSplitSigmaTy ty
647 check_valid_theta SigmaCtxt theta `thenTc_`
648 check_tau_type (decRank rank) ubx_tup tau `thenTc_`
649 checkFreeness tvs theta `thenTc_`
650 checkAmbiguity tvs theta (tyVarsOfType tau)
652 ----------------------------------------
653 check_arg_type :: Type -> TcM ()
654 -- The sort of type that can instantiate a type variable,
655 -- or be the argument of a type constructor.
656 -- Not an unboxed tuple, not a forall.
657 -- Other unboxed types are very occasionally allowed as type
658 -- arguments depending on the kind of the type constructor
660 -- For example, we want to reject things like:
662 -- instance Ord a => Ord (forall s. T s a)
664 -- g :: T s (forall b.b)
666 -- NB: unboxed tuples can have polymorphic or unboxed args.
667 -- This happens in the workers for functions returning
668 -- product types with polymorphic components.
669 -- But not in user code.
670 -- Anyway, they are dealt with by a special case in check_tau_type
673 = check_tau_type (Rank 0) UT_NotOk ty `thenTc_`
674 checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty)
676 ----------------------------------------
677 check_tau_type :: Rank -> UbxTupFlag -> Type -> TcM ()
678 -- Rank is allowed rank for function args
679 -- No foralls otherwise
681 check_tau_type rank ubx_tup ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty)
682 check_tau_type rank ubx_tup (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags ->
683 check_source_ty dflags TypeCtxt sty
684 check_tau_type rank ubx_tup (TyVarTy _) = returnTc ()
685 check_tau_type rank ubx_tup ty@(FunTy arg_ty res_ty)
686 = check_poly_type rank UT_NotOk arg_ty `thenTc_`
687 check_tau_type rank UT_Ok res_ty
689 check_tau_type rank ubx_tup (AppTy ty1 ty2)
690 = check_arg_type ty1 `thenTc_` check_arg_type ty2
692 check_tau_type rank ubx_tup (NoteTy note ty)
693 = check_tau_type rank ubx_tup ty
694 -- Synonym notes are built only when the synonym is
695 -- saturated (see Type.mkSynTy)
696 -- Not checking the 'note' part allows us to instantiate a synonym
697 -- defn with a for-all type, but that seems OK too
699 check_tau_type rank ubx_tup ty@(TyConApp tc tys)
701 = -- NB: Type.mkSynTy builds a TyConApp (not a NoteTy) for an unsaturated
702 -- synonym application, leaving it to checkValidType (i.e. right here
704 checkTc syn_arity_ok arity_msg `thenTc_`
705 mapTc_ check_arg_type tys
707 | isUnboxedTupleTyCon tc
708 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
709 checkTc (ubx_tup_ok gla_exts) ubx_tup_msg `thenTc_`
710 mapTc_ (check_tau_type (Rank 0) UT_Ok) tys
711 -- Args are allowed to be unlifted, or
712 -- more unboxed tuples, so can't use check_arg_ty
715 = mapTc_ check_arg_type tys
718 ubx_tup_ok gla_exts = case ubx_tup of { UT_Ok -> gla_exts; other -> False }
720 syn_arity_ok = tc_arity <= n_args
721 -- It's OK to have an *over-applied* type synonym
722 -- data Tree a b = ...
723 -- type Foo a = Tree [a]
724 -- f :: Foo a b -> ...
726 tc_arity = tyConArity tc
728 arity_msg = arityErr "Type synonym" (tyConName tc) tc_arity n_args
729 ubx_tup_msg = ubxArgTyErr ty
731 ----------------------------------------
732 forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty
733 unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty
734 ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty
735 kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind
741 is ambiguous if P contains generic variables
742 (i.e. one of the Vs) that are not mentioned in tau
744 However, we need to take account of functional dependencies
745 when we speak of 'mentioned in tau'. Example:
746 class C a b | a -> b where ...
748 forall x y. (C x y) => x
749 is not ambiguous because x is mentioned and x determines y
751 NB; the ambiguity check is only used for *user* types, not for types
752 coming from inteface files. The latter can legitimately have
753 ambiguous types. Example
755 class S a where s :: a -> (Int,Int)
756 instance S Char where s _ = (1,1)
757 f:: S a => [a] -> Int -> (Int,Int)
758 f (_::[a]) x = (a*x,b)
759 where (a,b) = s (undefined::a)
761 Here the worker for f gets the type
762 fw :: forall a. S a => Int -> (# Int, Int #)
764 If the list of tv_names is empty, we have a monotype, and then we
765 don't need to check for ambiguity either, because the test can't fail
769 checkAmbiguity :: [TyVar] -> ThetaType -> TyVarSet -> TcM ()
770 checkAmbiguity forall_tyvars theta tau_tyvars
771 = mapTc_ complain (filter is_ambig theta)
773 complain pred = addErrTc (ambigErr pred)
774 extended_tau_vars = grow theta tau_tyvars
775 is_ambig pred = any ambig_var (varSetElems (tyVarsOfPred pred))
777 ambig_var ct_var = (ct_var `elem` forall_tyvars) &&
778 not (ct_var `elemVarSet` extended_tau_vars)
780 is_free ct_var = not (ct_var `elem` forall_tyvars)
783 = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
784 nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
785 ptext SLIT("must be reachable from the type after the '=>'"))]
788 In addition, GHC insists that at least one type variable
789 in each constraint is in V. So we disallow a type like
790 forall a. Eq b => b -> b
791 even in a scope where b is in scope.
794 checkFreeness forall_tyvars theta
795 = mapTc_ complain (filter is_free theta)
797 is_free pred = not (isIPPred pred)
798 && not (any bound_var (varSetElems (tyVarsOfPred pred)))
799 bound_var ct_var = ct_var `elem` forall_tyvars
800 complain pred = addErrTc (freeErr pred)
803 = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
804 ptext SLIT("are already in scope"),
805 nest 4 (ptext SLIT("At least one must be universally quantified here"))
810 %************************************************************************
812 \subsection{Checking a theta or source type}
814 %************************************************************************
818 = ClassSCCtxt Name -- Superclasses of clas
819 | SigmaCtxt -- Context of a normal for-all type
820 | DataTyCtxt Name -- Context of a data decl
821 | TypeCtxt -- Source type in an ordinary type
822 | InstThetaCtxt -- Context of an instance decl
823 | InstHeadCtxt -- Head of an instance decl
825 pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
826 pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type")
827 pprSourceTyCtxt (DataTyCtxt tc) = ptext SLIT("the context of the data type declaration for") <+> quotes (ppr tc)
828 pprSourceTyCtxt InstThetaCtxt = ptext SLIT("the context of an instance declaration")
829 pprSourceTyCtxt InstHeadCtxt = ptext SLIT("the head of an instance declaration")
830 pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type")
834 checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM ()
835 checkValidTheta ctxt theta
836 = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta)
838 -------------------------
839 check_valid_theta ctxt []
841 check_valid_theta ctxt theta
842 = getDOptsTc `thenNF_Tc` \ dflags ->
843 warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_`
844 mapTc_ (check_source_ty dflags ctxt) theta
846 (_,dups) = removeDups tcCmpPred theta
848 -------------------------
849 check_source_ty dflags ctxt pred@(ClassP cls tys)
850 = -- Class predicates are valid in all contexts
851 mapTc_ check_arg_type tys `thenTc_`
852 checkTc (arity == n_tys) arity_err `thenTc_`
853 checkTc (all tyvar_head tys || arby_preds_ok)
854 (predTyVarErr pred $$ how_to_allow)
857 class_name = className cls
858 arity = classArity cls
860 arity_err = arityErr "Class" class_name arity n_tys
862 arby_preds_ok = case ctxt of
863 InstHeadCtxt -> True -- We check for instance-head formation
864 -- in checkValidInstHead
865 InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags
866 other -> dopt Opt_GlasgowExts dflags
868 how_to_allow = case ctxt of
869 InstHeadCtxt -> empty -- Should not happen
870 InstThetaCtxt -> parens undecidableMsg
871 other -> parens (ptext SLIT("Use -fglasgow-exts to permit this"))
873 check_source_ty dflags SigmaCtxt (IParam _ ty) = check_arg_type ty
874 -- Implicit parameters only allows in type
875 -- signatures; not in instance decls, superclasses etc
876 -- The reason for not allowing implicit params in instances is a bit subtle
877 -- If we allowed instance (?x::Int, Eq a) => Foo [a] where ...
878 -- then when we saw (e :: (?x::Int) => t) it would be unclear how to
879 -- discharge all the potential usas of the ?x in e. For example, a
880 -- constraint Foo [Int] might come out of e,and applying the
881 -- instance decl would show up two uses of ?x.
883 check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys
886 check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty)
888 -------------------------
889 tyvar_head ty -- Haskell 98 allows predicates of form
890 | tcIsTyVarTy ty = True -- C (a ty1 .. tyn)
891 | otherwise -- where a is a type variable
892 = case tcSplitAppTy_maybe ty of
893 Just (ty, _) -> tyvar_head ty
898 badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty
899 predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred
900 dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
902 checkThetaCtxt ctxt theta
903 = vcat [ptext SLIT("In the context:") <+> pprTheta theta,
904 ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
908 %************************************************************************
910 \subsection{Checking for a decent instance head type}
912 %************************************************************************
914 @checkValidInstHead@ checks the type {\em and} its syntactic constraints:
915 it must normally look like: @instance Foo (Tycon a b c ...) ...@
917 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
918 flag is on, or (2)~the instance is imported (they must have been
919 compiled elsewhere). In these cases, we let them go through anyway.
921 We can also have instances for functions: @instance Foo (a -> b) ...@.
924 checkValidInstHead :: Type -> TcM (Class, [TcType])
926 checkValidInstHead ty -- Should be a source type
927 = case tcSplitPredTy_maybe ty of {
928 Nothing -> failWithTc (instTypeErr (ppr ty) empty) ;
931 case getClassPredTys_maybe pred of {
932 Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ;
935 getDOptsTc `thenNF_Tc` \ dflags ->
936 mapTc_ check_arg_type tys `thenTc_`
937 check_inst_head dflags clas tys `thenTc_`
941 check_inst_head dflags clas tys
943 -- A user declaration of a CCallable/CReturnable instance
944 -- must be for a "boxed primitive" type.
945 (clas `hasKey` cCallableClassKey
946 && not (ccallable_type first_ty))
947 || (clas `hasKey` cReturnableClassKey
948 && not (creturnable_type first_ty))
949 = failWithTc (nonBoxedPrimCCallErr clas first_ty)
951 -- If GlasgowExts then check at least one isn't a type variable
952 | dopt Opt_GlasgowExts dflags
953 = check_tyvars dflags clas tys
955 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
957 Just (tycon, arg_tys) <- tcSplitTyConApp_maybe first_ty,
958 not (isSynTyCon tycon), -- ...but not a synonym
959 all tcIsTyVarTy arg_tys, -- Applied to type variables
960 equalLength (varSetElems (tyVarsOfTypes arg_tys)) arg_tys
961 -- This last condition checks that all the type variables are distinct
965 = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg)
970 ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty
971 creturnable_type ty = isFFIImportResultTy dflags ty
973 head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
974 text "where T is not a synonym, and a,b,c are distinct type variables")
976 check_tyvars dflags clas tys
977 -- Check that at least one isn't a type variable
978 -- unless -fallow-undecideable-instances
979 | dopt Opt_AllowUndecidableInstances dflags = returnTc ()
980 | not (all tcIsTyVarTy tys) = returnTc ()
981 | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg)
983 msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")
986 undecidableMsg = ptext SLIT("Use -fallow-undecidable-instances to permit this")
990 instTypeErr pp_ty msg
991 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty,
994 nonBoxedPrimCCallErr clas inst_ty
995 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
996 4 (pprClassPred clas [inst_ty])