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, TcRhoType, TcTyVarSet,
12 --------------------------------
13 -- Creating new mutable type variables
15 newTyVarTy, -- Kind -> NF_TcM TcType
16 newTyVarTys, -- Int -> Kind -> NF_TcM [TcType]
17 newKindVar, newKindVars, newBoxityVar,
19 --------------------------------
21 tcInstTyVar, tcInstTyVars,
22 tcInstSigVars, tcInstType,
25 --------------------------------
26 -- Checking type validity
27 Rank, UserTypeCtxt(..), checkValidType, pprUserTypeCtxt,
28 SourceTyCtxt(..), checkValidTheta,
29 checkValidInstHead, instTypeErr,
31 --------------------------------
33 unifyTauTy, unifyTauTyList, unifyTauTyLists,
34 unifyFunTy, unifyListTy, unifyTupleTy,
35 unifyKind, unifyKinds, unifyOpenTypeKind,
37 --------------------------------
39 zonkTcTyVar, zonkTcTyVars, zonkTcTyVarsAndFV, zonkTcSigTyVars,
40 zonkTcType, zonkTcTypes, zonkTcClassConstraints, zonkTcThetaType,
41 zonkTcPredType, zonkTcTypeToType, zonkTcTyVarToTyVar, zonkKindEnv,
45 #include "HsVersions.h"
49 import TypeRep ( Type(..), SourceType(..), TyNote(..), -- Friend; can see representation
50 Kind, TauType, ThetaType,
53 import TcType ( tcEqType, tcCmpPred,
54 tcSplitRhoTy, tcSplitPredTy_maybe, tcSplitAppTy_maybe,
55 tcSplitTyConApp_maybe, tcSplitFunTy_maybe, tcSplitForAllTys,
56 tcGetTyVar, tcIsTyVarTy, tcSplitSigmaTy, isUnLiftedType, isIPPred,
58 mkAppTy, mkTyVarTy, mkTyVarTys, mkFunTy, mkTyConApp,
59 tyVarsOfPred, getClassPredTys_maybe,
61 liftedTypeKind, unliftedTypeKind, openTypeKind, defaultKind, superKind,
62 superBoxity, liftedBoxity, hasMoreBoxityInfo, typeKind,
63 tyVarsOfType, tyVarsOfTypes, tidyOpenType, tidyOpenTypes, tidyTyVar,
66 isFFIArgumentTy, isFFIImportResultTy
68 import Subst ( Subst, mkTopTyVarSubst, substTy )
69 import Class ( classArity, className )
70 import TyCon ( TyCon, mkPrimTyCon, isSynTyCon, isUnboxedTupleTyCon,
71 isTupleTyCon, tyConArity, tupleTyConBoxity, tyConName )
72 import PrimRep ( PrimRep(VoidRep) )
73 import Var ( TyVar, varName, tyVarKind, tyVarName, isTyVar, mkTyVar,
74 isMutTyVar, isSigTyVar )
77 import TcMonad -- TcType, amongst others
78 import TysWiredIn ( voidTy, listTyCon, mkListTy, mkTupleTy )
79 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
80 import ForeignCall ( Safety(..) )
81 import FunDeps ( grow )
82 import PprType ( pprPred, pprSourceType, pprTheta, pprClassPred )
83 import Name ( Name, NamedThing(..), setNameUnique, mkSysLocalName,
84 mkLocalName, mkDerivedTyConOcc, isSystemName
87 import BasicTypes ( Boxity, Arity, isBoxed )
88 import CmdLineOpts ( dopt, DynFlag(..) )
89 import Unique ( Uniquable(..) )
90 import SrcLoc ( noSrcLoc )
91 import Util ( nOfThem )
92 import ListSetOps ( removeDups )
97 %************************************************************************
99 \subsection{New type variables}
101 %************************************************************************
104 newTyVar :: Kind -> NF_TcM TcTyVar
106 = tcGetUnique `thenNF_Tc` \ uniq ->
107 tcNewMutTyVar (mkSysLocalName uniq SLIT("t")) kind
109 newTyVarTy :: Kind -> NF_TcM TcType
111 = newTyVar kind `thenNF_Tc` \ tc_tyvar ->
112 returnNF_Tc (TyVarTy tc_tyvar)
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 SLIT("k")) superKind `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 SLIT("bx")) superBoxity `thenNF_Tc` \ kv ->
130 returnNF_Tc (TyVarTy kv)
134 %************************************************************************
136 \subsection{Type instantiation}
138 %************************************************************************
140 I don't understand why this is needed
141 An old comments says "No need for tcSplitForAllTyM because a type
142 variable can't be instantiated to a for-all type"
143 But the same is true of rho types!
146 tcSplitRhoTyM :: TcType -> NF_TcM (TcThetaType, TcType)
150 -- A type variable is never instantiated to a dictionary type,
151 -- so we don't need to do a tcReadVar on the "arg".
152 go syn_t (FunTy arg res) ts = case tcSplitPredTy_maybe arg of
153 Just pair -> go res res (pair:ts)
154 Nothing -> returnNF_Tc (reverse ts, syn_t)
155 go syn_t (NoteTy n t) ts = go syn_t t ts
156 go syn_t (TyVarTy tv) ts = getTcTyVar tv `thenNF_Tc` \ maybe_ty ->
158 Just ty | not (tcIsTyVarTy ty) -> go syn_t ty ts
159 other -> returnNF_Tc (reverse ts, syn_t)
160 go syn_t (UsageTy _ t) ts = go syn_t t ts
161 go syn_t t ts = returnNF_Tc (reverse ts, syn_t)
165 %************************************************************************
167 \subsection{Type instantiation}
169 %************************************************************************
171 Instantiating a bunch of type variables
174 tcInstTyVars :: [TyVar]
175 -> NF_TcM ([TcTyVar], [TcType], Subst)
178 = mapNF_Tc tcInstTyVar tyvars `thenNF_Tc` \ tc_tyvars ->
180 tys = mkTyVarTys tc_tyvars
182 returnNF_Tc (tc_tyvars, tys, mkTopTyVarSubst tyvars tys)
183 -- Since the tyvars are freshly made,
184 -- they cannot possibly be captured by
185 -- any existing for-alls. Hence mkTopTyVarSubst
188 = tcGetUnique `thenNF_Tc` \ uniq ->
190 name = setNameUnique (tyVarName tyvar) uniq
191 -- Note that we don't change the print-name
192 -- This won't confuse the type checker but there's a chance
193 -- that two different tyvars will print the same way
194 -- in an error message. -dppr-debug will show up the difference
195 -- Better watch out for this. If worst comes to worst, just
196 -- use mkSysLocalName.
198 tcNewMutTyVar name (tyVarKind tyvar)
200 tcInstSigVars tyvars -- Very similar to tcInstTyVar
201 = tcGetUniques `thenNF_Tc` \ uniqs ->
202 listTc [ ASSERT( not (kind `eqKind` openTypeKind) ) -- Shouldn't happen
203 tcNewSigTyVar name kind
204 | (tyvar, uniq) <- tyvars `zip` uniqs,
205 let name = setNameUnique (tyVarName tyvar) uniq,
206 let kind = tyVarKind tyvar
210 @tcInstType@ instantiates the outer-level for-alls of a TcType with
211 fresh type variables, splits off the dictionary part, and returns the results.
214 tcInstType :: TcType -> NF_TcM ([TcTyVar], TcThetaType, TcType)
216 = case tcSplitForAllTys ty of
217 ([], rho) -> -- There may be overloading but no type variables;
218 -- (?x :: Int) => Int -> Int
220 (theta, tau) = tcSplitRhoTy rho -- Used to be tcSplitRhoTyM
222 returnNF_Tc ([], theta, tau)
224 (tyvars, rho) -> tcInstTyVars tyvars `thenNF_Tc` \ (tyvars', _, tenv) ->
226 (theta, tau) = tcSplitRhoTy (substTy tenv rho) -- Used to be tcSplitRhoTyM
228 returnNF_Tc (tyvars', theta, tau)
233 %************************************************************************
235 \subsection{Putting and getting mutable type variables}
237 %************************************************************************
240 putTcTyVar :: TcTyVar -> TcType -> NF_TcM TcType
241 getTcTyVar :: TcTyVar -> NF_TcM (Maybe TcType)
248 | not (isMutTyVar tyvar)
249 = pprTrace "putTcTyVar" (ppr tyvar) $
253 = ASSERT( isMutTyVar tyvar )
254 UASSERT2( not (isUTy ty), ppr tyvar <+> ppr ty )
255 tcWriteMutTyVar tyvar (Just ty) `thenNF_Tc_`
259 Getting is more interesting. The easy thing to do is just to read, thus:
262 getTcTyVar tyvar = tcReadMutTyVar tyvar
265 But it's more fun to short out indirections on the way: If this
266 version returns a TyVar, then that TyVar is unbound. If it returns
267 any other type, then there might be bound TyVars embedded inside it.
269 We return Nothing iff the original box was unbound.
273 | not (isMutTyVar tyvar)
274 = pprTrace "getTcTyVar" (ppr tyvar) $
275 returnNF_Tc (Just (mkTyVarTy tyvar))
278 = ASSERT2( isMutTyVar tyvar, ppr tyvar )
279 tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
281 Just ty -> short_out ty `thenNF_Tc` \ ty' ->
282 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
283 returnNF_Tc (Just ty')
285 Nothing -> returnNF_Tc Nothing
287 short_out :: TcType -> NF_TcM TcType
288 short_out ty@(TyVarTy tyvar)
289 | not (isMutTyVar tyvar)
293 = tcReadMutTyVar tyvar `thenNF_Tc` \ maybe_ty ->
295 Just ty' -> short_out ty' `thenNF_Tc` \ ty' ->
296 tcWriteMutTyVar tyvar (Just ty') `thenNF_Tc_`
299 other -> returnNF_Tc ty
301 short_out other_ty = returnNF_Tc other_ty
305 %************************************************************************
307 \subsection{Zonking -- the exernal interfaces}
309 %************************************************************************
311 ----------------- Type variables
314 zonkTcTyVars :: [TcTyVar] -> NF_TcM [TcType]
315 zonkTcTyVars tyvars = mapNF_Tc zonkTcTyVar tyvars
317 zonkTcTyVarsAndFV :: [TcTyVar] -> NF_TcM TcTyVarSet
318 zonkTcTyVarsAndFV tyvars = mapNF_Tc zonkTcTyVar tyvars `thenNF_Tc` \ tys ->
319 returnNF_Tc (tyVarsOfTypes tys)
321 zonkTcTyVar :: TcTyVar -> NF_TcM TcType
322 zonkTcTyVar tyvar = zonkTyVar (\ tv -> returnNF_Tc (TyVarTy tv)) tyvar
324 zonkTcSigTyVars :: [TcTyVar] -> NF_TcM [TcTyVar]
325 -- This guy is to zonk the tyvars we're about to feed into tcSimplify
326 -- Usually this job is done by checkSigTyVars, but in a couple of places
327 -- that is overkill, so we use this simpler chap
328 zonkTcSigTyVars tyvars
329 = zonkTcTyVars tyvars `thenNF_Tc` \ tys ->
330 returnNF_Tc (map (tcGetTyVar "zonkTcSigTyVars") tys)
333 ----------------- Types
336 zonkTcType :: TcType -> NF_TcM TcType
337 zonkTcType ty = zonkType (\ tv -> returnNF_Tc (TyVarTy tv)) ty
339 zonkTcTypes :: [TcType] -> NF_TcM [TcType]
340 zonkTcTypes tys = mapNF_Tc zonkTcType tys
342 zonkTcClassConstraints cts = mapNF_Tc zonk cts
343 where zonk (clas, tys)
344 = zonkTcTypes tys `thenNF_Tc` \ new_tys ->
345 returnNF_Tc (clas, new_tys)
347 zonkTcThetaType :: TcThetaType -> NF_TcM TcThetaType
348 zonkTcThetaType theta = mapNF_Tc zonkTcPredType theta
350 zonkTcPredType :: TcPredType -> NF_TcM TcPredType
351 zonkTcPredType (ClassP c ts) =
352 zonkTcTypes ts `thenNF_Tc` \ new_ts ->
353 returnNF_Tc (ClassP c new_ts)
354 zonkTcPredType (IParam n t) =
355 zonkTcType t `thenNF_Tc` \ new_t ->
356 returnNF_Tc (IParam n new_t)
359 ------------------- These ...ToType, ...ToKind versions
360 are used at the end of type checking
363 zonkKindEnv :: [(Name, TcKind)] -> NF_TcM [(Name, Kind)]
365 = mapNF_Tc zonk_it pairs
367 zonk_it (name, tc_kind) = zonkType zonk_unbound_kind_var tc_kind `thenNF_Tc` \ kind ->
368 returnNF_Tc (name, kind)
370 -- When zonking a kind, we want to
371 -- zonk a *kind* variable to (Type *)
372 -- zonk a *boxity* variable to *
373 zonk_unbound_kind_var kv | tyVarKind kv `eqKind` superKind = putTcTyVar kv liftedTypeKind
374 | tyVarKind kv `eqKind` superBoxity = putTcTyVar kv liftedBoxity
375 | otherwise = pprPanic "zonkKindEnv" (ppr kv)
377 zonkTcTypeToType :: TcType -> NF_TcM Type
378 zonkTcTypeToType ty = zonkType zonk_unbound_tyvar ty
380 -- Zonk a mutable but unbound type variable to
381 -- Void if it has kind Lifted
383 -- We know it's unbound even though we don't carry an environment,
384 -- because at the binding site for a type variable we bind the
385 -- mutable tyvar to a fresh immutable one. So the mutable store
386 -- plays the role of an environment. If we come across a mutable
387 -- type variable that isn't so bound, it must be completely free.
388 zonk_unbound_tyvar tv
389 | kind `eqKind` liftedTypeKind || kind `eqKind` openTypeKind
390 = putTcTyVar tv voidTy -- Just to avoid creating a new tycon in
391 -- this vastly common case
393 = putTcTyVar tv (TyConApp (mk_void_tycon tv kind) [])
397 mk_void_tycon tv kind -- Make a new TyCon with the same kind as the
398 -- type variable tv. Same name too, apart from
399 -- making it start with a colon (sigh)
400 -- I dread to think what will happen if this gets out into an
401 -- interface file. Catastrophe likely. Major sigh.
402 = pprTrace "Urk! Inventing strangely-kinded void TyCon" (ppr tc_name) $
403 mkPrimTyCon tc_name kind 0 [] VoidRep
405 tc_name = mkLocalName (getUnique tv) (mkDerivedTyConOcc (getOccName tv)) noSrcLoc
407 -- zonkTcTyVarToTyVar is applied to the *binding* occurrence
408 -- of a type variable, at the *end* of type checking. It changes
409 -- the *mutable* type variable into an *immutable* one.
411 -- It does this by making an immutable version of tv and binds tv to it.
412 -- Now any bound occurences of the original type variable will get
413 -- zonked to the immutable version.
415 zonkTcTyVarToTyVar :: TcTyVar -> NF_TcM TyVar
416 zonkTcTyVarToTyVar tv
418 -- Make an immutable version, defaulting
419 -- the kind to lifted if necessary
420 immut_tv = mkTyVar (tyVarName tv) (defaultKind (tyVarKind tv))
421 immut_tv_ty = mkTyVarTy immut_tv
423 zap tv = putTcTyVar tv immut_tv_ty
424 -- Bind the mutable version to the immutable one
426 -- If the type variable is mutable, then bind it to immut_tv_ty
427 -- so that all other occurrences of the tyvar will get zapped too
428 zonkTyVar zap tv `thenNF_Tc` \ ty2 ->
430 WARN( not (immut_tv_ty `tcEqType` ty2), ppr tv $$ ppr immut_tv $$ ppr ty2 )
436 %************************************************************************
438 \subsection{Zonking -- the main work-horses: zonkType, zonkTyVar}
440 %* For internal use only! *
442 %************************************************************************
445 -- zonkType is used for Kinds as well
447 -- For unbound, mutable tyvars, zonkType uses the function given to it
448 -- For tyvars bound at a for-all, zonkType zonks them to an immutable
449 -- type variable and zonks the kind too
451 zonkType :: (TcTyVar -> NF_TcM Type) -- What to do with unbound mutable type variables
452 -- see zonkTcType, and zonkTcTypeToType
455 zonkType unbound_var_fn ty
458 go (TyConApp tycon tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
459 returnNF_Tc (TyConApp tycon tys')
461 go (NoteTy (SynNote ty1) ty2) = go ty1 `thenNF_Tc` \ ty1' ->
462 go ty2 `thenNF_Tc` \ ty2' ->
463 returnNF_Tc (NoteTy (SynNote ty1') ty2')
465 go (NoteTy (FTVNote _) ty2) = go ty2 -- Discard free-tyvar annotations
467 go (SourceTy p) = go_pred p `thenNF_Tc` \ p' ->
468 returnNF_Tc (SourceTy p')
470 go (FunTy arg res) = go arg `thenNF_Tc` \ arg' ->
471 go res `thenNF_Tc` \ res' ->
472 returnNF_Tc (FunTy arg' res')
474 go (AppTy fun arg) = go fun `thenNF_Tc` \ fun' ->
475 go arg `thenNF_Tc` \ arg' ->
476 returnNF_Tc (mkAppTy fun' arg')
478 go (UsageTy u ty) = go u `thenNF_Tc` \ u' ->
479 go ty `thenNF_Tc` \ ty' ->
480 returnNF_Tc (UsageTy u' ty')
482 -- The two interesting cases!
483 go (TyVarTy tyvar) = zonkTyVar unbound_var_fn tyvar
485 go (ForAllTy tyvar ty) = zonkTcTyVarToTyVar tyvar `thenNF_Tc` \ tyvar' ->
486 go ty `thenNF_Tc` \ ty' ->
487 returnNF_Tc (ForAllTy tyvar' ty')
489 go_pred (ClassP c tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
490 returnNF_Tc (ClassP c tys')
491 go_pred (NType tc tys) = mapNF_Tc go tys `thenNF_Tc` \ tys' ->
492 returnNF_Tc (NType tc tys')
493 go_pred (IParam n ty) = go ty `thenNF_Tc` \ ty' ->
494 returnNF_Tc (IParam n ty')
496 zonkTyVar :: (TcTyVar -> NF_TcM Type) -- What to do for an unbound mutable variable
497 -> TcTyVar -> NF_TcM TcType
498 zonkTyVar unbound_var_fn tyvar
499 | not (isMutTyVar tyvar) -- Not a mutable tyvar. This can happen when
500 -- zonking a forall type, when the bound type variable
501 -- needn't be mutable
502 = ASSERT( isTyVar tyvar ) -- Should not be any immutable kind vars
503 returnNF_Tc (TyVarTy tyvar)
506 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
508 Nothing -> unbound_var_fn tyvar -- Mutable and unbound
509 Just other_ty -> zonkType unbound_var_fn other_ty -- Bound
514 %************************************************************************
516 \subsection{Checking a user type}
518 %************************************************************************
520 When dealing with a user-written type, we first translate it from an HsType
521 to a Type, performing kind checking, and then check various things that should
522 be true about it. We don't want to perform these checks at the same time
523 as the initial translation because (a) they are unnecessary for interface-file
524 types and (b) when checking a mutually recursive group of type and class decls,
525 we can't "look" at the tycons/classes yet.
527 One thing we check for is 'rank'.
529 Rank 0: monotypes (no foralls)
530 Rank 1: foralls at the front only, Rank 0 inside
531 Rank 2: foralls at the front, Rank 1 on left of fn arrow,
533 basic ::= tyvar | T basic ... basic
535 r2 ::= forall tvs. cxt => r2a
536 r2a ::= r1 -> r2a | basic
537 r1 ::= forall tvs. cxt => r0
538 r0 ::= r0 -> r0 | basic
543 = FunSigCtxt Name -- Function type signature
544 | ExprSigCtxt -- Expression type signature
545 | ConArgCtxt Name -- Data constructor argument
546 | TySynCtxt Name -- RHS of a type synonym decl
547 | GenPatCtxt -- Pattern in generic decl
548 -- f{| a+b |} (Inl x) = ...
549 | PatSigCtxt -- Type sig in pattern
551 | ResSigCtxt -- Result type sig
553 | ForSigCtxt Name -- Foreign inport or export signature
554 | RuleSigCtxt Name -- Signature on a forall'd variable in a RULE
556 -- Notes re TySynCtxt
557 -- We allow type synonyms that aren't types; e.g. type List = []
559 -- If the RHS mentions tyvars that aren't in scope, we'll
560 -- quantify over them:
561 -- e.g. type T = a->a
562 -- will become type T = forall a. a->a
564 -- With gla-exts that's right, but for H98 we should complain.
567 pprUserTypeCtxt (FunSigCtxt n) = ptext SLIT("the type signature for") <+> quotes (ppr n)
568 pprUserTypeCtxt ExprSigCtxt = ptext SLIT("an expression type signature")
569 pprUserTypeCtxt (ConArgCtxt c) = ptext SLIT("the type of constructor") <+> quotes (ppr c)
570 pprUserTypeCtxt (TySynCtxt c) = ptext SLIT("the RHS of a type synonym declaration") <+> quotes (ppr c)
571 pprUserTypeCtxt GenPatCtxt = ptext SLIT("the type pattern of a generic definition")
572 pprUserTypeCtxt PatSigCtxt = ptext SLIT("a pattern type signature")
573 pprUserTypeCtxt ResSigCtxt = ptext SLIT("a result type signature")
574 pprUserTypeCtxt (ForSigCtxt n) = ptext SLIT("the foreign signature for") <+> quotes (ppr n)
575 pprUserTypeCtxt (RuleSigCtxt n) = ptext SLIT("the type signature on") <+> quotes (ppr n)
579 checkValidType :: UserTypeCtxt -> Type -> TcM ()
580 -- Checks that the type is valid for the given context
581 checkValidType ctxt ty
582 = doptsTc Opt_GlasgowExts `thenNF_Tc` \ gla_exts ->
589 FunSigCtxt _ | gla_exts -> 2
591 ConArgCtxt _ | gla_exts -> 2 -- We are given the type of the entire
592 | otherwise -> 1 -- constructor; hence rank 1 is ok
593 TySynCtxt _ | gla_exts -> 1
598 actual_kind = typeKind ty
600 actual_kind_is_lifted = actual_kind `eqKind` liftedTypeKind
602 kind_ok = case ctxt of
603 TySynCtxt _ -> True -- Any kind will do
604 GenPatCtxt -> actual_kind_is_lifted
605 ForSigCtxt _ -> actual_kind_is_lifted
606 other -> isTypeKind actual_kind
608 tcAddErrCtxt (checkTypeCtxt ctxt ty) $
610 -- Check that the thing has kind Type, and is lifted if necessary
611 checkTc kind_ok (kindErr actual_kind) `thenTc_`
613 -- Check the internal validity of the type itself
614 check_poly_type rank ty
617 checkTypeCtxt ctxt ty
618 = vcat [ptext SLIT("In the type:") <+> ppr_ty ty,
619 ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
621 -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
622 -- something strange like {Eq k} -> k -> k, because there is no
623 -- ForAll at the top of the type. Since this is going to the user
624 -- we want it to look like a proper Haskell type even then; hence the hack
626 -- This shows up in the complaint about
628 -- op :: Eq a => a -> a
629 ppr_ty ty | null forall_tvs && not (null theta) = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
632 (forall_tvs, theta, tau) = tcSplitSigmaTy ty
638 check_poly_type :: Rank -> Type -> TcM ()
639 check_poly_type rank ty
641 = check_tau_type 0 False ty
642 | otherwise -- rank > 0
644 (tvs, theta, tau) = tcSplitSigmaTy ty
646 check_valid_theta SigmaCtxt theta `thenTc_`
647 check_tau_type (rank-1) False tau `thenTc_`
648 checkAmbiguity tvs theta tau
650 ----------------------------------------
651 check_arg_type :: Type -> TcM ()
652 -- The sort of type that can instantiate a type variable,
653 -- or be the argument of a type constructor.
654 -- Not an unboxed tuple, not a forall.
655 -- Other unboxed types are very occasionally allowed as type
656 -- arguments depending on the kind of the type constructor
658 -- For example, we want to reject things like:
660 -- instance Ord a => Ord (forall s. T s a)
662 -- g :: T s (forall b.b)
664 -- NB: unboxed tuples can have polymorphic or unboxed args.
665 -- This happens in the workers for functions returning
666 -- product types with polymorphic components.
667 -- But not in user code
669 -- Question: what about nested unboxed tuples?
670 -- Currently rejected.
672 = check_tau_type 0 False ty `thenTc_`
673 checkTc (not (isUnLiftedType ty)) (unliftedArgErr ty)
675 ----------------------------------------
676 check_tau_type :: Rank -> Bool -> Type -> TcM ()
677 -- Rank is allowed rank for function args
678 -- No foralls otherwise
679 -- Bool is True iff unboxed tuple are allowed here
681 check_tau_type rank ubx_tup_ok ty@(UsageTy _ _) = failWithTc (usageTyErr ty)
682 check_tau_type rank ubx_tup_ok ty@(ForAllTy _ _) = failWithTc (forAllTyErr ty)
683 check_tau_type rank ubx_tup_ok (SourceTy sty) = getDOptsTc `thenNF_Tc` \ dflags ->
684 check_source_ty dflags TypeCtxt sty
685 check_tau_type rank ubx_tup_ok (TyVarTy _) = returnTc ()
686 check_tau_type rank ubx_tup_ok ty@(FunTy arg_ty res_ty)
687 = check_poly_type rank arg_ty `thenTc_`
688 check_tau_type rank True res_ty
690 check_tau_type rank ubx_tup_ok (AppTy ty1 ty2)
691 = check_arg_type ty1 `thenTc_` check_arg_type ty2
693 check_tau_type rank ubx_tup_ok (NoteTy note ty)
694 = check_note note `thenTc_` check_tau_type rank ubx_tup_ok ty
696 check_tau_type rank ubx_tup_ok ty@(TyConApp tc tys)
698 = checkTc syn_arity_ok arity_msg `thenTc_`
699 mapTc_ check_arg_type tys
701 | isUnboxedTupleTyCon tc
702 = checkTc ubx_tup_ok ubx_tup_msg `thenTc_`
703 mapTc_ (check_tau_type 0 True) tys -- Args are allowed to be unlifted, or
704 -- more unboxed tuples, so can't use check_arg_ty
707 = mapTc_ check_arg_type tys
710 syn_arity_ok = tc_arity <= n_args
711 -- It's OK to have an *over-applied* type synonym
712 -- data Tree a b = ...
713 -- type Foo a = Tree [a]
714 -- f :: Foo a b -> ...
716 tc_arity = tyConArity tc
718 arity_msg = arityErr "Type synonym" (tyConName tc) tc_arity n_args
719 ubx_tup_msg = ubxArgTyErr ty
721 ----------------------------------------
722 check_note (FTVNote _) = returnTc ()
723 check_note (SynNote ty) = check_tau_type 0 False ty
729 is ambiguous if P contains generic variables
730 (i.e. one of the Vs) that are not mentioned in tau
732 However, we need to take account of functional dependencies
733 when we speak of 'mentioned in tau'. Example:
734 class C a b | a -> b where ...
736 forall x y. (C x y) => x
737 is not ambiguous because x is mentioned and x determines y
739 NOTE: In addition, GHC insists that at least one type variable
740 in each constraint is in V. So we disallow a type like
741 forall a. Eq b => b -> b
742 even in a scope where b is in scope.
743 This is the is_free test below.
745 NB; the ambiguity check is only used for *user* types, not for types
746 coming from inteface files. The latter can legitimately have
747 ambiguous types. Example
749 class S a where s :: a -> (Int,Int)
750 instance S Char where s _ = (1,1)
751 f:: S a => [a] -> Int -> (Int,Int)
752 f (_::[a]) x = (a*x,b)
753 where (a,b) = s (undefined::a)
755 Here the worker for f gets the type
756 fw :: forall a. S a => Int -> (# Int, Int #)
758 If the list of tv_names is empty, we have a monotype, and then we
759 don't need to check for ambiguity either, because the test can't fail
763 checkAmbiguity :: [TyVar] -> ThetaType -> TauType -> TcM ()
764 checkAmbiguity forall_tyvars theta tau
765 = mapTc_ check_pred theta `thenTc_`
768 tau_vars = tyVarsOfType tau
769 extended_tau_vars = grow theta tau_vars
771 is_ambig ct_var = (ct_var `elem` forall_tyvars) &&
772 not (ct_var `elemVarSet` extended_tau_vars)
773 is_free ct_var = not (ct_var `elem` forall_tyvars)
775 check_pred pred = checkTc (not any_ambig) (ambigErr pred) `thenTc_`
776 checkTc (isIPPred pred || not all_free) (freeErr pred)
778 ct_vars = varSetElems (tyVarsOfPred pred)
779 all_free = all is_free ct_vars
780 any_ambig = any is_ambig ct_vars
785 = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
786 nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
787 ptext SLIT("must be reachable from the type after the =>"))]
791 = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
792 ptext SLIT("are already in scope"),
793 nest 4 (ptext SLIT("At least one must be universally quantified here"))
796 forAllTyErr ty = ptext SLIT("Illegal polymorphic type:") <+> ppr_ty ty
797 usageTyErr ty = ptext SLIT("Illegal usage type:") <+> ppr_ty ty
798 unliftedArgErr ty = ptext SLIT("Illegal unlifted type argument:") <+> ppr_ty ty
799 ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as function argument:") <+> ppr_ty ty
800 kindErr kind = ptext SLIT("Expecting an ordinary type, but found a type of kind") <+> ppr kind
803 %************************************************************************
805 \subsection{Checking a theta or source type}
807 %************************************************************************
811 = ClassSCCtxt Name -- Superclasses of clas
812 | SigmaCtxt -- Context of a normal for-all type
813 | DataTyCtxt Name -- Context of a data decl
814 | TypeCtxt -- Source type in an ordinary type
815 | InstThetaCtxt -- Context of an instance decl
816 | InstHeadCtxt -- Head of an instance decl
818 pprSourceTyCtxt (ClassSCCtxt c) = ptext SLIT("the super-classes of class") <+> quotes (ppr c)
819 pprSourceTyCtxt SigmaCtxt = ptext SLIT("the context of a polymorphic type")
820 pprSourceTyCtxt (DataTyCtxt tc) = ptext SLIT("the context of the data type declaration for") <+> quotes (ppr tc)
821 pprSourceTyCtxt InstThetaCtxt = ptext SLIT("the context of an instance declaration")
822 pprSourceTyCtxt InstHeadCtxt = ptext SLIT("the head of an instance declaration")
823 pprSourceTyCtxt TypeCtxt = ptext SLIT("the context of a type")
827 checkValidTheta :: SourceTyCtxt -> ThetaType -> TcM ()
828 checkValidTheta ctxt theta
829 = tcAddErrCtxt (checkThetaCtxt ctxt theta) (check_valid_theta ctxt theta)
831 -------------------------
832 check_valid_theta ctxt []
834 check_valid_theta ctxt theta
835 = getDOptsTc `thenNF_Tc` \ dflags ->
836 warnTc (not (null dups)) (dupPredWarn dups) `thenNF_Tc_`
837 mapTc_ (check_source_ty dflags ctxt) theta
839 (_,dups) = removeDups tcCmpPred theta
841 -------------------------
842 check_source_ty dflags ctxt pred@(ClassP cls tys)
843 = -- Class predicates are valid in all contexts
844 mapTc_ check_arg_type tys `thenTc_`
845 checkTc (arity == n_tys) arity_err `thenTc_`
846 checkTc (all tyvar_head tys || arby_preds_ok) (predTyVarErr pred)
849 class_name = className cls
850 arity = classArity cls
852 arity_err = arityErr "Class" class_name arity n_tys
854 arby_preds_ok = case ctxt of
855 InstHeadCtxt -> True -- We check for instance-head formation
856 -- in checkValidInstHead
857 InstThetaCtxt -> dopt Opt_AllowUndecidableInstances dflags
858 other -> dopt Opt_GlasgowExts dflags
860 check_source_ty dflags SigmaCtxt (IParam name ty) = check_arg_type ty
861 check_source_ty dflags TypeCtxt (NType tc tys) = mapTc_ check_arg_type tys
864 check_source_ty dflags ctxt sty = failWithTc (badSourceTyErr sty)
866 -------------------------
867 tyvar_head ty -- Haskell 98 allows predicates of form
868 | tcIsTyVarTy ty = True -- C (a ty1 .. tyn)
869 | otherwise -- where a is a type variable
870 = case tcSplitAppTy_maybe ty of
871 Just (ty, _) -> tyvar_head ty
876 badSourceTyErr sty = ptext SLIT("Illegal constraint") <+> pprSourceType sty
877 predTyVarErr pred = ptext SLIT("Non-type variables in constraint:") <+> pprPred pred
878 dupPredWarn dups = ptext SLIT("Duplicate constraint(s):") <+> pprWithCommas pprPred (map head dups)
880 checkThetaCtxt ctxt theta
881 = vcat [ptext SLIT("In the context:") <+> pprTheta theta,
882 ptext SLIT("While checking") <+> pprSourceTyCtxt ctxt ]
886 %************************************************************************
888 \subsection{Checking for a decent instance head type}
890 %************************************************************************
892 @checkValidInstHead@ checks the type {\em and} its syntactic constraints:
893 it must normally look like: @instance Foo (Tycon a b c ...) ...@
895 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
896 flag is on, or (2)~the instance is imported (they must have been
897 compiled elsewhere). In these cases, we let them go through anyway.
899 We can also have instances for functions: @instance Foo (a -> b) ...@.
902 checkValidInstHead :: Type -> TcM ()
904 checkValidInstHead ty -- Should be a source type
905 = case tcSplitPredTy_maybe ty of {
906 Nothing -> failWithTc (instTypeErr (ppr ty) empty) ;
909 case getClassPredTys_maybe pred of {
910 Nothing -> failWithTc (instTypeErr (pprPred pred) empty) ;
913 getDOptsTc `thenNF_Tc` \ dflags ->
914 mapTc_ check_arg_type tys `thenTc_`
915 check_inst_head dflags clas tys
918 check_inst_head dflags clas tys
920 -- A user declaration of a CCallable/CReturnable instance
921 -- must be for a "boxed primitive" type.
922 (clas `hasKey` cCallableClassKey
923 && not (ccallable_type first_ty))
924 || (clas `hasKey` cReturnableClassKey
925 && not (creturnable_type first_ty))
926 = failWithTc (nonBoxedPrimCCallErr clas first_ty)
928 -- If GlasgowExts then check at least one isn't a type variable
929 | dopt Opt_GlasgowExts dflags
930 = check_tyvars dflags clas tys
932 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
934 Just (tycon, arg_tys) <- tcSplitTyConApp_maybe first_ty,
935 not (isSynTyCon tycon), -- ...but not a synonym
936 all tcIsTyVarTy arg_tys, -- Applied to type variables
937 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
938 -- This last condition checks that all the type variables are distinct
942 = failWithTc (instTypeErr (pprClassPred clas tys) head_shape_msg)
947 ccallable_type ty = isFFIArgumentTy dflags PlayRisky ty
948 creturnable_type ty = isFFIImportResultTy dflags ty
950 head_shape_msg = parens (text "The instance type must be of form (T a b c)" $$
951 text "where T is not a synonym, and a,b,c are distinct type variables")
953 check_tyvars dflags clas tys
954 -- Check that at least one isn't a type variable
955 -- unless -fallow-undecideable-instances
956 | dopt Opt_AllowUndecidableInstances dflags = returnTc ()
957 | not (all tcIsTyVarTy tys) = returnTc ()
958 | otherwise = failWithTc (instTypeErr (pprClassPred clas tys) msg)
960 msg = parens (ptext SLIT("There must be at least one non-type-variable in the instance head")
961 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction"))
965 instTypeErr pp_ty msg
966 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes pp_ty,
969 nonBoxedPrimCCallErr clas inst_ty
970 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
971 4 (pprClassPred clas [inst_ty])
975 %************************************************************************
977 \subsection{Kind unification}
979 %************************************************************************
982 unifyKind :: TcKind -- Expected
986 = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $
989 unifyKinds :: [TcKind] -> [TcKind] -> TcM ()
990 unifyKinds [] [] = returnTc ()
991 unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_`
993 unifyKinds _ _ = panic "unifyKinds: length mis-match"
997 unifyOpenTypeKind :: TcKind -> TcM ()
998 -- Ensures that the argument kind is of the form (Type bx)
999 -- for some boxity bx
1001 unifyOpenTypeKind ty@(TyVarTy tyvar)
1002 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
1004 Just ty' -> unifyOpenTypeKind ty'
1005 other -> unify_open_kind_help ty
1007 unifyOpenTypeKind ty
1008 | isTypeKind ty = returnTc ()
1009 | otherwise = unify_open_kind_help ty
1011 unify_open_kind_help ty -- Revert to ordinary unification
1012 = newBoxityVar `thenNF_Tc` \ boxity ->
1013 unifyKind ty (mkTyConApp typeCon [boxity])
1017 %************************************************************************
1019 \subsection[Unify-exported]{Exported unification functions}
1021 %************************************************************************
1023 The exported functions are all defined as versions of some
1024 non-exported generic functions.
1026 Unify two @TauType@s. Dead straightforward.
1029 unifyTauTy :: TcTauType -> TcTauType -> TcM ()
1030 unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred
1031 = tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $
1032 uTys ty1 ty1 ty2 ty2
1035 @unifyTauTyList@ unifies corresponding elements of two lists of
1036 @TauType@s. It uses @uTys@ to do the real work. The lists should be
1037 of equal length. We charge down the list explicitly so that we can
1038 complain if their lengths differ.
1041 unifyTauTyLists :: [TcTauType] -> [TcTauType] -> TcM ()
1042 unifyTauTyLists [] [] = returnTc ()
1043 unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_`
1044 unifyTauTyLists tys1 tys2
1045 unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!"
1048 @unifyTauTyList@ takes a single list of @TauType@s and unifies them
1049 all together. It is used, for example, when typechecking explicit
1050 lists, when all the elts should be of the same type.
1053 unifyTauTyList :: [TcTauType] -> TcM ()
1054 unifyTauTyList [] = returnTc ()
1055 unifyTauTyList [ty] = returnTc ()
1056 unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenTc_`
1060 %************************************************************************
1062 \subsection[Unify-uTys]{@uTys@: getting down to business}
1064 %************************************************************************
1066 @uTys@ is the heart of the unifier. Each arg happens twice, because
1067 we want to report errors in terms of synomyms if poss. The first of
1068 the pair is used in error messages only; it is always the same as the
1069 second, except that if the first is a synonym then the second may be a
1070 de-synonym'd version. This way we get better error messages.
1072 We call the first one \tr{ps_ty1}, \tr{ps_ty2} for ``possible synomym''.
1075 uTys :: TcTauType -> TcTauType -- Error reporting ty1 and real ty1
1076 -- ty1 is the *expected* type
1078 -> TcTauType -> TcTauType -- Error reporting ty2 and real ty2
1079 -- ty2 is the *actual* type
1082 -- Always expand synonyms (see notes at end)
1083 -- (this also throws away FTVs)
1084 uTys ps_ty1 (NoteTy n1 ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
1085 uTys ps_ty1 ty1 ps_ty2 (NoteTy n2 ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
1087 -- Ignore usage annotations inside typechecker
1088 uTys ps_ty1 (UsageTy _ ty1) ps_ty2 ty2 = uTys ps_ty1 ty1 ps_ty2 ty2
1089 uTys ps_ty1 ty1 ps_ty2 (UsageTy _ ty2) = uTys ps_ty1 ty1 ps_ty2 ty2
1091 -- Variables; go for uVar
1092 uTys ps_ty1 (TyVarTy tyvar1) ps_ty2 ty2 = uVar False tyvar1 ps_ty2 ty2
1093 uTys ps_ty1 ty1 ps_ty2 (TyVarTy tyvar2) = uVar True tyvar2 ps_ty1 ty1
1094 -- "True" means args swapped
1097 uTys _ (SourceTy (IParam n1 t1)) _ (SourceTy (IParam n2 t2))
1098 | n1 == n2 = uTys t1 t1 t2 t2
1099 uTys _ (SourceTy (ClassP c1 tys1)) _ (SourceTy (ClassP c2 tys2))
1100 | c1 == c2 = unifyTauTyLists tys1 tys2
1101 uTys _ (SourceTy (NType tc1 tys1)) _ (SourceTy (NType tc2 tys2))
1102 | tc1 == tc2 = unifyTauTyLists tys1 tys2
1104 -- Functions; just check the two parts
1105 uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2)
1106 = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2
1108 -- Type constructors must match
1109 uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2)
1110 | con1 == con2 && length tys1 == length tys2
1111 = unifyTauTyLists tys1 tys2
1113 | con1 == openKindCon
1114 -- When we are doing kind checking, we might match a kind '?'
1115 -- against a kind '*' or '#'. Notably, CCallable :: ? -> *, and
1116 -- (CCallable Int) and (CCallable Int#) are both OK
1117 = unifyOpenTypeKind ps_ty2
1119 -- Applications need a bit of care!
1120 -- They can match FunTy and TyConApp, so use splitAppTy_maybe
1121 -- NB: we've already dealt with type variables and Notes,
1122 -- so if one type is an App the other one jolly well better be too
1123 uTys ps_ty1 (AppTy s1 t1) ps_ty2 ty2
1124 = case tcSplitAppTy_maybe ty2 of
1125 Just (s2,t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
1126 Nothing -> unifyMisMatch ps_ty1 ps_ty2
1128 -- Now the same, but the other way round
1129 -- Don't swap the types, because the error messages get worse
1130 uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2)
1131 = case tcSplitAppTy_maybe ty1 of
1132 Just (s1,t1) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2
1133 Nothing -> unifyMisMatch ps_ty1 ps_ty2
1135 -- Not expecting for-alls in unification
1136 -- ... but the error message from the unifyMisMatch more informative
1137 -- than a panic message!
1139 -- Anything else fails
1140 uTys ps_ty1 ty1 ps_ty2 ty2 = unifyMisMatch ps_ty1 ps_ty2
1146 If you are tempted to make a short cut on synonyms, as in this
1150 -- NO uTys (SynTy con1 args1 ty1) (SynTy con2 args2 ty2)
1151 -- NO = if (con1 == con2) then
1152 -- NO -- Good news! Same synonym constructors, so we can shortcut
1153 -- NO -- by unifying their arguments and ignoring their expansions.
1154 -- NO unifyTauTypeLists args1 args2
1156 -- NO -- Never mind. Just expand them and try again
1160 then THINK AGAIN. Here is the whole story, as detected and reported
1161 by Chris Okasaki \tr{<Chris_Okasaki@loch.mess.cs.cmu.edu>}:
1163 Here's a test program that should detect the problem:
1167 x = (1 :: Bogus Char) :: Bogus Bool
1170 The problem with [the attempted shortcut code] is that
1174 is not a sufficient condition to be able to use the shortcut!
1175 You also need to know that the type synonym actually USES all
1176 its arguments. For example, consider the following type synonym
1177 which does not use all its arguments.
1182 If you ever tried unifying, say, \tr{Bogus Char} with \tr{Bogus Bool},
1183 the unifier would blithely try to unify \tr{Char} with \tr{Bool} and
1184 would fail, even though the expanded forms (both \tr{Int}) should
1187 Similarly, unifying \tr{Bogus Char} with \tr{Bogus t} would
1188 unnecessarily bind \tr{t} to \tr{Char}.
1190 ... You could explicitly test for the problem synonyms and mark them
1191 somehow as needing expansion, perhaps also issuing a warning to the
1196 %************************************************************************
1198 \subsection[Unify-uVar]{@uVar@: unifying with a type variable}
1200 %************************************************************************
1202 @uVar@ is called when at least one of the types being unified is a
1203 variable. It does {\em not} assume that the variable is a fixed point
1204 of the substitution; rather, notice that @uVar@ (defined below) nips
1205 back into @uTys@ if it turns out that the variable is already bound.
1208 uVar :: Bool -- False => tyvar is the "expected"
1209 -- True => ty is the "expected" thing
1211 -> TcTauType -> TcTauType -- printing and real versions
1214 uVar swapped tv1 ps_ty2 ty2
1215 = getTcTyVar tv1 `thenNF_Tc` \ maybe_ty1 ->
1217 Just ty1 | swapped -> uTys ps_ty2 ty2 ty1 ty1 -- Swap back
1218 | otherwise -> uTys ty1 ty1 ps_ty2 ty2 -- Same order
1219 other -> uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
1221 -- Expand synonyms; ignore FTVs
1222 uUnboundVar swapped tv1 maybe_ty1 ps_ty2 (NoteTy n2 ty2)
1223 = uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2
1226 -- The both-type-variable case
1227 uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2)
1229 -- Same type variable => no-op
1233 -- Distinct type variables
1234 -- ASSERT maybe_ty1 /= Just
1236 = getTcTyVar tv2 `thenNF_Tc` \ maybe_ty2 ->
1238 Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2'
1240 Nothing | update_tv2
1242 -> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) )
1243 putTcTyVar tv2 (TyVarTy tv1) `thenNF_Tc_`
1247 -> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) )
1248 (putTcTyVar tv1 ps_ty2 `thenNF_Tc_`
1253 update_tv2 = (k2 `eqKind` openTypeKind) || (not (k1 `eqKind` openTypeKind) && nicer_to_update_tv2)
1254 -- Try to get rid of open type variables as soon as poss
1256 nicer_to_update_tv2 = isSigTyVar tv1
1257 -- Don't unify a signature type variable if poss
1258 || isSystemName (varName tv2)
1259 -- Try to update sys-y type variables in preference to sig-y ones
1261 -- Second one isn't a type variable
1262 uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2
1263 = -- Check that the kinds match
1264 checkKinds swapped tv1 non_var_ty2 `thenTc_`
1266 -- Check that tv1 isn't a type-signature type variable
1267 checkTcM (not (isSigTyVar tv1))
1268 (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenTc_`
1270 -- Check that we aren't losing boxity info (shouldn't happen)
1271 warnTc (not (typeKind non_var_ty2 `hasMoreBoxityInfo` tyVarKind tv1))
1272 ((ppr tv1 <+> ppr (tyVarKind tv1)) $$
1273 (ppr non_var_ty2 <+> ppr (typeKind non_var_ty2))) `thenNF_Tc_`
1276 -- Basically we want to update tv1 := ps_ty2
1277 -- because ps_ty2 has type-synonym info, which improves later error messages
1282 -- f :: (A a -> a -> ()) -> ()
1286 -- x = f (\ x p -> p x)
1288 -- In the application (p x), we try to match "t" with "A t". If we go
1289 -- ahead and bind t to A t (= ps_ty2), we'll lead the type checker into
1290 -- an infinite loop later.
1291 -- But we should not reject the program, because A t = ().
1292 -- Rather, we should bind t to () (= non_var_ty2).
1294 -- That's why we have this two-state occurs-check
1295 zonkTcType ps_ty2 `thenNF_Tc` \ ps_ty2' ->
1296 if not (tv1 `elemVarSet` tyVarsOfType ps_ty2') then
1297 putTcTyVar tv1 ps_ty2' `thenNF_Tc_`
1300 zonkTcType non_var_ty2 `thenNF_Tc` \ non_var_ty2' ->
1301 if not (tv1 `elemVarSet` tyVarsOfType non_var_ty2') then
1302 -- This branch rarely succeeds, except in strange cases
1303 -- like that in the example above
1304 putTcTyVar tv1 non_var_ty2' `thenNF_Tc_`
1307 failWithTcM (unifyOccurCheck tv1 ps_ty2')
1310 checkKinds swapped tv1 ty2
1311 -- We're about to unify a type variable tv1 with a non-tyvar-type ty2.
1312 -- We need to check that we don't unify a lifted type variable with an
1313 -- unlifted type: e.g. (id 3#) is illegal
1314 | tk1 `eqKind` liftedTypeKind && tk2 `eqKind` unliftedTypeKind
1315 = tcAddErrCtxtM (unifyKindCtxt swapped tv1 ty2) $
1320 (k1,k2) | swapped = (tk2,tk1)
1321 | otherwise = (tk1,tk2)
1327 %************************************************************************
1329 \subsection[Unify-fun]{@unifyFunTy@}
1331 %************************************************************************
1333 @unifyFunTy@ is used to avoid the fruitless creation of type variables.
1336 unifyFunTy :: TcType -- Fail if ty isn't a function type
1337 -> TcM (TcType, TcType) -- otherwise return arg and result types
1339 unifyFunTy ty@(TyVarTy tyvar)
1340 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
1342 Just ty' -> unifyFunTy ty'
1343 other -> unify_fun_ty_help ty
1346 = case tcSplitFunTy_maybe ty of
1347 Just arg_and_res -> returnTc arg_and_res
1348 Nothing -> unify_fun_ty_help ty
1350 unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification
1351 = newTyVarTy openTypeKind `thenNF_Tc` \ arg ->
1352 newTyVarTy openTypeKind `thenNF_Tc` \ res ->
1353 unifyTauTy ty (mkFunTy arg res) `thenTc_`
1358 unifyListTy :: TcType -- expected list type
1359 -> TcM TcType -- list element type
1361 unifyListTy ty@(TyVarTy tyvar)
1362 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
1364 Just ty' -> unifyListTy ty'
1365 other -> unify_list_ty_help ty
1368 = case tcSplitTyConApp_maybe ty of
1369 Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty
1370 other -> unify_list_ty_help ty
1372 unify_list_ty_help ty -- Revert to ordinary unification
1373 = newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty ->
1374 unifyTauTy ty (mkListTy elt_ty) `thenTc_`
1379 unifyTupleTy :: Boxity -> Arity -> TcType -> TcM [TcType]
1380 unifyTupleTy boxity arity ty@(TyVarTy tyvar)
1381 = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty ->
1383 Just ty' -> unifyTupleTy boxity arity ty'
1384 other -> unify_tuple_ty_help boxity arity ty
1386 unifyTupleTy boxity arity ty
1387 = case tcSplitTyConApp_maybe ty of
1388 Just (tycon, arg_tys)
1389 | isTupleTyCon tycon
1390 && tyConArity tycon == arity
1391 && tupleTyConBoxity tycon == boxity
1393 other -> unify_tuple_ty_help boxity arity ty
1395 unify_tuple_ty_help boxity arity ty
1396 = newTyVarTys arity kind `thenNF_Tc` \ arg_tys ->
1397 unifyTauTy ty (mkTupleTy boxity arity arg_tys) `thenTc_`
1400 kind | isBoxed boxity = liftedTypeKind
1401 | otherwise = openTypeKind
1405 %************************************************************************
1407 \subsection[Unify-context]{Errors and contexts}
1409 %************************************************************************
1415 unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred
1416 = zonkTcType ty1 `thenNF_Tc` \ ty1' ->
1417 zonkTcType ty2 `thenNF_Tc` \ ty2' ->
1418 returnNF_Tc (err ty1' ty2')
1420 err ty1 ty2 = (env1,
1423 text "Expected" <+> text s <> colon <+> ppr tidy_ty1,
1424 text "Inferred" <+> text s <> colon <+> ppr tidy_ty2
1427 (env1, [tidy_ty1,tidy_ty2]) = tidyOpenTypes tidy_env [ty1,ty2]
1429 unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 inferred
1430 -- tv1 is zonked already
1431 = zonkTcType ty2 `thenNF_Tc` \ ty2' ->
1432 returnNF_Tc (err ty2')
1434 err ty2 = (env2, ptext SLIT("When matching types") <+>
1435 sep [quotes pp_expected, ptext SLIT("and"), quotes pp_actual])
1437 (pp_expected, pp_actual) | swapped = (pp2, pp1)
1438 | otherwise = (pp1, pp2)
1439 (env1, tv1') = tidyTyVar tidy_env tv1
1440 (env2, ty2') = tidyOpenType env1 ty2
1444 unifyMisMatch ty1 ty2
1445 = zonkTcType ty1 `thenNF_Tc` \ ty1' ->
1446 zonkTcType ty2 `thenNF_Tc` \ ty2' ->
1448 (env, [tidy_ty1, tidy_ty2]) = tidyOpenTypes emptyTidyEnv [ty1',ty2']
1449 msg = hang (ptext SLIT("Couldn't match"))
1450 4 (sep [quotes (ppr tidy_ty1),
1451 ptext SLIT("against"),
1452 quotes (ppr tidy_ty2)])
1454 failWithTcM (env, msg)
1456 unifyWithSigErr tyvar ty
1457 = (env2, hang (ptext SLIT("Cannot unify the type-signature variable") <+> quotes (ppr tidy_tyvar))
1458 4 (ptext SLIT("with the type") <+> quotes (ppr tidy_ty)))
1460 (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
1461 (env2, tidy_ty) = tidyOpenType env1 ty
1463 unifyOccurCheck tyvar ty
1464 = (env2, hang (ptext SLIT("Occurs check: cannot construct the infinite type:"))
1465 4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty]))
1467 (env1, tidy_tyvar) = tidyTyVar emptyTidyEnv tyvar
1468 (env2, tidy_ty) = tidyOpenType env1 ty