2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
7 module TcMonoType ( tcHsSigType, tcHsType, tcIfaceType, tcHsTheta, tcHsPred,
11 kcHsTyVar, kcHsTyVars, mkTyClTyVars,
12 kcHsType, kcHsSigType, kcHsSigTypes,
13 kcHsLiftedSigType, kcHsContext,
14 tcAddScopedTyVars, tcHsTyVars, mkImmutTyVars,
16 TcSigInfo(..), tcTySig, mkTcSig, maybeSig
19 #include "HsVersions.h"
21 import HsSyn ( HsType(..), HsTyVarBndr(..),
22 Sig(..), HsPred(..), pprParendHsType, HsTupCon(..), hsTyVarNames )
23 import RnHsSyn ( RenamedHsType, RenamedHsPred, RenamedContext, RenamedSig, extractHsTyVars )
24 import TcHsSyn ( TcId )
27 import TcEnv ( tcExtendTyVarEnv, tcLookup, tcLookupGlobal,
29 TyThing(..), TcTyThing(..), tcExtendKindEnv
31 import TcMType ( newKindVar, zonkKindEnv, tcInstSigType,
32 checkValidType, UserTypeCtxt(..), pprUserTypeCtxt
34 import TcUnify ( unifyKind, unifyOpenTypeKind )
35 import TcType ( Type, Kind, SourceType(..), ThetaType, TyVarDetails(..),
36 TcTyVar, TcKind, TcThetaType, TcTauType,
37 mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy,
38 hoistForAllTys, zipFunTys,
39 mkSigmaTy, mkPredTy, mkTyConApp, mkAppTys,
40 liftedTypeKind, unliftedTypeKind, mkArrowKind,
41 mkArrowKinds, tcSplitFunTy_maybe
43 import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId )
45 import Id ( mkLocalId, idName, idType )
46 import Var ( TyVar, mkTyVar, tyVarKind )
47 import ErrUtils ( Message )
48 import TyCon ( TyCon, isSynTyCon, tyConKind )
49 import Class ( classTyCon )
52 import TysWiredIn ( mkListTy, mkPArrTy, mkTupleTy, genUnitTyCon )
53 import BasicTypes ( Boxity(..) )
54 import SrcLoc ( SrcLoc )
55 import Util ( lengthIs )
61 %************************************************************************
63 \subsection{Checking types}
65 %************************************************************************
67 Generally speaking we now type-check types in three phases
69 1. Kind check the HsType [kcHsType]
70 2. Convert from HsType to Type, and hoist the foralls [tcHsType]
71 3. Check the validity of the resulting type [checkValidType]
73 Often these steps are done one after the othe (tcHsSigType).
74 But in mutually recursive groups of type and class decls we do
75 1 kind-check the whole group
76 2 build TyCons/Classes in a knot-tied wa
77 3 check the validity of types in the now-unknotted TyCons/Classes
80 tcHsSigType :: UserTypeCtxt -> RenamedHsType -> TcM Type
81 -- Do kind checking, and hoist for-alls to the top
82 tcHsSigType ctxt ty = tcAddErrCtxt (checkTypeCtxt ctxt ty) (
83 kcTypeType ty `thenTc_`
86 checkValidType ctxt ty' `thenTc_`
90 = vcat [ptext SLIT("In the type:") <+> ppr ty,
91 ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
93 tcHsType :: RenamedHsType -> TcM Type
94 -- Don't do kind checking, nor validity checking,
95 -- but do hoist for-alls to the top
96 -- This is used in type and class decls, where kinding is
97 -- done in advance, and validity checking is done later
98 -- [Validity checking done later because of knot-tying issues.]
99 tcHsType ty = tc_type ty `thenTc` \ ty' ->
100 returnTc (hoistForAllTys ty')
102 tcHsTheta :: RenamedContext -> TcM ThetaType
103 -- Used when we are expecting a ClassContext (i.e. no implicit params)
104 -- Does not do validity checking, like tcHsType
105 tcHsTheta hs_theta = mapTc tc_pred hs_theta
107 -- In interface files the type is already kinded,
108 -- and we definitely don't want to hoist for-alls.
109 -- Otherwise we'll change
110 -- dmfail :: forall m:(*->*) Monad m => forall a:* => String -> m a
112 -- dmfail :: forall m:(*->*) a:* Monad m => String -> m a
113 -- which definitely isn't right!
114 tcIfaceType ty = tc_type ty
118 %************************************************************************
120 \subsection{Kind checking}
122 %************************************************************************
126 When we come across the binding site for some type variables, we
127 proceed in two stages
129 1. Figure out what kind each tyvar has
131 2. Create suitably-kinded tyvars,
133 and typecheck the body
135 To do step 1, we proceed thus:
137 1a. Bind each type variable to a kind variable
138 1b. Apply the kind checker
139 1c. Zonk the resulting kinds
141 The kind checker is passed to tcHsTyVars as an argument.
143 For example, when we find
144 (forall a m. m a -> m a)
145 we bind a,m to kind varibles and kind-check (m a -> m a). This
146 makes a get kind *, and m get kind *->*. Now we typecheck (m a -> m a)
147 in an environment that binds a and m suitably.
149 The kind checker passed to tcHsTyVars needs to look at enough to
150 establish the kind of the tyvar:
151 * For a group of type and class decls, it's just the group, not
152 the rest of the program
153 * For a tyvar bound in a pattern type signature, its the types
154 mentioned in the other type signatures in that bunch of patterns
155 * For a tyvar bound in a RULE, it's the type signatures on other
156 universally quantified variables in the rule
158 Note that this may occasionally give surprising results. For example:
160 data T a b = MkT (a b)
162 Here we deduce a::*->*, b::*.
163 But equally valid would be
164 a::(*->*)-> *, b::*->*
167 -- tcHsTyVars is used for type variables in type signatures
168 -- e.g. forall a. a->a
169 -- They are immutable, because they scope only over the signature
170 -- They may or may not be explicitly-kinded
171 tcHsTyVars :: [HsTyVarBndr Name]
172 -> TcM a -- The kind checker
173 -> ([TyVar] -> TcM b)
176 tcHsTyVars [] kind_check thing_inside = thing_inside []
177 -- A useful short cut for a common case!
179 tcHsTyVars tv_names kind_check thing_inside
180 = kcHsTyVars tv_names `thenNF_Tc` \ tv_names_w_kinds ->
181 tcExtendKindEnv tv_names_w_kinds kind_check `thenTc_`
182 zonkKindEnv tv_names_w_kinds `thenNF_Tc` \ tvs_w_kinds ->
184 tyvars = mkImmutTyVars tvs_w_kinds
186 tcExtendTyVarEnv tyvars (thing_inside tyvars)
190 tcAddScopedTyVars :: [RenamedHsType] -> TcM a -> TcM a
191 -- tcAddScopedTyVars is used for scoped type variables
192 -- added by pattern type signatures
193 -- e.g. \ (x::a) (y::a) -> x+y
194 -- They never have explicit kinds (because this is source-code only)
195 -- They are mutable (because they can get bound to a more specific type)
197 -- Find the not-already-in-scope signature type variables,
198 -- kind-check them, and bring them into scope
200 -- We no longer specify that these type variables must be univerally
201 -- quantified (lots of email on the subject). If you want to put that
202 -- back in, you need to
203 -- a) Do a checkSigTyVars after thing_inside
204 -- b) More insidiously, don't pass in expected_ty, else
205 -- we unify with it too early and checkSigTyVars barfs
206 -- Instead you have to pass in a fresh ty var, and unify
207 -- it with expected_ty afterwards
208 tcAddScopedTyVars [] thing_inside
209 = thing_inside -- Quick get-out for the empty case
211 tcAddScopedTyVars sig_tys thing_inside
212 = tcGetEnv `thenNF_Tc` \ env ->
214 all_sig_tvs = foldr (unionNameSets . extractHsTyVars) emptyNameSet sig_tys
215 sig_tvs = filter not_in_scope (nameSetToList all_sig_tvs)
216 not_in_scope tv = not (tcInLocalScope env tv)
218 mapNF_Tc newNamedKindVar sig_tvs `thenTc` \ kind_env ->
219 tcExtendKindEnv kind_env (kcHsSigTypes sig_tys) `thenTc_`
220 zonkKindEnv kind_env `thenNF_Tc` \ tvs_w_kinds ->
221 listTc [ tcNewMutTyVar name kind PatSigTv
222 | (name, kind) <- tvs_w_kinds] `thenNF_Tc` \ tyvars ->
223 tcExtendTyVarEnv tyvars thing_inside
228 kcHsTyVar :: HsTyVarBndr name -> NF_TcM (name, TcKind)
229 kcHsTyVars :: [HsTyVarBndr name] -> NF_TcM [(name, TcKind)]
231 kcHsTyVar (UserTyVar name) = newNamedKindVar name
232 kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (name, kind)
234 kcHsTyVars tvs = mapNF_Tc kcHsTyVar tvs
236 newNamedKindVar name = newKindVar `thenNF_Tc` \ kind ->
237 returnNF_Tc (name, kind)
239 ---------------------------
240 kcLiftedType :: RenamedHsType -> TcM ()
241 -- The type ty must be a *lifted* *type*
243 = kcHsType ty `thenTc` \ kind ->
244 tcAddErrCtxt (typeKindCtxt ty) $
245 unifyKind liftedTypeKind kind
247 ---------------------------
248 kcTypeType :: RenamedHsType -> TcM ()
249 -- The type ty must be a *type*, but it can be lifted or unlifted.
251 = kcHsType ty `thenTc` \ kind ->
252 tcAddErrCtxt (typeKindCtxt ty) $
253 unifyOpenTypeKind kind
255 ---------------------------
256 kcHsSigType, kcHsLiftedSigType :: RenamedHsType -> TcM ()
257 -- Used for type signatures
258 kcHsSigType = kcTypeType
259 kcHsSigTypes tys = mapTc_ kcHsSigType tys
260 kcHsLiftedSigType = kcLiftedType
262 ---------------------------
263 kcHsType :: RenamedHsType -> TcM TcKind
264 kcHsType (HsTyVar name) = kcTyVar name
266 kcHsType (HsListTy ty)
267 = kcLiftedType ty `thenTc` \ tau_ty ->
268 returnTc liftedTypeKind
270 kcHsType (HsPArrTy ty)
271 = kcLiftedType ty `thenTc` \ tau_ty ->
272 returnTc liftedTypeKind
274 kcHsType (HsTupleTy (HsTupCon _ boxity _) tys)
275 = mapTc kcTypeType tys `thenTc_`
276 returnTc (case boxity of
277 Boxed -> liftedTypeKind
278 Unboxed -> unliftedTypeKind)
280 kcHsType (HsFunTy ty1 ty2)
281 = kcTypeType ty1 `thenTc_`
282 kcTypeType ty2 `thenTc_`
283 returnTc liftedTypeKind
285 kcHsType (HsNumTy _) -- The unit type for generics
286 = returnTc liftedTypeKind
288 kcHsType ty@(HsOpTy ty1 op ty2)
289 = kcTyVar op `thenTc` \ op_kind ->
290 kcHsType ty1 `thenTc` \ ty1_kind ->
291 kcHsType ty2 `thenTc` \ ty2_kind ->
292 tcAddErrCtxt (appKindCtxt (ppr ty)) $
293 kcAppKind op_kind ty1_kind `thenTc` \ op_kind' ->
294 kcAppKind op_kind' ty2_kind
296 kcHsType (HsPredTy pred)
297 = kcHsPred pred `thenTc_`
298 returnTc liftedTypeKind
300 kcHsType ty@(HsAppTy ty1 ty2)
301 = kcHsType ty1 `thenTc` \ tc_kind ->
302 kcHsType ty2 `thenTc` \ arg_kind ->
303 tcAddErrCtxt (appKindCtxt (ppr ty)) $
304 kcAppKind tc_kind arg_kind
306 kcHsType (HsForAllTy (Just tv_names) context ty)
307 = kcHsTyVars tv_names `thenNF_Tc` \ kind_env ->
308 tcExtendKindEnv kind_env $
309 kcHsContext context `thenTc_`
310 kcHsType ty `thenTc_`
311 returnTc liftedTypeKind
313 ---------------------------
314 kcAppKind fun_kind arg_kind
315 = case tcSplitFunTy_maybe fun_kind of
316 Just (arg_kind', res_kind)
317 -> unifyKind arg_kind arg_kind' `thenTc_`
320 Nothing -> newKindVar `thenNF_Tc` \ res_kind ->
321 unifyKind fun_kind (mkArrowKind arg_kind res_kind) `thenTc_`
325 ---------------------------
326 kc_pred :: RenamedHsPred -> TcM TcKind -- Does *not* check for a saturated
327 -- application (reason: used from TcDeriv)
328 kc_pred pred@(HsIParam name ty)
331 kc_pred pred@(HsClassP cls tys)
332 = kcClass cls `thenTc` \ kind ->
333 mapTc kcHsType tys `thenTc` \ arg_kinds ->
334 newKindVar `thenNF_Tc` \ kv ->
335 unifyKind kind (mkArrowKinds arg_kinds kv) `thenTc_`
338 ---------------------------
339 kcHsContext ctxt = mapTc_ kcHsPred ctxt
341 kcHsPred pred -- Checks that the result is of kind liftedType
342 = tcAddErrCtxt (appKindCtxt (ppr pred)) $
343 kc_pred pred `thenTc` \ kind ->
344 unifyKind liftedTypeKind kind `thenTc_`
348 ---------------------------
349 kcTyVar name -- Could be a tyvar or a tycon
350 = tcLookup name `thenTc` \ thing ->
352 AThing kind -> returnTc kind
353 ATyVar tv -> returnTc (tyVarKind tv)
354 AGlobal (ATyCon tc) -> returnTc (tyConKind tc)
355 other -> failWithTc (wrongThingErr "type" thing name)
357 kcClass cls -- Must be a class
358 = tcLookup cls `thenNF_Tc` \ thing ->
360 AThing kind -> returnTc kind
361 AGlobal (AClass cls) -> returnTc (tyConKind (classTyCon cls))
362 other -> failWithTc (wrongThingErr "class" thing cls)
365 %************************************************************************
369 %************************************************************************
371 tc_type, the main work horse
372 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
378 tc_type is used to typecheck the types in the RHS of data
379 constructors. In the case of recursive data types, that means that
380 the type constructors themselves are (partly) black holes. e.g.
382 data T a = MkT a [T a]
384 While typechecking the [T a] on the RHS, T itself is not yet fully
385 defined. That in turn places restrictions on what you can check in
386 tcHsType; if you poke on too much you get a black hole. I keep
387 forgetting this, hence this warning!
389 So tc_type does no validity-checking. Instead that's all done
390 by TcMType.checkValidType
392 --------------------------
393 *** END OF BIG WARNING ***
394 --------------------------
398 tc_type :: RenamedHsType -> TcM Type
400 tc_type ty@(HsTyVar name)
403 tc_type (HsListTy ty)
404 = tc_type ty `thenTc` \ tau_ty ->
405 returnTc (mkListTy tau_ty)
407 tc_type (HsPArrTy ty)
408 = tc_type ty `thenTc` \ tau_ty ->
409 returnTc (mkPArrTy tau_ty)
411 tc_type (HsTupleTy (HsTupCon _ boxity arity) tys)
412 = ASSERT( tys `lengthIs` arity )
413 tc_types tys `thenTc` \ tau_tys ->
414 returnTc (mkTupleTy boxity arity tau_tys)
416 tc_type (HsFunTy ty1 ty2)
417 = tc_type ty1 `thenTc` \ tau_ty1 ->
418 tc_type ty2 `thenTc` \ tau_ty2 ->
419 returnTc (mkFunTy tau_ty1 tau_ty2)
423 returnTc (mkTyConApp genUnitTyCon [])
425 tc_type (HsOpTy ty1 op ty2)
426 = tc_type ty1 `thenTc` \ tau_ty1 ->
427 tc_type ty2 `thenTc` \ tau_ty2 ->
428 tc_fun_type op [tau_ty1,tau_ty2]
430 tc_type (HsAppTy ty1 ty2) = tc_app ty1 [ty2]
432 tc_type (HsPredTy pred)
433 = tc_pred pred `thenTc` \ pred' ->
434 returnTc (mkPredTy pred')
436 tc_type full_ty@(HsForAllTy (Just tv_names) ctxt ty)
438 kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
440 tcHsTyVars tv_names kind_check $ \ tyvars ->
441 mapTc tc_pred ctxt `thenTc` \ theta ->
442 tc_type ty `thenTc` \ tau ->
443 returnTc (mkSigmaTy tyvars theta tau)
445 tc_types arg_tys = mapTc tc_type arg_tys
448 Help functions for type applications
449 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
452 tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
453 tc_app (HsAppTy ty1 ty2) tys
454 = tc_app ty1 (ty2:tys)
457 = tcAddErrCtxt (appKindCtxt pp_app) $
458 tc_types tys `thenTc` \ arg_tys ->
460 HsTyVar fun -> tc_fun_type fun arg_tys
461 other -> tc_type ty `thenTc` \ fun_ty ->
462 returnNF_Tc (mkAppTys fun_ty arg_tys)
464 pp_app = ppr ty <+> sep (map pprParendHsType tys)
466 -- (tc_fun_type ty arg_tys) returns (mkAppTys ty arg_tys)
467 -- But not quite; for synonyms it checks the correct arity, and builds a SynTy
468 -- hence the rather strange functionality.
470 tc_fun_type name arg_tys
471 = tcLookup name `thenTc` \ thing ->
473 ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys)
476 | isSynTyCon tc -> returnTc (mkSynTy tc arg_tys)
477 | otherwise -> returnTc (mkTyConApp tc arg_tys)
479 other -> failWithTc (wrongThingErr "type constructor" thing name)
486 tcHsPred pred = kc_pred pred `thenTc_` tc_pred pred
487 -- Is happy with a partial application, e.g. (ST s)
490 tc_pred assn@(HsClassP class_name tys)
491 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
492 tc_types tys `thenTc` \ arg_tys ->
493 tcLookupGlobal class_name `thenTc` \ thing ->
495 AClass clas -> returnTc (ClassP clas arg_tys)
496 other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
498 tc_pred assn@(HsIParam name ty)
499 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
500 tc_type ty `thenTc` \ arg_ty ->
501 returnTc (IParam name arg_ty)
506 %************************************************************************
508 \subsection{Type variables, with knot tying!}
510 %************************************************************************
513 mkImmutTyVars :: [(Name,Kind)] -> [TyVar]
514 mkImmutTyVars pairs = [mkTyVar name kind | (name, kind) <- pairs]
516 mkTyClTyVars :: Kind -- Kind of the tycon or class
517 -> [HsTyVarBndr Name]
519 mkTyClTyVars kind tyvar_names
520 = mkImmutTyVars tyvars_w_kinds
522 (tyvars_w_kinds, _) = zipFunTys (hsTyVarNames tyvar_names) kind
526 %************************************************************************
528 \subsection{Signatures}
530 %************************************************************************
532 @tcSigs@ checks the signatures for validity, and returns a list of
533 {\em freshly-instantiated} signatures. That is, the types are already
534 split up, and have fresh type variables installed. All non-type-signature
535 "RenamedSigs" are ignored.
537 The @TcSigInfo@ contains @TcTypes@ because they are unified with
538 the variable's type, and after that checked to see whether they've
544 Name -- N, the Name in corresponding binding
546 TcId -- *Polymorphic* binder for this value...
553 TcId -- *Monomorphic* binder for this value
554 -- Does *not* have name = N
557 [Inst] -- Empty if theta is null, or
558 -- (method mono_id) otherwise
560 SrcLoc -- Of the signature
562 instance Outputable TcSigInfo where
563 ppr (TySigInfo nm id tyvars theta tau _ inst loc) =
564 ppr nm <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
566 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
567 -- Search for a particular signature
568 maybeSig [] name = Nothing
569 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name
570 | name == sig_name = Just sig
571 | otherwise = maybeSig sigs name
576 tcTySig :: RenamedSig -> TcM TcSigInfo
578 tcTySig (Sig v ty src_loc)
579 = tcAddSrcLoc src_loc $
580 tcHsSigType (FunSigCtxt v) ty `thenTc` \ sigma_tc_ty ->
581 mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
584 mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo
585 mkTcSig poly_id src_loc
586 = -- Instantiate this type
587 -- It's important to do this even though in the error-free case
588 -- we could just split the sigma_tc_ty (since the tyvars don't
589 -- unified with anything). But in the case of an error, when
590 -- the tyvars *do* get unified with something, we want to carry on
591 -- typechecking the rest of the program with the function bound
592 -- to a pristine type, namely sigma_tc_ty
593 tcInstSigType SigTv (idType poly_id) `thenNF_Tc` \ (tyvars', theta', tau') ->
595 newMethodWithGivenTy SignatureOrigin
598 theta' tau' `thenNF_Tc` \ inst ->
599 -- We make a Method even if it's not overloaded; no harm
601 returnNF_Tc (TySigInfo (idName poly_id) poly_id tyvars' theta' tau'
602 (instToId inst) [inst] src_loc)
607 %************************************************************************
609 \subsection{Errors and contexts}
611 %************************************************************************
614 typeKindCtxt :: RenamedHsType -> Message
615 typeKindCtxt ty = sep [ptext SLIT("When checking that"),
616 nest 2 (quotes (ppr ty)),
617 ptext SLIT("is a type")]
619 appKindCtxt :: SDoc -> Message
620 appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
622 wrongThingErr expected thing name
623 = pp_thing thing <+> quotes (ppr name) <+> ptext SLIT("used as a") <+> text expected
625 pp_thing (AGlobal (ATyCon _)) = ptext SLIT("Type constructor")
626 pp_thing (AGlobal (AClass _)) = ptext SLIT("Class")
627 pp_thing (AGlobal (AnId _)) = ptext SLIT("Identifier")
628 pp_thing (ATyVar _) = ptext SLIT("Type variable")
629 pp_thing (ATcId _) = ptext SLIT("Local identifier")
630 pp_thing (AThing _) = ptext SLIT("Utterly bogus")