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, tcSigPolyId, tcSigMonoId
19 #include "HsVersions.h"
21 import HsSyn ( HsType(..), HsTyVarBndr(..), HsTyOp(..),
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, tcInstType,
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,
38 hoistForAllTys, zipFunTys,
39 mkSigmaTy, mkPredTy, mkGenTyConApp, 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, 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 (HsKindSig ty k)
267 = kcHsType ty `thenTc` \ k' ->
268 unifyKind k k' `thenTc_`
271 kcHsType (HsListTy ty)
272 = kcLiftedType ty `thenTc` \ tau_ty ->
273 returnTc liftedTypeKind
275 kcHsType (HsPArrTy ty)
276 = kcLiftedType ty `thenTc` \ tau_ty ->
277 returnTc liftedTypeKind
279 kcHsType (HsTupleTy (HsTupCon _ boxity _) tys)
280 = mapTc kcTypeType tys `thenTc_`
281 returnTc (case boxity of
282 Boxed -> liftedTypeKind
283 Unboxed -> unliftedTypeKind)
285 kcHsType (HsFunTy ty1 ty2)
286 = kcTypeType ty1 `thenTc_`
287 kcTypeType ty2 `thenTc_`
288 returnTc liftedTypeKind
290 kcHsType (HsOpTy ty1 HsArrow ty2)
291 = kcTypeType ty1 `thenTc_`
292 kcTypeType ty2 `thenTc_`
293 returnTc liftedTypeKind
295 kcHsType ty@(HsOpTy ty1 (HsTyOp op) ty2)
296 = kcTyVar op `thenTc` \ op_kind ->
297 kcHsType ty1 `thenTc` \ ty1_kind ->
298 kcHsType ty2 `thenTc` \ ty2_kind ->
299 tcAddErrCtxt (appKindCtxt (ppr ty)) $
300 kcAppKind op_kind ty1_kind `thenTc` \ op_kind' ->
301 kcAppKind op_kind' ty2_kind
303 kcHsType (HsNumTy _) -- The unit type for generics
304 = returnTc liftedTypeKind
306 kcHsType (HsPredTy pred)
307 = kcHsPred pred `thenTc_`
308 returnTc liftedTypeKind
310 kcHsType ty@(HsAppTy ty1 ty2)
311 = kcHsType ty1 `thenTc` \ tc_kind ->
312 kcHsType ty2 `thenTc` \ arg_kind ->
313 tcAddErrCtxt (appKindCtxt (ppr ty)) $
314 kcAppKind tc_kind arg_kind
316 kcHsType (HsForAllTy (Just tv_names) context ty)
317 = kcHsTyVars tv_names `thenNF_Tc` \ kind_env ->
318 tcExtendKindEnv kind_env $
319 kcHsContext context `thenTc_`
320 kcHsType ty `thenTc_`
321 returnTc liftedTypeKind
323 ---------------------------
324 kcAppKind fun_kind arg_kind
325 = case tcSplitFunTy_maybe fun_kind of
326 Just (arg_kind', res_kind)
327 -> unifyKind arg_kind arg_kind' `thenTc_`
330 Nothing -> newKindVar `thenNF_Tc` \ res_kind ->
331 unifyKind fun_kind (mkArrowKind arg_kind res_kind) `thenTc_`
335 ---------------------------
336 kc_pred :: RenamedHsPred -> TcM TcKind -- Does *not* check for a saturated
337 -- application (reason: used from TcDeriv)
338 kc_pred pred@(HsIParam name ty)
341 kc_pred pred@(HsClassP cls tys)
342 = kcClass cls `thenTc` \ kind ->
343 mapTc kcHsType tys `thenTc` \ arg_kinds ->
344 newKindVar `thenNF_Tc` \ kv ->
345 unifyKind kind (mkArrowKinds arg_kinds kv) `thenTc_`
348 ---------------------------
349 kcHsContext ctxt = mapTc_ kcHsPred ctxt
351 kcHsPred pred -- Checks that the result is of kind liftedType
352 = tcAddErrCtxt (appKindCtxt (ppr pred)) $
353 kc_pred pred `thenTc` \ kind ->
354 unifyKind liftedTypeKind kind `thenTc_`
358 ---------------------------
359 kcTyVar name -- Could be a tyvar or a tycon
360 = tcLookup name `thenTc` \ thing ->
362 AThing kind -> returnTc kind
363 ATyVar tv -> returnTc (tyVarKind tv)
364 AGlobal (ATyCon tc) -> returnTc (tyConKind tc)
365 other -> failWithTc (wrongThingErr "type" thing name)
367 kcClass cls -- Must be a class
368 = tcLookup cls `thenNF_Tc` \ thing ->
370 AThing kind -> returnTc kind
371 AGlobal (AClass cls) -> returnTc (tyConKind (classTyCon cls))
372 other -> failWithTc (wrongThingErr "class" thing cls)
375 %************************************************************************
379 %************************************************************************
381 tc_type, the main work horse
382 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
388 tc_type is used to typecheck the types in the RHS of data
389 constructors. In the case of recursive data types, that means that
390 the type constructors themselves are (partly) black holes. e.g.
392 data T a = MkT a [T a]
394 While typechecking the [T a] on the RHS, T itself is not yet fully
395 defined. That in turn places restrictions on what you can check in
396 tcHsType; if you poke on too much you get a black hole. I keep
397 forgetting this, hence this warning!
399 So tc_type does no validity-checking. Instead that's all done
400 by TcMType.checkValidType
402 --------------------------
403 *** END OF BIG WARNING ***
404 --------------------------
408 tc_type :: RenamedHsType -> TcM Type
410 tc_type ty@(HsTyVar name)
413 tc_type (HsKindSig ty k)
414 = tc_type ty -- Kind checking done already
416 tc_type (HsListTy ty)
417 = tc_type ty `thenTc` \ tau_ty ->
418 returnTc (mkListTy tau_ty)
420 tc_type (HsPArrTy ty)
421 = tc_type ty `thenTc` \ tau_ty ->
422 returnTc (mkPArrTy tau_ty)
424 tc_type (HsTupleTy (HsTupCon _ boxity arity) tys)
425 = ASSERT( tys `lengthIs` arity )
426 tc_types tys `thenTc` \ tau_tys ->
427 returnTc (mkTupleTy boxity arity tau_tys)
429 tc_type (HsFunTy ty1 ty2)
430 = tc_type ty1 `thenTc` \ tau_ty1 ->
431 tc_type ty2 `thenTc` \ tau_ty2 ->
432 returnTc (mkFunTy tau_ty1 tau_ty2)
434 tc_type (HsOpTy ty1 HsArrow ty2)
435 = tc_type ty1 `thenTc` \ tau_ty1 ->
436 tc_type ty2 `thenTc` \ tau_ty2 ->
437 returnTc (mkFunTy tau_ty1 tau_ty2)
439 tc_type (HsOpTy ty1 (HsTyOp op) ty2)
440 = tc_type ty1 `thenTc` \ tau_ty1 ->
441 tc_type ty2 `thenTc` \ tau_ty2 ->
442 tc_fun_type op [tau_ty1,tau_ty2]
446 returnTc (mkTyConApp genUnitTyCon [])
448 tc_type (HsAppTy ty1 ty2) = tc_app ty1 [ty2]
450 tc_type (HsPredTy pred)
451 = tc_pred pred `thenTc` \ pred' ->
452 returnTc (mkPredTy pred')
454 tc_type full_ty@(HsForAllTy (Just tv_names) ctxt ty)
456 kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
458 tcHsTyVars tv_names kind_check $ \ tyvars ->
459 mapTc tc_pred ctxt `thenTc` \ theta ->
460 tc_type ty `thenTc` \ tau ->
461 returnTc (mkSigmaTy tyvars theta tau)
463 tc_types arg_tys = mapTc tc_type arg_tys
466 Help functions for type applications
467 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
470 tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
471 tc_app (HsAppTy ty1 ty2) tys
472 = tc_app ty1 (ty2:tys)
475 = tcAddErrCtxt (appKindCtxt pp_app) $
476 tc_types tys `thenTc` \ arg_tys ->
478 HsTyVar fun -> tc_fun_type fun arg_tys
479 other -> tc_type ty `thenTc` \ fun_ty ->
480 returnNF_Tc (mkAppTys fun_ty arg_tys)
482 pp_app = ppr ty <+> sep (map pprParendHsType tys)
484 -- (tc_fun_type ty arg_tys) returns (mkAppTys ty arg_tys)
485 -- But not quite; for synonyms it checks the correct arity, and builds a SynTy
486 -- hence the rather strange functionality.
488 tc_fun_type name arg_tys
489 = tcLookup name `thenTc` \ thing ->
491 ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys)
493 AGlobal (ATyCon tc) -> returnTc (mkGenTyConApp tc arg_tys)
495 other -> failWithTc (wrongThingErr "type constructor" thing name)
502 tcHsPred pred = kc_pred pred `thenTc_` tc_pred pred
503 -- Is happy with a partial application, e.g. (ST s)
506 tc_pred assn@(HsClassP class_name tys)
507 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
508 tc_types tys `thenTc` \ arg_tys ->
509 tcLookupGlobal class_name `thenTc` \ thing ->
511 AClass clas -> returnTc (ClassP clas arg_tys)
512 other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
514 tc_pred assn@(HsIParam name ty)
515 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
516 tc_type ty `thenTc` \ arg_ty ->
517 returnTc (IParam name arg_ty)
522 %************************************************************************
524 \subsection{Type variables, with knot tying!}
526 %************************************************************************
529 mkImmutTyVars :: [(Name,Kind)] -> [TyVar]
530 mkImmutTyVars pairs = [mkTyVar name kind | (name, kind) <- pairs]
532 mkTyClTyVars :: Kind -- Kind of the tycon or class
533 -> [HsTyVarBndr Name]
535 mkTyClTyVars kind tyvar_names
536 = mkImmutTyVars tyvars_w_kinds
538 (tyvars_w_kinds, _) = zipFunTys (hsTyVarNames tyvar_names) kind
542 %************************************************************************
544 \subsection{Signatures}
546 %************************************************************************
548 @tcSigs@ checks the signatures for validity, and returns a list of
549 {\em freshly-instantiated} signatures. That is, the types are already
550 split up, and have fresh type variables installed. All non-type-signature
551 "RenamedSigs" are ignored.
553 The @TcSigInfo@ contains @TcTypes@ because they are unified with
554 the variable's type, and after that checked to see whether they've
560 TcId -- *Polymorphic* binder for this value...
567 TcId -- *Monomorphic* binder for this value
568 -- Does *not* have name = N
571 [Inst] -- Empty if theta is null, or
572 -- (method mono_id) otherwise
574 SrcLoc -- Of the signature
576 instance Outputable TcSigInfo where
577 ppr (TySigInfo id tyvars theta tau _ inst loc) =
578 ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
580 tcSigPolyId :: TcSigInfo -> TcId
581 tcSigPolyId (TySigInfo id _ _ _ _ _ _) = id
583 tcSigMonoId :: TcSigInfo -> TcId
584 tcSigMonoId (TySigInfo _ _ _ _ id _ _) = id
586 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
587 -- Search for a particular signature
588 maybeSig [] name = Nothing
589 maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name
590 | name == idName sig_id = Just sig
591 | otherwise = maybeSig sigs name
596 tcTySig :: RenamedSig -> TcM TcSigInfo
598 tcTySig (Sig v ty src_loc)
599 = tcAddSrcLoc src_loc $
600 tcHsSigType (FunSigCtxt v) ty `thenTc` \ sigma_tc_ty ->
601 mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
604 mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo
605 mkTcSig poly_id src_loc
606 = -- Instantiate this type
607 -- It's important to do this even though in the error-free case
608 -- we could just split the sigma_tc_ty (since the tyvars don't
609 -- unified with anything). But in the case of an error, when
610 -- the tyvars *do* get unified with something, we want to carry on
611 -- typechecking the rest of the program with the function bound
612 -- to a pristine type, namely sigma_tc_ty
613 tcInstType SigTv (idType poly_id) `thenNF_Tc` \ (tyvars', theta', tau') ->
615 newMethodWithGivenTy SignatureOrigin
618 theta' tau' `thenNF_Tc` \ inst ->
619 -- We make a Method even if it's not overloaded; no harm
621 returnNF_Tc (TySigInfo poly_id tyvars' theta' tau'
622 (instToId inst) [inst] src_loc)
627 %************************************************************************
629 \subsection{Errors and contexts}
631 %************************************************************************
634 typeKindCtxt :: RenamedHsType -> Message
635 typeKindCtxt ty = sep [ptext SLIT("When checking that"),
636 nest 2 (quotes (ppr ty)),
637 ptext SLIT("is a type")]
639 appKindCtxt :: SDoc -> Message
640 appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
642 wrongThingErr expected thing name
643 = pp_thing thing <+> quotes (ppr name) <+> ptext SLIT("used as a") <+> text expected
645 pp_thing (AGlobal (ATyCon _)) = ptext SLIT("Type constructor")
646 pp_thing (AGlobal (AClass _)) = ptext SLIT("Class")
647 pp_thing (AGlobal (AnId _)) = ptext SLIT("Identifier")
648 pp_thing (ATyVar _) = ptext SLIT("Type variable")
649 pp_thing (ATcId _) = ptext SLIT("Local identifier")
650 pp_thing (AThing _) = ptext SLIT("Utterly bogus")