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 (HsParTy ty) -- Skip parentheses markers
306 kcHsType (HsNumTy _) -- The unit type for generics
307 = returnTc liftedTypeKind
309 kcHsType (HsPredTy pred)
310 = kcHsPred pred `thenTc_`
311 returnTc liftedTypeKind
313 kcHsType ty@(HsAppTy ty1 ty2)
314 = kcHsType ty1 `thenTc` \ tc_kind ->
315 kcHsType ty2 `thenTc` \ arg_kind ->
316 tcAddErrCtxt (appKindCtxt (ppr ty)) $
317 kcAppKind tc_kind arg_kind
319 kcHsType (HsForAllTy (Just tv_names) context ty)
320 = kcHsTyVars tv_names `thenNF_Tc` \ kind_env ->
321 tcExtendKindEnv kind_env $
322 kcHsContext context `thenTc_`
323 kcHsType ty `thenTc_`
324 returnTc liftedTypeKind
326 ---------------------------
327 kcAppKind fun_kind arg_kind
328 = case tcSplitFunTy_maybe fun_kind of
329 Just (arg_kind', res_kind)
330 -> unifyKind arg_kind arg_kind' `thenTc_`
333 Nothing -> newKindVar `thenNF_Tc` \ res_kind ->
334 unifyKind fun_kind (mkArrowKind arg_kind res_kind) `thenTc_`
338 ---------------------------
339 kc_pred :: RenamedHsPred -> TcM TcKind -- Does *not* check for a saturated
340 -- application (reason: used from TcDeriv)
341 kc_pred pred@(HsIParam name ty)
344 kc_pred pred@(HsClassP cls tys)
345 = kcClass cls `thenTc` \ kind ->
346 mapTc kcHsType tys `thenTc` \ arg_kinds ->
347 newKindVar `thenNF_Tc` \ kv ->
348 unifyKind kind (mkArrowKinds arg_kinds kv) `thenTc_`
351 ---------------------------
352 kcHsContext ctxt = mapTc_ kcHsPred ctxt
354 kcHsPred pred -- Checks that the result is of kind liftedType
355 = tcAddErrCtxt (appKindCtxt (ppr pred)) $
356 kc_pred pred `thenTc` \ kind ->
357 unifyKind liftedTypeKind kind `thenTc_`
361 ---------------------------
362 kcTyVar name -- Could be a tyvar or a tycon
363 = tcLookup name `thenTc` \ thing ->
365 AThing kind -> returnTc kind
366 ATyVar tv -> returnTc (tyVarKind tv)
367 AGlobal (ATyCon tc) -> returnTc (tyConKind tc)
368 other -> failWithTc (wrongThingErr "type" thing name)
370 kcClass cls -- Must be a class
371 = tcLookup cls `thenNF_Tc` \ thing ->
373 AThing kind -> returnTc kind
374 AGlobal (AClass cls) -> returnTc (tyConKind (classTyCon cls))
375 other -> failWithTc (wrongThingErr "class" thing cls)
378 %************************************************************************
382 %************************************************************************
384 tc_type, the main work horse
385 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 tc_type is used to typecheck the types in the RHS of data
392 constructors. In the case of recursive data types, that means that
393 the type constructors themselves are (partly) black holes. e.g.
395 data T a = MkT a [T a]
397 While typechecking the [T a] on the RHS, T itself is not yet fully
398 defined. That in turn places restrictions on what you can check in
399 tcHsType; if you poke on too much you get a black hole. I keep
400 forgetting this, hence this warning!
402 So tc_type does no validity-checking. Instead that's all done
403 by TcMType.checkValidType
405 --------------------------
406 *** END OF BIG WARNING ***
407 --------------------------
411 tc_type :: RenamedHsType -> TcM Type
413 tc_type ty@(HsTyVar name)
416 tc_type (HsKindSig ty k)
417 = tc_type ty -- Kind checking done already
419 tc_type (HsListTy ty)
420 = tc_type ty `thenTc` \ tau_ty ->
421 returnTc (mkListTy tau_ty)
423 tc_type (HsPArrTy ty)
424 = tc_type ty `thenTc` \ tau_ty ->
425 returnTc (mkPArrTy tau_ty)
427 tc_type (HsTupleTy (HsTupCon _ boxity arity) tys)
428 = ASSERT( tys `lengthIs` arity )
429 tc_types tys `thenTc` \ tau_tys ->
430 returnTc (mkTupleTy boxity arity tau_tys)
432 tc_type (HsFunTy ty1 ty2)
433 = tc_type ty1 `thenTc` \ tau_ty1 ->
434 tc_type ty2 `thenTc` \ tau_ty2 ->
435 returnTc (mkFunTy tau_ty1 tau_ty2)
437 tc_type (HsOpTy ty1 HsArrow ty2)
438 = tc_type ty1 `thenTc` \ tau_ty1 ->
439 tc_type ty2 `thenTc` \ tau_ty2 ->
440 returnTc (mkFunTy tau_ty1 tau_ty2)
442 tc_type (HsOpTy ty1 (HsTyOp op) ty2)
443 = tc_type ty1 `thenTc` \ tau_ty1 ->
444 tc_type ty2 `thenTc` \ tau_ty2 ->
445 tc_fun_type op [tau_ty1,tau_ty2]
447 tc_type (HsParTy ty) -- Remove the parentheses markers
452 returnTc (mkTyConApp genUnitTyCon [])
454 tc_type (HsAppTy ty1 ty2) = tc_app ty1 [ty2]
456 tc_type (HsPredTy pred)
457 = tc_pred pred `thenTc` \ pred' ->
458 returnTc (mkPredTy pred')
460 tc_type full_ty@(HsForAllTy (Just tv_names) ctxt ty)
462 kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
464 tcHsTyVars tv_names kind_check $ \ tyvars ->
465 mapTc tc_pred ctxt `thenTc` \ theta ->
466 tc_type ty `thenTc` \ tau ->
467 returnTc (mkSigmaTy tyvars theta tau)
469 tc_types arg_tys = mapTc tc_type arg_tys
472 Help functions for type applications
473 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
476 tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
477 tc_app (HsAppTy ty1 ty2) tys
478 = tc_app ty1 (ty2:tys)
481 = tcAddErrCtxt (appKindCtxt pp_app) $
482 tc_types tys `thenTc` \ arg_tys ->
484 HsTyVar fun -> tc_fun_type fun arg_tys
485 other -> tc_type ty `thenTc` \ fun_ty ->
486 returnNF_Tc (mkAppTys fun_ty arg_tys)
488 pp_app = ppr ty <+> sep (map pprParendHsType tys)
490 -- (tc_fun_type ty arg_tys) returns (mkAppTys ty arg_tys)
491 -- But not quite; for synonyms it checks the correct arity, and builds a SynTy
492 -- hence the rather strange functionality.
494 tc_fun_type name arg_tys
495 = tcLookup name `thenTc` \ thing ->
497 ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys)
499 AGlobal (ATyCon tc) -> returnTc (mkGenTyConApp tc arg_tys)
501 other -> failWithTc (wrongThingErr "type constructor" thing name)
508 tcHsPred pred = kc_pred pred `thenTc_` tc_pred pred
509 -- Is happy with a partial application, e.g. (ST s)
512 tc_pred assn@(HsClassP class_name tys)
513 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
514 tc_types tys `thenTc` \ arg_tys ->
515 tcLookupGlobal class_name `thenTc` \ thing ->
517 AClass clas -> returnTc (ClassP clas arg_tys)
518 other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
520 tc_pred assn@(HsIParam name ty)
521 = tcAddErrCtxt (appKindCtxt (ppr assn)) $
522 tc_type ty `thenTc` \ arg_ty ->
523 returnTc (IParam name arg_ty)
528 %************************************************************************
530 \subsection{Type variables, with knot tying!}
532 %************************************************************************
535 mkImmutTyVars :: [(Name,Kind)] -> [TyVar]
536 mkImmutTyVars pairs = [mkTyVar name kind | (name, kind) <- pairs]
538 mkTyClTyVars :: Kind -- Kind of the tycon or class
539 -> [HsTyVarBndr Name]
541 mkTyClTyVars kind tyvar_names
542 = mkImmutTyVars tyvars_w_kinds
544 (tyvars_w_kinds, _) = zipFunTys (hsTyVarNames tyvar_names) kind
548 %************************************************************************
550 \subsection{Signatures}
552 %************************************************************************
554 @tcSigs@ checks the signatures for validity, and returns a list of
555 {\em freshly-instantiated} signatures. That is, the types are already
556 split up, and have fresh type variables installed. All non-type-signature
557 "RenamedSigs" are ignored.
559 The @TcSigInfo@ contains @TcTypes@ because they are unified with
560 the variable's type, and after that checked to see whether they've
566 TcId -- *Polymorphic* binder for this value...
573 TcId -- *Monomorphic* binder for this value
574 -- Does *not* have name = N
577 [Inst] -- Empty if theta is null, or
578 -- (method mono_id) otherwise
580 SrcLoc -- Of the signature
582 instance Outputable TcSigInfo where
583 ppr (TySigInfo id tyvars theta tau _ inst loc) =
584 ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
586 tcSigPolyId :: TcSigInfo -> TcId
587 tcSigPolyId (TySigInfo id _ _ _ _ _ _) = id
589 tcSigMonoId :: TcSigInfo -> TcId
590 tcSigMonoId (TySigInfo _ _ _ _ id _ _) = id
592 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
593 -- Search for a particular signature
594 maybeSig [] name = Nothing
595 maybeSig (sig@(TySigInfo sig_id _ _ _ _ _ _) : sigs) name
596 | name == idName sig_id = Just sig
597 | otherwise = maybeSig sigs name
602 tcTySig :: RenamedSig -> TcM TcSigInfo
604 tcTySig (Sig v ty src_loc)
605 = tcAddSrcLoc src_loc $
606 tcHsSigType (FunSigCtxt v) ty `thenTc` \ sigma_tc_ty ->
607 mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
610 mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo
611 mkTcSig poly_id src_loc
612 = -- Instantiate this type
613 -- It's important to do this even though in the error-free case
614 -- we could just split the sigma_tc_ty (since the tyvars don't
615 -- unified with anything). But in the case of an error, when
616 -- the tyvars *do* get unified with something, we want to carry on
617 -- typechecking the rest of the program with the function bound
618 -- to a pristine type, namely sigma_tc_ty
619 tcInstType SigTv (idType poly_id) `thenNF_Tc` \ (tyvars', theta', tau') ->
621 newMethodWithGivenTy SignatureOrigin
624 theta' tau' `thenNF_Tc` \ inst ->
625 -- We make a Method even if it's not overloaded; no harm
627 returnNF_Tc (TySigInfo poly_id tyvars' theta' tau'
628 (instToId inst) [inst] src_loc)
633 %************************************************************************
635 \subsection{Errors and contexts}
637 %************************************************************************
640 typeKindCtxt :: RenamedHsType -> Message
641 typeKindCtxt ty = sep [ptext SLIT("When checking that"),
642 nest 2 (quotes (ppr ty)),
643 ptext SLIT("is a type")]
645 appKindCtxt :: SDoc -> Message
646 appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
648 wrongThingErr expected thing name
649 = pp_thing thing <+> quotes (ppr name) <+> ptext SLIT("used as a") <+> text expected
651 pp_thing (AGlobal (ATyCon _)) = ptext SLIT("Type constructor")
652 pp_thing (AGlobal (AClass _)) = ptext SLIT("Class")
653 pp_thing (AGlobal (AnId _)) = ptext SLIT("Identifier")
654 pp_thing (ATyVar _) = ptext SLIT("Type variable")
655 pp_thing (ATcId _) = ptext SLIT("Local identifier")
656 pp_thing (AThing _) = ptext SLIT("Utterly bogus")