2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
9 tcHsSigType, tcHsDeriv,
10 tcHsInstHead, tcHsQuantifiedType,
14 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
15 kcCheckHsType, kcHsContext, kcHsType,
17 -- Typechecking kinded types
18 tcHsKindedContext, tcHsKindedType, tcHsBangType,
19 tcTyVarBndrs, dsHsType, tcLHsConResTy,
22 -- Pattern type signatures
23 tcHsPatSigType, tcPatSig
26 #include "HsVersions.h"
36 import {- Kind parts of -} Type
56 ----------------------------
58 ----------------------------
60 Generally speaking we now type-check types in three phases
62 1. kcHsType: kind check the HsType
63 *includes* performing any TH type splices;
64 so it returns a translated, and kind-annotated, type
66 2. dsHsType: convert from HsType to Type:
68 expand type synonyms [mkGenTyApps]
69 hoist the foralls [tcHsType]
71 3. checkValidType: check the validity of the resulting type
73 Often these steps are done one after the other (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 way
77 3 check the validity of types in the now-unknotted TyCons/Classes
79 For example, when we find
80 (forall a m. m a -> m a)
81 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
82 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
83 an environment that binds a and m suitably.
85 The kind checker passed to tcHsTyVars needs to look at enough to
86 establish the kind of the tyvar:
87 * For a group of type and class decls, it's just the group, not
88 the rest of the program
89 * For a tyvar bound in a pattern type signature, its the types
90 mentioned in the other type signatures in that bunch of patterns
91 * For a tyvar bound in a RULE, it's the type signatures on other
92 universally quantified variables in the rule
94 Note that this may occasionally give surprising results. For example:
96 data T a b = MkT (a b)
98 Here we deduce a::*->*, b::*
99 But equally valid would be a::(*->*)-> *, b::*->*
104 Some of the validity check could in principle be done by the kind checker,
107 - During desugaring, we normalise by expanding type synonyms. Only
108 after this step can we check things like type-synonym saturation
109 e.g. type T k = k Int
111 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
112 and then S is saturated. This is a GHC extension.
114 - Similarly, also a GHC extension, we look through synonyms before complaining
115 about the form of a class or instance declaration
117 - Ambiguity checks involve functional dependencies, and it's easier to wait
118 until knots have been resolved before poking into them
120 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
121 finished building the loop. So to keep things simple, we postpone most validity
122 checking until step (3).
126 During step (1) we might fault in a TyCon defined in another module, and it might
127 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
128 knot around type declarations with ARecThing, so that the fault-in code can get
129 the TyCon being defined.
132 %************************************************************************
134 \subsection{Checking types}
136 %************************************************************************
139 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
140 -- Do kind checking, and hoist for-alls to the top
141 -- NB: it's important that the foralls that come from the top-level
142 -- HsForAllTy in hs_ty occur *first* in the returned type.
143 -- See Note [Scoped] with TcSigInfo
144 tcHsSigType ctxt hs_ty
145 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
146 do { kinded_ty <- kcTypeType hs_ty
147 ; ty <- tcHsKindedType kinded_ty
148 ; checkValidType ctxt ty
151 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Type)
152 -- Typecheck an instance head. We can't use
153 -- tcHsSigType, because it's not a valid user type.
155 = do { kinded_ty <- kcHsSigType hs_ty
156 ; poly_ty <- tcHsKindedType kinded_ty
157 ; return (tcSplitSigmaTy poly_ty) }
159 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
160 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
161 -- except that we want to keep the tvs separate
162 tcHsQuantifiedType tv_names hs_ty
163 = kcHsTyVars tv_names $ \ tv_names' ->
164 do { kc_ty <- kcHsSigType hs_ty
165 ; tcTyVarBndrs tv_names' $ \ tvs ->
166 do { ty <- dsHsType kc_ty
167 ; return (tvs, ty) } }
169 -- Used for the deriving(...) items
170 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
171 tcHsDeriv = tc_hs_deriv []
173 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
174 -> TcM ([TyVar], Class, [Type])
175 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
176 = kcHsTyVars tv_names $ \ tv_names' ->
177 do { cls_kind <- kcClass cls_name
178 ; (tys, _res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
179 ; tcTyVarBndrs tv_names' $ \ tyvars ->
180 do { arg_tys <- dsHsTypes tys
181 ; cls <- tcLookupClass cls_name
182 ; return (tyvars, cls, arg_tys) }}
184 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
185 = -- Funny newtype deriving form
187 -- where C has arity 2. Hence can't use regular functions
188 tc_hs_deriv (tv_names1 ++ tv_names2) ty
191 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
194 These functions are used during knot-tying in
195 type and class declarations, when we have to
196 separate kind-checking, desugaring, and validity checking
199 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
200 -- Used for type signatures
201 kcHsSigType ty = kcTypeType ty
202 kcHsLiftedSigType ty = kcLiftedType ty
204 tcHsKindedType :: LHsType Name -> TcM Type
205 -- Don't do kind checking, nor validity checking.
206 -- This is used in type and class decls, where kinding is
207 -- done in advance, and validity checking is done later
208 -- [Validity checking done later because of knot-tying issues.]
209 tcHsKindedType hs_ty = dsHsType hs_ty
211 tcHsBangType :: LHsType Name -> TcM Type
212 -- Permit a bang, but discard it
213 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
214 tcHsBangType ty = tcHsKindedType ty
216 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
217 -- Used when we are expecting a ClassContext (i.e. no implicit params)
218 -- Does not do validity checking, like tcHsKindedType
219 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
223 %************************************************************************
225 The main kind checker: kcHsType
227 %************************************************************************
229 First a couple of simple wrappers for kcHsType
232 ---------------------------
233 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
234 -- The type ty must be a *lifted* *type*
235 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
237 ---------------------------
238 kcTypeType :: LHsType Name -> TcM (LHsType Name)
239 -- The type ty must be a *type*, but it can be lifted or
240 -- unlifted or an unboxed tuple.
241 kcTypeType ty = kcCheckHsType ty openTypeKind
243 ---------------------------
244 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
245 -- Check that the type has the specified kind
246 -- Be sure to use checkExpectedKind, rather than simply unifying
247 -- with OpenTypeKind, because it gives better error messages
248 kcCheckHsType (L span ty) exp_kind
250 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
251 -- Add the context round the inner check only
252 -- because checkExpectedKind already mentions
253 -- 'ty' by name in any error message
255 ; checkExpectedKind (strip ty) act_kind exp_kind
256 ; return (L span ty') }
258 -- Wrap a context around only if we want to show that contexts.
259 add_ctxt (HsPredTy _) thing = thing
260 -- Omit invisble ones and ones user's won't grok (HsPred p).
261 add_ctxt (HsForAllTy _ _ (L _ []) _) thing = thing
262 -- Omit wrapping if the theta-part is empty
263 -- Reason: the recursive call to kcLiftedType, in the ForAllTy
264 -- case of kc_hs_type, will do the wrapping instead
265 -- and we don't want to duplicate
266 add_ctxt other_ty thing = addErrCtxt (typeCtxt other_ty) thing
268 -- We infer the kind of the type, and then complain if it's
269 -- not right. But we don't want to complain about
270 -- (ty) or !(ty) or forall a. ty
271 -- when the real difficulty is with the 'ty' part.
272 strip (HsParTy (L _ ty)) = strip ty
273 strip (HsBangTy _ (L _ ty)) = strip ty
274 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
278 Here comes the main function
281 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
282 kcHsType ty = wrapLocFstM kc_hs_type ty
283 -- kcHsType *returns* the kind of the type, rather than taking an expected
284 -- kind as argument as tcExpr does.
286 -- (a) the kind of (->) is
287 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
288 -- so we'd need to generate huge numbers of bx variables.
289 -- (b) kinds are so simple that the error messages are fine
291 -- The translated type has explicitly-kinded type-variable binders
293 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
294 kc_hs_type (HsParTy ty) = do
295 (ty', kind) <- kcHsType ty
296 return (HsParTy ty', kind)
298 kc_hs_type (HsTyVar name) = do
300 return (HsTyVar name, kind)
302 kc_hs_type (HsListTy ty) = do
303 ty' <- kcLiftedType ty
304 return (HsListTy ty', liftedTypeKind)
306 kc_hs_type (HsPArrTy ty) = do
307 ty' <- kcLiftedType ty
308 return (HsPArrTy ty', liftedTypeKind)
310 kc_hs_type (HsNumTy n)
311 = return (HsNumTy n, liftedTypeKind)
313 kc_hs_type (HsKindSig ty k) = do
314 ty' <- kcCheckHsType ty k
315 return (HsKindSig ty' k, k)
317 kc_hs_type (HsTupleTy Boxed tys) = do
318 tys' <- mapM kcLiftedType tys
319 return (HsTupleTy Boxed tys', liftedTypeKind)
321 kc_hs_type (HsTupleTy Unboxed tys) = do
322 tys' <- mapM kcTypeType tys
323 return (HsTupleTy Unboxed tys', ubxTupleKind)
325 kc_hs_type (HsFunTy ty1 ty2) = do
326 ty1' <- kcCheckHsType ty1 argTypeKind
327 ty2' <- kcTypeType ty2
328 return (HsFunTy ty1' ty2', liftedTypeKind)
330 kc_hs_type (HsOpTy ty1 op ty2) = do
331 op_kind <- addLocM kcTyVar op
332 ([ty1',ty2'], res_kind) <- kcApps op_kind (ppr op) [ty1,ty2]
333 return (HsOpTy ty1' op ty2', res_kind)
335 kc_hs_type (HsAppTy ty1 ty2) = do
336 (fun_ty', fun_kind) <- kcHsType fun_ty
337 ((arg_ty':arg_tys'), res_kind) <- kcApps fun_kind (ppr fun_ty) arg_tys
338 return (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
340 (fun_ty, arg_tys) = split ty1 [ty2]
341 split (L _ (HsAppTy f a)) as = split f (a:as)
343 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
344 -- the application; they are
347 kc_hs_type (HsPredTy (HsEqualP _ _))
350 kc_hs_type (HsPredTy pred) = do
351 pred' <- kcHsPred pred
352 return (HsPredTy pred', liftedTypeKind)
354 kc_hs_type (HsForAllTy exp tv_names context ty)
355 = kcHsTyVars tv_names $ \ tv_names' ->
356 do { ctxt' <- kcHsContext context
357 ; ty' <- kcLiftedType ty
358 -- The body of a forall is usually a type, but in principle
359 -- there's no reason to prohibit *unlifted* types.
360 -- In fact, GHC can itself construct a function with an
361 -- unboxed tuple inside a for-all (via CPR analyis; see
362 -- typecheck/should_compile/tc170)
364 -- Still, that's only for internal interfaces, which aren't
365 -- kind-checked, so we only allow liftedTypeKind here
367 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
369 kc_hs_type (HsBangTy b ty) = do
370 (ty', kind) <- kcHsType ty
371 return (HsBangTy b ty', kind)
373 kc_hs_type ty@(HsSpliceTy _)
374 = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
376 -- remove the doc nodes here, no need to worry about the location since
377 -- its the same for a doc node and it's child type node
378 kc_hs_type (HsDocTy ty _)
379 = kc_hs_type (unLoc ty)
381 ---------------------------
382 kcApps :: TcKind -- Function kind
384 -> [LHsType Name] -- Arg types
385 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
386 kcApps fun_kind ppr_fun args = do
387 (arg_kinds, res_kind) <- split_fk fun_kind (length args)
388 args' <- zipWithM kc_arg args arg_kinds
389 return (args', res_kind)
391 split_fk fk 0 = return ([], fk)
392 split_fk fk n = do mb_fk <- unifyFunKind fk
394 Nothing -> failWithTc too_many_args
395 Just (ak,fk') -> do (aks, rk) <- split_fk fk' (n-1)
398 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
400 too_many_args = ptext (sLit "Kind error:") <+> quotes ppr_fun <+>
401 ptext (sLit "is applied to too many type arguments")
403 ---------------------------
404 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
405 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
407 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
408 kcHsLPred = wrapLocM kcHsPred
410 kcHsPred :: HsPred Name -> TcM (HsPred Name)
411 kcHsPred pred = do -- Checks that the result is of kind liftedType
412 (pred', kind) <- kc_pred pred
413 checkExpectedKind pred kind liftedTypeKind
416 ---------------------------
417 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
418 -- Does *not* check for a saturated
419 -- application (reason: used from TcDeriv)
420 kc_pred (HsIParam name ty)
421 = do { (ty', kind) <- kcHsType ty
422 ; return (HsIParam name ty', kind)
424 kc_pred (HsClassP cls tys)
425 = do { kind <- kcClass cls
426 ; (tys', res_kind) <- kcApps kind (ppr cls) tys
427 ; return (HsClassP cls tys', res_kind)
429 kc_pred (HsEqualP ty1 ty2)
430 = do { (ty1', kind1) <- kcHsType ty1
431 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
432 ; (ty2', kind2) <- kcHsType ty2
433 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
434 ; checkExpectedKind ty2 kind2 kind1
435 ; return (HsEqualP ty1' ty2', liftedTypeKind)
438 ---------------------------
439 kcTyVar :: Name -> TcM TcKind
440 kcTyVar name = do -- Could be a tyvar or a tycon
441 traceTc (text "lk1" <+> ppr name)
442 thing <- tcLookup name
443 traceTc (text "lk2" <+> ppr name <+> ppr thing)
445 ATyVar _ ty -> return (typeKind ty)
446 AThing kind -> return kind
447 AGlobal (ATyCon tc) -> return (tyConKind tc)
448 _ -> wrongThingErr "type" thing name
450 kcClass :: Name -> TcM TcKind
451 kcClass cls = do -- Must be a class
452 thing <- tcLookup cls
454 AThing kind -> return kind
455 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
456 _ -> wrongThingErr "class" thing cls
460 %************************************************************************
464 %************************************************************************
468 * Transforms from HsType to Type
471 It cannot fail, and does no validity checking, except for
472 structural matters, such as
473 (a) spurious ! annotations.
474 (b) a class used as a type
477 dsHsType :: LHsType Name -> TcM Type
478 -- All HsTyVarBndrs in the intput type are kind-annotated
479 dsHsType ty = ds_type (unLoc ty)
481 ds_type :: HsType Name -> TcM Type
482 ds_type ty@(HsTyVar _)
485 ds_type (HsParTy ty) -- Remove the parentheses markers
488 ds_type ty@(HsBangTy _ _) -- No bangs should be here
489 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
491 ds_type (HsKindSig ty _)
492 = dsHsType ty -- Kind checking done already
494 ds_type (HsListTy ty) = do
495 tau_ty <- dsHsType ty
496 checkWiredInTyCon listTyCon
497 return (mkListTy tau_ty)
499 ds_type (HsPArrTy ty) = do
500 tau_ty <- dsHsType ty
501 checkWiredInTyCon parrTyCon
502 return (mkPArrTy tau_ty)
504 ds_type (HsTupleTy boxity tys) = do
505 tau_tys <- dsHsTypes tys
506 checkWiredInTyCon tycon
507 return (mkTyConApp tycon tau_tys)
509 tycon = tupleTyCon boxity (length tys)
511 ds_type (HsFunTy ty1 ty2) = do
512 tau_ty1 <- dsHsType ty1
513 tau_ty2 <- dsHsType ty2
514 return (mkFunTy tau_ty1 tau_ty2)
516 ds_type (HsOpTy ty1 (L span op) ty2) = do
517 tau_ty1 <- dsHsType ty1
518 tau_ty2 <- dsHsType ty2
519 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
523 tc <- tcLookupTyCon genUnitTyConName
524 return (mkTyConApp tc [])
526 ds_type ty@(HsAppTy _ _)
529 ds_type (HsPredTy pred) = do
530 pred' <- dsHsPred pred
531 return (mkPredTy pred')
533 ds_type (HsForAllTy _ tv_names ctxt ty)
534 = tcTyVarBndrs tv_names $ \ tyvars -> do
535 theta <- mapM dsHsLPred (unLoc ctxt)
537 return (mkSigmaTy tyvars theta tau)
539 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
541 ds_type (HsDocTy ty _) -- Remove the doc comment
544 dsHsTypes :: [LHsType Name] -> TcM [Type]
545 dsHsTypes arg_tys = mapM dsHsType arg_tys
548 Help functions for type applications
549 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
552 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
553 ds_app (HsAppTy ty1 ty2) tys
554 = ds_app (unLoc ty1) (ty2:tys)
557 arg_tys <- dsHsTypes tys
559 HsTyVar fun -> ds_var_app fun arg_tys
560 _ -> do fun_ty <- ds_type ty
561 return (mkAppTys fun_ty arg_tys)
563 ds_var_app :: Name -> [Type] -> TcM Type
564 ds_var_app name arg_tys = do
565 thing <- tcLookup name
567 ATyVar _ ty -> return (mkAppTys ty arg_tys)
568 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
569 _ -> wrongThingErr "type" thing name
577 dsHsLPred :: LHsPred Name -> TcM PredType
578 dsHsLPred pred = dsHsPred (unLoc pred)
580 dsHsPred :: HsPred Name -> TcM PredType
581 dsHsPred (HsClassP class_name tys)
582 = do { arg_tys <- dsHsTypes tys
583 ; clas <- tcLookupClass class_name
584 ; return (ClassP clas arg_tys)
586 dsHsPred (HsEqualP ty1 ty2)
587 = do { arg_ty1 <- dsHsType ty1
588 ; arg_ty2 <- dsHsType ty2
589 ; return (EqPred arg_ty1 arg_ty2)
591 dsHsPred (HsIParam name ty)
592 = do { arg_ty <- dsHsType ty
593 ; return (IParam name arg_ty)
597 GADT constructor signatures
600 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
601 tcLHsConResTy (L span res_ty)
603 case get_args res_ty [] of
604 (HsTyVar tc_name, args)
605 -> do { args' <- mapM dsHsType args
606 ; thing <- tcLookup tc_name
608 AGlobal (ATyCon tc) -> return (tc, args')
609 _ -> failWithTc (badGadtDecl res_ty) }
610 _ -> failWithTc (badGadtDecl res_ty)
612 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
613 -- because that causes a black hole, and for good reason. Building
614 -- the type means expanding type synonyms, and we can't do that
615 -- inside the "knot". So we have to work by steam.
616 get_args (HsAppTy (L _ fun) arg) args = get_args fun (arg:args)
617 get_args (HsParTy (L _ ty)) args = get_args ty args
618 get_args (HsOpTy ty1 (L _ tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
619 get_args ty args = (ty, args)
621 badGadtDecl :: HsType Name -> SDoc
623 = hang (ptext (sLit "Malformed constructor result type:"))
626 typeCtxt :: HsType Name -> SDoc
627 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
630 %************************************************************************
632 Type-variable binders
634 %************************************************************************
638 kcHsTyVars :: [LHsTyVarBndr Name]
639 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
640 -- They scope over the thing inside
642 kcHsTyVars tvs thing_inside = do
643 bndrs <- mapM (wrapLocM kcHsTyVar) tvs
644 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
646 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
647 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
648 kcHsTyVar (UserTyVar name) = KindedTyVar name <$> newKindVar
649 kcHsTyVar (KindedTyVar name kind) = return (KindedTyVar name kind)
652 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
653 -> ([TyVar] -> TcM r)
655 -- Used when type-checking types/classes/type-decls
656 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
657 tcTyVarBndrs bndrs thing_inside = do
658 tyvars <- mapM (zonk . unLoc) bndrs
659 tcExtendTyVarEnv tyvars (thing_inside tyvars)
661 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
662 ; return (mkTyVar name kind') }
663 zonk (UserTyVar name) = WARN( True, ptext (sLit "Un-kinded tyvar") <+> ppr name )
664 return (mkTyVar name liftedTypeKind)
666 -----------------------------------
667 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
668 -- GADT decls can have a (perhaps partial) kind signature
669 -- e.g. data T :: * -> * -> * where ...
670 -- This function makes up suitable (kinded) type variables for
671 -- the argument kinds, and checks that the result kind is indeed *.
672 -- We use it also to make up argument type variables for for data instances.
673 tcDataKindSig Nothing = return []
674 tcDataKindSig (Just kind)
675 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
676 ; span <- getSrcSpanM
677 ; us <- newUniqueSupply
678 ; let uniqs = uniqsFromSupply us
679 ; return [ mk_tv span uniq str kind
680 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
682 (arg_kinds, res_kind) = splitKindFunTys kind
683 mk_tv loc uniq str kind = mkTyVar name kind
685 name = mkInternalName uniq occ loc
686 occ = mkOccName tvName str
688 names :: [String] -- a,b,c...aa,ab,ac etc
689 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
691 badKindSig :: Kind -> SDoc
693 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
698 %************************************************************************
700 Scoped type variables
702 %************************************************************************
705 tcAddScopedTyVars is used for scoped type variables added by pattern
707 e.g. \ ((x::a), (y::a)) -> x+y
708 They never have explicit kinds (because this is source-code only)
709 They are mutable (because they can get bound to a more specific type).
711 Usually we kind-infer and expand type splices, and then
712 tupecheck/desugar the type. That doesn't work well for scoped type
713 variables, because they scope left-right in patterns. (e.g. in the
714 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
716 The current not-very-good plan is to
717 * find all the types in the patterns
718 * find their free tyvars
720 * bring the kinded type vars into scope
721 * BUT throw away the kind-checked type
722 (we'll kind-check it again when we type-check the pattern)
724 This is bad because throwing away the kind checked type throws away
725 its splices. But too bad for now. [July 03]
728 We no longer specify that these type variables must be univerally
729 quantified (lots of email on the subject). If you want to put that
731 a) Do a checkSigTyVars after thing_inside
732 b) More insidiously, don't pass in expected_ty, else
733 we unify with it too early and checkSigTyVars barfs
734 Instead you have to pass in a fresh ty var, and unify
735 it with expected_ty afterwards
738 tcHsPatSigType :: UserTypeCtxt
739 -> LHsType Name -- The type signature
740 -> TcM ([TyVar], -- Newly in-scope type variables
741 Type) -- The signature
742 -- Used for type-checking type signatures in
743 -- (a) patterns e.g f (x::Int) = e
744 -- (b) result signatures e.g. g x :: Int = e
745 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
747 tcHsPatSigType ctxt hs_ty
748 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
749 do { -- Find the type variables that are mentioned in the type
750 -- but not already in scope. These are the ones that
751 -- should be bound by the pattern signature
752 in_scope <- getInLocalScope
753 ; let span = getLoc hs_ty
754 sig_tvs = [ L span (UserTyVar n)
755 | n <- nameSetToList (extractHsTyVars hs_ty),
758 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
759 ; checkValidType ctxt sig_ty
760 ; return (tyvars, sig_ty)
763 tcPatSig :: UserTypeCtxt
766 -> TcM (TcType, -- The type to use for "inside" the signature
767 [(Name, TcType)], -- The new bit of type environment, binding
768 -- the scoped type variables
769 CoercionI) -- Coercion due to unification with actual ty
770 tcPatSig ctxt sig res_ty
771 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
773 ; if null sig_tvs then do {
774 -- The type signature binds no type variables,
775 -- and hence is rigid, so use it to zap the res_ty
776 coi <- boxyUnify sig_ty res_ty
777 ; return (sig_ty, [], coi)
780 -- Type signature binds at least one scoped type variable
782 -- A pattern binding cannot bind scoped type variables
783 -- The renamer fails with a name-out-of-scope error
784 -- if a pattern binding tries to bind a type variable,
785 -- So we just have an ASSERT here
786 ; let in_pat_bind = case ctxt of
787 BindPatSigCtxt -> True
789 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
791 -- Check that pat_ty is rigid
792 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
794 -- Now match the pattern signature against res_ty
795 -- For convenience, and uniform-looking error messages
796 -- we do the matching by allocating meta type variables,
797 -- unifying, and reading out the results.
798 -- This is a strictly local operation.
799 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
800 ; coi <- boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty)
802 ; sig_tv_tys <- mapM readFilledBox box_tvs
804 -- Check that each is bound to a distinct type variable,
805 -- and one that is not already in scope
806 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
807 ; binds_in_scope <- getScopedTyVarBinds
808 ; check binds_in_scope tv_binds
811 ; return (res_ty, tv_binds, coi)
814 check _ [] = return ()
815 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
816 ; check ((n,ty):in_scope) rest }
818 check_one in_scope n ty
819 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
820 -- Must bind to a type variable
822 ; checkTc (null dups) (dupInScope n (head dups) ty)
823 -- Must not bind to the same type variable
824 -- as some other in-scope type variable
828 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
832 %************************************************************************
834 Scoped type variables
836 %************************************************************************
839 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
840 pprHsSigCtxt ctxt hs_ty = vcat [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
841 nest 2 (pp_sig ctxt) ]
843 pp_sig (FunSigCtxt n) = pp_n_colon n
844 pp_sig (ConArgCtxt n) = pp_n_colon n
845 pp_sig (ForSigCtxt n) = pp_n_colon n
846 pp_sig _ = ppr (unLoc hs_ty)
848 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
850 wobblyPatSig :: [Var] -> SDoc
852 = hang (ptext (sLit "A pattern type signature cannot bind scoped type variables")
853 <+> pprQuotedList sig_tvs)
854 2 (ptext (sLit "unless the pattern has a rigid type context"))
856 scopedNonVar :: Name -> Type -> SDoc
858 = vcat [sep [ptext (sLit "The scoped type variable") <+> quotes (ppr n),
859 nest 2 (ptext (sLit "is bound to the type") <+> quotes (ppr ty))],
860 nest 2 (ptext (sLit "You can only bind scoped type variables to type variables"))]
862 dupInScope :: Name -> Name -> Type -> SDoc
864 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
865 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
866 ptext (sLit "Distinct scoped type variables must be distinct")])
868 wrongEqualityErr :: TcM (HsType Name, TcKind)
870 = failWithTc (text "Equality predicate used as a type")