2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
8 tcHsSigType, tcHsDeriv,
12 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
13 kcCheckHsType, kcHsContext, kcHsType,
15 -- Typechecking kinded types
16 tcHsKindedContext, tcHsKindedType, tcHsBangType,
17 tcTyVarBndrs, dsHsType, tcLHsConSig, tcDataKindSig,
19 tcHsPatSigType, tcAddLetBoundTyVars,
21 TcSigInfo(..), TcSigFun, lookupSig
24 #include "HsVersions.h"
26 import HsSyn ( HsType(..), LHsType, HsTyVarBndr(..), LHsTyVarBndr, HsBang,
27 LHsContext, HsPred(..), LHsPred, LHsBinds,
28 getBangStrictness, collectSigTysFromHsBinds )
29 import RnHsSyn ( extractHsTyVars )
31 import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnvTvs,
32 tcLookup, tcLookupClass, tcLookupTyCon,
33 TyThing(..), getInLocalScope, wrongThingErr
35 import TcMType ( newKindVar, newMetaTyVar, zonkTcKindToKind,
36 checkValidType, UserTypeCtxt(..), pprHsSigCtxt
38 import TcUnify ( unifyFunKind, checkExpectedKind )
39 import TcIface ( checkWiredInTyCon )
40 import TcType ( Type, PredType(..), ThetaType,
41 MetaDetails(Flexi), hoistForAllTys,
42 TcType, TcTyVar, TcKind, TcThetaType, TcTauType,
43 mkFunTy, mkSigmaTy, mkPredTy, mkGenTyConApp,
44 mkTyConApp, mkAppTys, typeKind )
45 import Kind ( Kind, isLiftedTypeKind, liftedTypeKind, ubxTupleKind,
46 openTypeKind, argTypeKind, splitKindFunTys )
48 import Var ( TyVar, mkTyVar )
49 import TyCon ( TyCon, tyConKind )
50 import Class ( Class, classTyCon )
51 import Name ( Name, mkInternalName )
52 import OccName ( mkOccName, tvName )
54 import PrelNames ( genUnitTyConName )
55 import TysWiredIn ( mkListTy, listTyCon, mkPArrTy, parrTyCon, tupleTyCon )
56 import Bag ( bagToList )
57 import BasicTypes ( Boxity(..) )
58 import SrcLoc ( Located(..), unLoc, noLoc, srcSpanStart )
59 import UniqSupply ( uniqsFromSupply )
64 ----------------------------
66 ----------------------------
68 Generally speaking we now type-check types in three phases
70 1. kcHsType: kind check the HsType
71 *includes* performing any TH type splices;
72 so it returns a translated, and kind-annotated, type
74 2. dsHsType: convert from HsType to Type:
76 expand type synonyms [mkGenTyApps]
77 hoist the foralls [tcHsType]
79 3. checkValidType: check the validity of the resulting type
81 Often these steps are done one after the other (tcHsSigType).
82 But in mutually recursive groups of type and class decls we do
83 1 kind-check the whole group
84 2 build TyCons/Classes in a knot-tied way
85 3 check the validity of types in the now-unknotted TyCons/Classes
87 For example, when we find
88 (forall a m. m a -> m a)
89 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
90 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
91 an environment that binds a and m suitably.
93 The kind checker passed to tcHsTyVars needs to look at enough to
94 establish the kind of the tyvar:
95 * For a group of type and class decls, it's just the group, not
96 the rest of the program
97 * For a tyvar bound in a pattern type signature, its the types
98 mentioned in the other type signatures in that bunch of patterns
99 * For a tyvar bound in a RULE, it's the type signatures on other
100 universally quantified variables in the rule
102 Note that this may occasionally give surprising results. For example:
104 data T a b = MkT (a b)
106 Here we deduce a::*->*, b::*
107 But equally valid would be a::(*->*)-> *, b::*->*
112 Some of the validity check could in principle be done by the kind checker,
115 - During desugaring, we normalise by expanding type synonyms. Only
116 after this step can we check things like type-synonym saturation
117 e.g. type T k = k Int
119 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
120 and then S is saturated. This is a GHC extension.
122 - Similarly, also a GHC extension, we look through synonyms before complaining
123 about the form of a class or instance declaration
125 - Ambiguity checks involve functional dependencies, and it's easier to wait
126 until knots have been resolved before poking into them
128 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
129 finished building the loop. So to keep things simple, we postpone most validity
130 checking until step (3).
134 During step (1) we might fault in a TyCon defined in another module, and it might
135 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
136 knot around type declarations with ARecThing, so that the fault-in code can get
137 the TyCon being defined.
140 %************************************************************************
142 \subsection{Checking types}
144 %************************************************************************
147 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
148 -- Do kind checking, and hoist for-alls to the top
149 -- NB: it's important that the foralls that come from the top-level
150 -- HsForAllTy in hs_ty occur *first* in the returned type.
151 -- See Note [Scoped] with TcSigInfo
152 tcHsSigType ctxt hs_ty
153 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
154 do { kinded_ty <- kcTypeType hs_ty
155 ; ty <- tcHsKindedType kinded_ty
156 ; checkValidType ctxt ty
159 -- Used for the deriving(...) items
160 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
161 tcHsDeriv = addLocM (tc_hs_deriv [])
163 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
164 = kcHsTyVars tv_names $ \ tv_names' ->
165 do { cls_kind <- kcClass cls_name
166 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
167 ; tcTyVarBndrs tv_names' $ \ tyvars ->
168 do { arg_tys <- dsHsTypes tys
169 ; cls <- tcLookupClass cls_name
170 ; return (tyvars, cls, arg_tys) }}
172 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
173 = -- Funny newtype deriving form
175 -- where C has arity 2. Hence can't use regular functions
176 tc_hs_deriv (tv_names1 ++ tv_names2) ty
179 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
182 These functions are used during knot-tying in
183 type and class declarations, when we have to
184 separate kind-checking, desugaring, and validity checking
187 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
188 -- Used for type signatures
189 kcHsSigType ty = kcTypeType ty
190 kcHsLiftedSigType ty = kcLiftedType ty
192 tcHsKindedType :: LHsType Name -> TcM Type
193 -- Don't do kind checking, nor validity checking,
194 -- but do hoist for-alls to the top
195 -- This is used in type and class decls, where kinding is
196 -- done in advance, and validity checking is done later
197 -- [Validity checking done later because of knot-tying issues.]
199 = do { ty <- dsHsType hs_ty
200 ; return (hoistForAllTys ty) }
202 tcHsBangType :: LHsType Name -> TcM Type
203 -- Permit a bang, but discard it
204 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
205 tcHsBangType ty = tcHsKindedType ty
207 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
208 -- Used when we are expecting a ClassContext (i.e. no implicit params)
209 -- Does not do validity checking, like tcHsKindedType
210 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
214 %************************************************************************
216 The main kind checker: kcHsType
218 %************************************************************************
220 First a couple of simple wrappers for kcHsType
223 ---------------------------
224 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
225 -- The type ty must be a *lifted* *type*
226 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
228 ---------------------------
229 kcTypeType :: LHsType Name -> TcM (LHsType Name)
230 -- The type ty must be a *type*, but it can be lifted or
231 -- unlifted or an unboxed tuple.
232 kcTypeType ty = kcCheckHsType ty openTypeKind
234 ---------------------------
235 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
236 -- Check that the type has the specified kind
237 -- Be sure to use checkExpectedKind, rather than simply unifying
238 -- with OpenTypeKind, because it gives better error messages
239 kcCheckHsType (L span ty) exp_kind
241 do { (ty', act_kind) <- addErrCtxt (typeCtxt ty) $
243 -- Add the context round the inner check only
244 -- because checkExpectedKind already mentions
245 -- 'ty' by name in any error message
246 ; checkExpectedKind ty act_kind exp_kind
247 ; return (L span ty') }
250 Here comes the main function
253 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
254 kcHsType ty = wrapLocFstM kc_hs_type ty
255 -- kcHsType *returns* the kind of the type, rather than taking an expected
256 -- kind as argument as tcExpr does.
258 -- (a) the kind of (->) is
259 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
260 -- so we'd need to generate huge numbers of bx variables.
261 -- (b) kinds are so simple that the error messages are fine
263 -- The translated type has explicitly-kinded type-variable binders
265 kc_hs_type (HsParTy ty)
266 = kcHsType ty `thenM` \ (ty', kind) ->
267 returnM (HsParTy ty', kind)
269 kc_hs_type (HsTyVar name)
270 = kcTyVar name `thenM` \ kind ->
271 returnM (HsTyVar name, kind)
273 kc_hs_type (HsListTy ty)
274 = kcLiftedType ty `thenM` \ ty' ->
275 returnM (HsListTy ty', liftedTypeKind)
277 kc_hs_type (HsPArrTy ty)
278 = kcLiftedType ty `thenM` \ ty' ->
279 returnM (HsPArrTy ty', liftedTypeKind)
281 kc_hs_type (HsNumTy n)
282 = returnM (HsNumTy n, liftedTypeKind)
284 kc_hs_type (HsKindSig ty k)
285 = kcCheckHsType ty k `thenM` \ ty' ->
286 returnM (HsKindSig ty' k, k)
288 kc_hs_type (HsTupleTy Boxed tys)
289 = mappM kcLiftedType tys `thenM` \ tys' ->
290 returnM (HsTupleTy Boxed tys', liftedTypeKind)
292 kc_hs_type (HsTupleTy Unboxed tys)
293 = mappM kcTypeType tys `thenM` \ tys' ->
294 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
296 kc_hs_type (HsFunTy ty1 ty2)
297 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
298 kcTypeType ty2 `thenM` \ ty2' ->
299 returnM (HsFunTy ty1' ty2', liftedTypeKind)
301 kc_hs_type ty@(HsOpTy ty1 op ty2)
302 = addLocM kcTyVar op `thenM` \ op_kind ->
303 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
304 returnM (HsOpTy ty1' op ty2', res_kind)
306 kc_hs_type ty@(HsAppTy ty1 ty2)
307 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
308 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
309 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
311 (fun_ty, arg_tys) = split ty1 [ty2]
312 split (L _ (HsAppTy f a)) as = split f (a:as)
314 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
315 -- the application; they are never used
317 kc_hs_type (HsPredTy pred)
318 = kcHsPred pred `thenM` \ pred' ->
319 returnM (HsPredTy pred', liftedTypeKind)
321 kc_hs_type (HsForAllTy exp tv_names context ty)
322 = kcHsTyVars tv_names $ \ tv_names' ->
323 kcHsContext context `thenM` \ ctxt' ->
324 kcLiftedType ty `thenM` \ ty' ->
325 -- The body of a forall is usually a type, but in principle
326 -- there's no reason to prohibit *unlifted* types.
327 -- In fact, GHC can itself construct a function with an
328 -- unboxed tuple inside a for-all (via CPR analyis; see
329 -- typecheck/should_compile/tc170)
331 -- Still, that's only for internal interfaces, which aren't
332 -- kind-checked, so we only allow liftedTypeKind here
333 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
335 kc_hs_type (HsBangTy b ty)
336 = do { (ty', kind) <- kcHsType ty
337 ; return (HsBangTy b ty', kind) }
339 kc_hs_type ty@(HsSpliceTy _)
340 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
343 ---------------------------
344 kcApps :: TcKind -- Function kind
346 -> [LHsType Name] -- Arg types
347 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
348 kcApps fun_kind ppr_fun args
349 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
350 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
351 returnM (args', res_kind)
353 split_fk fk 0 = returnM ([], fk)
354 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
356 Nothing -> failWithTc too_many_args
357 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
360 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
362 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
363 ptext SLIT("is applied to too many type arguments")
365 ---------------------------
366 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
367 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
369 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
370 kcHsLPred = wrapLocM kcHsPred
372 kcHsPred :: HsPred Name -> TcM (HsPred Name)
373 kcHsPred pred -- Checks that the result is of kind liftedType
374 = kc_pred pred `thenM` \ (pred', kind) ->
375 checkExpectedKind pred kind liftedTypeKind `thenM_`
378 ---------------------------
379 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
380 -- Does *not* check for a saturated
381 -- application (reason: used from TcDeriv)
382 kc_pred pred@(HsIParam name ty)
383 = kcHsType ty `thenM` \ (ty', kind) ->
384 returnM (HsIParam name ty', kind)
386 kc_pred pred@(HsClassP cls tys)
387 = kcClass cls `thenM` \ kind ->
388 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
389 returnM (HsClassP cls tys', res_kind)
391 ---------------------------
392 kcTyVar :: Name -> TcM TcKind
393 kcTyVar name -- Could be a tyvar or a tycon
394 = traceTc (text "lk1" <+> ppr name) `thenM_`
395 tcLookup name `thenM` \ thing ->
396 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
398 ATyVar _ ty -> returnM (typeKind ty)
399 AThing kind -> returnM kind
400 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
401 other -> wrongThingErr "type" thing name
403 kcClass :: Name -> TcM TcKind
404 kcClass cls -- Must be a class
405 = tcLookup cls `thenM` \ thing ->
407 AThing kind -> returnM kind
408 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
409 other -> wrongThingErr "class" thing cls
413 %************************************************************************
417 %************************************************************************
421 * Transforms from HsType to Type
424 It cannot fail, and does no validity checking, except for
425 structural matters, such as
426 (a) spurious ! annotations.
427 (b) a class used as a type
430 dsHsType :: LHsType Name -> TcM Type
431 -- All HsTyVarBndrs in the intput type are kind-annotated
432 dsHsType ty = ds_type (unLoc ty)
434 ds_type ty@(HsTyVar name)
437 ds_type (HsParTy ty) -- Remove the parentheses markers
440 ds_type ty@(HsBangTy _ _) -- No bangs should be here
441 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
443 ds_type (HsKindSig ty k)
444 = dsHsType ty -- Kind checking done already
446 ds_type (HsListTy ty)
447 = dsHsType ty `thenM` \ tau_ty ->
448 checkWiredInTyCon listTyCon `thenM_`
449 returnM (mkListTy tau_ty)
451 ds_type (HsPArrTy ty)
452 = dsHsType ty `thenM` \ tau_ty ->
453 checkWiredInTyCon parrTyCon `thenM_`
454 returnM (mkPArrTy tau_ty)
456 ds_type (HsTupleTy boxity tys)
457 = dsHsTypes tys `thenM` \ tau_tys ->
458 checkWiredInTyCon tycon `thenM_`
459 returnM (mkTyConApp tycon tau_tys)
461 tycon = tupleTyCon boxity (length tys)
463 ds_type (HsFunTy ty1 ty2)
464 = dsHsType ty1 `thenM` \ tau_ty1 ->
465 dsHsType ty2 `thenM` \ tau_ty2 ->
466 returnM (mkFunTy tau_ty1 tau_ty2)
468 ds_type (HsOpTy ty1 (L span op) ty2)
469 = dsHsType ty1 `thenM` \ tau_ty1 ->
470 dsHsType ty2 `thenM` \ tau_ty2 ->
471 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
475 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
476 returnM (mkTyConApp tc [])
478 ds_type ty@(HsAppTy _ _)
481 ds_type (HsPredTy pred)
482 = dsHsPred pred `thenM` \ pred' ->
483 returnM (mkPredTy pred')
485 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
486 = tcTyVarBndrs tv_names $ \ tyvars ->
487 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
488 dsHsType ty `thenM` \ tau ->
489 returnM (mkSigmaTy tyvars theta tau)
491 dsHsTypes arg_tys = mappM dsHsType arg_tys
494 Help functions for type applications
495 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
498 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
499 ds_app (HsAppTy ty1 ty2) tys
500 = ds_app (unLoc ty1) (ty2:tys)
503 = dsHsTypes tys `thenM` \ arg_tys ->
505 HsTyVar fun -> ds_var_app fun arg_tys
506 other -> ds_type ty `thenM` \ fun_ty ->
507 returnM (mkAppTys fun_ty arg_tys)
509 ds_var_app :: Name -> [Type] -> TcM Type
510 ds_var_app name arg_tys
511 = tcLookup name `thenM` \ thing ->
513 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
514 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
515 other -> wrongThingErr "type" thing name
523 dsHsLPred :: LHsPred Name -> TcM PredType
524 dsHsLPred pred = dsHsPred (unLoc pred)
526 dsHsPred pred@(HsClassP class_name tys)
527 = dsHsTypes tys `thenM` \ arg_tys ->
528 tcLookupClass class_name `thenM` \ clas ->
529 returnM (ClassP clas arg_tys)
531 dsHsPred (HsIParam name ty)
532 = dsHsType ty `thenM` \ arg_ty ->
533 returnM (IParam name arg_ty)
536 GADT constructor signatures
539 tcLHsConSig :: LHsType Name
540 -> TcM ([TcTyVar], TcThetaType,
543 -- Take apart the type signature for a data constructor
544 -- The difference is that there can be bangs at the top of
545 -- the argument types, and kind-checking is the right place to check
546 tcLHsConSig sig@(L span (HsForAllTy exp tv_names ctxt ty))
548 addErrCtxt (gadtSigCtxt sig) $
549 tcTyVarBndrs tv_names $ \ tyvars ->
550 do { theta <- mappM dsHsLPred (unLoc ctxt)
551 ; (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
552 ; return (tyvars, theta, bangs, arg_tys, tc, res_tys) }
554 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
555 ; return ([], [], bangs, arg_tys, tc, res_tys) }
558 tc_con_sig_tau (L _ (HsFunTy arg ty))
559 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
560 ; arg_ty <- tcHsBangType arg
561 ; return (getBangStrictness arg : bangs,
562 arg_ty : arg_tys, tc, res_tys) }
565 = do { (tc, res_tys) <- tc_con_res ty []
566 ; return ([], [], tc, res_tys) }
569 tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
570 = do { res_ty' <- dsHsType res_ty
571 ; tc_con_res fun (res_ty' : res_tys) }
573 tc_con_res ty@(L _ (HsTyVar name)) res_tys
574 = do { thing <- tcLookup name
576 AGlobal (ATyCon tc) -> return (tc, res_tys)
577 other -> failWithTc (badGadtDecl ty)
580 tc_con_res ty _ = failWithTc (badGadtDecl ty)
583 = hang (ptext SLIT("In the signature of a data constructor:"))
586 = hang (ptext SLIT("Malformed constructor signature:"))
589 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
592 %************************************************************************
594 Type-variable binders
596 %************************************************************************
600 kcHsTyVars :: [LHsTyVarBndr Name]
601 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
602 -- They scope over the thing inside
604 kcHsTyVars tvs thing_inside
605 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
606 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
608 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
609 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
610 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
611 returnM (KindedTyVar name kind)
612 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
615 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
616 -> ([TyVar] -> TcM r)
618 -- Used when type-checking types/classes/type-decls
619 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
620 tcTyVarBndrs bndrs thing_inside
621 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
622 tcExtendTyVarEnv tyvars (thing_inside tyvars)
624 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
625 returnM (mkTyVar name kind')
626 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
627 returnM (mkTyVar name liftedTypeKind)
629 -----------------------------------
630 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
631 -- GADT decls can have a (perhpas partial) kind signature
632 -- e.g. data T :: * -> * -> * where ...
633 -- This function makes up suitable (kinded) type variables for
634 -- the argument kinds, and checks that the result kind is indeed *
635 tcDataKindSig Nothing = return []
636 tcDataKindSig (Just kind)
637 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
638 ; span <- getSrcSpanM
639 ; us <- newUniqueSupply
640 ; let loc = srcSpanStart span
641 uniqs = uniqsFromSupply us
642 ; return [ mk_tv loc uniq str kind
643 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
645 (arg_kinds, res_kind) = splitKindFunTys kind
646 mk_tv loc uniq str kind = mkTyVar name kind
648 name = mkInternalName uniq occ loc
649 occ = mkOccName tvName str
651 names :: [String] -- a,b,c...aa,ab,ac etc
652 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
654 badKindSig :: Kind -> SDoc
656 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
661 %************************************************************************
663 Scoped type variables
665 %************************************************************************
668 tcAddScopedTyVars is used for scoped type variables added by pattern
670 e.g. \ ((x::a), (y::a)) -> x+y
671 They never have explicit kinds (because this is source-code only)
672 They are mutable (because they can get bound to a more specific type).
674 Usually we kind-infer and expand type splices, and then
675 tupecheck/desugar the type. That doesn't work well for scoped type
676 variables, because they scope left-right in patterns. (e.g. in the
677 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
679 The current not-very-good plan is to
680 * find all the types in the patterns
681 * find their free tyvars
683 * bring the kinded type vars into scope
684 * BUT throw away the kind-checked type
685 (we'll kind-check it again when we type-check the pattern)
687 This is bad because throwing away the kind checked type throws away
688 its splices. But too bad for now. [July 03]
691 We no longer specify that these type variables must be univerally
692 quantified (lots of email on the subject). If you want to put that
694 a) Do a checkSigTyVars after thing_inside
695 b) More insidiously, don't pass in expected_ty, else
696 we unify with it too early and checkSigTyVars barfs
697 Instead you have to pass in a fresh ty var, and unify
698 it with expected_ty afterwards
701 tcPatSigBndrs :: LHsType Name
702 -> TcM ([TcTyVar], -- Brought into scope
703 LHsType Name) -- Kinded, but not yet desugared
706 = do { in_scope <- getInLocalScope
707 ; span <- getSrcSpanM
708 ; let sig_tvs = [ L span (UserTyVar n)
709 | n <- nameSetToList (extractHsTyVars hs_ty),
711 -- The tyvars we want are the free type variables of
712 -- the type that are not already in scope
714 -- Behave like kcHsType on a ForAll type
715 -- i.e. make kinded tyvars with mutable kinds,
716 -- and kind-check the enclosed types
717 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
718 { kinded_ty <- kcTypeType hs_ty
719 ; return (kinded_tvs, kinded_ty) }
721 -- Zonk the mutable kinds and bring the tyvars into scope
722 -- Just like the call to tcTyVarBndrs in ds_type (HsForAllTy case),
723 -- except that it brings *meta* tyvars into scope, not regular ones
725 -- [Out of date, but perhaps should be resurrected]
726 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
727 -- error messages when type variables escape:
728 -- Inferred type is less polymorphic than expected
729 -- Quantified type variable `t' escapes
730 -- It is mentioned in the environment:
731 -- t is bound by the pattern type signature at tcfail103.hs:6
732 ; tyvars <- mapM (zonk . unLoc) kinded_tvs
733 ; return (tyvars, kinded_ty) }
735 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
736 newMetaTyVar name kind' Flexi
737 -- Scoped type variables are bound to a *type*, hence Flexi
738 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
739 returnM (mkTyVar name liftedTypeKind)
741 tcHsPatSigType :: UserTypeCtxt
742 -> LHsType Name -- The type signature
743 -> TcM ([TcTyVar], -- Newly in-scope type variables
744 TcType) -- The signature
746 tcHsPatSigType ctxt hs_ty
747 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
748 do { (tyvars, kinded_ty) <- tcPatSigBndrs hs_ty
750 -- Complete processing of the type, and check its validity
751 ; tcExtendTyVarEnv tyvars $ do
752 { sig_ty <- tcHsKindedType kinded_ty
753 ; checkValidType ctxt sig_ty
754 ; return (tyvars, sig_ty) }
757 tcAddLetBoundTyVars :: LHsBinds Name -> TcM a -> TcM a
758 -- Turgid funciton, used for type variables bound by the patterns of a let binding
760 tcAddLetBoundTyVars binds thing_inside
761 = go (collectSigTysFromHsBinds (bagToList binds)) thing_inside
763 go [] thing_inside = thing_inside
764 go (hs_ty:hs_tys) thing_inside
765 = do { (tyvars, _kinded_ty) <- tcPatSigBndrs hs_ty
766 ; tcExtendTyVarEnv tyvars (go hs_tys thing_inside) }
770 %************************************************************************
772 \subsection{Signatures}
774 %************************************************************************
776 @tcSigs@ checks the signatures for validity, and returns a list of
777 {\em freshly-instantiated} signatures. That is, the types are already
778 split up, and have fresh type variables installed. All non-type-signature
779 "RenamedSigs" are ignored.
781 The @TcSigInfo@ contains @TcTypes@ because they are unified with
782 the variable's type, and after that checked to see whether they've
788 sig_id :: TcId, -- *Polymorphic* binder for this value...
790 sig_scoped :: [Name], -- Names for any scoped type variables
791 -- Invariant: correspond 1-1 with an initial
792 -- segment of sig_tvs (see Note [Scoped])
794 sig_tvs :: [TcTyVar], -- Instantiated type variables
795 -- See Note [Instantiate sig]
797 sig_theta :: TcThetaType, -- Instantiated theta
798 sig_tau :: TcTauType, -- Instantiated tau
799 sig_loc :: InstLoc -- The location of the signature
803 -- There may be more instantiated type variables than scoped
804 -- ones. For example:
805 -- type T a = forall b. b -> (a,b)
806 -- f :: forall c. T c
807 -- Here, the signature for f will have one scoped type variable, c,
808 -- but two instantiated type variables, c' and b'.
810 -- We assume that the scoped ones are at the *front* of sig_tvs,
811 -- and remember the names from the original HsForAllTy in sig_scoped
813 -- Note [Instantiate sig]
814 -- It's vital to instantiate a type signature with fresh variable.
816 -- type S = forall a. a->a
820 -- Here, we must use distinct type variables when checking f,g's right hand sides.
821 -- (Instantiation is only necessary because of type synonyms. Otherwise,
822 -- it's all cool; each signature has distinct type variables from the renamer.)
824 type TcSigFun = Name -> Maybe TcSigInfo
826 instance Outputable TcSigInfo where
827 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
828 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
830 lookupSig :: [TcSigInfo] -> TcSigFun -- Search for a particular signature
831 lookupSig [] name = Nothing
832 lookupSig (sig : sigs) name
833 | name == idName (sig_id sig) = Just sig
834 | otherwise = lookupSig sigs name