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, tcLHsConResTy,
20 -- Pattern type signatures
21 tcHsPatSigType, tcPatSig
24 #include "HsVersions.h"
26 import HsSyn ( HsType(..), LHsType, HsTyVarBndr(..), LHsTyVarBndr,
27 LHsContext, HsPred(..), LHsPred, HsExplicitForAll(..) )
28 import RnHsSyn ( extractHsTyVars )
30 import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnvTvs,
31 tcLookup, tcLookupClass, tcLookupTyCon,
32 TyThing(..), getInLocalScope, getScopedTyVarBinds,
35 import TcMType ( newKindVar,
37 tcInstBoxyTyVar, readFilledBox,
40 import TcUnify ( boxyUnify, unifyFunKind, checkExpectedKind )
41 import TcIface ( checkWiredInTyCon )
42 import TcType ( Type, PredType(..), ThetaType, BoxySigmaType,
43 TcType, TcKind, isRigidTy,
44 UserTypeCtxt(..), pprUserTypeCtxt,
45 substTyWith, mkTyVarTys, tcEqType,
46 tcIsTyVarTy, mkFunTy, mkSigmaTy, mkPredTy,
47 mkTyConApp, mkAppTys, typeKind )
48 import Kind ( Kind, isLiftedTypeKind, liftedTypeKind, ubxTupleKind,
49 openTypeKind, argTypeKind, splitKindFunTys )
50 import Var ( TyVar, mkTyVar, tyVarName )
51 import TyCon ( TyCon, tyConKind )
52 import Class ( Class, classTyCon )
53 import Name ( Name, mkInternalName )
54 import OccName ( mkOccName, tvName )
56 import PrelNames ( genUnitTyConName )
57 import TysWiredIn ( mkListTy, listTyCon, mkPArrTy, parrTyCon, tupleTyCon )
58 import BasicTypes ( Boxity(..) )
59 import SrcLoc ( Located(..), unLoc, noLoc, getLoc, srcSpanStart )
60 import UniqSupply ( uniqsFromSupply )
65 ----------------------------
67 ----------------------------
69 Generally speaking we now type-check types in three phases
71 1. kcHsType: kind check the HsType
72 *includes* performing any TH type splices;
73 so it returns a translated, and kind-annotated, type
75 2. dsHsType: convert from HsType to Type:
77 expand type synonyms [mkGenTyApps]
78 hoist the foralls [tcHsType]
80 3. checkValidType: check the validity of the resulting type
82 Often these steps are done one after the other (tcHsSigType).
83 But in mutually recursive groups of type and class decls we do
84 1 kind-check the whole group
85 2 build TyCons/Classes in a knot-tied way
86 3 check the validity of types in the now-unknotted TyCons/Classes
88 For example, when we find
89 (forall a m. m a -> m a)
90 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
91 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
92 an environment that binds a and m suitably.
94 The kind checker passed to tcHsTyVars needs to look at enough to
95 establish the kind of the tyvar:
96 * For a group of type and class decls, it's just the group, not
97 the rest of the program
98 * For a tyvar bound in a pattern type signature, its the types
99 mentioned in the other type signatures in that bunch of patterns
100 * For a tyvar bound in a RULE, it's the type signatures on other
101 universally quantified variables in the rule
103 Note that this may occasionally give surprising results. For example:
105 data T a b = MkT (a b)
107 Here we deduce a::*->*, b::*
108 But equally valid would be a::(*->*)-> *, b::*->*
113 Some of the validity check could in principle be done by the kind checker,
116 - During desugaring, we normalise by expanding type synonyms. Only
117 after this step can we check things like type-synonym saturation
118 e.g. type T k = k Int
120 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
121 and then S is saturated. This is a GHC extension.
123 - Similarly, also a GHC extension, we look through synonyms before complaining
124 about the form of a class or instance declaration
126 - Ambiguity checks involve functional dependencies, and it's easier to wait
127 until knots have been resolved before poking into them
129 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
130 finished building the loop. So to keep things simple, we postpone most validity
131 checking until step (3).
135 During step (1) we might fault in a TyCon defined in another module, and it might
136 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
137 knot around type declarations with ARecThing, so that the fault-in code can get
138 the TyCon being defined.
141 %************************************************************************
143 \subsection{Checking types}
145 %************************************************************************
148 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
149 -- Do kind checking, and hoist for-alls to the top
150 -- NB: it's important that the foralls that come from the top-level
151 -- HsForAllTy in hs_ty occur *first* in the returned type.
152 -- See Note [Scoped] with TcSigInfo
153 tcHsSigType ctxt hs_ty
154 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
155 do { kinded_ty <- kcTypeType hs_ty
156 ; ty <- tcHsKindedType kinded_ty
157 ; checkValidType ctxt ty
160 -- Used for the deriving(...) items
161 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
162 tcHsDeriv = addLocM (tc_hs_deriv [])
164 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
165 = kcHsTyVars tv_names $ \ tv_names' ->
166 do { cls_kind <- kcClass cls_name
167 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
168 ; tcTyVarBndrs tv_names' $ \ tyvars ->
169 do { arg_tys <- dsHsTypes tys
170 ; cls <- tcLookupClass cls_name
171 ; return (tyvars, cls, arg_tys) }}
173 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
174 = -- Funny newtype deriving form
176 -- where C has arity 2. Hence can't use regular functions
177 tc_hs_deriv (tv_names1 ++ tv_names2) ty
180 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
183 These functions are used during knot-tying in
184 type and class declarations, when we have to
185 separate kind-checking, desugaring, and validity checking
188 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
189 -- Used for type signatures
190 kcHsSigType ty = kcTypeType ty
191 kcHsLiftedSigType ty = kcLiftedType ty
193 tcHsKindedType :: LHsType Name -> TcM Type
194 -- Don't do kind checking, nor validity checking.
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.]
198 tcHsKindedType hs_ty = dsHsType hs_ty
200 tcHsBangType :: LHsType Name -> TcM Type
201 -- Permit a bang, but discard it
202 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
203 tcHsBangType ty = tcHsKindedType ty
205 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
206 -- Used when we are expecting a ClassContext (i.e. no implicit params)
207 -- Does not do validity checking, like tcHsKindedType
208 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
212 %************************************************************************
214 The main kind checker: kcHsType
216 %************************************************************************
218 First a couple of simple wrappers for kcHsType
221 ---------------------------
222 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
223 -- The type ty must be a *lifted* *type*
224 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
226 ---------------------------
227 kcTypeType :: LHsType Name -> TcM (LHsType Name)
228 -- The type ty must be a *type*, but it can be lifted or
229 -- unlifted or an unboxed tuple.
230 kcTypeType ty = kcCheckHsType ty openTypeKind
232 ---------------------------
233 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
234 -- Check that the type has the specified kind
235 -- Be sure to use checkExpectedKind, rather than simply unifying
236 -- with OpenTypeKind, because it gives better error messages
237 kcCheckHsType (L span ty) exp_kind
239 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
240 -- Add the context round the inner check only
241 -- because checkExpectedKind already mentions
242 -- 'ty' by name in any error message
244 ; checkExpectedKind (strip ty) act_kind exp_kind
245 ; return (L span ty') }
247 -- Wrap a context around only if we want to show that contexts.
248 -- Omit invisble ones and ones user's won't grok (HsPred p).
249 add_ctxt (HsPredTy p) thing = thing
250 add_ctxt (HsForAllTy Implicit tvs (L _ []) (L _ ty)) thing = add_ctxt ty thing
251 add_ctxt other_ty thing = addErrCtxt (typeCtxt ty) thing
253 -- We infer the kind of the type, and then complain if it's
254 -- not right. But we don't want to complain about
255 -- (ty) or !(ty) or forall a. ty
256 -- when the real difficulty is with the 'ty' part.
257 strip (HsParTy (L _ ty)) = strip ty
258 strip (HsBangTy _ (L _ ty)) = strip ty
259 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
263 Here comes the main function
266 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
267 kcHsType ty = wrapLocFstM kc_hs_type ty
268 -- kcHsType *returns* the kind of the type, rather than taking an expected
269 -- kind as argument as tcExpr does.
271 -- (a) the kind of (->) is
272 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
273 -- so we'd need to generate huge numbers of bx variables.
274 -- (b) kinds are so simple that the error messages are fine
276 -- The translated type has explicitly-kinded type-variable binders
278 kc_hs_type (HsParTy ty)
279 = kcHsType ty `thenM` \ (ty', kind) ->
280 returnM (HsParTy ty', kind)
282 kc_hs_type (HsTyVar name)
283 = kcTyVar name `thenM` \ kind ->
284 returnM (HsTyVar name, kind)
286 kc_hs_type (HsListTy ty)
287 = kcLiftedType ty `thenM` \ ty' ->
288 returnM (HsListTy ty', liftedTypeKind)
290 kc_hs_type (HsPArrTy ty)
291 = kcLiftedType ty `thenM` \ ty' ->
292 returnM (HsPArrTy ty', liftedTypeKind)
294 kc_hs_type (HsNumTy n)
295 = returnM (HsNumTy n, liftedTypeKind)
297 kc_hs_type (HsKindSig ty k)
298 = kcCheckHsType ty k `thenM` \ ty' ->
299 returnM (HsKindSig ty' k, k)
301 kc_hs_type (HsTupleTy Boxed tys)
302 = mappM kcLiftedType tys `thenM` \ tys' ->
303 returnM (HsTupleTy Boxed tys', liftedTypeKind)
305 kc_hs_type (HsTupleTy Unboxed tys)
306 = mappM kcTypeType tys `thenM` \ tys' ->
307 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
309 kc_hs_type (HsFunTy ty1 ty2)
310 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
311 kcTypeType ty2 `thenM` \ ty2' ->
312 returnM (HsFunTy ty1' ty2', liftedTypeKind)
314 kc_hs_type ty@(HsOpTy ty1 op ty2)
315 = addLocM kcTyVar op `thenM` \ op_kind ->
316 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
317 returnM (HsOpTy ty1' op ty2', res_kind)
319 kc_hs_type ty@(HsAppTy ty1 ty2)
320 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
321 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
322 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
324 (fun_ty, arg_tys) = split ty1 [ty2]
325 split (L _ (HsAppTy f a)) as = split f (a:as)
327 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
328 -- the application; they are never used
330 kc_hs_type (HsPredTy pred)
331 = kcHsPred pred `thenM` \ pred' ->
332 returnM (HsPredTy pred', liftedTypeKind)
334 kc_hs_type (HsForAllTy exp tv_names context ty)
335 = kcHsTyVars tv_names $ \ tv_names' ->
336 kcHsContext context `thenM` \ ctxt' ->
337 kcLiftedType ty `thenM` \ ty' ->
338 -- The body of a forall is usually a type, but in principle
339 -- there's no reason to prohibit *unlifted* types.
340 -- In fact, GHC can itself construct a function with an
341 -- unboxed tuple inside a for-all (via CPR analyis; see
342 -- typecheck/should_compile/tc170)
344 -- Still, that's only for internal interfaces, which aren't
345 -- kind-checked, so we only allow liftedTypeKind here
346 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
348 kc_hs_type (HsBangTy b ty)
349 = do { (ty', kind) <- kcHsType ty
350 ; return (HsBangTy b ty', kind) }
352 kc_hs_type ty@(HsSpliceTy _)
353 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
356 ---------------------------
357 kcApps :: TcKind -- Function kind
359 -> [LHsType Name] -- Arg types
360 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
361 kcApps fun_kind ppr_fun args
362 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
363 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
364 returnM (args', res_kind)
366 split_fk fk 0 = returnM ([], fk)
367 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
369 Nothing -> failWithTc too_many_args
370 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
373 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
375 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
376 ptext SLIT("is applied to too many type arguments")
378 ---------------------------
379 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
380 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
382 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
383 kcHsLPred = wrapLocM kcHsPred
385 kcHsPred :: HsPred Name -> TcM (HsPred Name)
386 kcHsPred pred -- Checks that the result is of kind liftedType
387 = kc_pred pred `thenM` \ (pred', kind) ->
388 checkExpectedKind pred kind liftedTypeKind `thenM_`
391 ---------------------------
392 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
393 -- Does *not* check for a saturated
394 -- application (reason: used from TcDeriv)
395 kc_pred pred@(HsIParam name ty)
396 = kcHsType ty `thenM` \ (ty', kind) ->
397 returnM (HsIParam name ty', kind)
399 kc_pred pred@(HsClassP cls tys)
400 = kcClass cls `thenM` \ kind ->
401 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
402 returnM (HsClassP cls tys', res_kind)
404 ---------------------------
405 kcTyVar :: Name -> TcM TcKind
406 kcTyVar name -- Could be a tyvar or a tycon
407 = traceTc (text "lk1" <+> ppr name) `thenM_`
408 tcLookup name `thenM` \ thing ->
409 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
411 ATyVar _ ty -> returnM (typeKind ty)
412 AThing kind -> returnM kind
413 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
414 other -> wrongThingErr "type" thing name
416 kcClass :: Name -> TcM TcKind
417 kcClass cls -- Must be a class
418 = tcLookup cls `thenM` \ thing ->
420 AThing kind -> returnM kind
421 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
422 other -> wrongThingErr "class" thing cls
426 %************************************************************************
430 %************************************************************************
434 * Transforms from HsType to Type
437 It cannot fail, and does no validity checking, except for
438 structural matters, such as
439 (a) spurious ! annotations.
440 (b) a class used as a type
443 dsHsType :: LHsType Name -> TcM Type
444 -- All HsTyVarBndrs in the intput type are kind-annotated
445 dsHsType ty = ds_type (unLoc ty)
447 ds_type ty@(HsTyVar name)
450 ds_type (HsParTy ty) -- Remove the parentheses markers
453 ds_type ty@(HsBangTy _ _) -- No bangs should be here
454 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
456 ds_type (HsKindSig ty k)
457 = dsHsType ty -- Kind checking done already
459 ds_type (HsListTy ty)
460 = dsHsType ty `thenM` \ tau_ty ->
461 checkWiredInTyCon listTyCon `thenM_`
462 returnM (mkListTy tau_ty)
464 ds_type (HsPArrTy ty)
465 = dsHsType ty `thenM` \ tau_ty ->
466 checkWiredInTyCon parrTyCon `thenM_`
467 returnM (mkPArrTy tau_ty)
469 ds_type (HsTupleTy boxity tys)
470 = dsHsTypes tys `thenM` \ tau_tys ->
471 checkWiredInTyCon tycon `thenM_`
472 returnM (mkTyConApp tycon tau_tys)
474 tycon = tupleTyCon boxity (length tys)
476 ds_type (HsFunTy ty1 ty2)
477 = dsHsType ty1 `thenM` \ tau_ty1 ->
478 dsHsType ty2 `thenM` \ tau_ty2 ->
479 returnM (mkFunTy tau_ty1 tau_ty2)
481 ds_type (HsOpTy ty1 (L span op) ty2)
482 = dsHsType ty1 `thenM` \ tau_ty1 ->
483 dsHsType ty2 `thenM` \ tau_ty2 ->
484 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
488 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
489 returnM (mkTyConApp tc [])
491 ds_type ty@(HsAppTy _ _)
494 ds_type (HsPredTy pred)
495 = dsHsPred pred `thenM` \ pred' ->
496 returnM (mkPredTy pred')
498 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
499 = tcTyVarBndrs tv_names $ \ tyvars ->
500 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
501 dsHsType ty `thenM` \ tau ->
502 returnM (mkSigmaTy tyvars theta tau)
504 dsHsTypes arg_tys = mappM dsHsType arg_tys
507 Help functions for type applications
508 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
511 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
512 ds_app (HsAppTy ty1 ty2) tys
513 = ds_app (unLoc ty1) (ty2:tys)
516 = dsHsTypes tys `thenM` \ arg_tys ->
518 HsTyVar fun -> ds_var_app fun arg_tys
519 other -> ds_type ty `thenM` \ fun_ty ->
520 returnM (mkAppTys fun_ty arg_tys)
522 ds_var_app :: Name -> [Type] -> TcM Type
523 ds_var_app name arg_tys
524 = tcLookup name `thenM` \ thing ->
526 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
527 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
528 other -> wrongThingErr "type" thing name
536 dsHsLPred :: LHsPred Name -> TcM PredType
537 dsHsLPred pred = dsHsPred (unLoc pred)
539 dsHsPred pred@(HsClassP class_name tys)
540 = dsHsTypes tys `thenM` \ arg_tys ->
541 tcLookupClass class_name `thenM` \ clas ->
542 returnM (ClassP clas arg_tys)
544 dsHsPred (HsIParam name ty)
545 = dsHsType ty `thenM` \ arg_ty ->
546 returnM (IParam name arg_ty)
549 GADT constructor signatures
552 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
554 = addErrCtxt (gadtResCtxt res_ty) $
555 case get_largs res_ty [] of
556 (HsTyVar tc_name, args)
557 -> do { args' <- mapM dsHsType args
558 ; thing <- tcLookup tc_name
560 AGlobal (ATyCon tc) -> return (tc, args')
561 other -> failWithTc (badGadtDecl res_ty) }
562 other -> failWithTc (badGadtDecl res_ty)
564 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
565 -- because that causes a black hole, and for good reason. Building
566 -- the type means expanding type synonyms, and we can't do that
567 -- inside the "knot". So we have to work by steam.
568 get_largs (L _ ty) args = get_args ty args
569 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
570 get_args (HsParTy ty) args = get_largs ty args
571 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
572 get_args ty args = (ty, args)
575 = hang (ptext SLIT("In the result type of a data constructor:"))
578 = hang (ptext SLIT("Malformed constructor result type:"))
581 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
584 %************************************************************************
586 Type-variable binders
588 %************************************************************************
592 kcHsTyVars :: [LHsTyVarBndr Name]
593 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
594 -- They scope over the thing inside
596 kcHsTyVars tvs thing_inside
597 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
598 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
600 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
601 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
602 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
603 returnM (KindedTyVar name kind)
604 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
607 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
608 -> ([TyVar] -> TcM r)
610 -- Used when type-checking types/classes/type-decls
611 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
612 tcTyVarBndrs bndrs thing_inside
613 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
614 tcExtendTyVarEnv tyvars (thing_inside tyvars)
616 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
617 ; return (mkTyVar name kind') }
618 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
619 return (mkTyVar name liftedTypeKind)
621 -----------------------------------
622 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
623 -- GADT decls can have a (perhaps partial) kind signature
624 -- e.g. data T :: * -> * -> * where ...
625 -- This function makes up suitable (kinded) type variables for
626 -- the argument kinds, and checks that the result kind is indeed *
627 tcDataKindSig Nothing = return []
628 tcDataKindSig (Just kind)
629 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
630 ; span <- getSrcSpanM
631 ; us <- newUniqueSupply
632 ; let loc = srcSpanStart span
633 uniqs = uniqsFromSupply us
634 ; return [ mk_tv loc uniq str kind
635 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
637 (arg_kinds, res_kind) = splitKindFunTys kind
638 mk_tv loc uniq str kind = mkTyVar name kind
640 name = mkInternalName uniq occ loc
641 occ = mkOccName tvName str
643 names :: [String] -- a,b,c...aa,ab,ac etc
644 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
646 badKindSig :: Kind -> SDoc
648 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
653 %************************************************************************
655 Scoped type variables
657 %************************************************************************
660 tcAddScopedTyVars is used for scoped type variables added by pattern
662 e.g. \ ((x::a), (y::a)) -> x+y
663 They never have explicit kinds (because this is source-code only)
664 They are mutable (because they can get bound to a more specific type).
666 Usually we kind-infer and expand type splices, and then
667 tupecheck/desugar the type. That doesn't work well for scoped type
668 variables, because they scope left-right in patterns. (e.g. in the
669 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
671 The current not-very-good plan is to
672 * find all the types in the patterns
673 * find their free tyvars
675 * bring the kinded type vars into scope
676 * BUT throw away the kind-checked type
677 (we'll kind-check it again when we type-check the pattern)
679 This is bad because throwing away the kind checked type throws away
680 its splices. But too bad for now. [July 03]
683 We no longer specify that these type variables must be univerally
684 quantified (lots of email on the subject). If you want to put that
686 a) Do a checkSigTyVars after thing_inside
687 b) More insidiously, don't pass in expected_ty, else
688 we unify with it too early and checkSigTyVars barfs
689 Instead you have to pass in a fresh ty var, and unify
690 it with expected_ty afterwards
693 tcHsPatSigType :: UserTypeCtxt
694 -> LHsType Name -- The type signature
695 -> TcM ([TyVar], -- Newly in-scope type variables
696 Type) -- The signature
697 -- Used for type-checking type signatures in
698 -- (a) patterns e.g f (x::Int) = e
699 -- (b) result signatures e.g. g x :: Int = e
700 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
702 tcHsPatSigType ctxt hs_ty
703 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
704 do { -- Find the type variables that are mentioned in the type
705 -- but not already in scope. These are the ones that
706 -- should be bound by the pattern signature
707 in_scope <- getInLocalScope
708 ; let span = getLoc hs_ty
709 sig_tvs = [ L span (UserTyVar n)
710 | n <- nameSetToList (extractHsTyVars hs_ty),
713 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
714 -- except that we want to keep the tvs separate
715 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
716 { kinded_ty <- kcTypeType hs_ty
717 ; return (kinded_tvs, kinded_ty) }
718 ; tcTyVarBndrs kinded_tvs $ \ tyvars -> do
719 { sig_ty <- dsHsType kinded_ty
720 ; checkValidType ctxt sig_ty
721 ; return (tyvars, sig_ty)
724 tcPatSig :: UserTypeCtxt
727 -> TcM (TcType, -- The type to use for "inside" the signature
728 [(Name,TcType)]) -- The new bit of type environment, binding
729 -- the scoped type variables
730 tcPatSig ctxt sig res_ty
731 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
733 ; if null sig_tvs then do {
734 -- The type signature binds no type variables,
735 -- and hence is rigid, so use it to zap the res_ty
736 boxyUnify sig_ty res_ty
737 ; return (sig_ty, [])
740 -- Type signature binds at least one scoped type variable
742 -- A pattern binding cannot bind scoped type variables
743 -- The renamer fails with a name-out-of-scope error
744 -- if a pattern binding tries to bind a type variable,
745 -- So we just have an ASSERT here
746 ; let in_pat_bind = case ctxt of
747 BindPatSigCtxt -> True
749 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
751 -- Check that pat_ty is rigid
752 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
754 -- Now match the pattern signature against res_ty
755 -- For convenience, and uniform-looking error messages
756 -- we do the matching by allocating meta type variables,
757 -- unifying, and reading out the results.
758 -- This is a strictly local operation.
759 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
760 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
761 ; sig_tv_tys <- mapM readFilledBox box_tvs
763 -- Check that each is bound to a distinct type variable,
764 -- and one that is not already in scope
765 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
766 ; binds_in_scope <- getScopedTyVarBinds
767 ; check binds_in_scope tv_binds
770 ; return (res_ty, tv_binds)
773 check in_scope [] = return ()
774 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
775 ; check ((n,ty):in_scope) rest }
777 check_one in_scope n ty
778 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
779 -- Must bind to a type variable
781 ; checkTc (null dups) (dupInScope n (head dups) ty)
782 -- Must not bind to the same type variable
783 -- as some other in-scope type variable
787 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
791 %************************************************************************
793 Scoped type variables
795 %************************************************************************
798 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
799 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
800 nest 2 (pp_sig ctxt) ]
802 pp_sig (FunSigCtxt n) = pp_n_colon n
803 pp_sig (ConArgCtxt n) = pp_n_colon n
804 pp_sig (ForSigCtxt n) = pp_n_colon n
805 pp_sig (RuleSigCtxt n) = pp_n_colon n
806 pp_sig other = ppr (unLoc hs_ty)
808 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
812 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
813 <+> pprQuotedList sig_tvs)
814 2 (ptext SLIT("unless the pattern has a rigid type context"))
817 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
818 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
819 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
822 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
823 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
824 ptext SLIT("Distinct scoped type variables must be distinct")])