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 -- but do hoist for-alls to the top
196 -- This is used in type and class decls, where kinding is
197 -- done in advance, and validity checking is done later
198 -- [Validity checking done later because of knot-tying issues.]
199 tcHsKindedType hs_ty = dsHsType hs_ty
201 tcHsBangType :: LHsType Name -> TcM Type
202 -- Permit a bang, but discard it
203 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
204 tcHsBangType ty = tcHsKindedType ty
206 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
207 -- Used when we are expecting a ClassContext (i.e. no implicit params)
208 -- Does not do validity checking, like tcHsKindedType
209 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
213 %************************************************************************
215 The main kind checker: kcHsType
217 %************************************************************************
219 First a couple of simple wrappers for kcHsType
222 ---------------------------
223 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
224 -- The type ty must be a *lifted* *type*
225 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
227 ---------------------------
228 kcTypeType :: LHsType Name -> TcM (LHsType Name)
229 -- The type ty must be a *type*, but it can be lifted or
230 -- unlifted or an unboxed tuple.
231 kcTypeType ty = kcCheckHsType ty openTypeKind
233 ---------------------------
234 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
235 -- Check that the type has the specified kind
236 -- Be sure to use checkExpectedKind, rather than simply unifying
237 -- with OpenTypeKind, because it gives better error messages
238 kcCheckHsType (L span ty) exp_kind
240 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
241 -- Add the context round the inner check only
242 -- because checkExpectedKind already mentions
243 -- 'ty' by name in any error message
245 ; checkExpectedKind ty act_kind exp_kind
246 ; return (L span ty') }
248 -- Wrap a context around only if we want to
249 -- show that contexts. Omit invisble ones
250 -- and ones user's won't grok (HsPred p).
251 add_ctxt (HsPredTy p) thing = thing
252 add_ctxt (HsForAllTy Implicit tvs (L _ []) ty) thing = thing
253 add_ctxt other_ty thing = addErrCtxt (typeCtxt ty) thing
256 Here comes the main function
259 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
260 kcHsType ty = wrapLocFstM kc_hs_type ty
261 -- kcHsType *returns* the kind of the type, rather than taking an expected
262 -- kind as argument as tcExpr does.
264 -- (a) the kind of (->) is
265 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
266 -- so we'd need to generate huge numbers of bx variables.
267 -- (b) kinds are so simple that the error messages are fine
269 -- The translated type has explicitly-kinded type-variable binders
271 kc_hs_type (HsParTy ty)
272 = kcHsType ty `thenM` \ (ty', kind) ->
273 returnM (HsParTy ty', kind)
275 kc_hs_type (HsTyVar name)
276 = kcTyVar name `thenM` \ kind ->
277 returnM (HsTyVar name, kind)
279 kc_hs_type (HsListTy ty)
280 = kcLiftedType ty `thenM` \ ty' ->
281 returnM (HsListTy ty', liftedTypeKind)
283 kc_hs_type (HsPArrTy ty)
284 = kcLiftedType ty `thenM` \ ty' ->
285 returnM (HsPArrTy ty', liftedTypeKind)
287 kc_hs_type (HsNumTy n)
288 = returnM (HsNumTy n, liftedTypeKind)
290 kc_hs_type (HsKindSig ty k)
291 = kcCheckHsType ty k `thenM` \ ty' ->
292 returnM (HsKindSig ty' k, k)
294 kc_hs_type (HsTupleTy Boxed tys)
295 = mappM kcLiftedType tys `thenM` \ tys' ->
296 returnM (HsTupleTy Boxed tys', liftedTypeKind)
298 kc_hs_type (HsTupleTy Unboxed tys)
299 = mappM kcTypeType tys `thenM` \ tys' ->
300 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
302 kc_hs_type (HsFunTy ty1 ty2)
303 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
304 kcTypeType ty2 `thenM` \ ty2' ->
305 returnM (HsFunTy ty1' ty2', liftedTypeKind)
307 kc_hs_type ty@(HsOpTy ty1 op ty2)
308 = addLocM kcTyVar op `thenM` \ op_kind ->
309 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
310 returnM (HsOpTy ty1' op ty2', res_kind)
312 kc_hs_type ty@(HsAppTy ty1 ty2)
313 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
314 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
315 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
317 (fun_ty, arg_tys) = split ty1 [ty2]
318 split (L _ (HsAppTy f a)) as = split f (a:as)
320 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
321 -- the application; they are never used
323 kc_hs_type (HsPredTy pred)
324 = kcHsPred pred `thenM` \ pred' ->
325 returnM (HsPredTy pred', liftedTypeKind)
327 kc_hs_type (HsForAllTy exp tv_names context ty)
328 = kcHsTyVars tv_names $ \ tv_names' ->
329 kcHsContext context `thenM` \ ctxt' ->
330 kcLiftedType ty `thenM` \ ty' ->
331 -- The body of a forall is usually a type, but in principle
332 -- there's no reason to prohibit *unlifted* types.
333 -- In fact, GHC can itself construct a function with an
334 -- unboxed tuple inside a for-all (via CPR analyis; see
335 -- typecheck/should_compile/tc170)
337 -- Still, that's only for internal interfaces, which aren't
338 -- kind-checked, so we only allow liftedTypeKind here
339 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
341 kc_hs_type (HsBangTy b ty)
342 = do { (ty', kind) <- kcHsType ty
343 ; return (HsBangTy b ty', kind) }
345 kc_hs_type ty@(HsSpliceTy _)
346 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
349 ---------------------------
350 kcApps :: TcKind -- Function kind
352 -> [LHsType Name] -- Arg types
353 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
354 kcApps fun_kind ppr_fun args
355 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
356 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
357 returnM (args', res_kind)
359 split_fk fk 0 = returnM ([], fk)
360 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
362 Nothing -> failWithTc too_many_args
363 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
366 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
368 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
369 ptext SLIT("is applied to too many type arguments")
371 ---------------------------
372 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
373 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
375 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
376 kcHsLPred = wrapLocM kcHsPred
378 kcHsPred :: HsPred Name -> TcM (HsPred Name)
379 kcHsPred pred -- Checks that the result is of kind liftedType
380 = kc_pred pred `thenM` \ (pred', kind) ->
381 checkExpectedKind pred kind liftedTypeKind `thenM_`
384 ---------------------------
385 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
386 -- Does *not* check for a saturated
387 -- application (reason: used from TcDeriv)
388 kc_pred pred@(HsIParam name ty)
389 = kcHsType ty `thenM` \ (ty', kind) ->
390 returnM (HsIParam name ty', kind)
392 kc_pred pred@(HsClassP cls tys)
393 = kcClass cls `thenM` \ kind ->
394 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
395 returnM (HsClassP cls tys', res_kind)
397 ---------------------------
398 kcTyVar :: Name -> TcM TcKind
399 kcTyVar name -- Could be a tyvar or a tycon
400 = traceTc (text "lk1" <+> ppr name) `thenM_`
401 tcLookup name `thenM` \ thing ->
402 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
404 ATyVar _ ty -> returnM (typeKind ty)
405 AThing kind -> returnM kind
406 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
407 other -> wrongThingErr "type" thing name
409 kcClass :: Name -> TcM TcKind
410 kcClass cls -- Must be a class
411 = tcLookup cls `thenM` \ thing ->
413 AThing kind -> returnM kind
414 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
415 other -> wrongThingErr "class" thing cls
419 %************************************************************************
423 %************************************************************************
427 * Transforms from HsType to Type
430 It cannot fail, and does no validity checking, except for
431 structural matters, such as
432 (a) spurious ! annotations.
433 (b) a class used as a type
436 dsHsType :: LHsType Name -> TcM Type
437 -- All HsTyVarBndrs in the intput type are kind-annotated
438 dsHsType ty = ds_type (unLoc ty)
440 ds_type ty@(HsTyVar name)
443 ds_type (HsParTy ty) -- Remove the parentheses markers
446 ds_type ty@(HsBangTy _ _) -- No bangs should be here
447 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
449 ds_type (HsKindSig ty k)
450 = dsHsType ty -- Kind checking done already
452 ds_type (HsListTy ty)
453 = dsHsType ty `thenM` \ tau_ty ->
454 checkWiredInTyCon listTyCon `thenM_`
455 returnM (mkListTy tau_ty)
457 ds_type (HsPArrTy ty)
458 = dsHsType ty `thenM` \ tau_ty ->
459 checkWiredInTyCon parrTyCon `thenM_`
460 returnM (mkPArrTy tau_ty)
462 ds_type (HsTupleTy boxity tys)
463 = dsHsTypes tys `thenM` \ tau_tys ->
464 checkWiredInTyCon tycon `thenM_`
465 returnM (mkTyConApp tycon tau_tys)
467 tycon = tupleTyCon boxity (length tys)
469 ds_type (HsFunTy ty1 ty2)
470 = dsHsType ty1 `thenM` \ tau_ty1 ->
471 dsHsType ty2 `thenM` \ tau_ty2 ->
472 returnM (mkFunTy tau_ty1 tau_ty2)
474 ds_type (HsOpTy ty1 (L span op) ty2)
475 = dsHsType ty1 `thenM` \ tau_ty1 ->
476 dsHsType ty2 `thenM` \ tau_ty2 ->
477 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
481 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
482 returnM (mkTyConApp tc [])
484 ds_type ty@(HsAppTy _ _)
487 ds_type (HsPredTy pred)
488 = dsHsPred pred `thenM` \ pred' ->
489 returnM (mkPredTy pred')
491 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
492 = tcTyVarBndrs tv_names $ \ tyvars ->
493 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
494 dsHsType ty `thenM` \ tau ->
495 returnM (mkSigmaTy tyvars theta tau)
497 dsHsTypes arg_tys = mappM dsHsType arg_tys
500 Help functions for type applications
501 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
504 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
505 ds_app (HsAppTy ty1 ty2) tys
506 = ds_app (unLoc ty1) (ty2:tys)
509 = dsHsTypes tys `thenM` \ arg_tys ->
511 HsTyVar fun -> ds_var_app fun arg_tys
512 other -> ds_type ty `thenM` \ fun_ty ->
513 returnM (mkAppTys fun_ty arg_tys)
515 ds_var_app :: Name -> [Type] -> TcM Type
516 ds_var_app name arg_tys
517 = tcLookup name `thenM` \ thing ->
519 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
520 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
521 other -> wrongThingErr "type" thing name
529 dsHsLPred :: LHsPred Name -> TcM PredType
530 dsHsLPred pred = dsHsPred (unLoc pred)
532 dsHsPred pred@(HsClassP class_name tys)
533 = dsHsTypes tys `thenM` \ arg_tys ->
534 tcLookupClass class_name `thenM` \ clas ->
535 returnM (ClassP clas arg_tys)
537 dsHsPred (HsIParam name ty)
538 = dsHsType ty `thenM` \ arg_ty ->
539 returnM (IParam name arg_ty)
542 GADT constructor signatures
545 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
546 tcLHsConResTy ty@(L span _)
548 addErrCtxt (gadtResCtxt ty) $
551 tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
552 = do { res_ty' <- dsHsType res_ty
553 ; tc_con_res fun (res_ty' : res_tys) }
555 tc_con_res ty@(L _ (HsTyVar name)) res_tys
556 = do { thing <- tcLookup name
558 AGlobal (ATyCon tc) -> return (tc, res_tys)
559 other -> failWithTc (badGadtDecl ty)
562 tc_con_res ty _ = failWithTc (badGadtDecl ty)
565 = hang (ptext SLIT("In the result type of a data constructor:"))
568 = hang (ptext SLIT("Malformed constructor result type:"))
571 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
574 %************************************************************************
576 Type-variable binders
578 %************************************************************************
582 kcHsTyVars :: [LHsTyVarBndr Name]
583 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
584 -- They scope over the thing inside
586 kcHsTyVars tvs thing_inside
587 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
588 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
590 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
591 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
592 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
593 returnM (KindedTyVar name kind)
594 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
597 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
598 -> ([TyVar] -> TcM r)
600 -- Used when type-checking types/classes/type-decls
601 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
602 tcTyVarBndrs bndrs thing_inside
603 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
604 tcExtendTyVarEnv tyvars (thing_inside tyvars)
606 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
607 ; return (mkTyVar name kind') }
608 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
609 return (mkTyVar name liftedTypeKind)
611 -----------------------------------
612 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
613 -- GADT decls can have a (perhpas partial) kind signature
614 -- e.g. data T :: * -> * -> * where ...
615 -- This function makes up suitable (kinded) type variables for
616 -- the argument kinds, and checks that the result kind is indeed *
617 tcDataKindSig Nothing = return []
618 tcDataKindSig (Just kind)
619 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
620 ; span <- getSrcSpanM
621 ; us <- newUniqueSupply
622 ; let loc = srcSpanStart span
623 uniqs = uniqsFromSupply us
624 ; return [ mk_tv loc uniq str kind
625 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
627 (arg_kinds, res_kind) = splitKindFunTys kind
628 mk_tv loc uniq str kind = mkTyVar name kind
630 name = mkInternalName uniq occ loc
631 occ = mkOccName tvName str
633 names :: [String] -- a,b,c...aa,ab,ac etc
634 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
636 badKindSig :: Kind -> SDoc
638 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
643 %************************************************************************
645 Scoped type variables
647 %************************************************************************
650 tcAddScopedTyVars is used for scoped type variables added by pattern
652 e.g. \ ((x::a), (y::a)) -> x+y
653 They never have explicit kinds (because this is source-code only)
654 They are mutable (because they can get bound to a more specific type).
656 Usually we kind-infer and expand type splices, and then
657 tupecheck/desugar the type. That doesn't work well for scoped type
658 variables, because they scope left-right in patterns. (e.g. in the
659 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
661 The current not-very-good plan is to
662 * find all the types in the patterns
663 * find their free tyvars
665 * bring the kinded type vars into scope
666 * BUT throw away the kind-checked type
667 (we'll kind-check it again when we type-check the pattern)
669 This is bad because throwing away the kind checked type throws away
670 its splices. But too bad for now. [July 03]
673 We no longer specify that these type variables must be univerally
674 quantified (lots of email on the subject). If you want to put that
676 a) Do a checkSigTyVars after thing_inside
677 b) More insidiously, don't pass in expected_ty, else
678 we unify with it too early and checkSigTyVars barfs
679 Instead you have to pass in a fresh ty var, and unify
680 it with expected_ty afterwards
683 tcHsPatSigType :: UserTypeCtxt
684 -> LHsType Name -- The type signature
685 -> TcM ([TyVar], -- Newly in-scope type variables
686 Type) -- The signature
687 -- Used for type-checking type signatures in
688 -- (a) patterns e.g f (x::Int) = e
689 -- (b) result signatures e.g. g x :: Int = e
690 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
692 tcHsPatSigType ctxt hs_ty
693 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
694 do { -- Find the type variables that are mentioned in the type
695 -- but not already in scope. These are the ones that
696 -- should be bound by the pattern signature
697 in_scope <- getInLocalScope
698 ; let span = getLoc hs_ty
699 sig_tvs = [ L span (UserTyVar n)
700 | n <- nameSetToList (extractHsTyVars hs_ty),
703 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
704 -- except that we want to keep the tvs separate
705 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
706 { kinded_ty <- kcTypeType hs_ty
707 ; return (kinded_tvs, kinded_ty) }
708 ; tcTyVarBndrs kinded_tvs $ \ tyvars -> do
709 { sig_ty <- dsHsType kinded_ty
710 ; checkValidType ctxt sig_ty
711 ; return (tyvars, sig_ty)
714 tcPatSig :: UserTypeCtxt
717 -> TcM (TcType, -- The type to use for "inside" the signature
718 [(Name,TcType)]) -- The new bit of type environment, binding
719 -- the scoped type variables
720 tcPatSig ctxt sig res_ty
721 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
723 ; if null sig_tvs then do {
724 -- The type signature binds no type variables,
725 -- and hence is rigid, so use it to zap the res_ty
726 boxyUnify sig_ty res_ty
727 ; return (sig_ty, [])
730 -- Type signature binds at least one scoped type variable
732 -- A pattern binding cannot bind scoped type variables
733 -- The renamer fails with a name-out-of-scope error
734 -- if a pattern binding tries to bind a type variable,
735 -- So we just have an ASSERT here
736 ; let in_pat_bind = case ctxt of
737 BindPatSigCtxt -> True
739 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
741 -- Check that pat_ty is rigid
742 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
744 -- Now match the pattern signature against res_ty
745 -- For convenience, and uniform-looking error messages
746 -- we do the matching by allocating meta type variables,
747 -- unifying, and reading out the results.
748 -- This is a strictly local operation.
749 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
750 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
751 ; sig_tv_tys <- mapM readFilledBox box_tvs
753 -- Check that each is bound to a distinct type variable,
754 -- and one that is not already in scope
755 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
756 ; binds_in_scope <- getScopedTyVarBinds
757 ; check binds_in_scope tv_binds
760 ; return (res_ty, tv_binds)
763 check in_scope [] = return ()
764 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
765 ; check ((n,ty):in_scope) rest }
767 check_one in_scope n ty
768 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
769 -- Must bind to a type variable
771 ; checkTc (null dups) (dupInScope n (head dups) ty)
772 -- Must not bind to the same type variable
773 -- as some other in-scope type variable
777 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
781 %************************************************************************
783 Scoped type variables
785 %************************************************************************
788 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
789 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
790 nest 2 (pp_sig ctxt) ]
792 pp_sig (FunSigCtxt n) = pp_n_colon n
793 pp_sig (ConArgCtxt n) = pp_n_colon n
794 pp_sig (ForSigCtxt n) = pp_n_colon n
795 pp_sig (RuleSigCtxt n) = pp_n_colon n
796 pp_sig other = ppr (unLoc hs_ty)
798 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
802 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
803 <+> pprQuotedList sig_tvs)
804 2 (ptext SLIT("unless the pattern has a rigid type context"))
807 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
808 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
809 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
812 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
813 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
814 ptext SLIT("Distinct scoped type variables must be distinct")])