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 )
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 parts of -} Type ( 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 add_ctxt (HsPredTy p) thing = thing
249 -- Omit invisble ones and ones user's won't grok (HsPred p).
250 add_ctxt (HsForAllTy _ _ (L _ []) _) thing = thing
251 -- Omit wrapping if the theta-part is empty
252 -- Reason: the recursive call to kcLiftedType, in the ForAllTy
253 -- case of kc_hs_type, will do the wrapping instead
254 -- and we don't want to duplicate
255 add_ctxt other_ty thing = addErrCtxt (typeCtxt other_ty) thing
257 -- We infer the kind of the type, and then complain if it's
258 -- not right. But we don't want to complain about
259 -- (ty) or !(ty) or forall a. ty
260 -- when the real difficulty is with the 'ty' part.
261 strip (HsParTy (L _ ty)) = strip ty
262 strip (HsBangTy _ (L _ ty)) = strip ty
263 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
267 Here comes the main function
270 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
271 kcHsType ty = wrapLocFstM kc_hs_type ty
272 -- kcHsType *returns* the kind of the type, rather than taking an expected
273 -- kind as argument as tcExpr does.
275 -- (a) the kind of (->) is
276 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
277 -- so we'd need to generate huge numbers of bx variables.
278 -- (b) kinds are so simple that the error messages are fine
280 -- The translated type has explicitly-kinded type-variable binders
282 kc_hs_type (HsParTy ty)
283 = kcHsType ty `thenM` \ (ty', kind) ->
284 returnM (HsParTy ty', kind)
286 kc_hs_type (HsTyVar name)
287 = kcTyVar name `thenM` \ kind ->
288 returnM (HsTyVar name, kind)
290 kc_hs_type (HsListTy ty)
291 = kcLiftedType ty `thenM` \ ty' ->
292 returnM (HsListTy ty', liftedTypeKind)
294 kc_hs_type (HsPArrTy ty)
295 = kcLiftedType ty `thenM` \ ty' ->
296 returnM (HsPArrTy ty', liftedTypeKind)
298 kc_hs_type (HsNumTy n)
299 = returnM (HsNumTy n, liftedTypeKind)
301 kc_hs_type (HsKindSig ty k)
302 = kcCheckHsType ty k `thenM` \ ty' ->
303 returnM (HsKindSig ty' k, k)
305 kc_hs_type (HsTupleTy Boxed tys)
306 = mappM kcLiftedType tys `thenM` \ tys' ->
307 returnM (HsTupleTy Boxed tys', liftedTypeKind)
309 kc_hs_type (HsTupleTy Unboxed tys)
310 = mappM kcTypeType tys `thenM` \ tys' ->
311 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
313 kc_hs_type (HsFunTy ty1 ty2)
314 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
315 kcTypeType ty2 `thenM` \ ty2' ->
316 returnM (HsFunTy ty1' ty2', liftedTypeKind)
318 kc_hs_type ty@(HsOpTy ty1 op ty2)
319 = addLocM kcTyVar op `thenM` \ op_kind ->
320 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
321 returnM (HsOpTy ty1' op ty2', res_kind)
323 kc_hs_type ty@(HsAppTy ty1 ty2)
324 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
325 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
326 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
328 (fun_ty, arg_tys) = split ty1 [ty2]
329 split (L _ (HsAppTy f a)) as = split f (a:as)
331 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
332 -- the application; they are never used
334 kc_hs_type (HsPredTy pred)
335 = kcHsPred pred `thenM` \ pred' ->
336 returnM (HsPredTy pred', liftedTypeKind)
338 kc_hs_type (HsForAllTy exp tv_names context ty)
339 = kcHsTyVars tv_names $ \ tv_names' ->
340 do { ctxt' <- kcHsContext context
341 ; ty' <- kcLiftedType ty
342 -- The body of a forall is usually a type, but in principle
343 -- there's no reason to prohibit *unlifted* types.
344 -- In fact, GHC can itself construct a function with an
345 -- unboxed tuple inside a for-all (via CPR analyis; see
346 -- typecheck/should_compile/tc170)
348 -- Still, that's only for internal interfaces, which aren't
349 -- kind-checked, so we only allow liftedTypeKind here
351 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
353 kc_hs_type (HsBangTy b ty)
354 = do { (ty', kind) <- kcHsType ty
355 ; return (HsBangTy b ty', kind) }
357 kc_hs_type ty@(HsSpliceTy _)
358 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
361 ---------------------------
362 kcApps :: TcKind -- Function kind
364 -> [LHsType Name] -- Arg types
365 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
366 kcApps fun_kind ppr_fun args
367 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
368 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
369 returnM (args', res_kind)
371 split_fk fk 0 = returnM ([], fk)
372 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
374 Nothing -> failWithTc too_many_args
375 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
378 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
380 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
381 ptext SLIT("is applied to too many type arguments")
383 ---------------------------
384 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
385 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
387 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
388 kcHsLPred = wrapLocM kcHsPred
390 kcHsPred :: HsPred Name -> TcM (HsPred Name)
391 kcHsPred pred -- Checks that the result is of kind liftedType
392 = kc_pred pred `thenM` \ (pred', kind) ->
393 checkExpectedKind pred kind liftedTypeKind `thenM_`
396 ---------------------------
397 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
398 -- Does *not* check for a saturated
399 -- application (reason: used from TcDeriv)
400 kc_pred pred@(HsIParam name ty)
401 = kcHsType ty `thenM` \ (ty', kind) ->
402 returnM (HsIParam name ty', kind)
404 kc_pred pred@(HsClassP cls tys)
405 = kcClass cls `thenM` \ kind ->
406 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
407 returnM (HsClassP cls tys', res_kind)
409 ---------------------------
410 kcTyVar :: Name -> TcM TcKind
411 kcTyVar name -- Could be a tyvar or a tycon
412 = traceTc (text "lk1" <+> ppr name) `thenM_`
413 tcLookup name `thenM` \ thing ->
414 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
416 ATyVar _ ty -> returnM (typeKind ty)
417 AThing kind -> returnM kind
418 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
419 other -> wrongThingErr "type" thing name
421 kcClass :: Name -> TcM TcKind
422 kcClass cls -- Must be a class
423 = tcLookup cls `thenM` \ thing ->
425 AThing kind -> returnM kind
426 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
427 other -> wrongThingErr "class" thing cls
431 %************************************************************************
435 %************************************************************************
439 * Transforms from HsType to Type
442 It cannot fail, and does no validity checking, except for
443 structural matters, such as
444 (a) spurious ! annotations.
445 (b) a class used as a type
448 dsHsType :: LHsType Name -> TcM Type
449 -- All HsTyVarBndrs in the intput type are kind-annotated
450 dsHsType ty = ds_type (unLoc ty)
452 ds_type ty@(HsTyVar name)
455 ds_type (HsParTy ty) -- Remove the parentheses markers
458 ds_type ty@(HsBangTy _ _) -- No bangs should be here
459 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
461 ds_type (HsKindSig ty k)
462 = dsHsType ty -- Kind checking done already
464 ds_type (HsListTy ty)
465 = dsHsType ty `thenM` \ tau_ty ->
466 checkWiredInTyCon listTyCon `thenM_`
467 returnM (mkListTy tau_ty)
469 ds_type (HsPArrTy ty)
470 = dsHsType ty `thenM` \ tau_ty ->
471 checkWiredInTyCon parrTyCon `thenM_`
472 returnM (mkPArrTy tau_ty)
474 ds_type (HsTupleTy boxity tys)
475 = dsHsTypes tys `thenM` \ tau_tys ->
476 checkWiredInTyCon tycon `thenM_`
477 returnM (mkTyConApp tycon tau_tys)
479 tycon = tupleTyCon boxity (length tys)
481 ds_type (HsFunTy ty1 ty2)
482 = dsHsType ty1 `thenM` \ tau_ty1 ->
483 dsHsType ty2 `thenM` \ tau_ty2 ->
484 returnM (mkFunTy tau_ty1 tau_ty2)
486 ds_type (HsOpTy ty1 (L span op) ty2)
487 = dsHsType ty1 `thenM` \ tau_ty1 ->
488 dsHsType ty2 `thenM` \ tau_ty2 ->
489 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
493 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
494 returnM (mkTyConApp tc [])
496 ds_type ty@(HsAppTy _ _)
499 ds_type (HsPredTy pred)
500 = dsHsPred pred `thenM` \ pred' ->
501 returnM (mkPredTy pred')
503 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
504 = tcTyVarBndrs tv_names $ \ tyvars ->
505 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
506 dsHsType ty `thenM` \ tau ->
507 returnM (mkSigmaTy tyvars theta tau)
509 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
511 dsHsTypes arg_tys = mappM dsHsType arg_tys
514 Help functions for type applications
515 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
518 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
519 ds_app (HsAppTy ty1 ty2) tys
520 = ds_app (unLoc ty1) (ty2:tys)
523 = dsHsTypes tys `thenM` \ arg_tys ->
525 HsTyVar fun -> ds_var_app fun arg_tys
526 other -> ds_type ty `thenM` \ fun_ty ->
527 returnM (mkAppTys fun_ty arg_tys)
529 ds_var_app :: Name -> [Type] -> TcM Type
530 ds_var_app name arg_tys
531 = tcLookup name `thenM` \ thing ->
533 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
534 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
535 other -> wrongThingErr "type" thing name
543 dsHsLPred :: LHsPred Name -> TcM PredType
544 dsHsLPred pred = dsHsPred (unLoc pred)
546 dsHsPred pred@(HsClassP class_name tys)
547 = dsHsTypes tys `thenM` \ arg_tys ->
548 tcLookupClass class_name `thenM` \ clas ->
549 returnM (ClassP clas arg_tys)
551 dsHsPred (HsIParam name ty)
552 = dsHsType ty `thenM` \ arg_ty ->
553 returnM (IParam name arg_ty)
556 GADT constructor signatures
559 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
561 = addErrCtxt (gadtResCtxt res_ty) $
562 case get_largs res_ty [] of
563 (HsTyVar tc_name, args)
564 -> do { args' <- mapM dsHsType args
565 ; thing <- tcLookup tc_name
567 AGlobal (ATyCon tc) -> return (tc, args')
568 other -> failWithTc (badGadtDecl res_ty) }
569 other -> failWithTc (badGadtDecl res_ty)
571 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
572 -- because that causes a black hole, and for good reason. Building
573 -- the type means expanding type synonyms, and we can't do that
574 -- inside the "knot". So we have to work by steam.
575 get_largs (L _ ty) args = get_args ty args
576 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
577 get_args (HsParTy ty) args = get_largs ty args
578 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
579 get_args ty args = (ty, args)
582 = hang (ptext SLIT("In the result type of a data constructor:"))
585 = hang (ptext SLIT("Malformed constructor result type:"))
588 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
591 %************************************************************************
593 Type-variable binders
595 %************************************************************************
599 kcHsTyVars :: [LHsTyVarBndr Name]
600 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
601 -- They scope over the thing inside
603 kcHsTyVars tvs thing_inside
604 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
605 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
607 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
608 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
609 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
610 returnM (KindedTyVar name kind)
611 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
614 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
615 -> ([TyVar] -> TcM r)
617 -- Used when type-checking types/classes/type-decls
618 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
619 tcTyVarBndrs bndrs thing_inside
620 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
621 tcExtendTyVarEnv tyvars (thing_inside tyvars)
623 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
624 ; return (mkTyVar name kind') }
625 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
626 return (mkTyVar name liftedTypeKind)
628 -----------------------------------
629 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
630 -- GADT decls can have a (perhaps partial) kind signature
631 -- e.g. data T :: * -> * -> * where ...
632 -- This function makes up suitable (kinded) type variables for
633 -- the argument kinds, and checks that the result kind is indeed *
634 tcDataKindSig Nothing = return []
635 tcDataKindSig (Just kind)
636 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
637 ; span <- getSrcSpanM
638 ; us <- newUniqueSupply
639 ; let loc = srcSpanStart span
640 uniqs = uniqsFromSupply us
641 ; return [ mk_tv loc uniq str kind
642 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
644 (arg_kinds, res_kind) = splitKindFunTys kind
645 mk_tv loc uniq str kind = mkTyVar name kind
647 name = mkInternalName uniq occ loc
648 occ = mkOccName tvName str
650 names :: [String] -- a,b,c...aa,ab,ac etc
651 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
653 badKindSig :: Kind -> SDoc
655 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
660 %************************************************************************
662 Scoped type variables
664 %************************************************************************
667 tcAddScopedTyVars is used for scoped type variables added by pattern
669 e.g. \ ((x::a), (y::a)) -> x+y
670 They never have explicit kinds (because this is source-code only)
671 They are mutable (because they can get bound to a more specific type).
673 Usually we kind-infer and expand type splices, and then
674 tupecheck/desugar the type. That doesn't work well for scoped type
675 variables, because they scope left-right in patterns. (e.g. in the
676 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
678 The current not-very-good plan is to
679 * find all the types in the patterns
680 * find their free tyvars
682 * bring the kinded type vars into scope
683 * BUT throw away the kind-checked type
684 (we'll kind-check it again when we type-check the pattern)
686 This is bad because throwing away the kind checked type throws away
687 its splices. But too bad for now. [July 03]
690 We no longer specify that these type variables must be univerally
691 quantified (lots of email on the subject). If you want to put that
693 a) Do a checkSigTyVars after thing_inside
694 b) More insidiously, don't pass in expected_ty, else
695 we unify with it too early and checkSigTyVars barfs
696 Instead you have to pass in a fresh ty var, and unify
697 it with expected_ty afterwards
700 tcHsPatSigType :: UserTypeCtxt
701 -> LHsType Name -- The type signature
702 -> TcM ([TyVar], -- Newly in-scope type variables
703 Type) -- The signature
704 -- Used for type-checking type signatures in
705 -- (a) patterns e.g f (x::Int) = e
706 -- (b) result signatures e.g. g x :: Int = e
707 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
709 tcHsPatSigType ctxt hs_ty
710 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
711 do { -- Find the type variables that are mentioned in the type
712 -- but not already in scope. These are the ones that
713 -- should be bound by the pattern signature
714 in_scope <- getInLocalScope
715 ; let span = getLoc hs_ty
716 sig_tvs = [ L span (UserTyVar n)
717 | n <- nameSetToList (extractHsTyVars hs_ty),
720 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
721 -- except that we want to keep the tvs separate
722 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
723 { kinded_ty <- kcTypeType hs_ty
724 ; return (kinded_tvs, kinded_ty) }
725 ; tcTyVarBndrs kinded_tvs $ \ tyvars -> do
726 { sig_ty <- dsHsType kinded_ty
727 ; checkValidType ctxt sig_ty
728 ; return (tyvars, sig_ty)
731 tcPatSig :: UserTypeCtxt
734 -> TcM (TcType, -- The type to use for "inside" the signature
735 [(Name,TcType)]) -- The new bit of type environment, binding
736 -- the scoped type variables
737 tcPatSig ctxt sig res_ty
738 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
740 ; if null sig_tvs then do {
741 -- The type signature binds no type variables,
742 -- and hence is rigid, so use it to zap the res_ty
743 boxyUnify sig_ty res_ty
744 ; return (sig_ty, [])
747 -- Type signature binds at least one scoped type variable
749 -- A pattern binding cannot bind scoped type variables
750 -- The renamer fails with a name-out-of-scope error
751 -- if a pattern binding tries to bind a type variable,
752 -- So we just have an ASSERT here
753 ; let in_pat_bind = case ctxt of
754 BindPatSigCtxt -> True
756 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
758 -- Check that pat_ty is rigid
759 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
761 -- Now match the pattern signature against res_ty
762 -- For convenience, and uniform-looking error messages
763 -- we do the matching by allocating meta type variables,
764 -- unifying, and reading out the results.
765 -- This is a strictly local operation.
766 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
767 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
768 ; sig_tv_tys <- mapM readFilledBox box_tvs
770 -- Check that each is bound to a distinct type variable,
771 -- and one that is not already in scope
772 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
773 ; binds_in_scope <- getScopedTyVarBinds
774 ; check binds_in_scope tv_binds
777 ; return (res_ty, tv_binds)
780 check in_scope [] = return ()
781 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
782 ; check ((n,ty):in_scope) rest }
784 check_one in_scope n ty
785 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
786 -- Must bind to a type variable
788 ; checkTc (null dups) (dupInScope n (head dups) ty)
789 -- Must not bind to the same type variable
790 -- as some other in-scope type variable
794 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
798 %************************************************************************
800 Scoped type variables
802 %************************************************************************
805 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
806 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
807 nest 2 (pp_sig ctxt) ]
809 pp_sig (FunSigCtxt n) = pp_n_colon n
810 pp_sig (ConArgCtxt n) = pp_n_colon n
811 pp_sig (ForSigCtxt n) = pp_n_colon n
812 pp_sig (RuleSigCtxt n) = pp_n_colon n
813 pp_sig other = ppr (unLoc hs_ty)
815 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
819 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
820 <+> pprQuotedList sig_tvs)
821 2 (ptext SLIT("unless the pattern has a rigid type context"))
824 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
825 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
826 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
829 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
830 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
831 ptext SLIT("Distinct scoped type variables must be distinct")])