2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
9 -- The above warning supression flag is a temporary kludge.
10 -- While working on this module you are encouraged to remove it and fix
11 -- any warnings in the module. See
12 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 tcHsSigType, tcHsDeriv,
17 tcHsInstHead, tcHsQuantifiedType,
21 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
22 kcCheckHsType, kcHsContext, kcHsType,
24 -- Typechecking kinded types
25 tcHsKindedContext, tcHsKindedType, tcHsBangType,
26 tcTyVarBndrs, dsHsType, tcLHsConResTy,
29 -- Pattern type signatures
30 tcHsPatSigType, tcPatSig
33 #include "HsVersions.h"
43 import {- Kind parts of -} Type
61 ----------------------------
63 ----------------------------
65 Generally speaking we now type-check types in three phases
67 1. kcHsType: kind check the HsType
68 *includes* performing any TH type splices;
69 so it returns a translated, and kind-annotated, type
71 2. dsHsType: convert from HsType to Type:
73 expand type synonyms [mkGenTyApps]
74 hoist the foralls [tcHsType]
76 3. checkValidType: check the validity of the resulting type
78 Often these steps are done one after the other (tcHsSigType).
79 But in mutually recursive groups of type and class decls we do
80 1 kind-check the whole group
81 2 build TyCons/Classes in a knot-tied way
82 3 check the validity of types in the now-unknotted TyCons/Classes
84 For example, when we find
85 (forall a m. m a -> m a)
86 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
87 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
88 an environment that binds a and m suitably.
90 The kind checker passed to tcHsTyVars needs to look at enough to
91 establish the kind of the tyvar:
92 * For a group of type and class decls, it's just the group, not
93 the rest of the program
94 * For a tyvar bound in a pattern type signature, its the types
95 mentioned in the other type signatures in that bunch of patterns
96 * For a tyvar bound in a RULE, it's the type signatures on other
97 universally quantified variables in the rule
99 Note that this may occasionally give surprising results. For example:
101 data T a b = MkT (a b)
103 Here we deduce a::*->*, b::*
104 But equally valid would be a::(*->*)-> *, b::*->*
109 Some of the validity check could in principle be done by the kind checker,
112 - During desugaring, we normalise by expanding type synonyms. Only
113 after this step can we check things like type-synonym saturation
114 e.g. type T k = k Int
116 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
117 and then S is saturated. This is a GHC extension.
119 - Similarly, also a GHC extension, we look through synonyms before complaining
120 about the form of a class or instance declaration
122 - Ambiguity checks involve functional dependencies, and it's easier to wait
123 until knots have been resolved before poking into them
125 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
126 finished building the loop. So to keep things simple, we postpone most validity
127 checking until step (3).
131 During step (1) we might fault in a TyCon defined in another module, and it might
132 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
133 knot around type declarations with ARecThing, so that the fault-in code can get
134 the TyCon being defined.
137 %************************************************************************
139 \subsection{Checking types}
141 %************************************************************************
144 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
145 -- Do kind checking, and hoist for-alls to the top
146 -- NB: it's important that the foralls that come from the top-level
147 -- HsForAllTy in hs_ty occur *first* in the returned type.
148 -- See Note [Scoped] with TcSigInfo
149 tcHsSigType ctxt hs_ty
150 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
151 do { kinded_ty <- kcTypeType hs_ty
152 ; ty <- tcHsKindedType kinded_ty
153 ; checkValidType ctxt ty
156 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Type)
157 -- Typecheck an instance head. We can't use
158 -- tcHsSigType, because it's not a valid user type.
160 = do { kinded_ty <- kcHsSigType hs_ty
161 ; poly_ty <- tcHsKindedType kinded_ty
162 ; return (tcSplitSigmaTy poly_ty) }
164 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
165 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
166 -- except that we want to keep the tvs separate
167 tcHsQuantifiedType tv_names hs_ty
168 = kcHsTyVars tv_names $ \ tv_names' ->
169 do { kc_ty <- kcHsSigType hs_ty
170 ; tcTyVarBndrs tv_names' $ \ tvs ->
171 do { ty <- dsHsType kc_ty
172 ; return (tvs, ty) } }
174 -- Used for the deriving(...) items
175 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
176 tcHsDeriv = addLocM (tc_hs_deriv [])
178 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
179 = kcHsTyVars tv_names $ \ tv_names' ->
180 do { cls_kind <- kcClass cls_name
181 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
182 ; tcTyVarBndrs tv_names' $ \ tyvars ->
183 do { arg_tys <- dsHsTypes tys
184 ; cls <- tcLookupClass cls_name
185 ; return (tyvars, cls, arg_tys) }}
187 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
188 = -- Funny newtype deriving form
190 -- where C has arity 2. Hence can't use regular functions
191 tc_hs_deriv (tv_names1 ++ tv_names2) ty
194 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
197 These functions are used during knot-tying in
198 type and class declarations, when we have to
199 separate kind-checking, desugaring, and validity checking
202 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
203 -- Used for type signatures
204 kcHsSigType ty = kcTypeType ty
205 kcHsLiftedSigType ty = kcLiftedType ty
207 tcHsKindedType :: LHsType Name -> TcM Type
208 -- Don't do kind checking, nor validity checking.
209 -- This is used in type and class decls, where kinding is
210 -- done in advance, and validity checking is done later
211 -- [Validity checking done later because of knot-tying issues.]
212 tcHsKindedType hs_ty = dsHsType hs_ty
214 tcHsBangType :: LHsType Name -> TcM Type
215 -- Permit a bang, but discard it
216 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
217 tcHsBangType ty = tcHsKindedType ty
219 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
220 -- Used when we are expecting a ClassContext (i.e. no implicit params)
221 -- Does not do validity checking, like tcHsKindedType
222 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
226 %************************************************************************
228 The main kind checker: kcHsType
230 %************************************************************************
232 First a couple of simple wrappers for kcHsType
235 ---------------------------
236 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
237 -- The type ty must be a *lifted* *type*
238 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
240 ---------------------------
241 kcTypeType :: LHsType Name -> TcM (LHsType Name)
242 -- The type ty must be a *type*, but it can be lifted or
243 -- unlifted or an unboxed tuple.
244 kcTypeType ty = kcCheckHsType ty openTypeKind
246 ---------------------------
247 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
248 -- Check that the type has the specified kind
249 -- Be sure to use checkExpectedKind, rather than simply unifying
250 -- with OpenTypeKind, because it gives better error messages
251 kcCheckHsType (L span ty) exp_kind
253 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
254 -- Add the context round the inner check only
255 -- because checkExpectedKind already mentions
256 -- 'ty' by name in any error message
258 ; checkExpectedKind (strip ty) act_kind exp_kind
259 ; return (L span ty') }
261 -- Wrap a context around only if we want to show that contexts.
262 add_ctxt (HsPredTy p) thing = thing
263 -- Omit invisble ones and ones user's won't grok (HsPred p).
264 add_ctxt (HsForAllTy _ _ (L _ []) _) thing = thing
265 -- Omit wrapping if the theta-part is empty
266 -- Reason: the recursive call to kcLiftedType, in the ForAllTy
267 -- case of kc_hs_type, will do the wrapping instead
268 -- and we don't want to duplicate
269 add_ctxt other_ty thing = addErrCtxt (typeCtxt other_ty) thing
271 -- We infer the kind of the type, and then complain if it's
272 -- not right. But we don't want to complain about
273 -- (ty) or !(ty) or forall a. ty
274 -- when the real difficulty is with the 'ty' part.
275 strip (HsParTy (L _ ty)) = strip ty
276 strip (HsBangTy _ (L _ ty)) = strip ty
277 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
281 Here comes the main function
284 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
285 kcHsType ty = wrapLocFstM kc_hs_type ty
286 -- kcHsType *returns* the kind of the type, rather than taking an expected
287 -- kind as argument as tcExpr does.
289 -- (a) the kind of (->) is
290 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
291 -- so we'd need to generate huge numbers of bx variables.
292 -- (b) kinds are so simple that the error messages are fine
294 -- The translated type has explicitly-kinded type-variable binders
296 kc_hs_type (HsParTy ty) = do
297 (ty', kind) <- kcHsType ty
298 return (HsParTy ty', kind)
300 kc_hs_type (HsTyVar name) = do
302 return (HsTyVar name, kind)
304 kc_hs_type (HsListTy ty) = do
305 ty' <- kcLiftedType ty
306 return (HsListTy ty', liftedTypeKind)
308 kc_hs_type (HsPArrTy ty) = do
309 ty' <- kcLiftedType ty
310 return (HsPArrTy ty', liftedTypeKind)
312 kc_hs_type (HsNumTy n)
313 = return (HsNumTy n, liftedTypeKind)
315 kc_hs_type (HsKindSig ty k) = do
316 ty' <- kcCheckHsType ty k
317 return (HsKindSig ty' k, k)
319 kc_hs_type (HsTupleTy Boxed tys) = do
320 tys' <- mapM kcLiftedType tys
321 return (HsTupleTy Boxed tys', liftedTypeKind)
323 kc_hs_type (HsTupleTy Unboxed tys) = do
324 tys' <- mapM kcTypeType tys
325 return (HsTupleTy Unboxed tys', ubxTupleKind)
327 kc_hs_type (HsFunTy ty1 ty2) = do
328 ty1' <- kcCheckHsType ty1 argTypeKind
329 ty2' <- kcTypeType ty2
330 return (HsFunTy ty1' ty2', liftedTypeKind)
332 kc_hs_type ty@(HsOpTy ty1 op ty2) = do
333 op_kind <- addLocM kcTyVar op
334 ([ty1',ty2'], res_kind) <- kcApps op_kind (ppr op) [ty1,ty2]
335 return (HsOpTy ty1' op ty2', res_kind)
337 kc_hs_type ty@(HsAppTy ty1 ty2) = do
338 (fun_ty', fun_kind) <- kcHsType fun_ty
339 ((arg_ty':arg_tys'), res_kind) <- kcApps fun_kind (ppr fun_ty) arg_tys
340 return (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
342 (fun_ty, arg_tys) = split ty1 [ty2]
343 split (L _ (HsAppTy f a)) as = split f (a:as)
345 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
346 -- the application; they are
349 kc_hs_type ty@(HsPredTy (HsEqualP _ _))
352 kc_hs_type (HsPredTy pred) = do
353 pred' <- kcHsPred pred
354 return (HsPredTy pred', liftedTypeKind)
356 kc_hs_type (HsForAllTy exp tv_names context ty)
357 = kcHsTyVars tv_names $ \ tv_names' ->
358 do { ctxt' <- kcHsContext context
359 ; ty' <- kcLiftedType ty
360 -- The body of a forall is usually a type, but in principle
361 -- there's no reason to prohibit *unlifted* types.
362 -- In fact, GHC can itself construct a function with an
363 -- unboxed tuple inside a for-all (via CPR analyis; see
364 -- typecheck/should_compile/tc170)
366 -- Still, that's only for internal interfaces, which aren't
367 -- kind-checked, so we only allow liftedTypeKind here
369 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
371 kc_hs_type (HsBangTy b ty) = do
372 (ty', kind) <- kcHsType ty
373 return (HsBangTy b ty', kind)
375 kc_hs_type ty@(HsSpliceTy _)
376 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
378 -- remove the doc nodes here, no need to worry about the location since
379 -- its the same for a doc node and it's child type node
380 kc_hs_type (HsDocTy ty _)
381 = kc_hs_type (unLoc ty)
383 ---------------------------
384 kcApps :: TcKind -- Function kind
386 -> [LHsType Name] -- Arg types
387 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
388 kcApps fun_kind ppr_fun args = do
389 (arg_kinds, res_kind) <- split_fk fun_kind (length args)
390 args' <- zipWithM kc_arg args arg_kinds
391 return (args', res_kind)
393 split_fk fk 0 = return ([], fk)
394 split_fk fk n = do mb_fk <- unifyFunKind fk
396 Nothing -> failWithTc too_many_args
397 Just (ak,fk') -> do (aks, rk) <- split_fk fk' (n-1)
400 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
402 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
403 ptext SLIT("is applied to too many type arguments")
405 ---------------------------
406 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
407 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
409 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
410 kcHsLPred = wrapLocM kcHsPred
412 kcHsPred :: HsPred Name -> TcM (HsPred Name)
413 kcHsPred pred = do -- Checks that the result is of kind liftedType
414 (pred', kind) <- kc_pred pred
415 checkExpectedKind pred kind liftedTypeKind
418 ---------------------------
419 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
420 -- Does *not* check for a saturated
421 -- application (reason: used from TcDeriv)
422 kc_pred pred@(HsIParam name ty)
423 = do { (ty', kind) <- kcHsType ty
424 ; return (HsIParam name ty', kind)
426 kc_pred pred@(HsClassP cls tys)
427 = do { kind <- kcClass cls
428 ; (tys', res_kind) <- kcApps kind (ppr cls) tys
429 ; return (HsClassP cls tys', res_kind)
431 kc_pred pred@(HsEqualP ty1 ty2)
432 = do { (ty1', kind1) <- kcHsType ty1
433 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
434 ; (ty2', kind2) <- kcHsType ty2
435 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
436 ; checkExpectedKind ty2 kind2 kind1
437 ; return (HsEqualP ty1' ty2', liftedTypeKind)
440 ---------------------------
441 kcTyVar :: Name -> TcM TcKind
442 kcTyVar name = do -- Could be a tyvar or a tycon
443 traceTc (text "lk1" <+> ppr name)
444 thing <- tcLookup name
445 traceTc (text "lk2" <+> ppr name <+> ppr thing)
447 ATyVar _ ty -> return (typeKind ty)
448 AThing kind -> return kind
449 AGlobal (ATyCon tc) -> return (tyConKind tc)
450 other -> wrongThingErr "type" thing name
452 kcClass :: Name -> TcM TcKind
453 kcClass cls = do -- Must be a class
454 thing <- tcLookup cls
456 AThing kind -> return kind
457 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
458 other -> wrongThingErr "class" thing cls
462 %************************************************************************
466 %************************************************************************
470 * Transforms from HsType to Type
473 It cannot fail, and does no validity checking, except for
474 structural matters, such as
475 (a) spurious ! annotations.
476 (b) a class used as a type
479 dsHsType :: LHsType Name -> TcM Type
480 -- All HsTyVarBndrs in the intput type are kind-annotated
481 dsHsType ty = ds_type (unLoc ty)
483 ds_type ty@(HsTyVar name)
486 ds_type (HsParTy ty) -- Remove the parentheses markers
489 ds_type ty@(HsBangTy _ _) -- No bangs should be here
490 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
492 ds_type (HsKindSig ty k)
493 = dsHsType ty -- Kind checking done already
495 ds_type (HsListTy ty) = do
496 tau_ty <- dsHsType ty
497 checkWiredInTyCon listTyCon
498 return (mkListTy tau_ty)
500 ds_type (HsPArrTy ty) = do
501 tau_ty <- dsHsType ty
502 checkWiredInTyCon parrTyCon
503 return (mkPArrTy tau_ty)
505 ds_type (HsTupleTy boxity tys) = do
506 tau_tys <- dsHsTypes tys
507 checkWiredInTyCon tycon
508 return (mkTyConApp tycon tau_tys)
510 tycon = tupleTyCon boxity (length tys)
512 ds_type (HsFunTy ty1 ty2) = do
513 tau_ty1 <- dsHsType ty1
514 tau_ty2 <- dsHsType ty2
515 return (mkFunTy tau_ty1 tau_ty2)
517 ds_type (HsOpTy ty1 (L span op) ty2) = do
518 tau_ty1 <- dsHsType ty1
519 tau_ty2 <- dsHsType ty2
520 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
524 tc <- tcLookupTyCon genUnitTyConName
525 return (mkTyConApp tc [])
527 ds_type ty@(HsAppTy _ _)
530 ds_type (HsPredTy pred) = do
531 pred' <- dsHsPred pred
532 return (mkPredTy pred')
534 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
535 = tcTyVarBndrs tv_names $ \ tyvars -> do
536 theta <- mapM dsHsLPred (unLoc ctxt)
538 return (mkSigmaTy tyvars theta tau)
540 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
542 ds_type (HsDocTy ty _) -- Remove the doc comment
545 dsHsTypes arg_tys = mapM dsHsType arg_tys
548 Help functions for type applications
549 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
552 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
553 ds_app (HsAppTy ty1 ty2) tys
554 = ds_app (unLoc ty1) (ty2:tys)
557 arg_tys <- dsHsTypes tys
559 HsTyVar fun -> ds_var_app fun arg_tys
560 other -> do fun_ty <- ds_type ty
561 return (mkAppTys fun_ty arg_tys)
563 ds_var_app :: Name -> [Type] -> TcM Type
564 ds_var_app name arg_tys = do
565 thing <- tcLookup name
567 ATyVar _ ty -> return (mkAppTys ty arg_tys)
568 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
569 other -> wrongThingErr "type" thing name
577 dsHsLPred :: LHsPred Name -> TcM PredType
578 dsHsLPred pred = dsHsPred (unLoc pred)
580 dsHsPred pred@(HsClassP class_name tys)
581 = do { arg_tys <- dsHsTypes tys
582 ; clas <- tcLookupClass class_name
583 ; return (ClassP clas arg_tys)
585 dsHsPred pred@(HsEqualP ty1 ty2)
586 = do { arg_ty1 <- dsHsType ty1
587 ; arg_ty2 <- dsHsType ty2
588 ; return (EqPred arg_ty1 arg_ty2)
590 dsHsPred (HsIParam name ty)
591 = do { arg_ty <- dsHsType ty
592 ; return (IParam name arg_ty)
596 GADT constructor signatures
599 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
601 = addErrCtxt (gadtResCtxt res_ty) $
602 case get_largs res_ty [] of
603 (HsTyVar tc_name, args)
604 -> do { args' <- mapM dsHsType args
605 ; thing <- tcLookup tc_name
607 AGlobal (ATyCon tc) -> return (tc, args')
608 other -> failWithTc (badGadtDecl res_ty) }
609 other -> failWithTc (badGadtDecl res_ty)
611 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
612 -- because that causes a black hole, and for good reason. Building
613 -- the type means expanding type synonyms, and we can't do that
614 -- inside the "knot". So we have to work by steam.
615 get_largs (L _ ty) args = get_args ty args
616 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
617 get_args (HsParTy ty) args = get_largs ty args
618 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
619 get_args ty args = (ty, args)
622 = hang (ptext SLIT("In the result type of a data constructor:"))
625 = hang (ptext SLIT("Malformed constructor result type:"))
628 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
631 %************************************************************************
633 Type-variable binders
635 %************************************************************************
639 kcHsTyVars :: [LHsTyVarBndr Name]
640 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
641 -- They scope over the thing inside
643 kcHsTyVars tvs thing_inside = do
644 bndrs <- mapM (wrapLocM kcHsTyVar) tvs
645 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
647 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
648 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
649 kcHsTyVar (UserTyVar name) = KindedTyVar name <$> newKindVar
650 kcHsTyVar (KindedTyVar name kind) = return (KindedTyVar name kind)
653 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
654 -> ([TyVar] -> TcM r)
656 -- Used when type-checking types/classes/type-decls
657 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
658 tcTyVarBndrs bndrs thing_inside = do
659 tyvars <- mapM (zonk . unLoc) bndrs
660 tcExtendTyVarEnv tyvars (thing_inside tyvars)
662 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
663 ; return (mkTyVar name kind') }
664 zonk (UserTyVar name) = WARN( True, ptext SLIT("Un-kinded tyvar") <+> ppr name )
665 return (mkTyVar name liftedTypeKind)
667 -----------------------------------
668 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
669 -- GADT decls can have a (perhaps partial) kind signature
670 -- e.g. data T :: * -> * -> * where ...
671 -- This function makes up suitable (kinded) type variables for
672 -- the argument kinds, and checks that the result kind is indeed *.
673 -- We use it also to make up argument type variables for for data instances.
674 tcDataKindSig Nothing = return []
675 tcDataKindSig (Just kind)
676 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
677 ; span <- getSrcSpanM
678 ; us <- newUniqueSupply
679 ; let uniqs = uniqsFromSupply us
680 ; return [ mk_tv span uniq str kind
681 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
683 (arg_kinds, res_kind) = splitKindFunTys kind
684 mk_tv loc uniq str kind = mkTyVar name kind
686 name = mkInternalName uniq occ loc
687 occ = mkOccName tvName str
689 names :: [String] -- a,b,c...aa,ab,ac etc
690 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
692 badKindSig :: Kind -> SDoc
694 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
699 %************************************************************************
701 Scoped type variables
703 %************************************************************************
706 tcAddScopedTyVars is used for scoped type variables added by pattern
708 e.g. \ ((x::a), (y::a)) -> x+y
709 They never have explicit kinds (because this is source-code only)
710 They are mutable (because they can get bound to a more specific type).
712 Usually we kind-infer and expand type splices, and then
713 tupecheck/desugar the type. That doesn't work well for scoped type
714 variables, because they scope left-right in patterns. (e.g. in the
715 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
717 The current not-very-good plan is to
718 * find all the types in the patterns
719 * find their free tyvars
721 * bring the kinded type vars into scope
722 * BUT throw away the kind-checked type
723 (we'll kind-check it again when we type-check the pattern)
725 This is bad because throwing away the kind checked type throws away
726 its splices. But too bad for now. [July 03]
729 We no longer specify that these type variables must be univerally
730 quantified (lots of email on the subject). If you want to put that
732 a) Do a checkSigTyVars after thing_inside
733 b) More insidiously, don't pass in expected_ty, else
734 we unify with it too early and checkSigTyVars barfs
735 Instead you have to pass in a fresh ty var, and unify
736 it with expected_ty afterwards
739 tcHsPatSigType :: UserTypeCtxt
740 -> LHsType Name -- The type signature
741 -> TcM ([TyVar], -- Newly in-scope type variables
742 Type) -- The signature
743 -- Used for type-checking type signatures in
744 -- (a) patterns e.g f (x::Int) = e
745 -- (b) result signatures e.g. g x :: Int = e
746 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
748 tcHsPatSigType ctxt hs_ty
749 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
750 do { -- Find the type variables that are mentioned in the type
751 -- but not already in scope. These are the ones that
752 -- should be bound by the pattern signature
753 in_scope <- getInLocalScope
754 ; let span = getLoc hs_ty
755 sig_tvs = [ L span (UserTyVar n)
756 | n <- nameSetToList (extractHsTyVars hs_ty),
759 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
760 ; checkValidType ctxt sig_ty
761 ; return (tyvars, sig_ty)
764 tcPatSig :: UserTypeCtxt
767 -> TcM (TcType, -- The type to use for "inside" the signature
768 [(Name,TcType)]) -- The new bit of type environment, binding
769 -- the scoped type variables
770 tcPatSig ctxt sig res_ty
771 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
773 ; if null sig_tvs then do {
774 -- The type signature binds no type variables,
775 -- and hence is rigid, so use it to zap the res_ty
776 boxyUnify sig_ty res_ty
777 ; return (sig_ty, [])
780 -- Type signature binds at least one scoped type variable
782 -- A pattern binding cannot bind scoped type variables
783 -- The renamer fails with a name-out-of-scope error
784 -- if a pattern binding tries to bind a type variable,
785 -- So we just have an ASSERT here
786 ; let in_pat_bind = case ctxt of
787 BindPatSigCtxt -> True
789 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
791 -- Check that pat_ty is rigid
792 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
794 -- Now match the pattern signature against res_ty
795 -- For convenience, and uniform-looking error messages
796 -- we do the matching by allocating meta type variables,
797 -- unifying, and reading out the results.
798 -- This is a strictly local operation.
799 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
800 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
801 ; sig_tv_tys <- mapM readFilledBox box_tvs
803 -- Check that each is bound to a distinct type variable,
804 -- and one that is not already in scope
805 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
806 ; binds_in_scope <- getScopedTyVarBinds
807 ; check binds_in_scope tv_binds
810 ; return (res_ty, tv_binds)
813 check in_scope [] = return ()
814 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
815 ; check ((n,ty):in_scope) rest }
817 check_one in_scope n ty
818 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
819 -- Must bind to a type variable
821 ; checkTc (null dups) (dupInScope n (head dups) ty)
822 -- Must not bind to the same type variable
823 -- as some other in-scope type variable
827 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
831 %************************************************************************
833 Scoped type variables
835 %************************************************************************
838 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
839 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
840 nest 2 (pp_sig ctxt) ]
842 pp_sig (FunSigCtxt n) = pp_n_colon n
843 pp_sig (ConArgCtxt n) = pp_n_colon n
844 pp_sig (ForSigCtxt n) = pp_n_colon n
845 pp_sig other = ppr (unLoc hs_ty)
847 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
851 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
852 <+> pprQuotedList sig_tvs)
853 2 (ptext SLIT("unless the pattern has a rigid type context"))
856 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
857 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
858 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
861 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
862 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
863 ptext SLIT("Distinct scoped type variables must be distinct")])
866 = failWithTc (text "Equality predicate used as a type")