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
59 ----------------------------
61 ----------------------------
63 Generally speaking we now type-check types in three phases
65 1. kcHsType: kind check the HsType
66 *includes* performing any TH type splices;
67 so it returns a translated, and kind-annotated, type
69 2. dsHsType: convert from HsType to Type:
71 expand type synonyms [mkGenTyApps]
72 hoist the foralls [tcHsType]
74 3. checkValidType: check the validity of the resulting type
76 Often these steps are done one after the other (tcHsSigType).
77 But in mutually recursive groups of type and class decls we do
78 1 kind-check the whole group
79 2 build TyCons/Classes in a knot-tied way
80 3 check the validity of types in the now-unknotted TyCons/Classes
82 For example, when we find
83 (forall a m. m a -> m a)
84 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
85 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
86 an environment that binds a and m suitably.
88 The kind checker passed to tcHsTyVars needs to look at enough to
89 establish the kind of the tyvar:
90 * For a group of type and class decls, it's just the group, not
91 the rest of the program
92 * For a tyvar bound in a pattern type signature, its the types
93 mentioned in the other type signatures in that bunch of patterns
94 * For a tyvar bound in a RULE, it's the type signatures on other
95 universally quantified variables in the rule
97 Note that this may occasionally give surprising results. For example:
99 data T a b = MkT (a b)
101 Here we deduce a::*->*, b::*
102 But equally valid would be a::(*->*)-> *, b::*->*
107 Some of the validity check could in principle be done by the kind checker,
110 - During desugaring, we normalise by expanding type synonyms. Only
111 after this step can we check things like type-synonym saturation
112 e.g. type T k = k Int
114 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
115 and then S is saturated. This is a GHC extension.
117 - Similarly, also a GHC extension, we look through synonyms before complaining
118 about the form of a class or instance declaration
120 - Ambiguity checks involve functional dependencies, and it's easier to wait
121 until knots have been resolved before poking into them
123 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
124 finished building the loop. So to keep things simple, we postpone most validity
125 checking until step (3).
129 During step (1) we might fault in a TyCon defined in another module, and it might
130 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
131 knot around type declarations with ARecThing, so that the fault-in code can get
132 the TyCon being defined.
135 %************************************************************************
137 \subsection{Checking types}
139 %************************************************************************
142 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
143 -- Do kind checking, and hoist for-alls to the top
144 -- NB: it's important that the foralls that come from the top-level
145 -- HsForAllTy in hs_ty occur *first* in the returned type.
146 -- See Note [Scoped] with TcSigInfo
147 tcHsSigType ctxt hs_ty
148 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
149 do { kinded_ty <- kcTypeType hs_ty
150 ; ty <- tcHsKindedType kinded_ty
151 ; checkValidType ctxt ty
154 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Type)
155 -- Typecheck an instance head. We can't use
156 -- tcHsSigType, because it's not a valid user type.
158 = do { kinded_ty <- kcHsSigType hs_ty
159 ; poly_ty <- tcHsKindedType kinded_ty
160 ; return (tcSplitSigmaTy poly_ty) }
162 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
163 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
164 -- except that we want to keep the tvs separate
165 tcHsQuantifiedType tv_names hs_ty
166 = kcHsTyVars tv_names $ \ tv_names' ->
167 do { kc_ty <- kcHsSigType hs_ty
168 ; tcTyVarBndrs tv_names' $ \ tvs ->
169 do { ty <- dsHsType kc_ty
170 ; return (tvs, ty) } }
172 -- Used for the deriving(...) items
173 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
174 tcHsDeriv = addLocM (tc_hs_deriv [])
176 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
177 = kcHsTyVars tv_names $ \ tv_names' ->
178 do { cls_kind <- kcClass cls_name
179 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
180 ; tcTyVarBndrs tv_names' $ \ tyvars ->
181 do { arg_tys <- dsHsTypes tys
182 ; cls <- tcLookupClass cls_name
183 ; return (tyvars, cls, arg_tys) }}
185 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
186 = -- Funny newtype deriving form
188 -- where C has arity 2. Hence can't use regular functions
189 tc_hs_deriv (tv_names1 ++ tv_names2) ty
192 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
195 These functions are used during knot-tying in
196 type and class declarations, when we have to
197 separate kind-checking, desugaring, and validity checking
200 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
201 -- Used for type signatures
202 kcHsSigType ty = kcTypeType ty
203 kcHsLiftedSigType ty = kcLiftedType ty
205 tcHsKindedType :: LHsType Name -> TcM Type
206 -- Don't do kind checking, nor validity checking.
207 -- This is used in type and class decls, where kinding is
208 -- done in advance, and validity checking is done later
209 -- [Validity checking done later because of knot-tying issues.]
210 tcHsKindedType hs_ty = dsHsType hs_ty
212 tcHsBangType :: LHsType Name -> TcM Type
213 -- Permit a bang, but discard it
214 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
215 tcHsBangType ty = tcHsKindedType ty
217 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
218 -- Used when we are expecting a ClassContext (i.e. no implicit params)
219 -- Does not do validity checking, like tcHsKindedType
220 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
224 %************************************************************************
226 The main kind checker: kcHsType
228 %************************************************************************
230 First a couple of simple wrappers for kcHsType
233 ---------------------------
234 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
235 -- The type ty must be a *lifted* *type*
236 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
238 ---------------------------
239 kcTypeType :: LHsType Name -> TcM (LHsType Name)
240 -- The type ty must be a *type*, but it can be lifted or
241 -- unlifted or an unboxed tuple.
242 kcTypeType ty = kcCheckHsType ty openTypeKind
244 ---------------------------
245 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
246 -- Check that the type has the specified kind
247 -- Be sure to use checkExpectedKind, rather than simply unifying
248 -- with OpenTypeKind, because it gives better error messages
249 kcCheckHsType (L span ty) exp_kind
251 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
252 -- Add the context round the inner check only
253 -- because checkExpectedKind already mentions
254 -- 'ty' by name in any error message
256 ; checkExpectedKind (strip ty) act_kind exp_kind
257 ; return (L span ty') }
259 -- Wrap a context around only if we want to show that contexts.
260 add_ctxt (HsPredTy p) thing = thing
261 -- Omit invisble ones and ones user's won't grok (HsPred p).
262 add_ctxt (HsForAllTy _ _ (L _ []) _) thing = thing
263 -- Omit wrapping if the theta-part is empty
264 -- Reason: the recursive call to kcLiftedType, in the ForAllTy
265 -- case of kc_hs_type, will do the wrapping instead
266 -- and we don't want to duplicate
267 add_ctxt other_ty thing = addErrCtxt (typeCtxt other_ty) thing
269 -- We infer the kind of the type, and then complain if it's
270 -- not right. But we don't want to complain about
271 -- (ty) or !(ty) or forall a. ty
272 -- when the real difficulty is with the 'ty' part.
273 strip (HsParTy (L _ ty)) = strip ty
274 strip (HsBangTy _ (L _ ty)) = strip ty
275 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
279 Here comes the main function
282 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
283 kcHsType ty = wrapLocFstM kc_hs_type ty
284 -- kcHsType *returns* the kind of the type, rather than taking an expected
285 -- kind as argument as tcExpr does.
287 -- (a) the kind of (->) is
288 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
289 -- so we'd need to generate huge numbers of bx variables.
290 -- (b) kinds are so simple that the error messages are fine
292 -- The translated type has explicitly-kinded type-variable binders
294 kc_hs_type (HsParTy ty)
295 = kcHsType ty `thenM` \ (ty', kind) ->
296 returnM (HsParTy ty', kind)
298 kc_hs_type (HsTyVar name)
299 = kcTyVar name `thenM` \ kind ->
300 returnM (HsTyVar name, kind)
302 kc_hs_type (HsListTy ty)
303 = kcLiftedType ty `thenM` \ ty' ->
304 returnM (HsListTy ty', liftedTypeKind)
306 kc_hs_type (HsPArrTy ty)
307 = kcLiftedType ty `thenM` \ ty' ->
308 returnM (HsPArrTy ty', liftedTypeKind)
310 kc_hs_type (HsNumTy n)
311 = returnM (HsNumTy n, liftedTypeKind)
313 kc_hs_type (HsKindSig ty k)
314 = kcCheckHsType ty k `thenM` \ ty' ->
315 returnM (HsKindSig ty' k, k)
317 kc_hs_type (HsTupleTy Boxed tys)
318 = mappM kcLiftedType tys `thenM` \ tys' ->
319 returnM (HsTupleTy Boxed tys', liftedTypeKind)
321 kc_hs_type (HsTupleTy Unboxed tys)
322 = mappM kcTypeType tys `thenM` \ tys' ->
323 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
325 kc_hs_type (HsFunTy ty1 ty2)
326 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
327 kcTypeType ty2 `thenM` \ ty2' ->
328 returnM (HsFunTy ty1' ty2', liftedTypeKind)
330 kc_hs_type ty@(HsOpTy ty1 op ty2)
331 = addLocM kcTyVar op `thenM` \ op_kind ->
332 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
333 returnM (HsOpTy ty1' op ty2', res_kind)
335 kc_hs_type ty@(HsAppTy ty1 ty2)
336 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
337 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
338 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
340 (fun_ty, arg_tys) = split ty1 [ty2]
341 split (L _ (HsAppTy f a)) as = split f (a:as)
343 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
344 -- the application; they are
347 kc_hs_type ty@(HsPredTy (HsEqualP _ _))
350 kc_hs_type (HsPredTy pred)
351 = kcHsPred pred `thenM` \ pred' ->
352 returnM (HsPredTy pred', liftedTypeKind)
354 kc_hs_type (HsForAllTy exp tv_names context ty)
355 = kcHsTyVars tv_names $ \ tv_names' ->
356 do { ctxt' <- kcHsContext context
357 ; ty' <- kcLiftedType ty
358 -- The body of a forall is usually a type, but in principle
359 -- there's no reason to prohibit *unlifted* types.
360 -- In fact, GHC can itself construct a function with an
361 -- unboxed tuple inside a for-all (via CPR analyis; see
362 -- typecheck/should_compile/tc170)
364 -- Still, that's only for internal interfaces, which aren't
365 -- kind-checked, so we only allow liftedTypeKind here
367 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
369 kc_hs_type (HsBangTy b ty)
370 = do { (ty', kind) <- kcHsType ty
371 ; return (HsBangTy b ty', kind) }
373 kc_hs_type ty@(HsSpliceTy _)
374 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
376 -- remove the doc nodes here, no need to worry about the location since
377 -- its the same for a doc node and it's child type node
378 kc_hs_type (HsDocTy ty _)
379 = kc_hs_type (unLoc ty)
381 ---------------------------
382 kcApps :: TcKind -- Function kind
384 -> [LHsType Name] -- Arg types
385 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
386 kcApps fun_kind ppr_fun args
387 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
388 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
389 returnM (args', res_kind)
391 split_fk fk 0 = returnM ([], fk)
392 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
394 Nothing -> failWithTc too_many_args
395 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
398 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
400 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
401 ptext SLIT("is applied to too many type arguments")
403 ---------------------------
404 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
405 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
407 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
408 kcHsLPred = wrapLocM kcHsPred
410 kcHsPred :: HsPred Name -> TcM (HsPred Name)
411 kcHsPred pred -- Checks that the result is of kind liftedType
412 = kc_pred pred `thenM` \ (pred', kind) ->
413 checkExpectedKind pred kind liftedTypeKind `thenM_`
416 ---------------------------
417 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
418 -- Does *not* check for a saturated
419 -- application (reason: used from TcDeriv)
420 kc_pred pred@(HsIParam name ty)
421 = do { (ty', kind) <- kcHsType ty
422 ; returnM (HsIParam name ty', kind)
424 kc_pred pred@(HsClassP cls tys)
425 = do { kind <- kcClass cls
426 ; (tys', res_kind) <- kcApps kind (ppr cls) tys
427 ; returnM (HsClassP cls tys', res_kind)
429 kc_pred pred@(HsEqualP ty1 ty2)
430 = do { (ty1', kind1) <- kcHsType ty1
431 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
432 ; (ty2', kind2) <- kcHsType ty2
433 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
434 ; checkExpectedKind ty2 kind2 kind1
435 ; returnM (HsEqualP ty1' ty2', liftedTypeKind)
438 ---------------------------
439 kcTyVar :: Name -> TcM TcKind
440 kcTyVar name -- Could be a tyvar or a tycon
441 = traceTc (text "lk1" <+> ppr name) `thenM_`
442 tcLookup name `thenM` \ thing ->
443 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
445 ATyVar _ ty -> returnM (typeKind ty)
446 AThing kind -> returnM kind
447 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
448 other -> wrongThingErr "type" thing name
450 kcClass :: Name -> TcM TcKind
451 kcClass cls -- Must be a class
452 = tcLookup cls `thenM` \ thing ->
454 AThing kind -> returnM kind
455 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
456 other -> wrongThingErr "class" thing cls
460 %************************************************************************
464 %************************************************************************
468 * Transforms from HsType to Type
471 It cannot fail, and does no validity checking, except for
472 structural matters, such as
473 (a) spurious ! annotations.
474 (b) a class used as a type
477 dsHsType :: LHsType Name -> TcM Type
478 -- All HsTyVarBndrs in the intput type are kind-annotated
479 dsHsType ty = ds_type (unLoc ty)
481 ds_type ty@(HsTyVar name)
484 ds_type (HsParTy ty) -- Remove the parentheses markers
487 ds_type ty@(HsBangTy _ _) -- No bangs should be here
488 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
490 ds_type (HsKindSig ty k)
491 = dsHsType ty -- Kind checking done already
493 ds_type (HsListTy ty)
494 = dsHsType ty `thenM` \ tau_ty ->
495 checkWiredInTyCon listTyCon `thenM_`
496 returnM (mkListTy tau_ty)
498 ds_type (HsPArrTy ty)
499 = dsHsType ty `thenM` \ tau_ty ->
500 checkWiredInTyCon parrTyCon `thenM_`
501 returnM (mkPArrTy tau_ty)
503 ds_type (HsTupleTy boxity tys)
504 = dsHsTypes tys `thenM` \ tau_tys ->
505 checkWiredInTyCon tycon `thenM_`
506 returnM (mkTyConApp tycon tau_tys)
508 tycon = tupleTyCon boxity (length tys)
510 ds_type (HsFunTy ty1 ty2)
511 = dsHsType ty1 `thenM` \ tau_ty1 ->
512 dsHsType ty2 `thenM` \ tau_ty2 ->
513 returnM (mkFunTy tau_ty1 tau_ty2)
515 ds_type (HsOpTy ty1 (L span op) ty2)
516 = dsHsType ty1 `thenM` \ tau_ty1 ->
517 dsHsType ty2 `thenM` \ tau_ty2 ->
518 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
522 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
523 returnM (mkTyConApp tc [])
525 ds_type ty@(HsAppTy _ _)
528 ds_type (HsPredTy pred)
529 = dsHsPred pred `thenM` \ pred' ->
530 returnM (mkPredTy pred')
532 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
533 = tcTyVarBndrs tv_names $ \ tyvars ->
534 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
535 dsHsType ty `thenM` \ tau ->
536 returnM (mkSigmaTy tyvars theta tau)
538 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
540 ds_type (HsDocTy ty _) -- Remove the doc comment
543 dsHsTypes arg_tys = mappM dsHsType arg_tys
546 Help functions for type applications
547 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
550 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
551 ds_app (HsAppTy ty1 ty2) tys
552 = ds_app (unLoc ty1) (ty2:tys)
555 = dsHsTypes tys `thenM` \ arg_tys ->
557 HsTyVar fun -> ds_var_app fun arg_tys
558 other -> ds_type ty `thenM` \ fun_ty ->
559 returnM (mkAppTys fun_ty arg_tys)
561 ds_var_app :: Name -> [Type] -> TcM Type
562 ds_var_app name arg_tys
563 = tcLookup name `thenM` \ thing ->
565 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
566 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
567 other -> wrongThingErr "type" thing name
575 dsHsLPred :: LHsPred Name -> TcM PredType
576 dsHsLPred pred = dsHsPred (unLoc pred)
578 dsHsPred pred@(HsClassP class_name tys)
579 = do { arg_tys <- dsHsTypes tys
580 ; clas <- tcLookupClass class_name
581 ; returnM (ClassP clas arg_tys)
583 dsHsPred pred@(HsEqualP ty1 ty2)
584 = do { arg_ty1 <- dsHsType ty1
585 ; arg_ty2 <- dsHsType ty2
586 ; returnM (EqPred arg_ty1 arg_ty2)
588 dsHsPred (HsIParam name ty)
589 = do { arg_ty <- dsHsType ty
590 ; returnM (IParam name arg_ty)
594 GADT constructor signatures
597 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
599 = addErrCtxt (gadtResCtxt res_ty) $
600 case get_largs res_ty [] of
601 (HsTyVar tc_name, args)
602 -> do { args' <- mapM dsHsType args
603 ; thing <- tcLookup tc_name
605 AGlobal (ATyCon tc) -> return (tc, args')
606 other -> failWithTc (badGadtDecl res_ty) }
607 other -> failWithTc (badGadtDecl res_ty)
609 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
610 -- because that causes a black hole, and for good reason. Building
611 -- the type means expanding type synonyms, and we can't do that
612 -- inside the "knot". So we have to work by steam.
613 get_largs (L _ ty) args = get_args ty args
614 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
615 get_args (HsParTy ty) args = get_largs ty args
616 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
617 get_args ty args = (ty, args)
620 = hang (ptext SLIT("In the result type of a data constructor:"))
623 = hang (ptext SLIT("Malformed constructor result type:"))
626 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
629 %************************************************************************
631 Type-variable binders
633 %************************************************************************
637 kcHsTyVars :: [LHsTyVarBndr Name]
638 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
639 -- They scope over the thing inside
641 kcHsTyVars tvs thing_inside
642 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
643 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
645 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
646 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
647 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
648 returnM (KindedTyVar name kind)
649 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
652 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
653 -> ([TyVar] -> TcM r)
655 -- Used when type-checking types/classes/type-decls
656 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
657 tcTyVarBndrs bndrs thing_inside
658 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
659 tcExtendTyVarEnv tyvars (thing_inside tyvars)
661 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
662 ; return (mkTyVar name kind') }
663 zonk (UserTyVar name) = WARN( True, ptext SLIT("Un-kinded tyvar") <+> ppr name )
664 return (mkTyVar name liftedTypeKind)
666 -----------------------------------
667 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
668 -- GADT decls can have a (perhaps partial) kind signature
669 -- e.g. data T :: * -> * -> * where ...
670 -- This function makes up suitable (kinded) type variables for
671 -- the argument kinds, and checks that the result kind is indeed *.
672 -- We use it also to make up argument type variables for for data instances.
673 tcDataKindSig Nothing = return []
674 tcDataKindSig (Just kind)
675 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
676 ; span <- getSrcSpanM
677 ; us <- newUniqueSupply
678 ; let uniqs = uniqsFromSupply us
679 ; return [ mk_tv span uniq str kind
680 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
682 (arg_kinds, res_kind) = splitKindFunTys kind
683 mk_tv loc uniq str kind = mkTyVar name kind
685 name = mkInternalName uniq occ loc
686 occ = mkOccName tvName str
688 names :: [String] -- a,b,c...aa,ab,ac etc
689 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
691 badKindSig :: Kind -> SDoc
693 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
698 %************************************************************************
700 Scoped type variables
702 %************************************************************************
705 tcAddScopedTyVars is used for scoped type variables added by pattern
707 e.g. \ ((x::a), (y::a)) -> x+y
708 They never have explicit kinds (because this is source-code only)
709 They are mutable (because they can get bound to a more specific type).
711 Usually we kind-infer and expand type splices, and then
712 tupecheck/desugar the type. That doesn't work well for scoped type
713 variables, because they scope left-right in patterns. (e.g. in the
714 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
716 The current not-very-good plan is to
717 * find all the types in the patterns
718 * find their free tyvars
720 * bring the kinded type vars into scope
721 * BUT throw away the kind-checked type
722 (we'll kind-check it again when we type-check the pattern)
724 This is bad because throwing away the kind checked type throws away
725 its splices. But too bad for now. [July 03]
728 We no longer specify that these type variables must be univerally
729 quantified (lots of email on the subject). If you want to put that
731 a) Do a checkSigTyVars after thing_inside
732 b) More insidiously, don't pass in expected_ty, else
733 we unify with it too early and checkSigTyVars barfs
734 Instead you have to pass in a fresh ty var, and unify
735 it with expected_ty afterwards
738 tcHsPatSigType :: UserTypeCtxt
739 -> LHsType Name -- The type signature
740 -> TcM ([TyVar], -- Newly in-scope type variables
741 Type) -- The signature
742 -- Used for type-checking type signatures in
743 -- (a) patterns e.g f (x::Int) = e
744 -- (b) result signatures e.g. g x :: Int = e
745 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
747 tcHsPatSigType ctxt hs_ty
748 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
749 do { -- Find the type variables that are mentioned in the type
750 -- but not already in scope. These are the ones that
751 -- should be bound by the pattern signature
752 in_scope <- getInLocalScope
753 ; let span = getLoc hs_ty
754 sig_tvs = [ L span (UserTyVar n)
755 | n <- nameSetToList (extractHsTyVars hs_ty),
758 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
759 ; checkValidType ctxt sig_ty
760 ; return (tyvars, sig_ty)
763 tcPatSig :: UserTypeCtxt
766 -> TcM (TcType, -- The type to use for "inside" the signature
767 [(Name,TcType)]) -- The new bit of type environment, binding
768 -- the scoped type variables
769 tcPatSig ctxt sig res_ty
770 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
772 ; if null sig_tvs then do {
773 -- The type signature binds no type variables,
774 -- and hence is rigid, so use it to zap the res_ty
775 boxyUnify sig_ty res_ty
776 ; return (sig_ty, [])
779 -- Type signature binds at least one scoped type variable
781 -- A pattern binding cannot bind scoped type variables
782 -- The renamer fails with a name-out-of-scope error
783 -- if a pattern binding tries to bind a type variable,
784 -- So we just have an ASSERT here
785 ; let in_pat_bind = case ctxt of
786 BindPatSigCtxt -> True
788 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
790 -- Check that pat_ty is rigid
791 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
793 -- Now match the pattern signature against res_ty
794 -- For convenience, and uniform-looking error messages
795 -- we do the matching by allocating meta type variables,
796 -- unifying, and reading out the results.
797 -- This is a strictly local operation.
798 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
799 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
800 ; sig_tv_tys <- mapM readFilledBox box_tvs
802 -- Check that each is bound to a distinct type variable,
803 -- and one that is not already in scope
804 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
805 ; binds_in_scope <- getScopedTyVarBinds
806 ; check binds_in_scope tv_binds
809 ; return (res_ty, tv_binds)
812 check in_scope [] = return ()
813 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
814 ; check ((n,ty):in_scope) rest }
816 check_one in_scope n ty
817 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
818 -- Must bind to a type variable
820 ; checkTc (null dups) (dupInScope n (head dups) ty)
821 -- Must not bind to the same type variable
822 -- as some other in-scope type variable
826 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
830 %************************************************************************
832 Scoped type variables
834 %************************************************************************
837 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
838 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
839 nest 2 (pp_sig ctxt) ]
841 pp_sig (FunSigCtxt n) = pp_n_colon n
842 pp_sig (ConArgCtxt n) = pp_n_colon n
843 pp_sig (ForSigCtxt n) = pp_n_colon n
844 pp_sig other = ppr (unLoc hs_ty)
846 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
850 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
851 <+> pprQuotedList sig_tvs)
852 2 (ptext SLIT("unless the pattern has a rigid type context"))
855 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
856 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
857 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
860 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
861 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
862 ptext SLIT("Distinct scoped type variables must be distinct")])
865 = failWithTc (text "Equality predicate used as a type")