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 tcHsSigType, tcHsDeriv,
10 tcHsInstHead, tcHsQuantifiedType,
14 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
15 kcCheckHsType, kcHsContext, kcHsType,
17 -- Typechecking kinded types
18 tcHsKindedContext, tcHsKindedType, tcHsBangType,
19 tcTyVarBndrs, dsHsType, tcLHsConResTy,
22 -- Pattern type signatures
23 tcHsPatSigType, tcPatSig
26 #include "HsVersions.h"
36 import {- Kind parts of -} Type
52 ----------------------------
54 ----------------------------
56 Generally speaking we now type-check types in three phases
58 1. kcHsType: kind check the HsType
59 *includes* performing any TH type splices;
60 so it returns a translated, and kind-annotated, type
62 2. dsHsType: convert from HsType to Type:
64 expand type synonyms [mkGenTyApps]
65 hoist the foralls [tcHsType]
67 3. checkValidType: check the validity of the resulting type
69 Often these steps are done one after the other (tcHsSigType).
70 But in mutually recursive groups of type and class decls we do
71 1 kind-check the whole group
72 2 build TyCons/Classes in a knot-tied way
73 3 check the validity of types in the now-unknotted TyCons/Classes
75 For example, when we find
76 (forall a m. m a -> m a)
77 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
78 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
79 an environment that binds a and m suitably.
81 The kind checker passed to tcHsTyVars needs to look at enough to
82 establish the kind of the tyvar:
83 * For a group of type and class decls, it's just the group, not
84 the rest of the program
85 * For a tyvar bound in a pattern type signature, its the types
86 mentioned in the other type signatures in that bunch of patterns
87 * For a tyvar bound in a RULE, it's the type signatures on other
88 universally quantified variables in the rule
90 Note that this may occasionally give surprising results. For example:
92 data T a b = MkT (a b)
94 Here we deduce a::*->*, b::*
95 But equally valid would be a::(*->*)-> *, b::*->*
100 Some of the validity check could in principle be done by the kind checker,
103 - During desugaring, we normalise by expanding type synonyms. Only
104 after this step can we check things like type-synonym saturation
105 e.g. type T k = k Int
107 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
108 and then S is saturated. This is a GHC extension.
110 - Similarly, also a GHC extension, we look through synonyms before complaining
111 about the form of a class or instance declaration
113 - Ambiguity checks involve functional dependencies, and it's easier to wait
114 until knots have been resolved before poking into them
116 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
117 finished building the loop. So to keep things simple, we postpone most validity
118 checking until step (3).
122 During step (1) we might fault in a TyCon defined in another module, and it might
123 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
124 knot around type declarations with ARecThing, so that the fault-in code can get
125 the TyCon being defined.
128 %************************************************************************
130 \subsection{Checking types}
132 %************************************************************************
135 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
136 -- Do kind checking, and hoist for-alls to the top
137 -- NB: it's important that the foralls that come from the top-level
138 -- HsForAllTy in hs_ty occur *first* in the returned type.
139 -- See Note [Scoped] with TcSigInfo
140 tcHsSigType ctxt hs_ty
141 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
142 do { kinded_ty <- kcTypeType hs_ty
143 ; ty <- tcHsKindedType kinded_ty
144 ; checkValidType ctxt ty
147 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Type)
148 -- Typecheck an instance head. We can't use
149 -- tcHsSigType, because it's not a valid user type.
151 = do { kinded_ty <- kcHsSigType hs_ty
152 ; poly_ty <- tcHsKindedType kinded_ty
153 ; return (tcSplitSigmaTy poly_ty) }
155 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
156 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
157 -- except that we want to keep the tvs separate
158 tcHsQuantifiedType tv_names hs_ty
159 = kcHsTyVars tv_names $ \ tv_names' ->
160 do { kc_ty <- kcHsSigType hs_ty
161 ; tcTyVarBndrs tv_names' $ \ tvs ->
162 do { ty <- dsHsType kc_ty
163 ; return (tvs, ty) } }
165 -- Used for the deriving(...) items
166 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
167 tcHsDeriv = addLocM (tc_hs_deriv [])
169 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
170 = kcHsTyVars tv_names $ \ tv_names' ->
171 do { cls_kind <- kcClass cls_name
172 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
173 ; tcTyVarBndrs tv_names' $ \ tyvars ->
174 do { arg_tys <- dsHsTypes tys
175 ; cls <- tcLookupClass cls_name
176 ; return (tyvars, cls, arg_tys) }}
178 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
179 = -- Funny newtype deriving form
181 -- where C has arity 2. Hence can't use regular functions
182 tc_hs_deriv (tv_names1 ++ tv_names2) ty
185 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
188 These functions are used during knot-tying in
189 type and class declarations, when we have to
190 separate kind-checking, desugaring, and validity checking
193 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
194 -- Used for type signatures
195 kcHsSigType ty = kcTypeType ty
196 kcHsLiftedSigType ty = kcLiftedType ty
198 tcHsKindedType :: LHsType Name -> TcM Type
199 -- Don't do kind checking, nor validity checking.
200 -- This is used in type and class decls, where kinding is
201 -- done in advance, and validity checking is done later
202 -- [Validity checking done later because of knot-tying issues.]
203 tcHsKindedType hs_ty = dsHsType hs_ty
205 tcHsBangType :: LHsType Name -> TcM Type
206 -- Permit a bang, but discard it
207 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
208 tcHsBangType ty = tcHsKindedType ty
210 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
211 -- Used when we are expecting a ClassContext (i.e. no implicit params)
212 -- Does not do validity checking, like tcHsKindedType
213 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
217 %************************************************************************
219 The main kind checker: kcHsType
221 %************************************************************************
223 First a couple of simple wrappers for kcHsType
226 ---------------------------
227 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
228 -- The type ty must be a *lifted* *type*
229 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
231 ---------------------------
232 kcTypeType :: LHsType Name -> TcM (LHsType Name)
233 -- The type ty must be a *type*, but it can be lifted or
234 -- unlifted or an unboxed tuple.
235 kcTypeType ty = kcCheckHsType ty openTypeKind
237 ---------------------------
238 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
239 -- Check that the type has the specified kind
240 -- Be sure to use checkExpectedKind, rather than simply unifying
241 -- with OpenTypeKind, because it gives better error messages
242 kcCheckHsType (L span ty) exp_kind
244 do { (ty', act_kind) <- add_ctxt ty (kc_hs_type ty)
245 -- Add the context round the inner check only
246 -- because checkExpectedKind already mentions
247 -- 'ty' by name in any error message
249 ; checkExpectedKind (strip ty) act_kind exp_kind
250 ; return (L span ty') }
252 -- Wrap a context around only if we want to show that contexts.
253 add_ctxt (HsPredTy p) thing = thing
254 -- Omit invisble ones and ones user's won't grok (HsPred p).
255 add_ctxt (HsForAllTy _ _ (L _ []) _) thing = thing
256 -- Omit wrapping if the theta-part is empty
257 -- Reason: the recursive call to kcLiftedType, in the ForAllTy
258 -- case of kc_hs_type, will do the wrapping instead
259 -- and we don't want to duplicate
260 add_ctxt other_ty thing = addErrCtxt (typeCtxt other_ty) thing
262 -- We infer the kind of the type, and then complain if it's
263 -- not right. But we don't want to complain about
264 -- (ty) or !(ty) or forall a. ty
265 -- when the real difficulty is with the 'ty' part.
266 strip (HsParTy (L _ ty)) = strip ty
267 strip (HsBangTy _ (L _ ty)) = strip ty
268 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
272 Here comes the main function
275 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
276 kcHsType ty = wrapLocFstM kc_hs_type ty
277 -- kcHsType *returns* the kind of the type, rather than taking an expected
278 -- kind as argument as tcExpr does.
280 -- (a) the kind of (->) is
281 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
282 -- so we'd need to generate huge numbers of bx variables.
283 -- (b) kinds are so simple that the error messages are fine
285 -- The translated type has explicitly-kinded type-variable binders
287 kc_hs_type (HsParTy ty)
288 = kcHsType ty `thenM` \ (ty', kind) ->
289 returnM (HsParTy ty', kind)
291 kc_hs_type (HsTyVar name)
292 = kcTyVar name `thenM` \ kind ->
293 returnM (HsTyVar name, kind)
295 kc_hs_type (HsListTy ty)
296 = kcLiftedType ty `thenM` \ ty' ->
297 returnM (HsListTy ty', liftedTypeKind)
299 kc_hs_type (HsPArrTy ty)
300 = kcLiftedType ty `thenM` \ ty' ->
301 returnM (HsPArrTy ty', liftedTypeKind)
303 kc_hs_type (HsNumTy n)
304 = returnM (HsNumTy n, liftedTypeKind)
306 kc_hs_type (HsKindSig ty k)
307 = kcCheckHsType ty k `thenM` \ ty' ->
308 returnM (HsKindSig ty' k, k)
310 kc_hs_type (HsTupleTy Boxed tys)
311 = mappM kcLiftedType tys `thenM` \ tys' ->
312 returnM (HsTupleTy Boxed tys', liftedTypeKind)
314 kc_hs_type (HsTupleTy Unboxed tys)
315 = mappM kcTypeType tys `thenM` \ tys' ->
316 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
318 kc_hs_type (HsFunTy ty1 ty2)
319 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
320 kcTypeType ty2 `thenM` \ ty2' ->
321 returnM (HsFunTy ty1' ty2', liftedTypeKind)
323 kc_hs_type ty@(HsOpTy ty1 op ty2)
324 = addLocM kcTyVar op `thenM` \ op_kind ->
325 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
326 returnM (HsOpTy ty1' op ty2', res_kind)
328 kc_hs_type ty@(HsAppTy ty1 ty2)
329 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
330 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
331 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
333 (fun_ty, arg_tys) = split ty1 [ty2]
334 split (L _ (HsAppTy f a)) as = split f (a:as)
336 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
337 -- the application; they are never used
339 kc_hs_type (HsPredTy pred)
340 = kcHsPred pred `thenM` \ pred' ->
341 returnM (HsPredTy pred', liftedTypeKind)
343 kc_hs_type (HsForAllTy exp tv_names context ty)
344 = kcHsTyVars tv_names $ \ tv_names' ->
345 do { ctxt' <- kcHsContext context
346 ; ty' <- kcLiftedType ty
347 -- The body of a forall is usually a type, but in principle
348 -- there's no reason to prohibit *unlifted* types.
349 -- In fact, GHC can itself construct a function with an
350 -- unboxed tuple inside a for-all (via CPR analyis; see
351 -- typecheck/should_compile/tc170)
353 -- Still, that's only for internal interfaces, which aren't
354 -- kind-checked, so we only allow liftedTypeKind here
356 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
358 kc_hs_type (HsBangTy b ty)
359 = do { (ty', kind) <- kcHsType ty
360 ; return (HsBangTy b ty', kind) }
362 kc_hs_type ty@(HsSpliceTy _)
363 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
365 -- remove the doc nodes here, no need to worry about the location since
366 -- its the same for a doc node and it's child type node
367 kc_hs_type (HsDocTy ty _)
368 = kc_hs_type (unLoc ty)
370 ---------------------------
371 kcApps :: TcKind -- Function kind
373 -> [LHsType Name] -- Arg types
374 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
375 kcApps fun_kind ppr_fun args
376 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
377 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
378 returnM (args', res_kind)
380 split_fk fk 0 = returnM ([], fk)
381 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
383 Nothing -> failWithTc too_many_args
384 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
387 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
389 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
390 ptext SLIT("is applied to too many type arguments")
392 ---------------------------
393 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
394 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
396 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
397 kcHsLPred = wrapLocM kcHsPred
399 kcHsPred :: HsPred Name -> TcM (HsPred Name)
400 kcHsPred pred -- Checks that the result is of kind liftedType
401 = kc_pred pred `thenM` \ (pred', kind) ->
402 checkExpectedKind pred kind liftedTypeKind `thenM_`
405 ---------------------------
406 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
407 -- Does *not* check for a saturated
408 -- application (reason: used from TcDeriv)
409 kc_pred pred@(HsIParam name ty)
410 = do { (ty', kind) <- kcHsType ty
411 ; returnM (HsIParam name ty', kind)
413 kc_pred pred@(HsClassP cls tys)
414 = do { kind <- kcClass cls
415 ; (tys', res_kind) <- kcApps kind (ppr cls) tys
416 ; returnM (HsClassP cls tys', res_kind)
418 kc_pred pred@(HsEqualP ty1 ty2)
419 = do { (ty1', kind1) <- kcHsType ty1
420 ; checkExpectedKind ty1 kind1 liftedTypeKind
421 ; (ty2', kind2) <- kcHsType ty2
422 ; checkExpectedKind ty2 kind2 liftedTypeKind
423 ; returnM (HsEqualP ty1 ty2, liftedTypeKind)
426 ---------------------------
427 kcTyVar :: Name -> TcM TcKind
428 kcTyVar name -- Could be a tyvar or a tycon
429 = traceTc (text "lk1" <+> ppr name) `thenM_`
430 tcLookup name `thenM` \ thing ->
431 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
433 ATyVar _ ty -> returnM (typeKind ty)
434 AThing kind -> returnM kind
435 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
436 other -> wrongThingErr "type" thing name
438 kcClass :: Name -> TcM TcKind
439 kcClass cls -- Must be a class
440 = tcLookup cls `thenM` \ thing ->
442 AThing kind -> returnM kind
443 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
444 other -> wrongThingErr "class" thing cls
448 %************************************************************************
452 %************************************************************************
456 * Transforms from HsType to Type
459 It cannot fail, and does no validity checking, except for
460 structural matters, such as
461 (a) spurious ! annotations.
462 (b) a class used as a type
465 dsHsType :: LHsType Name -> TcM Type
466 -- All HsTyVarBndrs in the intput type are kind-annotated
467 dsHsType ty = ds_type (unLoc ty)
469 ds_type ty@(HsTyVar name)
472 ds_type (HsParTy ty) -- Remove the parentheses markers
475 ds_type ty@(HsBangTy _ _) -- No bangs should be here
476 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
478 ds_type (HsKindSig ty k)
479 = dsHsType ty -- Kind checking done already
481 ds_type (HsListTy ty)
482 = dsHsType ty `thenM` \ tau_ty ->
483 checkWiredInTyCon listTyCon `thenM_`
484 returnM (mkListTy tau_ty)
486 ds_type (HsPArrTy ty)
487 = dsHsType ty `thenM` \ tau_ty ->
488 checkWiredInTyCon parrTyCon `thenM_`
489 returnM (mkPArrTy tau_ty)
491 ds_type (HsTupleTy boxity tys)
492 = dsHsTypes tys `thenM` \ tau_tys ->
493 checkWiredInTyCon tycon `thenM_`
494 returnM (mkTyConApp tycon tau_tys)
496 tycon = tupleTyCon boxity (length tys)
498 ds_type (HsFunTy ty1 ty2)
499 = dsHsType ty1 `thenM` \ tau_ty1 ->
500 dsHsType ty2 `thenM` \ tau_ty2 ->
501 returnM (mkFunTy tau_ty1 tau_ty2)
503 ds_type (HsOpTy ty1 (L span op) ty2)
504 = dsHsType ty1 `thenM` \ tau_ty1 ->
505 dsHsType ty2 `thenM` \ tau_ty2 ->
506 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
510 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
511 returnM (mkTyConApp tc [])
513 ds_type ty@(HsAppTy _ _)
516 ds_type (HsPredTy pred)
517 = dsHsPred pred `thenM` \ pred' ->
518 returnM (mkPredTy pred')
520 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
521 = tcTyVarBndrs tv_names $ \ tyvars ->
522 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
523 dsHsType ty `thenM` \ tau ->
524 returnM (mkSigmaTy tyvars theta tau)
526 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
528 ds_type (HsDocTy ty _) -- Remove the doc comment
531 dsHsTypes arg_tys = mappM dsHsType arg_tys
534 Help functions for type applications
535 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
538 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
539 ds_app (HsAppTy ty1 ty2) tys
540 = ds_app (unLoc ty1) (ty2:tys)
543 = dsHsTypes tys `thenM` \ arg_tys ->
545 HsTyVar fun -> ds_var_app fun arg_tys
546 other -> ds_type ty `thenM` \ fun_ty ->
547 returnM (mkAppTys fun_ty arg_tys)
549 ds_var_app :: Name -> [Type] -> TcM Type
550 ds_var_app name arg_tys
551 = tcLookup name `thenM` \ thing ->
553 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
554 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
555 other -> wrongThingErr "type" thing name
563 dsHsLPred :: LHsPred Name -> TcM PredType
564 dsHsLPred pred = dsHsPred (unLoc pred)
566 dsHsPred pred@(HsClassP class_name tys)
567 = do { arg_tys <- dsHsTypes tys
568 ; clas <- tcLookupClass class_name
569 ; returnM (ClassP clas arg_tys)
571 dsHsPred pred@(HsEqualP ty1 ty2)
572 = do { arg_ty1 <- dsHsType ty1
573 ; arg_ty2 <- dsHsType ty2
574 ; returnM (EqPred arg_ty1 arg_ty2)
576 dsHsPred (HsIParam name ty)
577 = do { arg_ty <- dsHsType ty
578 ; returnM (IParam name arg_ty)
582 GADT constructor signatures
585 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
587 = addErrCtxt (gadtResCtxt res_ty) $
588 case get_largs res_ty [] of
589 (HsTyVar tc_name, args)
590 -> do { args' <- mapM dsHsType args
591 ; thing <- tcLookup tc_name
593 AGlobal (ATyCon tc) -> return (tc, args')
594 other -> failWithTc (badGadtDecl res_ty) }
595 other -> failWithTc (badGadtDecl res_ty)
597 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
598 -- because that causes a black hole, and for good reason. Building
599 -- the type means expanding type synonyms, and we can't do that
600 -- inside the "knot". So we have to work by steam.
601 get_largs (L _ ty) args = get_args ty args
602 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
603 get_args (HsParTy ty) args = get_largs ty args
604 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
605 get_args ty args = (ty, args)
608 = hang (ptext SLIT("In the result type of a data constructor:"))
611 = hang (ptext SLIT("Malformed constructor result type:"))
614 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
617 %************************************************************************
619 Type-variable binders
621 %************************************************************************
625 kcHsTyVars :: [LHsTyVarBndr Name]
626 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
627 -- They scope over the thing inside
629 kcHsTyVars tvs thing_inside
630 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
631 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
633 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
634 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
635 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
636 returnM (KindedTyVar name kind)
637 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
640 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
641 -> ([TyVar] -> TcM r)
643 -- Used when type-checking types/classes/type-decls
644 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
645 tcTyVarBndrs bndrs thing_inside
646 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
647 tcExtendTyVarEnv tyvars (thing_inside tyvars)
649 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
650 ; return (mkTyVar name kind') }
651 zonk (UserTyVar name) = WARN( True, ptext SLIT("Un-kinded tyvar") <+> ppr name )
652 return (mkTyVar name liftedTypeKind)
654 -----------------------------------
655 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
656 -- GADT decls can have a (perhaps partial) kind signature
657 -- e.g. data T :: * -> * -> * where ...
658 -- This function makes up suitable (kinded) type variables for
659 -- the argument kinds, and checks that the result kind is indeed *.
660 -- We use it also to make up argument type variables for for data instances.
661 tcDataKindSig Nothing = return []
662 tcDataKindSig (Just kind)
663 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
664 ; span <- getSrcSpanM
665 ; us <- newUniqueSupply
666 ; let loc = srcSpanStart span
667 uniqs = uniqsFromSupply us
668 ; return [ mk_tv loc uniq str kind
669 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
671 (arg_kinds, res_kind) = splitKindFunTys kind
672 mk_tv loc uniq str kind = mkTyVar name kind
674 name = mkInternalName uniq occ loc
675 occ = mkOccName tvName str
677 names :: [String] -- a,b,c...aa,ab,ac etc
678 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
680 badKindSig :: Kind -> SDoc
682 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
687 %************************************************************************
689 Scoped type variables
691 %************************************************************************
694 tcAddScopedTyVars is used for scoped type variables added by pattern
696 e.g. \ ((x::a), (y::a)) -> x+y
697 They never have explicit kinds (because this is source-code only)
698 They are mutable (because they can get bound to a more specific type).
700 Usually we kind-infer and expand type splices, and then
701 tupecheck/desugar the type. That doesn't work well for scoped type
702 variables, because they scope left-right in patterns. (e.g. in the
703 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
705 The current not-very-good plan is to
706 * find all the types in the patterns
707 * find their free tyvars
709 * bring the kinded type vars into scope
710 * BUT throw away the kind-checked type
711 (we'll kind-check it again when we type-check the pattern)
713 This is bad because throwing away the kind checked type throws away
714 its splices. But too bad for now. [July 03]
717 We no longer specify that these type variables must be univerally
718 quantified (lots of email on the subject). If you want to put that
720 a) Do a checkSigTyVars after thing_inside
721 b) More insidiously, don't pass in expected_ty, else
722 we unify with it too early and checkSigTyVars barfs
723 Instead you have to pass in a fresh ty var, and unify
724 it with expected_ty afterwards
727 tcHsPatSigType :: UserTypeCtxt
728 -> LHsType Name -- The type signature
729 -> TcM ([TyVar], -- Newly in-scope type variables
730 Type) -- The signature
731 -- Used for type-checking type signatures in
732 -- (a) patterns e.g f (x::Int) = e
733 -- (b) result signatures e.g. g x :: Int = e
734 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
736 tcHsPatSigType ctxt hs_ty
737 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
738 do { -- Find the type variables that are mentioned in the type
739 -- but not already in scope. These are the ones that
740 -- should be bound by the pattern signature
741 in_scope <- getInLocalScope
742 ; let span = getLoc hs_ty
743 sig_tvs = [ L span (UserTyVar n)
744 | n <- nameSetToList (extractHsTyVars hs_ty),
747 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
748 ; checkValidType ctxt sig_ty
749 ; return (tyvars, sig_ty)
752 tcPatSig :: UserTypeCtxt
755 -> TcM (TcType, -- The type to use for "inside" the signature
756 [(Name,TcType)]) -- The new bit of type environment, binding
757 -- the scoped type variables
758 tcPatSig ctxt sig res_ty
759 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
761 ; if null sig_tvs then do {
762 -- The type signature binds no type variables,
763 -- and hence is rigid, so use it to zap the res_ty
764 boxyUnify sig_ty res_ty
765 ; return (sig_ty, [])
768 -- Type signature binds at least one scoped type variable
770 -- A pattern binding cannot bind scoped type variables
771 -- The renamer fails with a name-out-of-scope error
772 -- if a pattern binding tries to bind a type variable,
773 -- So we just have an ASSERT here
774 ; let in_pat_bind = case ctxt of
775 BindPatSigCtxt -> True
777 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
779 -- Check that pat_ty is rigid
780 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
782 -- Now match the pattern signature against res_ty
783 -- For convenience, and uniform-looking error messages
784 -- we do the matching by allocating meta type variables,
785 -- unifying, and reading out the results.
786 -- This is a strictly local operation.
787 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
788 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
789 ; sig_tv_tys <- mapM readFilledBox box_tvs
791 -- Check that each is bound to a distinct type variable,
792 -- and one that is not already in scope
793 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
794 ; binds_in_scope <- getScopedTyVarBinds
795 ; check binds_in_scope tv_binds
798 ; return (res_ty, tv_binds)
801 check in_scope [] = return ()
802 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
803 ; check ((n,ty):in_scope) rest }
805 check_one in_scope n ty
806 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
807 -- Must bind to a type variable
809 ; checkTc (null dups) (dupInScope n (head dups) ty)
810 -- Must not bind to the same type variable
811 -- as some other in-scope type variable
815 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
819 %************************************************************************
821 Scoped type variables
823 %************************************************************************
826 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
827 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
828 nest 2 (pp_sig ctxt) ]
830 pp_sig (FunSigCtxt n) = pp_n_colon n
831 pp_sig (ConArgCtxt n) = pp_n_colon n
832 pp_sig (ForSigCtxt n) = pp_n_colon n
833 pp_sig other = ppr (unLoc hs_ty)
835 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
839 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
840 <+> pprQuotedList sig_tvs)
841 2 (ptext SLIT("unless the pattern has a rigid type context"))
844 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
845 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
846 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
849 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
850 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
851 ptext SLIT("Distinct scoped type variables must be distinct")])