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 never used
346 kc_hs_type (HsPredTy pred)
347 = kcHsPred pred `thenM` \ pred' ->
348 returnM (HsPredTy pred', liftedTypeKind)
350 kc_hs_type (HsForAllTy exp tv_names context ty)
351 = kcHsTyVars tv_names $ \ tv_names' ->
352 do { ctxt' <- kcHsContext context
353 ; ty' <- kcLiftedType ty
354 -- The body of a forall is usually a type, but in principle
355 -- there's no reason to prohibit *unlifted* types.
356 -- In fact, GHC can itself construct a function with an
357 -- unboxed tuple inside a for-all (via CPR analyis; see
358 -- typecheck/should_compile/tc170)
360 -- Still, that's only for internal interfaces, which aren't
361 -- kind-checked, so we only allow liftedTypeKind here
363 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
365 kc_hs_type (HsBangTy b ty)
366 = do { (ty', kind) <- kcHsType ty
367 ; return (HsBangTy b ty', kind) }
369 kc_hs_type ty@(HsSpliceTy _)
370 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
372 -- remove the doc nodes here, no need to worry about the location since
373 -- its the same for a doc node and it's child type node
374 kc_hs_type (HsDocTy ty _)
375 = kc_hs_type (unLoc ty)
377 ---------------------------
378 kcApps :: TcKind -- Function kind
380 -> [LHsType Name] -- Arg types
381 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
382 kcApps fun_kind ppr_fun args
383 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
384 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
385 returnM (args', res_kind)
387 split_fk fk 0 = returnM ([], fk)
388 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
390 Nothing -> failWithTc too_many_args
391 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
394 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
396 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
397 ptext SLIT("is applied to too many type arguments")
399 ---------------------------
400 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
401 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
403 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
404 kcHsLPred = wrapLocM kcHsPred
406 kcHsPred :: HsPred Name -> TcM (HsPred Name)
407 kcHsPred pred -- Checks that the result is of kind liftedType
408 = kc_pred pred `thenM` \ (pred', kind) ->
409 checkExpectedKind pred kind liftedTypeKind `thenM_`
412 ---------------------------
413 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
414 -- Does *not* check for a saturated
415 -- application (reason: used from TcDeriv)
416 kc_pred pred@(HsIParam name ty)
417 = do { (ty', kind) <- kcHsType ty
418 ; returnM (HsIParam name ty', kind)
420 kc_pred pred@(HsClassP cls tys)
421 = do { kind <- kcClass cls
422 ; (tys', res_kind) <- kcApps kind (ppr cls) tys
423 ; returnM (HsClassP cls tys', res_kind)
425 kc_pred pred@(HsEqualP ty1 ty2)
426 = do { (ty1', kind1) <- kcHsType ty1
427 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
428 ; (ty2', kind2) <- kcHsType ty2
429 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
430 ; checkExpectedKind ty2 kind2 kind1
431 ; returnM (HsEqualP ty1' ty2', liftedTypeKind)
434 ---------------------------
435 kcTyVar :: Name -> TcM TcKind
436 kcTyVar name -- Could be a tyvar or a tycon
437 = traceTc (text "lk1" <+> ppr name) `thenM_`
438 tcLookup name `thenM` \ thing ->
439 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
441 ATyVar _ ty -> returnM (typeKind ty)
442 AThing kind -> returnM kind
443 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
444 other -> wrongThingErr "type" thing name
446 kcClass :: Name -> TcM TcKind
447 kcClass cls -- Must be a class
448 = tcLookup cls `thenM` \ thing ->
450 AThing kind -> returnM kind
451 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
452 other -> wrongThingErr "class" thing cls
456 %************************************************************************
460 %************************************************************************
464 * Transforms from HsType to Type
467 It cannot fail, and does no validity checking, except for
468 structural matters, such as
469 (a) spurious ! annotations.
470 (b) a class used as a type
473 dsHsType :: LHsType Name -> TcM Type
474 -- All HsTyVarBndrs in the intput type are kind-annotated
475 dsHsType ty = ds_type (unLoc ty)
477 ds_type ty@(HsTyVar name)
480 ds_type (HsParTy ty) -- Remove the parentheses markers
483 ds_type ty@(HsBangTy _ _) -- No bangs should be here
484 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
486 ds_type (HsKindSig ty k)
487 = dsHsType ty -- Kind checking done already
489 ds_type (HsListTy ty)
490 = dsHsType ty `thenM` \ tau_ty ->
491 checkWiredInTyCon listTyCon `thenM_`
492 returnM (mkListTy tau_ty)
494 ds_type (HsPArrTy ty)
495 = dsHsType ty `thenM` \ tau_ty ->
496 checkWiredInTyCon parrTyCon `thenM_`
497 returnM (mkPArrTy tau_ty)
499 ds_type (HsTupleTy boxity tys)
500 = dsHsTypes tys `thenM` \ tau_tys ->
501 checkWiredInTyCon tycon `thenM_`
502 returnM (mkTyConApp tycon tau_tys)
504 tycon = tupleTyCon boxity (length tys)
506 ds_type (HsFunTy ty1 ty2)
507 = dsHsType ty1 `thenM` \ tau_ty1 ->
508 dsHsType ty2 `thenM` \ tau_ty2 ->
509 returnM (mkFunTy tau_ty1 tau_ty2)
511 ds_type (HsOpTy ty1 (L span op) ty2)
512 = dsHsType ty1 `thenM` \ tau_ty1 ->
513 dsHsType ty2 `thenM` \ tau_ty2 ->
514 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
518 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
519 returnM (mkTyConApp tc [])
521 ds_type ty@(HsAppTy _ _)
524 ds_type (HsPredTy pred)
525 = dsHsPred pred `thenM` \ pred' ->
526 returnM (mkPredTy pred')
528 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
529 = tcTyVarBndrs tv_names $ \ tyvars ->
530 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
531 dsHsType ty `thenM` \ tau ->
532 returnM (mkSigmaTy tyvars theta tau)
534 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
536 ds_type (HsDocTy ty _) -- Remove the doc comment
539 dsHsTypes arg_tys = mappM dsHsType arg_tys
542 Help functions for type applications
543 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
546 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
547 ds_app (HsAppTy ty1 ty2) tys
548 = ds_app (unLoc ty1) (ty2:tys)
551 = dsHsTypes tys `thenM` \ arg_tys ->
553 HsTyVar fun -> ds_var_app fun arg_tys
554 other -> ds_type ty `thenM` \ fun_ty ->
555 returnM (mkAppTys fun_ty arg_tys)
557 ds_var_app :: Name -> [Type] -> TcM Type
558 ds_var_app name arg_tys
559 = tcLookup name `thenM` \ thing ->
561 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
562 AGlobal (ATyCon tc) -> returnM (mkTyConApp tc arg_tys)
563 other -> wrongThingErr "type" thing name
571 dsHsLPred :: LHsPred Name -> TcM PredType
572 dsHsLPred pred = dsHsPred (unLoc pred)
574 dsHsPred pred@(HsClassP class_name tys)
575 = do { arg_tys <- dsHsTypes tys
576 ; clas <- tcLookupClass class_name
577 ; returnM (ClassP clas arg_tys)
579 dsHsPred pred@(HsEqualP ty1 ty2)
580 = do { arg_ty1 <- dsHsType ty1
581 ; arg_ty2 <- dsHsType ty2
582 ; returnM (EqPred arg_ty1 arg_ty2)
584 dsHsPred (HsIParam name ty)
585 = do { arg_ty <- dsHsType ty
586 ; returnM (IParam name arg_ty)
590 GADT constructor signatures
593 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
595 = addErrCtxt (gadtResCtxt res_ty) $
596 case get_largs res_ty [] of
597 (HsTyVar tc_name, args)
598 -> do { args' <- mapM dsHsType args
599 ; thing <- tcLookup tc_name
601 AGlobal (ATyCon tc) -> return (tc, args')
602 other -> failWithTc (badGadtDecl res_ty) }
603 other -> failWithTc (badGadtDecl res_ty)
605 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
606 -- because that causes a black hole, and for good reason. Building
607 -- the type means expanding type synonyms, and we can't do that
608 -- inside the "knot". So we have to work by steam.
609 get_largs (L _ ty) args = get_args ty args
610 get_args (HsAppTy fun arg) args = get_largs fun (arg:args)
611 get_args (HsParTy ty) args = get_largs ty args
612 get_args (HsOpTy ty1 (L span tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
613 get_args ty args = (ty, args)
616 = hang (ptext SLIT("In the result type of a data constructor:"))
619 = hang (ptext SLIT("Malformed constructor result type:"))
622 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
625 %************************************************************************
627 Type-variable binders
629 %************************************************************************
633 kcHsTyVars :: [LHsTyVarBndr Name]
634 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
635 -- They scope over the thing inside
637 kcHsTyVars tvs thing_inside
638 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
639 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
641 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
642 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
643 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
644 returnM (KindedTyVar name kind)
645 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
648 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
649 -> ([TyVar] -> TcM r)
651 -- Used when type-checking types/classes/type-decls
652 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
653 tcTyVarBndrs bndrs thing_inside
654 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
655 tcExtendTyVarEnv tyvars (thing_inside tyvars)
657 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
658 ; return (mkTyVar name kind') }
659 zonk (UserTyVar name) = WARN( True, ptext SLIT("Un-kinded tyvar") <+> ppr name )
660 return (mkTyVar name liftedTypeKind)
662 -----------------------------------
663 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
664 -- GADT decls can have a (perhaps partial) kind signature
665 -- e.g. data T :: * -> * -> * where ...
666 -- This function makes up suitable (kinded) type variables for
667 -- the argument kinds, and checks that the result kind is indeed *.
668 -- We use it also to make up argument type variables for for data instances.
669 tcDataKindSig Nothing = return []
670 tcDataKindSig (Just kind)
671 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
672 ; span <- getSrcSpanM
673 ; us <- newUniqueSupply
674 ; let uniqs = uniqsFromSupply us
675 ; return [ mk_tv span uniq str kind
676 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
678 (arg_kinds, res_kind) = splitKindFunTys kind
679 mk_tv loc uniq str kind = mkTyVar name kind
681 name = mkInternalName uniq occ loc
682 occ = mkOccName tvName str
684 names :: [String] -- a,b,c...aa,ab,ac etc
685 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
687 badKindSig :: Kind -> SDoc
689 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
694 %************************************************************************
696 Scoped type variables
698 %************************************************************************
701 tcAddScopedTyVars is used for scoped type variables added by pattern
703 e.g. \ ((x::a), (y::a)) -> x+y
704 They never have explicit kinds (because this is source-code only)
705 They are mutable (because they can get bound to a more specific type).
707 Usually we kind-infer and expand type splices, and then
708 tupecheck/desugar the type. That doesn't work well for scoped type
709 variables, because they scope left-right in patterns. (e.g. in the
710 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
712 The current not-very-good plan is to
713 * find all the types in the patterns
714 * find their free tyvars
716 * bring the kinded type vars into scope
717 * BUT throw away the kind-checked type
718 (we'll kind-check it again when we type-check the pattern)
720 This is bad because throwing away the kind checked type throws away
721 its splices. But too bad for now. [July 03]
724 We no longer specify that these type variables must be univerally
725 quantified (lots of email on the subject). If you want to put that
727 a) Do a checkSigTyVars after thing_inside
728 b) More insidiously, don't pass in expected_ty, else
729 we unify with it too early and checkSigTyVars barfs
730 Instead you have to pass in a fresh ty var, and unify
731 it with expected_ty afterwards
734 tcHsPatSigType :: UserTypeCtxt
735 -> LHsType Name -- The type signature
736 -> TcM ([TyVar], -- Newly in-scope type variables
737 Type) -- The signature
738 -- Used for type-checking type signatures in
739 -- (a) patterns e.g f (x::Int) = e
740 -- (b) result signatures e.g. g x :: Int = e
741 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
743 tcHsPatSigType ctxt hs_ty
744 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
745 do { -- Find the type variables that are mentioned in the type
746 -- but not already in scope. These are the ones that
747 -- should be bound by the pattern signature
748 in_scope <- getInLocalScope
749 ; let span = getLoc hs_ty
750 sig_tvs = [ L span (UserTyVar n)
751 | n <- nameSetToList (extractHsTyVars hs_ty),
754 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
755 ; checkValidType ctxt sig_ty
756 ; return (tyvars, sig_ty)
759 tcPatSig :: UserTypeCtxt
762 -> TcM (TcType, -- The type to use for "inside" the signature
763 [(Name,TcType)]) -- The new bit of type environment, binding
764 -- the scoped type variables
765 tcPatSig ctxt sig res_ty
766 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
768 ; if null sig_tvs then do {
769 -- The type signature binds no type variables,
770 -- and hence is rigid, so use it to zap the res_ty
771 boxyUnify sig_ty res_ty
772 ; return (sig_ty, [])
775 -- Type signature binds at least one scoped type variable
777 -- A pattern binding cannot bind scoped type variables
778 -- The renamer fails with a name-out-of-scope error
779 -- if a pattern binding tries to bind a type variable,
780 -- So we just have an ASSERT here
781 ; let in_pat_bind = case ctxt of
782 BindPatSigCtxt -> True
784 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
786 -- Check that pat_ty is rigid
787 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
789 -- Now match the pattern signature against res_ty
790 -- For convenience, and uniform-looking error messages
791 -- we do the matching by allocating meta type variables,
792 -- unifying, and reading out the results.
793 -- This is a strictly local operation.
794 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
795 ; boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty) res_ty
796 ; sig_tv_tys <- mapM readFilledBox box_tvs
798 -- Check that each is bound to a distinct type variable,
799 -- and one that is not already in scope
800 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
801 ; binds_in_scope <- getScopedTyVarBinds
802 ; check binds_in_scope tv_binds
805 ; return (res_ty, tv_binds)
808 check in_scope [] = return ()
809 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
810 ; check ((n,ty):in_scope) rest }
812 check_one in_scope n ty
813 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
814 -- Must bind to a type variable
816 ; checkTc (null dups) (dupInScope n (head dups) ty)
817 -- Must not bind to the same type variable
818 -- as some other in-scope type variable
822 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
826 %************************************************************************
828 Scoped type variables
830 %************************************************************************
833 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
834 pprHsSigCtxt ctxt hs_ty = vcat [ ptext SLIT("In") <+> pprUserTypeCtxt ctxt <> colon,
835 nest 2 (pp_sig ctxt) ]
837 pp_sig (FunSigCtxt n) = pp_n_colon n
838 pp_sig (ConArgCtxt n) = pp_n_colon n
839 pp_sig (ForSigCtxt n) = pp_n_colon n
840 pp_sig other = ppr (unLoc hs_ty)
842 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
846 = hang (ptext SLIT("A pattern type signature cannot bind scoped type variables")
847 <+> pprQuotedList sig_tvs)
848 2 (ptext SLIT("unless the pattern has a rigid type context"))
851 = vcat [sep [ptext SLIT("The scoped type variable") <+> quotes (ppr n),
852 nest 2 (ptext SLIT("is bound to the type") <+> quotes (ppr ty))],
853 nest 2 (ptext SLIT("You can only bind scoped type variables to type variables"))]
856 = hang (ptext SLIT("The scoped type variables") <+> quotes (ppr n) <+> ptext SLIT("and") <+> quotes (ppr n'))
857 2 (vcat [ptext SLIT("are bound to the same type (variable)"),
858 ptext SLIT("Distinct scoped type variables must be distinct")])