2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
8 tcHsSigType, tcHsDeriv,
12 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
13 kcCheckHsType, kcHsContext, kcHsType,
15 -- Typechecking kinded types
16 tcHsKindedContext, tcHsKindedType, tcHsBangType,
17 tcTyVarBndrs, dsHsType, tcLHsConSig, tcDataKindSig,
19 tcHsPatSigType, tcAddLetBoundTyVars,
21 TcSigInfo(..), TcSigFun, lookupSig
24 #include "HsVersions.h"
26 import HsSyn ( HsType(..), LHsType, HsTyVarBndr(..), LHsTyVarBndr, HsBang,
27 LHsContext, HsPred(..), LHsPred, LHsBinds,
28 getBangStrictness, collectSigTysFromHsBinds )
29 import RnHsSyn ( extractHsTyVars )
31 import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnv,
32 tcLookup, tcLookupClass, tcLookupTyCon,
33 TyThing(..), getInLocalScope, wrongThingErr
35 import TcMType ( newKindVar, newMetaTyVar, zonkTcKindToKind,
36 checkValidType, UserTypeCtxt(..), pprHsSigCtxt
38 import TcUnify ( unifyFunKind, checkExpectedKind )
39 import TcType ( Type, PredType(..), ThetaType,
40 MetaDetails(Flexi), hoistForAllTys,
41 TcType, TcTyVar, TcKind, TcThetaType, TcTauType,
43 mkSigmaTy, mkPredTy, mkGenTyConApp, mkTyConApp, mkAppTys,
45 import Kind ( Kind, isLiftedTypeKind, liftedTypeKind, ubxTupleKind,
46 openTypeKind, argTypeKind, splitKindFunTys )
48 import Var ( TyVar, mkTyVar )
49 import TyCon ( TyCon, tyConKind )
50 import Class ( Class, classTyCon )
51 import Name ( Name, mkInternalName )
52 import OccName ( mkOccName, tvName )
54 import PrelNames ( genUnitTyConName )
55 import TysWiredIn ( mkListTy, mkPArrTy, mkTupleTy )
56 import Bag ( bagToList )
57 import BasicTypes ( Boxity(..) )
58 import SrcLoc ( Located(..), unLoc, noLoc, srcSpanStart )
59 import UniqSupply ( uniqsFromSupply )
64 ----------------------------
66 ----------------------------
68 Generally speaking we now type-check types in three phases
70 1. kcHsType: kind check the HsType
71 *includes* performing any TH type splices;
72 so it returns a translated, and kind-annotated, type
74 2. dsHsType: convert from HsType to Type:
76 expand type synonyms [mkGenTyApps]
77 hoist the foralls [tcHsType]
79 3. checkValidType: check the validity of the resulting type
81 Often these steps are done one after the other (tcHsSigType).
82 But in mutually recursive groups of type and class decls we do
83 1 kind-check the whole group
84 2 build TyCons/Classes in a knot-tied way
85 3 check the validity of types in the now-unknotted TyCons/Classes
87 For example, when we find
88 (forall a m. m a -> m a)
89 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
90 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
91 an environment that binds a and m suitably.
93 The kind checker passed to tcHsTyVars needs to look at enough to
94 establish the kind of the tyvar:
95 * For a group of type and class decls, it's just the group, not
96 the rest of the program
97 * For a tyvar bound in a pattern type signature, its the types
98 mentioned in the other type signatures in that bunch of patterns
99 * For a tyvar bound in a RULE, it's the type signatures on other
100 universally quantified variables in the rule
102 Note that this may occasionally give surprising results. For example:
104 data T a b = MkT (a b)
106 Here we deduce a::*->*, b::*
107 But equally valid would be a::(*->*)-> *, b::*->*
112 Some of the validity check could in principle be done by the kind checker,
115 - During desugaring, we normalise by expanding type synonyms. Only
116 after this step can we check things like type-synonym saturation
117 e.g. type T k = k Int
119 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
120 and then S is saturated. This is a GHC extension.
122 - Similarly, also a GHC extension, we look through synonyms before complaining
123 about the form of a class or instance declaration
125 - Ambiguity checks involve functional dependencies, and it's easier to wait
126 until knots have been resolved before poking into them
128 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
129 finished building the loop. So to keep things simple, we postpone most validity
130 checking until step (3).
134 During step (1) we might fault in a TyCon defined in another module, and it might
135 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
136 knot around type declarations with ARecThing, so that the fault-in code can get
137 the TyCon being defined.
140 %************************************************************************
142 \subsection{Checking types}
144 %************************************************************************
147 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
148 -- Do kind checking, and hoist for-alls to the top
149 -- NB: it's important that the foralls that come from the top-level
150 -- HsForAllTy in hs_ty occur *first* in the returned type.
151 -- See Note [Scoped] with TcSigInfo
152 tcHsSigType ctxt hs_ty
153 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
154 do { kinded_ty <- kcTypeType hs_ty
155 ; ty <- tcHsKindedType kinded_ty
156 ; checkValidType ctxt ty
159 -- Used for the deriving(...) items
160 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
161 tcHsDeriv = addLocM (tc_hs_deriv [])
163 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
164 = kcHsTyVars tv_names $ \ tv_names' ->
165 do { cls_kind <- kcClass cls_name
166 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
167 ; tcTyVarBndrs tv_names' $ \ tyvars ->
168 do { arg_tys <- dsHsTypes tys
169 ; cls <- tcLookupClass cls_name
170 ; return (tyvars, cls, arg_tys) }}
172 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
173 = -- Funny newtype deriving form
175 -- where C has arity 2. Hence can't use regular functions
176 tc_hs_deriv (tv_names1 ++ tv_names2) ty
179 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
182 These functions are used during knot-tying in
183 type and class declarations, when we have to
184 separate kind-checking, desugaring, and validity checking
187 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
188 -- Used for type signatures
189 kcHsSigType ty = kcTypeType ty
190 kcHsLiftedSigType ty = kcLiftedType ty
192 tcHsKindedType :: LHsType Name -> TcM Type
193 -- Don't do kind checking, nor validity checking,
194 -- but do hoist for-alls to the top
195 -- This is used in type and class decls, where kinding is
196 -- done in advance, and validity checking is done later
197 -- [Validity checking done later because of knot-tying issues.]
199 = do { ty <- dsHsType hs_ty
200 ; return (hoistForAllTys ty) }
202 tcHsBangType :: LHsType Name -> TcM Type
203 -- Permit a bang, but discard it
204 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
205 tcHsBangType ty = tcHsKindedType ty
207 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
208 -- Used when we are expecting a ClassContext (i.e. no implicit params)
209 -- Does not do validity checking, like tcHsKindedType
210 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
214 %************************************************************************
216 The main kind checker: kcHsType
218 %************************************************************************
220 First a couple of simple wrappers for kcHsType
223 ---------------------------
224 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
225 -- The type ty must be a *lifted* *type*
226 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
228 ---------------------------
229 kcTypeType :: LHsType Name -> TcM (LHsType Name)
230 -- The type ty must be a *type*, but it can be lifted or
231 -- unlifted or an unboxed tuple.
232 kcTypeType ty = kcCheckHsType ty openTypeKind
234 ---------------------------
235 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
236 -- Check that the type has the specified kind
237 -- Be sure to use checkExpectedKind, rather than simply unifying
238 -- with OpenTypeKind, because it gives better error messages
239 kcCheckHsType (L span ty) exp_kind
241 kc_hs_type ty `thenM` \ (ty', act_kind) ->
242 checkExpectedKind ty act_kind exp_kind `thenM_`
246 Here comes the main function
249 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
250 kcHsType ty = wrapLocFstM kc_hs_type ty
251 -- kcHsType *returns* the kind of the type, rather than taking an expected
252 -- kind as argument as tcExpr does.
254 -- (a) the kind of (->) is
255 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
256 -- so we'd need to generate huge numbers of bx variables.
257 -- (b) kinds are so simple that the error messages are fine
259 -- The translated type has explicitly-kinded type-variable binders
261 kc_hs_type (HsParTy ty)
262 = kcHsType ty `thenM` \ (ty', kind) ->
263 returnM (HsParTy ty', kind)
265 kc_hs_type (HsTyVar name)
266 = kcTyVar name `thenM` \ kind ->
267 returnM (HsTyVar name, kind)
269 kc_hs_type (HsListTy ty)
270 = kcLiftedType ty `thenM` \ ty' ->
271 returnM (HsListTy ty', liftedTypeKind)
273 kc_hs_type (HsPArrTy ty)
274 = kcLiftedType ty `thenM` \ ty' ->
275 returnM (HsPArrTy ty', liftedTypeKind)
277 kc_hs_type (HsNumTy n)
278 = returnM (HsNumTy n, liftedTypeKind)
280 kc_hs_type (HsKindSig ty k)
281 = kcCheckHsType ty k `thenM` \ ty' ->
282 returnM (HsKindSig ty' k, k)
284 kc_hs_type (HsTupleTy Boxed tys)
285 = mappM kcLiftedType tys `thenM` \ tys' ->
286 returnM (HsTupleTy Boxed tys', liftedTypeKind)
288 kc_hs_type (HsTupleTy Unboxed tys)
289 = mappM kcTypeType tys `thenM` \ tys' ->
290 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
292 kc_hs_type (HsFunTy ty1 ty2)
293 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
294 kcTypeType ty2 `thenM` \ ty2' ->
295 returnM (HsFunTy ty1' ty2', liftedTypeKind)
297 kc_hs_type ty@(HsOpTy ty1 op ty2)
298 = addLocM kcTyVar op `thenM` \ op_kind ->
299 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
300 returnM (HsOpTy ty1' op ty2', res_kind)
302 kc_hs_type ty@(HsAppTy ty1 ty2)
303 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
304 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
305 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
307 (fun_ty, arg_tys) = split ty1 [ty2]
308 split (L _ (HsAppTy f a)) as = split f (a:as)
310 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
311 -- the application; they are never used
313 kc_hs_type (HsPredTy pred)
314 = kcHsPred pred `thenM` \ pred' ->
315 returnM (HsPredTy pred', liftedTypeKind)
317 kc_hs_type (HsForAllTy exp tv_names context ty)
318 = kcHsTyVars tv_names $ \ tv_names' ->
319 kcHsContext context `thenM` \ ctxt' ->
320 kcLiftedType ty `thenM` \ ty' ->
321 -- The body of a forall is usually a type, but in principle
322 -- there's no reason to prohibit *unlifted* types.
323 -- In fact, GHC can itself construct a function with an
324 -- unboxed tuple inside a for-all (via CPR analyis; see
325 -- typecheck/should_compile/tc170)
327 -- Still, that's only for internal interfaces, which aren't
328 -- kind-checked, so we only allow liftedTypeKind here
329 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
331 kc_hs_type (HsBangTy b ty)
332 = do { (ty', kind) <- kcHsType ty
333 ; return (HsBangTy b ty', kind) }
335 kc_hs_type ty@(HsSpliceTy _)
336 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
339 ---------------------------
340 kcApps :: TcKind -- Function kind
342 -> [LHsType Name] -- Arg types
343 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
344 kcApps fun_kind ppr_fun args
345 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
346 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
347 returnM (args', res_kind)
349 split_fk fk 0 = returnM ([], fk)
350 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
352 Nothing -> failWithTc too_many_args
353 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
356 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
358 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
359 ptext SLIT("is applied to too many type arguments")
361 ---------------------------
362 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
363 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
365 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
366 kcHsLPred = wrapLocM kcHsPred
368 kcHsPred :: HsPred Name -> TcM (HsPred Name)
369 kcHsPred pred -- Checks that the result is of kind liftedType
370 = kc_pred pred `thenM` \ (pred', kind) ->
371 checkExpectedKind pred kind liftedTypeKind `thenM_`
374 ---------------------------
375 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
376 -- Does *not* check for a saturated
377 -- application (reason: used from TcDeriv)
378 kc_pred pred@(HsIParam name ty)
379 = kcHsType ty `thenM` \ (ty', kind) ->
380 returnM (HsIParam name ty', kind)
382 kc_pred pred@(HsClassP cls tys)
383 = kcClass cls `thenM` \ kind ->
384 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
385 returnM (HsClassP cls tys', res_kind)
387 ---------------------------
388 kcTyVar :: Name -> TcM TcKind
389 kcTyVar name -- Could be a tyvar or a tycon
390 = traceTc (text "lk1" <+> ppr name) `thenM_`
391 tcLookup name `thenM` \ thing ->
392 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
394 ATyVar _ ty -> returnM (typeKind ty)
395 AThing kind -> returnM kind
396 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
397 other -> wrongThingErr "type" thing name
399 kcClass :: Name -> TcM TcKind
400 kcClass cls -- Must be a class
401 = tcLookup cls `thenM` \ thing ->
403 AThing kind -> returnM kind
404 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
405 other -> wrongThingErr "class" thing cls
409 %************************************************************************
413 %************************************************************************
417 * Transforms from HsType to Type
420 It cannot fail, and does no validity checking, except for
421 structural matters, such as spurious ! annotations.
424 dsHsType :: LHsType Name -> TcM Type
425 -- All HsTyVarBndrs in the intput type are kind-annotated
426 dsHsType ty = ds_type (unLoc ty)
428 ds_type ty@(HsTyVar name)
431 ds_type (HsParTy ty) -- Remove the parentheses markers
434 ds_type ty@(HsBangTy _ _) -- No bangs should be here
435 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
437 ds_type (HsKindSig ty k)
438 = dsHsType ty -- Kind checking done already
440 ds_type (HsListTy ty)
441 = dsHsType ty `thenM` \ tau_ty ->
442 returnM (mkListTy tau_ty)
444 ds_type (HsPArrTy ty)
445 = dsHsType ty `thenM` \ tau_ty ->
446 returnM (mkPArrTy tau_ty)
448 ds_type (HsTupleTy boxity tys)
449 = dsHsTypes tys `thenM` \ tau_tys ->
450 returnM (mkTupleTy boxity (length tys) tau_tys)
452 ds_type (HsFunTy ty1 ty2)
453 = dsHsType ty1 `thenM` \ tau_ty1 ->
454 dsHsType ty2 `thenM` \ tau_ty2 ->
455 returnM (mkFunTy tau_ty1 tau_ty2)
457 ds_type (HsOpTy ty1 (L span op) ty2)
458 = dsHsType ty1 `thenM` \ tau_ty1 ->
459 dsHsType ty2 `thenM` \ tau_ty2 ->
460 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
464 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
465 returnM (mkTyConApp tc [])
467 ds_type ty@(HsAppTy _ _)
470 ds_type (HsPredTy pred)
471 = dsHsPred pred `thenM` \ pred' ->
472 returnM (mkPredTy pred')
474 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
475 = tcTyVarBndrs tv_names $ \ tyvars ->
476 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
477 dsHsType ty `thenM` \ tau ->
478 returnM (mkSigmaTy tyvars theta tau)
480 dsHsTypes arg_tys = mappM dsHsType arg_tys
483 Help functions for type applications
484 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
487 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
488 ds_app (HsAppTy ty1 ty2) tys
489 = ds_app (unLoc ty1) (ty2:tys)
492 = dsHsTypes tys `thenM` \ arg_tys ->
494 HsTyVar fun -> ds_var_app fun arg_tys
495 other -> ds_type ty `thenM` \ fun_ty ->
496 returnM (mkAppTys fun_ty arg_tys)
498 ds_var_app :: Name -> [Type] -> TcM Type
499 ds_var_app name arg_tys
500 = tcLookup name `thenM` \ thing ->
502 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
503 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
504 other -> pprPanic "ds_app_type" (ppr name <+> ppr arg_tys)
512 dsHsLPred :: LHsPred Name -> TcM PredType
513 dsHsLPred pred = dsHsPred (unLoc pred)
515 dsHsPred pred@(HsClassP class_name tys)
516 = dsHsTypes tys `thenM` \ arg_tys ->
517 tcLookupClass class_name `thenM` \ clas ->
518 returnM (ClassP clas arg_tys)
520 dsHsPred (HsIParam name ty)
521 = dsHsType ty `thenM` \ arg_ty ->
522 returnM (IParam name arg_ty)
525 GADT constructor signatures
528 tcLHsConSig :: LHsType Name
529 -> TcM ([TcTyVar], TcThetaType,
532 -- Take apart the type signature for a data constructor
533 -- The difference is that there can be bangs at the top of
534 -- the argument types, and kind-checking is the right place to check
535 tcLHsConSig sig@(L span (HsForAllTy exp tv_names ctxt ty))
537 addErrCtxt (gadtSigCtxt sig) $
538 tcTyVarBndrs tv_names $ \ tyvars ->
539 do { theta <- mappM dsHsLPred (unLoc ctxt)
540 ; (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
541 ; return (tyvars, theta, bangs, arg_tys, tc, res_tys) }
543 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
544 ; return ([], [], bangs, arg_tys, tc, res_tys) }
547 tc_con_sig_tau (L _ (HsFunTy arg ty))
548 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
549 ; arg_ty <- tcHsBangType arg
550 ; return (getBangStrictness arg : bangs,
551 arg_ty : arg_tys, tc, res_tys) }
554 = do { (tc, res_tys) <- tc_con_res ty []
555 ; return ([], [], tc, res_tys) }
558 tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
559 = do { res_ty' <- dsHsType res_ty
560 ; tc_con_res fun (res_ty' : res_tys) }
562 tc_con_res ty@(L _ (HsTyVar name)) res_tys
563 = do { thing <- tcLookup name
565 AGlobal (ATyCon tc) -> return (tc, res_tys)
566 other -> failWithTc (badGadtDecl ty)
569 tc_con_res ty _ = failWithTc (badGadtDecl ty)
572 = hang (ptext SLIT("In the signature of a data constructor:"))
575 = hang (ptext SLIT("Malformed constructor signature:"))
579 %************************************************************************
581 Type-variable binders
583 %************************************************************************
587 kcHsTyVars :: [LHsTyVarBndr Name]
588 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
589 -- They scope over the thing inside
591 kcHsTyVars tvs thing_inside
592 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
593 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
596 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
597 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
598 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
599 returnM (KindedTyVar name kind)
600 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
603 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
604 -> ([TyVar] -> TcM r)
606 -- Used when type-checking types/classes/type-decls
607 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
608 tcTyVarBndrs bndrs thing_inside
609 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
610 tcExtendTyVarEnv tyvars (thing_inside tyvars)
612 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
613 returnM (mkTyVar name kind')
614 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
615 returnM (mkTyVar name liftedTypeKind)
617 -----------------------------------
618 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
619 -- GADT decls can have a (perhpas partial) kind signature
620 -- e.g. data T :: * -> * -> * where ...
621 -- This function makes up suitable (kinded) type variables for
622 -- the argument kinds, and checks that the result kind is indeed *
623 tcDataKindSig Nothing = return []
624 tcDataKindSig (Just kind)
625 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
626 ; span <- getSrcSpanM
627 ; us <- newUniqueSupply
628 ; let loc = srcSpanStart span
629 uniqs = uniqsFromSupply us
630 ; return [ mk_tv loc uniq str kind
631 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
633 (arg_kinds, res_kind) = splitKindFunTys kind
634 mk_tv loc uniq str kind = mkTyVar name kind
636 name = mkInternalName uniq occ loc
637 occ = mkOccName tvName str
639 names :: [String] -- a,b,c...aa,ab,ac etc
640 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
642 badKindSig :: Kind -> SDoc
644 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
649 %************************************************************************
651 Scoped type variables
653 %************************************************************************
656 tcAddScopedTyVars is used for scoped type variables added by pattern
658 e.g. \ ((x::a), (y::a)) -> x+y
659 They never have explicit kinds (because this is source-code only)
660 They are mutable (because they can get bound to a more specific type).
662 Usually we kind-infer and expand type splices, and then
663 tupecheck/desugar the type. That doesn't work well for scoped type
664 variables, because they scope left-right in patterns. (e.g. in the
665 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
667 The current not-very-good plan is to
668 * find all the types in the patterns
669 * find their free tyvars
671 * bring the kinded type vars into scope
672 * BUT throw away the kind-checked type
673 (we'll kind-check it again when we type-check the pattern)
675 This is bad because throwing away the kind checked type throws away
676 its splices. But too bad for now. [July 03]
679 We no longer specify that these type variables must be univerally
680 quantified (lots of email on the subject). If you want to put that
682 a) Do a checkSigTyVars after thing_inside
683 b) More insidiously, don't pass in expected_ty, else
684 we unify with it too early and checkSigTyVars barfs
685 Instead you have to pass in a fresh ty var, and unify
686 it with expected_ty afterwards
689 tcPatSigBndrs :: LHsType Name
690 -> TcM ([TcTyVar], -- Brought into scope
691 LHsType Name) -- Kinded, but not yet desugared
694 = do { in_scope <- getInLocalScope
695 ; span <- getSrcSpanM
696 ; let sig_tvs = [ L span (UserTyVar n)
697 | n <- nameSetToList (extractHsTyVars hs_ty),
699 -- The tyvars we want are the free type variables of
700 -- the type that are not already in scope
702 -- Behave like kcHsType on a ForAll type
703 -- i.e. make kinded tyvars with mutable kinds,
704 -- and kind-check the enclosed types
705 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
706 { kinded_ty <- kcTypeType hs_ty
707 ; return (kinded_tvs, kinded_ty) }
709 -- Zonk the mutable kinds and bring the tyvars into scope
710 -- Just like the call to tcTyVarBndrs in ds_type (HsForAllTy case),
711 -- except that it brings *meta* tyvars into scope, not regular ones
713 -- [Out of date, but perhaps should be resurrected]
714 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
715 -- error messages when type variables escape:
716 -- Inferred type is less polymorphic than expected
717 -- Quantified type variable `t' escapes
718 -- It is mentioned in the environment:
719 -- t is bound by the pattern type signature at tcfail103.hs:6
720 ; tyvars <- mapM (zonk . unLoc) kinded_tvs
721 ; return (tyvars, kinded_ty) }
723 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
724 newMetaTyVar name kind' Flexi
725 -- Scoped type variables are bound to a *type*, hence Flexi
726 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
727 returnM (mkTyVar name liftedTypeKind)
729 tcHsPatSigType :: UserTypeCtxt
730 -> LHsType Name -- The type signature
731 -> TcM ([TcTyVar], -- Newly in-scope type variables
732 TcType) -- The signature
734 tcHsPatSigType ctxt hs_ty
735 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
736 do { (tyvars, kinded_ty) <- tcPatSigBndrs hs_ty
738 -- Complete processing of the type, and check its validity
739 ; tcExtendTyVarEnv tyvars $ do
740 { sig_ty <- tcHsKindedType kinded_ty
741 ; checkValidType ctxt sig_ty
742 ; return (tyvars, sig_ty) }
745 tcAddLetBoundTyVars :: LHsBinds Name -> TcM a -> TcM a
746 -- Turgid funciton, used for type variables bound by the patterns of a let binding
748 tcAddLetBoundTyVars binds thing_inside
749 = go (collectSigTysFromHsBinds (bagToList binds)) thing_inside
751 go [] thing_inside = thing_inside
752 go (hs_ty:hs_tys) thing_inside
753 = do { (tyvars, _kinded_ty) <- tcPatSigBndrs hs_ty
754 ; tcExtendTyVarEnv tyvars (go hs_tys thing_inside) }
758 %************************************************************************
760 \subsection{Signatures}
762 %************************************************************************
764 @tcSigs@ checks the signatures for validity, and returns a list of
765 {\em freshly-instantiated} signatures. That is, the types are already
766 split up, and have fresh type variables installed. All non-type-signature
767 "RenamedSigs" are ignored.
769 The @TcSigInfo@ contains @TcTypes@ because they are unified with
770 the variable's type, and after that checked to see whether they've
776 sig_id :: TcId, -- *Polymorphic* binder for this value...
778 sig_scoped :: [Name], -- Names for any scoped type variables
779 -- Invariant: correspond 1-1 with an initial
780 -- segment of sig_tvs (see Note [Scoped])
782 sig_tvs :: [TcTyVar], -- Instantiated type variables
783 -- See Note [Instantiate sig]
785 sig_theta :: TcThetaType, -- Instantiated theta
786 sig_tau :: TcTauType, -- Instantiated tau
787 sig_loc :: InstLoc -- The location of the signature
791 -- There may be more instantiated type variables than scoped
792 -- ones. For example:
793 -- type T a = forall b. b -> (a,b)
794 -- f :: forall c. T c
795 -- Here, the signature for f will have one scoped type variable, c,
796 -- but two instantiated type variables, c' and b'.
798 -- We assume that the scoped ones are at the *front* of sig_tvs,
799 -- and remember the names from the original HsForAllTy in sig_scoped
801 -- Note [Instantiate sig]
802 -- It's vital to instantiate a type signature with fresh variable.
804 -- type S = forall a. a->a
808 -- Here, we must use distinct type variables when checking f,g's right hand sides.
809 -- (Instantiation is only necessary because of type synonyms. Otherwise,
810 -- it's all cool; each signature has distinct type variables from the renamer.)
812 type TcSigFun = Name -> Maybe TcSigInfo
814 instance Outputable TcSigInfo where
815 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
816 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
818 lookupSig :: [TcSigInfo] -> TcSigFun -- Search for a particular signature
819 lookupSig [] name = Nothing
820 lookupSig (sig : sigs) name
821 | name == idName (sig_id sig) = Just sig
822 | otherwise = lookupSig sigs name