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
422 (a) spurious ! annotations.
423 (b) a class used as a type
426 dsHsType :: LHsType Name -> TcM Type
427 -- All HsTyVarBndrs in the intput type are kind-annotated
428 dsHsType ty = ds_type (unLoc ty)
430 ds_type ty@(HsTyVar name)
433 ds_type (HsParTy ty) -- Remove the parentheses markers
436 ds_type ty@(HsBangTy _ _) -- No bangs should be here
437 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
439 ds_type (HsKindSig ty k)
440 = dsHsType ty -- Kind checking done already
442 ds_type (HsListTy ty)
443 = dsHsType ty `thenM` \ tau_ty ->
444 returnM (mkListTy tau_ty)
446 ds_type (HsPArrTy ty)
447 = dsHsType ty `thenM` \ tau_ty ->
448 returnM (mkPArrTy tau_ty)
450 ds_type (HsTupleTy boxity tys)
451 = dsHsTypes tys `thenM` \ tau_tys ->
452 returnM (mkTupleTy boxity (length tys) tau_tys)
454 ds_type (HsFunTy ty1 ty2)
455 = dsHsType ty1 `thenM` \ tau_ty1 ->
456 dsHsType ty2 `thenM` \ tau_ty2 ->
457 returnM (mkFunTy tau_ty1 tau_ty2)
459 ds_type (HsOpTy ty1 (L span op) ty2)
460 = dsHsType ty1 `thenM` \ tau_ty1 ->
461 dsHsType ty2 `thenM` \ tau_ty2 ->
462 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
466 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
467 returnM (mkTyConApp tc [])
469 ds_type ty@(HsAppTy _ _)
472 ds_type (HsPredTy pred)
473 = dsHsPred pred `thenM` \ pred' ->
474 returnM (mkPredTy pred')
476 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
477 = tcTyVarBndrs tv_names $ \ tyvars ->
478 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
479 dsHsType ty `thenM` \ tau ->
480 returnM (mkSigmaTy tyvars theta tau)
482 dsHsTypes arg_tys = mappM dsHsType arg_tys
485 Help functions for type applications
486 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
489 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
490 ds_app (HsAppTy ty1 ty2) tys
491 = ds_app (unLoc ty1) (ty2:tys)
494 = dsHsTypes tys `thenM` \ arg_tys ->
496 HsTyVar fun -> ds_var_app fun arg_tys
497 other -> ds_type ty `thenM` \ fun_ty ->
498 returnM (mkAppTys fun_ty arg_tys)
500 ds_var_app :: Name -> [Type] -> TcM Type
501 ds_var_app name arg_tys
502 = tcLookup name `thenM` \ thing ->
504 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
505 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
506 other -> wrongThingErr "type" thing name
514 dsHsLPred :: LHsPred Name -> TcM PredType
515 dsHsLPred pred = dsHsPred (unLoc pred)
517 dsHsPred pred@(HsClassP class_name tys)
518 = dsHsTypes tys `thenM` \ arg_tys ->
519 tcLookupClass class_name `thenM` \ clas ->
520 returnM (ClassP clas arg_tys)
522 dsHsPred (HsIParam name ty)
523 = dsHsType ty `thenM` \ arg_ty ->
524 returnM (IParam name arg_ty)
527 GADT constructor signatures
530 tcLHsConSig :: LHsType Name
531 -> TcM ([TcTyVar], TcThetaType,
534 -- Take apart the type signature for a data constructor
535 -- The difference is that there can be bangs at the top of
536 -- the argument types, and kind-checking is the right place to check
537 tcLHsConSig sig@(L span (HsForAllTy exp tv_names ctxt ty))
539 addErrCtxt (gadtSigCtxt sig) $
540 tcTyVarBndrs tv_names $ \ tyvars ->
541 do { theta <- mappM dsHsLPred (unLoc ctxt)
542 ; (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
543 ; return (tyvars, theta, bangs, arg_tys, tc, res_tys) }
545 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
546 ; return ([], [], bangs, arg_tys, tc, res_tys) }
549 tc_con_sig_tau (L _ (HsFunTy arg ty))
550 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
551 ; arg_ty <- tcHsBangType arg
552 ; return (getBangStrictness arg : bangs,
553 arg_ty : arg_tys, tc, res_tys) }
556 = do { (tc, res_tys) <- tc_con_res ty []
557 ; return ([], [], tc, res_tys) }
560 tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
561 = do { res_ty' <- dsHsType res_ty
562 ; tc_con_res fun (res_ty' : res_tys) }
564 tc_con_res ty@(L _ (HsTyVar name)) res_tys
565 = do { thing <- tcLookup name
567 AGlobal (ATyCon tc) -> return (tc, res_tys)
568 other -> failWithTc (badGadtDecl ty)
571 tc_con_res ty _ = failWithTc (badGadtDecl ty)
574 = hang (ptext SLIT("In the signature of a data constructor:"))
577 = hang (ptext SLIT("Malformed constructor signature:"))
581 %************************************************************************
583 Type-variable binders
585 %************************************************************************
589 kcHsTyVars :: [LHsTyVarBndr Name]
590 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
591 -- They scope over the thing inside
593 kcHsTyVars tvs thing_inside
594 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
595 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
598 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
599 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
600 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
601 returnM (KindedTyVar name kind)
602 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
605 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
606 -> ([TyVar] -> TcM r)
608 -- Used when type-checking types/classes/type-decls
609 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
610 tcTyVarBndrs bndrs thing_inside
611 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
612 tcExtendTyVarEnv tyvars (thing_inside tyvars)
614 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
615 returnM (mkTyVar name kind')
616 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
617 returnM (mkTyVar name liftedTypeKind)
619 -----------------------------------
620 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
621 -- GADT decls can have a (perhpas partial) kind signature
622 -- e.g. data T :: * -> * -> * where ...
623 -- This function makes up suitable (kinded) type variables for
624 -- the argument kinds, and checks that the result kind is indeed *
625 tcDataKindSig Nothing = return []
626 tcDataKindSig (Just kind)
627 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
628 ; span <- getSrcSpanM
629 ; us <- newUniqueSupply
630 ; let loc = srcSpanStart span
631 uniqs = uniqsFromSupply us
632 ; return [ mk_tv loc uniq str kind
633 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
635 (arg_kinds, res_kind) = splitKindFunTys kind
636 mk_tv loc uniq str kind = mkTyVar name kind
638 name = mkInternalName uniq occ loc
639 occ = mkOccName tvName str
641 names :: [String] -- a,b,c...aa,ab,ac etc
642 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
644 badKindSig :: Kind -> SDoc
646 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
651 %************************************************************************
653 Scoped type variables
655 %************************************************************************
658 tcAddScopedTyVars is used for scoped type variables added by pattern
660 e.g. \ ((x::a), (y::a)) -> x+y
661 They never have explicit kinds (because this is source-code only)
662 They are mutable (because they can get bound to a more specific type).
664 Usually we kind-infer and expand type splices, and then
665 tupecheck/desugar the type. That doesn't work well for scoped type
666 variables, because they scope left-right in patterns. (e.g. in the
667 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
669 The current not-very-good plan is to
670 * find all the types in the patterns
671 * find their free tyvars
673 * bring the kinded type vars into scope
674 * BUT throw away the kind-checked type
675 (we'll kind-check it again when we type-check the pattern)
677 This is bad because throwing away the kind checked type throws away
678 its splices. But too bad for now. [July 03]
681 We no longer specify that these type variables must be univerally
682 quantified (lots of email on the subject). If you want to put that
684 a) Do a checkSigTyVars after thing_inside
685 b) More insidiously, don't pass in expected_ty, else
686 we unify with it too early and checkSigTyVars barfs
687 Instead you have to pass in a fresh ty var, and unify
688 it with expected_ty afterwards
691 tcPatSigBndrs :: LHsType Name
692 -> TcM ([TcTyVar], -- Brought into scope
693 LHsType Name) -- Kinded, but not yet desugared
696 = do { in_scope <- getInLocalScope
697 ; span <- getSrcSpanM
698 ; let sig_tvs = [ L span (UserTyVar n)
699 | n <- nameSetToList (extractHsTyVars hs_ty),
701 -- The tyvars we want are the free type variables of
702 -- the type that are not already in scope
704 -- Behave like kcHsType on a ForAll type
705 -- i.e. make kinded tyvars with mutable kinds,
706 -- and kind-check the enclosed types
707 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
708 { kinded_ty <- kcTypeType hs_ty
709 ; return (kinded_tvs, kinded_ty) }
711 -- Zonk the mutable kinds and bring the tyvars into scope
712 -- Just like the call to tcTyVarBndrs in ds_type (HsForAllTy case),
713 -- except that it brings *meta* tyvars into scope, not regular ones
715 -- [Out of date, but perhaps should be resurrected]
716 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
717 -- error messages when type variables escape:
718 -- Inferred type is less polymorphic than expected
719 -- Quantified type variable `t' escapes
720 -- It is mentioned in the environment:
721 -- t is bound by the pattern type signature at tcfail103.hs:6
722 ; tyvars <- mapM (zonk . unLoc) kinded_tvs
723 ; return (tyvars, kinded_ty) }
725 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
726 newMetaTyVar name kind' Flexi
727 -- Scoped type variables are bound to a *type*, hence Flexi
728 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
729 returnM (mkTyVar name liftedTypeKind)
731 tcHsPatSigType :: UserTypeCtxt
732 -> LHsType Name -- The type signature
733 -> TcM ([TcTyVar], -- Newly in-scope type variables
734 TcType) -- The signature
736 tcHsPatSigType ctxt hs_ty
737 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
738 do { (tyvars, kinded_ty) <- tcPatSigBndrs hs_ty
740 -- Complete processing of the type, and check its validity
741 ; tcExtendTyVarEnv tyvars $ do
742 { sig_ty <- tcHsKindedType kinded_ty
743 ; checkValidType ctxt sig_ty
744 ; return (tyvars, sig_ty) }
747 tcAddLetBoundTyVars :: LHsBinds Name -> TcM a -> TcM a
748 -- Turgid funciton, used for type variables bound by the patterns of a let binding
750 tcAddLetBoundTyVars binds thing_inside
751 = go (collectSigTysFromHsBinds (bagToList binds)) thing_inside
753 go [] thing_inside = thing_inside
754 go (hs_ty:hs_tys) thing_inside
755 = do { (tyvars, _kinded_ty) <- tcPatSigBndrs hs_ty
756 ; tcExtendTyVarEnv tyvars (go hs_tys thing_inside) }
760 %************************************************************************
762 \subsection{Signatures}
764 %************************************************************************
766 @tcSigs@ checks the signatures for validity, and returns a list of
767 {\em freshly-instantiated} signatures. That is, the types are already
768 split up, and have fresh type variables installed. All non-type-signature
769 "RenamedSigs" are ignored.
771 The @TcSigInfo@ contains @TcTypes@ because they are unified with
772 the variable's type, and after that checked to see whether they've
778 sig_id :: TcId, -- *Polymorphic* binder for this value...
780 sig_scoped :: [Name], -- Names for any scoped type variables
781 -- Invariant: correspond 1-1 with an initial
782 -- segment of sig_tvs (see Note [Scoped])
784 sig_tvs :: [TcTyVar], -- Instantiated type variables
785 -- See Note [Instantiate sig]
787 sig_theta :: TcThetaType, -- Instantiated theta
788 sig_tau :: TcTauType, -- Instantiated tau
789 sig_loc :: InstLoc -- The location of the signature
793 -- There may be more instantiated type variables than scoped
794 -- ones. For example:
795 -- type T a = forall b. b -> (a,b)
796 -- f :: forall c. T c
797 -- Here, the signature for f will have one scoped type variable, c,
798 -- but two instantiated type variables, c' and b'.
800 -- We assume that the scoped ones are at the *front* of sig_tvs,
801 -- and remember the names from the original HsForAllTy in sig_scoped
803 -- Note [Instantiate sig]
804 -- It's vital to instantiate a type signature with fresh variable.
806 -- type S = forall a. a->a
810 -- Here, we must use distinct type variables when checking f,g's right hand sides.
811 -- (Instantiation is only necessary because of type synonyms. Otherwise,
812 -- it's all cool; each signature has distinct type variables from the renamer.)
814 type TcSigFun = Name -> Maybe TcSigInfo
816 instance Outputable TcSigInfo where
817 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
818 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
820 lookupSig :: [TcSigInfo] -> TcSigFun -- Search for a particular signature
821 lookupSig [] name = Nothing
822 lookupSig (sig : sigs) name
823 | name == idName (sig_id sig) = Just sig
824 | otherwise = lookupSig sigs name