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,
42 mkForAllTys, mkFunTys, tcEqType, isPredTy, mkFunTy,
43 mkSigmaTy, mkPredTy, mkGenTyConApp, mkTyConApp, mkAppTys,
44 tcSplitFunTy_maybe, tcSplitForAllTys, typeKind )
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 Type ( deShadowTy )
56 import TysWiredIn ( mkListTy, mkPArrTy, mkTupleTy )
57 import Bag ( bagToList )
58 import BasicTypes ( Boxity(..) )
59 import SrcLoc ( Located(..), unLoc, noLoc, srcSpanStart )
60 import UniqSupply ( uniqsFromSupply )
66 ----------------------------
68 ----------------------------
70 Generally speaking we now type-check types in three phases
72 1. kcHsType: kind check the HsType
73 *includes* performing any TH type splices;
74 so it returns a translated, and kind-annotated, type
76 2. dsHsType: convert from HsType to Type:
78 expand type synonyms [mkGenTyApps]
79 hoist the foralls [tcHsType]
81 3. checkValidType: check the validity of the resulting type
83 Often these steps are done one after the other (tcHsSigType).
84 But in mutually recursive groups of type and class decls we do
85 1 kind-check the whole group
86 2 build TyCons/Classes in a knot-tied way
87 3 check the validity of types in the now-unknotted TyCons/Classes
89 For example, when we find
90 (forall a m. m a -> m a)
91 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
92 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
93 an environment that binds a and m suitably.
95 The kind checker passed to tcHsTyVars needs to look at enough to
96 establish the kind of the tyvar:
97 * For a group of type and class decls, it's just the group, not
98 the rest of the program
99 * For a tyvar bound in a pattern type signature, its the types
100 mentioned in the other type signatures in that bunch of patterns
101 * For a tyvar bound in a RULE, it's the type signatures on other
102 universally quantified variables in the rule
104 Note that this may occasionally give surprising results. For example:
106 data T a b = MkT (a b)
108 Here we deduce a::*->*, b::*
109 But equally valid would be a::(*->*)-> *, b::*->*
114 Some of the validity check could in principle be done by the kind checker,
117 - During desugaring, we normalise by expanding type synonyms. Only
118 after this step can we check things like type-synonym saturation
119 e.g. type T k = k Int
121 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
122 and then S is saturated. This is a GHC extension.
124 - Similarly, also a GHC extension, we look through synonyms before complaining
125 about the form of a class or instance declaration
127 - Ambiguity checks involve functional dependencies, and it's easier to wait
128 until knots have been resolved before poking into them
130 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
131 finished building the loop. So to keep things simple, we postpone most validity
132 checking until step (3).
136 During step (1) we might fault in a TyCon defined in another module, and it might
137 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
138 knot around type declarations with ARecThing, so that the fault-in code can get
139 the TyCon being defined.
142 %************************************************************************
144 \subsection{Checking types}
146 %************************************************************************
149 tcHsSigType :: UserTypeCtxt -> LHsType Name -> TcM Type
150 -- Do kind checking, and hoist for-alls to the top
151 -- NB: it's important that the foralls that come from the top-level
152 -- HsForAllTy in hs_ty occur *first* in the returned type.
153 -- See Note [Scoped] with TcSigInfo
154 tcHsSigType ctxt hs_ty
155 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
156 do { kinded_ty <- kcTypeType hs_ty
157 ; ty <- tcHsKindedType kinded_ty
158 ; checkValidType ctxt ty
160 -- Used for the deriving(...) items
161 tcHsDeriv :: LHsType Name -> TcM ([TyVar], Class, [Type])
162 tcHsDeriv = addLocM (tc_hs_deriv [])
164 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
165 = kcHsTyVars tv_names $ \ tv_names' ->
166 do { cls_kind <- kcClass cls_name
167 ; (tys, res_kind) <- kcApps cls_kind (ppr cls_name) hs_tys
168 ; tcTyVarBndrs tv_names' $ \ tyvars ->
169 do { arg_tys <- dsHsTypes tys
170 ; cls <- tcLookupClass cls_name
171 ; return (tyvars, cls, arg_tys) }}
173 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
174 = -- Funny newtype deriving form
176 -- where C has arity 2. Hence can't use regular functions
177 tc_hs_deriv (tv_names1 ++ tv_names2) ty
180 = failWithTc (ptext SLIT("Illegal deriving item") <+> ppr other)
183 These functions are used during knot-tying in
184 type and class declarations, when we have to
185 separate kind-checking, desugaring, and validity checking
188 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
189 -- Used for type signatures
190 kcHsSigType ty = kcTypeType ty
191 kcHsLiftedSigType ty = kcLiftedType ty
193 tcHsKindedType :: LHsType Name -> TcM Type
194 -- Don't do kind checking, nor validity checking,
195 -- but do hoist for-alls to the top
196 -- This is used in type and class decls, where kinding is
197 -- done in advance, and validity checking is done later
198 -- [Validity checking done later because of knot-tying issues.]
200 = do { ty <- dsHsType hs_ty
201 ; return (hoistForAllTys ty) }
203 tcHsBangType :: LHsType Name -> TcM Type
204 -- Permit a bang, but discard it
205 tcHsBangType (L span (HsBangTy b ty)) = tcHsKindedType ty
206 tcHsBangType ty = tcHsKindedType ty
208 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
209 -- Used when we are expecting a ClassContext (i.e. no implicit params)
210 -- Does not do validity checking, like tcHsKindedType
211 tcHsKindedContext hs_theta = addLocM (mappM dsHsLPred) hs_theta
215 %************************************************************************
217 The main kind checker: kcHsType
219 %************************************************************************
221 First a couple of simple wrappers for kcHsType
224 ---------------------------
225 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
226 -- The type ty must be a *lifted* *type*
227 kcLiftedType ty = kcCheckHsType ty liftedTypeKind
229 ---------------------------
230 kcTypeType :: LHsType Name -> TcM (LHsType Name)
231 -- The type ty must be a *type*, but it can be lifted or
232 -- unlifted or an unboxed tuple.
233 kcTypeType ty = kcCheckHsType ty openTypeKind
235 ---------------------------
236 kcCheckHsType :: LHsType Name -> TcKind -> TcM (LHsType Name)
237 -- Check that the type has the specified kind
238 -- Be sure to use checkExpectedKind, rather than simply unifying
239 -- with OpenTypeKind, because it gives better error messages
240 kcCheckHsType (L span ty) exp_kind
242 kc_hs_type ty `thenM` \ (ty', act_kind) ->
243 checkExpectedKind ty act_kind exp_kind `thenM_`
247 Here comes the main function
250 kcHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
251 kcHsType ty = wrapLocFstM kc_hs_type ty
252 -- kcHsType *returns* the kind of the type, rather than taking an expected
253 -- kind as argument as tcExpr does.
255 -- (a) the kind of (->) is
256 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
257 -- so we'd need to generate huge numbers of bx variables.
258 -- (b) kinds are so simple that the error messages are fine
260 -- The translated type has explicitly-kinded type-variable binders
262 kc_hs_type (HsParTy ty)
263 = kcHsType ty `thenM` \ (ty', kind) ->
264 returnM (HsParTy ty', kind)
266 kc_hs_type (HsTyVar name)
267 = kcTyVar name `thenM` \ kind ->
268 returnM (HsTyVar name, kind)
270 kc_hs_type (HsListTy ty)
271 = kcLiftedType ty `thenM` \ ty' ->
272 returnM (HsListTy ty', liftedTypeKind)
274 kc_hs_type (HsPArrTy ty)
275 = kcLiftedType ty `thenM` \ ty' ->
276 returnM (HsPArrTy ty', liftedTypeKind)
278 kc_hs_type (HsNumTy n)
279 = returnM (HsNumTy n, liftedTypeKind)
281 kc_hs_type (HsKindSig ty k)
282 = kcCheckHsType ty k `thenM` \ ty' ->
283 returnM (HsKindSig ty' k, k)
285 kc_hs_type (HsTupleTy Boxed tys)
286 = mappM kcLiftedType tys `thenM` \ tys' ->
287 returnM (HsTupleTy Boxed tys', liftedTypeKind)
289 kc_hs_type (HsTupleTy Unboxed tys)
290 = mappM kcTypeType tys `thenM` \ tys' ->
291 returnM (HsTupleTy Unboxed tys', ubxTupleKind)
293 kc_hs_type (HsFunTy ty1 ty2)
294 = kcCheckHsType ty1 argTypeKind `thenM` \ ty1' ->
295 kcTypeType ty2 `thenM` \ ty2' ->
296 returnM (HsFunTy ty1' ty2', liftedTypeKind)
298 kc_hs_type ty@(HsOpTy ty1 op ty2)
299 = addLocM kcTyVar op `thenM` \ op_kind ->
300 kcApps op_kind (ppr op) [ty1,ty2] `thenM` \ ([ty1',ty2'], res_kind) ->
301 returnM (HsOpTy ty1' op ty2', res_kind)
303 kc_hs_type ty@(HsAppTy ty1 ty2)
304 = kcHsType fun_ty `thenM` \ (fun_ty', fun_kind) ->
305 kcApps fun_kind (ppr fun_ty) arg_tys `thenM` \ ((arg_ty':arg_tys'), res_kind) ->
306 returnM (foldl mk_app (HsAppTy fun_ty' arg_ty') arg_tys', res_kind)
308 (fun_ty, arg_tys) = split ty1 [ty2]
309 split (L _ (HsAppTy f a)) as = split f (a:as)
311 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
312 -- the application; they are never used
314 kc_hs_type (HsPredTy pred)
315 = kcHsPred pred `thenM` \ pred' ->
316 returnM (HsPredTy pred', liftedTypeKind)
318 kc_hs_type (HsForAllTy exp tv_names context ty)
319 = kcHsTyVars tv_names $ \ tv_names' ->
320 kcHsContext context `thenM` \ ctxt' ->
321 kcLiftedType ty `thenM` \ ty' ->
322 -- The body of a forall is usually a type, but in principle
323 -- there's no reason to prohibit *unlifted* types.
324 -- In fact, GHC can itself construct a function with an
325 -- unboxed tuple inside a for-all (via CPR analyis; see
326 -- typecheck/should_compile/tc170)
328 -- Still, that's only for internal interfaces, which aren't
329 -- kind-checked, so we only allow liftedTypeKind here
330 returnM (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind)
332 kc_hs_type (HsBangTy b ty)
333 = do { (ty', kind) <- kcHsType ty
334 ; return (HsBangTy b ty', kind) }
336 kc_hs_type ty@(HsSpliceTy _)
337 = failWithTc (ptext SLIT("Unexpected type splice:") <+> ppr ty)
340 ---------------------------
341 kcApps :: TcKind -- Function kind
343 -> [LHsType Name] -- Arg types
344 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
345 kcApps fun_kind ppr_fun args
346 = split_fk fun_kind (length args) `thenM` \ (arg_kinds, res_kind) ->
347 zipWithM kc_arg args arg_kinds `thenM` \ args' ->
348 returnM (args', res_kind)
350 split_fk fk 0 = returnM ([], fk)
351 split_fk fk n = unifyFunKind fk `thenM` \ mb_fk ->
353 Nothing -> failWithTc too_many_args
354 Just (ak,fk') -> split_fk fk' (n-1) `thenM` \ (aks, rk) ->
357 kc_arg arg arg_kind = kcCheckHsType arg arg_kind
359 too_many_args = ptext SLIT("Kind error:") <+> quotes ppr_fun <+>
360 ptext SLIT("is applied to too many type arguments")
362 ---------------------------
363 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
364 kcHsContext ctxt = wrapLocM (mappM kcHsLPred) ctxt
366 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
367 kcHsLPred = wrapLocM kcHsPred
369 kcHsPred :: HsPred Name -> TcM (HsPred Name)
370 kcHsPred pred -- Checks that the result is of kind liftedType
371 = kc_pred pred `thenM` \ (pred', kind) ->
372 checkExpectedKind pred kind liftedTypeKind `thenM_`
375 ---------------------------
376 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
377 -- Does *not* check for a saturated
378 -- application (reason: used from TcDeriv)
379 kc_pred pred@(HsIParam name ty)
380 = kcHsType ty `thenM` \ (ty', kind) ->
381 returnM (HsIParam name ty', kind)
383 kc_pred pred@(HsClassP cls tys)
384 = kcClass cls `thenM` \ kind ->
385 kcApps kind (ppr cls) tys `thenM` \ (tys', res_kind) ->
386 returnM (HsClassP cls tys', res_kind)
388 ---------------------------
389 kcTyVar :: Name -> TcM TcKind
390 kcTyVar name -- Could be a tyvar or a tycon
391 = traceTc (text "lk1" <+> ppr name) `thenM_`
392 tcLookup name `thenM` \ thing ->
393 traceTc (text "lk2" <+> ppr name <+> ppr thing) `thenM_`
395 ATyVar _ ty -> returnM (typeKind ty)
396 AThing kind -> returnM kind
397 AGlobal (ATyCon tc) -> returnM (tyConKind tc)
398 other -> wrongThingErr "type" thing name
400 kcClass :: Name -> TcM TcKind
401 kcClass cls -- Must be a class
402 = tcLookup cls `thenM` \ thing ->
404 AThing kind -> returnM kind
405 AGlobal (AClass cls) -> returnM (tyConKind (classTyCon cls))
406 other -> wrongThingErr "class" thing cls
410 %************************************************************************
414 %************************************************************************
418 * Transforms from HsType to Type
421 It cannot fail, and does no validity checking, except for
422 structural matters, such as spurious ! annotations.
425 dsHsType :: LHsType Name -> TcM Type
426 -- All HsTyVarBndrs in the intput type are kind-annotated
427 dsHsType ty = ds_type (unLoc ty)
429 ds_type ty@(HsTyVar name)
432 ds_type (HsParTy ty) -- Remove the parentheses markers
435 ds_type ty@(HsBangTy _ _) -- No bangs should be here
436 = failWithTc (ptext SLIT("Unexpected strictness annotation:") <+> ppr ty)
438 ds_type (HsKindSig ty k)
439 = dsHsType ty -- Kind checking done already
441 ds_type (HsListTy ty)
442 = dsHsType ty `thenM` \ tau_ty ->
443 returnM (mkListTy tau_ty)
445 ds_type (HsPArrTy ty)
446 = dsHsType ty `thenM` \ tau_ty ->
447 returnM (mkPArrTy tau_ty)
449 ds_type (HsTupleTy boxity tys)
450 = dsHsTypes tys `thenM` \ tau_tys ->
451 returnM (mkTupleTy boxity (length tys) tau_tys)
453 ds_type (HsFunTy ty1 ty2)
454 = dsHsType ty1 `thenM` \ tau_ty1 ->
455 dsHsType ty2 `thenM` \ tau_ty2 ->
456 returnM (mkFunTy tau_ty1 tau_ty2)
458 ds_type (HsOpTy ty1 (L span op) ty2)
459 = dsHsType ty1 `thenM` \ tau_ty1 ->
460 dsHsType ty2 `thenM` \ tau_ty2 ->
461 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
465 tcLookupTyCon genUnitTyConName `thenM` \ tc ->
466 returnM (mkTyConApp tc [])
468 ds_type ty@(HsAppTy _ _)
471 ds_type (HsPredTy pred)
472 = dsHsPred pred `thenM` \ pred' ->
473 returnM (mkPredTy pred')
475 ds_type full_ty@(HsForAllTy exp tv_names ctxt ty)
476 = tcTyVarBndrs tv_names $ \ tyvars ->
477 mappM dsHsLPred (unLoc ctxt) `thenM` \ theta ->
478 dsHsType ty `thenM` \ tau ->
479 returnM (mkSigmaTy tyvars theta tau)
481 dsHsTypes arg_tys = mappM dsHsType arg_tys
484 Help functions for type applications
485 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
488 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
489 ds_app (HsAppTy ty1 ty2) tys
490 = ds_app (unLoc ty1) (ty2:tys)
493 = dsHsTypes tys `thenM` \ arg_tys ->
495 HsTyVar fun -> ds_var_app fun arg_tys
496 other -> ds_type ty `thenM` \ fun_ty ->
497 returnM (mkAppTys fun_ty arg_tys)
499 ds_var_app :: Name -> [Type] -> TcM Type
500 ds_var_app name arg_tys
501 = tcLookup name `thenM` \ thing ->
503 ATyVar _ ty -> returnM (mkAppTys ty arg_tys)
504 AGlobal (ATyCon tc) -> returnM (mkGenTyConApp tc arg_tys)
505 other -> pprPanic "ds_app_type" (ppr name <+> ppr arg_tys)
513 dsHsLPred :: LHsPred Name -> TcM PredType
514 dsHsLPred pred = dsHsPred (unLoc pred)
516 dsHsPred pred@(HsClassP class_name tys)
517 = dsHsTypes tys `thenM` \ arg_tys ->
518 tcLookupClass class_name `thenM` \ clas ->
519 returnM (ClassP clas arg_tys)
521 dsHsPred (HsIParam name ty)
522 = dsHsType ty `thenM` \ arg_ty ->
523 returnM (IParam name arg_ty)
526 GADT constructor signatures
529 tcLHsConSig :: LHsType Name
530 -> TcM ([TcTyVar], TcThetaType,
533 -- Take apart the type signature for a data constructor
534 -- The difference is that there can be bangs at the top of
535 -- the argument types, and kind-checking is the right place to check
536 tcLHsConSig sig@(L span (HsForAllTy exp tv_names ctxt ty))
538 addErrCtxt (gadtSigCtxt sig) $
539 tcTyVarBndrs tv_names $ \ tyvars ->
540 do { theta <- mappM dsHsLPred (unLoc ctxt)
541 ; (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
542 ; return (tyvars, theta, bangs, arg_tys, tc, res_tys) }
544 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
545 ; return ([], [], bangs, arg_tys, tc, res_tys) }
548 tc_con_sig_tau (L _ (HsFunTy arg ty))
549 = do { (bangs, arg_tys, tc, res_tys) <- tc_con_sig_tau ty
550 ; arg_ty <- tcHsBangType arg
551 ; return (getBangStrictness arg : bangs,
552 arg_ty : arg_tys, tc, res_tys) }
555 = do { (tc, res_tys) <- tc_con_res ty []
556 ; return ([], [], tc, res_tys) }
559 tc_con_res (L _ (HsAppTy fun res_ty)) res_tys
560 = do { res_ty' <- dsHsType res_ty
561 ; tc_con_res fun (res_ty' : res_tys) }
563 tc_con_res ty@(L _ (HsTyVar name)) res_tys
564 = do { thing <- tcLookup name
566 AGlobal (ATyCon tc) -> return (tc, res_tys)
567 other -> failWithTc (badGadtDecl ty)
570 tc_con_res ty _ = failWithTc (badGadtDecl ty)
573 = hang (ptext SLIT("In the signature of a data constructor:"))
576 = hang (ptext SLIT("Malformed constructor signature:"))
580 %************************************************************************
582 Type-variable binders
584 %************************************************************************
588 kcHsTyVars :: [LHsTyVarBndr Name]
589 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
590 -- They scope over the thing inside
592 kcHsTyVars tvs thing_inside
593 = mappM (wrapLocM kcHsTyVar) tvs `thenM` \ bndrs ->
594 tcExtendKindEnv [(n,k) | L _ (KindedTyVar n k) <- bndrs]
597 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
598 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
599 kcHsTyVar (UserTyVar name) = newKindVar `thenM` \ kind ->
600 returnM (KindedTyVar name kind)
601 kcHsTyVar (KindedTyVar name kind) = returnM (KindedTyVar name kind)
604 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
605 -> ([TyVar] -> TcM r)
607 -- Used when type-checking types/classes/type-decls
608 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
609 tcTyVarBndrs bndrs thing_inside
610 = mapM (zonk . unLoc) bndrs `thenM` \ tyvars ->
611 tcExtendTyVarEnv tyvars (thing_inside tyvars)
613 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
614 returnM (mkTyVar name kind')
615 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
616 returnM (mkTyVar name liftedTypeKind)
618 -----------------------------------
619 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
620 -- GADT decls can have a (perhpas partial) kind signature
621 -- e.g. data T :: * -> * -> * where ...
622 -- This function makes up suitable (kinded) type variables for
623 -- the argument kinds, and checks that the result kind is indeed *
624 tcDataKindSig Nothing = return []
625 tcDataKindSig (Just kind)
626 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
627 ; span <- getSrcSpanM
628 ; us <- newUniqueSupply
629 ; let loc = srcSpanStart span
630 uniqs = uniqsFromSupply us
631 ; return [ mk_tv loc uniq str kind
632 | ((kind, str), uniq) <- arg_kinds `zip` names `zip` uniqs ] }
634 (arg_kinds, res_kind) = splitKindFunTys kind
635 mk_tv loc uniq str kind = mkTyVar name kind
637 name = mkInternalName uniq occ loc
638 occ = mkOccName tvName str
640 names :: [String] -- a,b,c...aa,ab,ac etc
641 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
643 badKindSig :: Kind -> SDoc
645 = hang (ptext SLIT("Kind signature on data type declaration has non-* return kind"))
650 %************************************************************************
652 Scoped type variables
654 %************************************************************************
657 tcAddScopedTyVars is used for scoped type variables added by pattern
659 e.g. \ ((x::a), (y::a)) -> x+y
660 They never have explicit kinds (because this is source-code only)
661 They are mutable (because they can get bound to a more specific type).
663 Usually we kind-infer and expand type splices, and then
664 tupecheck/desugar the type. That doesn't work well for scoped type
665 variables, because they scope left-right in patterns. (e.g. in the
666 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
668 The current not-very-good plan is to
669 * find all the types in the patterns
670 * find their free tyvars
672 * bring the kinded type vars into scope
673 * BUT throw away the kind-checked type
674 (we'll kind-check it again when we type-check the pattern)
676 This is bad because throwing away the kind checked type throws away
677 its splices. But too bad for now. [July 03]
680 We no longer specify that these type variables must be univerally
681 quantified (lots of email on the subject). If you want to put that
683 a) Do a checkSigTyVars after thing_inside
684 b) More insidiously, don't pass in expected_ty, else
685 we unify with it too early and checkSigTyVars barfs
686 Instead you have to pass in a fresh ty var, and unify
687 it with expected_ty afterwards
690 tcPatSigBndrs :: LHsType Name
691 -> TcM ([TcTyVar], -- Brought into scope
692 LHsType Name) -- Kinded, but not yet desugared
695 = do { in_scope <- getInLocalScope
696 ; span <- getSrcSpanM
697 ; let sig_tvs = [ L span (UserTyVar n)
698 | n <- nameSetToList (extractHsTyVars hs_ty),
700 -- The tyvars we want are the free type variables of
701 -- the type that are not already in scope
703 -- Behave like kcHsType on a ForAll type
704 -- i.e. make kinded tyvars with mutable kinds,
705 -- and kind-check the enclosed types
706 ; (kinded_tvs, kinded_ty) <- kcHsTyVars sig_tvs $ \ kinded_tvs -> do
707 { kinded_ty <- kcTypeType hs_ty
708 ; return (kinded_tvs, kinded_ty) }
710 -- Zonk the mutable kinds and bring the tyvars into scope
711 -- Just like the call to tcTyVarBndrs in ds_type (HsForAllTy case),
712 -- except that it brings *meta* tyvars into scope, not regular ones
714 -- [Out of date, but perhaps should be resurrected]
715 -- Furthermore, the tyvars are PatSigTvs, which means that we get better
716 -- error messages when type variables escape:
717 -- Inferred type is less polymorphic than expected
718 -- Quantified type variable `t' escapes
719 -- It is mentioned in the environment:
720 -- t is bound by the pattern type signature at tcfail103.hs:6
721 ; tyvars <- mapM (zonk . unLoc) kinded_tvs
722 ; return (tyvars, kinded_ty) }
724 zonk (KindedTyVar name kind) = zonkTcKindToKind kind `thenM` \ kind' ->
725 newMetaTyVar name kind' Flexi
726 -- Scoped type variables are bound to a *type*, hence Flexi
727 zonk (UserTyVar name) = pprTrace "Un-kinded tyvar" (ppr name) $
728 returnM (mkTyVar name liftedTypeKind)
730 tcHsPatSigType :: UserTypeCtxt
731 -> LHsType Name -- The type signature
732 -> TcM ([TcTyVar], -- Newly in-scope type variables
733 TcType) -- The signature
735 tcHsPatSigType ctxt hs_ty
736 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
737 do { (tyvars, kinded_ty) <- tcPatSigBndrs hs_ty
739 -- Complete processing of the type, and check its validity
740 ; tcExtendTyVarEnv tyvars $ do
741 { sig_ty <- tcHsKindedType kinded_ty
742 ; checkValidType ctxt sig_ty
743 ; return (tyvars, sig_ty) }
746 tcAddLetBoundTyVars :: LHsBinds Name -> TcM a -> TcM a
747 -- Turgid funciton, used for type variables bound by the patterns of a let binding
749 tcAddLetBoundTyVars binds thing_inside
750 = go (collectSigTysFromHsBinds (bagToList binds)) thing_inside
752 go [] thing_inside = thing_inside
753 go (hs_ty:hs_tys) thing_inside
754 = do { (tyvars, _kinded_ty) <- tcPatSigBndrs hs_ty
755 ; tcExtendTyVarEnv tyvars (go hs_tys thing_inside) }
759 %************************************************************************
761 \subsection{Signatures}
763 %************************************************************************
765 @tcSigs@ checks the signatures for validity, and returns a list of
766 {\em freshly-instantiated} signatures. That is, the types are already
767 split up, and have fresh type variables installed. All non-type-signature
768 "RenamedSigs" are ignored.
770 The @TcSigInfo@ contains @TcTypes@ because they are unified with
771 the variable's type, and after that checked to see whether they've
777 sig_id :: TcId, -- *Polymorphic* binder for this value...
779 sig_scoped :: [Name], -- Names for any scoped type variables
780 -- Invariant: correspond 1-1 with an initial
781 -- segment of sig_tvs (see Note [Scoped])
783 sig_tvs :: [TcTyVar], -- Instantiated type variables
784 -- See Note [Instantiate sig]
786 sig_theta :: TcThetaType, -- Instantiated theta
787 sig_tau :: TcTauType, -- Instantiated tau
788 sig_loc :: InstLoc -- The location of the signature
792 -- There may be more instantiated type variables than scoped
793 -- ones. For example:
794 -- type T a = forall b. b -> (a,b)
795 -- f :: forall c. T c
796 -- Here, the signature for f will have one scoped type variable, c,
797 -- but two instantiated type variables, c' and b'.
799 -- We assume that the scoped ones are at the *front* of sig_tvs,
800 -- and remember the names from the original HsForAllTy in sig_scoped
802 -- Note [Instantiate sig]
803 -- It's vital to instantiate a type signature with fresh variable.
805 -- type S = forall a. a->a
809 -- Here, we must use distinct type variables when checking f,g's right hand sides.
810 -- (Instantiation is only necessary because of type synonyms. Otherwise,
811 -- it's all cool; each signature has distinct type variables from the renamer.)
813 type TcSigFun = Name -> Maybe TcSigInfo
815 instance Outputable TcSigInfo where
816 ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau})
817 = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau
819 lookupSig :: [TcSigInfo] -> TcSigFun -- Search for a particular signature
820 lookupSig [] name = Nothing
821 lookupSig (sig : sigs) name
822 | name == idName (sig_id sig) = Just sig
823 | otherwise = lookupSig sigs name