2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
5 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
9 tcHsSigType, tcHsSigTypeNC, tcHsDeriv,
10 tcHsInstHead, tcHsQuantifiedType,
14 kcHsTyVars, kcHsSigType, kcHsLiftedSigType,
15 kcLHsType, kcCheckLHsType, kcHsContext,
17 -- Typechecking kinded types
18 tcHsKindedContext, tcHsKindedType, tcHsBangType,
19 tcTyVarBndrs, dsHsType, kcHsLPred, dsHsLPred,
20 tcDataKindSig, ExpKind(..), EkCtxt(..),
22 -- Pattern type signatures
23 tcHsPatSigType, tcPatSig
26 #include "HsVersions.h"
28 #ifdef GHCI /* Only if bootstrapped */
29 import {-# SOURCE #-} TcSplice( kcSpliceType )
40 import TysPrim ( ecKind )
41 import {- Kind parts of -} Type
58 ----------------------------
60 ----------------------------
62 Generally speaking we now type-check types in three phases
64 1. kcHsType: kind check the HsType
65 *includes* performing any TH type splices;
66 so it returns a translated, and kind-annotated, type
68 2. dsHsType: convert from HsType to Type:
70 expand type synonyms [mkGenTyApps]
71 hoist the foralls [tcHsType]
73 3. checkValidType: check the validity of the resulting type
75 Often these steps are done one after the other (tcHsSigType).
76 But in mutually recursive groups of type and class decls we do
77 1 kind-check the whole group
78 2 build TyCons/Classes in a knot-tied way
79 3 check the validity of types in the now-unknotted TyCons/Classes
81 For example, when we find
82 (forall a m. m a -> m a)
83 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
84 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
85 an environment that binds a and m suitably.
87 The kind checker passed to tcHsTyVars needs to look at enough to
88 establish the kind of the tyvar:
89 * For a group of type and class decls, it's just the group, not
90 the rest of the program
91 * For a tyvar bound in a pattern type signature, its the types
92 mentioned in the other type signatures in that bunch of patterns
93 * For a tyvar bound in a RULE, it's the type signatures on other
94 universally quantified variables in the rule
96 Note that this may occasionally give surprising results. For example:
98 data T a b = MkT (a b)
100 Here we deduce a::*->*, b::*
101 But equally valid would be a::(*->*)-> *, b::*->*
106 Some of the validity check could in principle be done by the kind checker,
109 - During desugaring, we normalise by expanding type synonyms. Only
110 after this step can we check things like type-synonym saturation
111 e.g. type T k = k Int
113 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
114 and then S is saturated. This is a GHC extension.
116 - Similarly, also a GHC extension, we look through synonyms before complaining
117 about the form of a class or instance declaration
119 - Ambiguity checks involve functional dependencies, and it's easier to wait
120 until knots have been resolved before poking into them
122 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
123 finished building the loop. So to keep things simple, we postpone most validity
124 checking until step (3).
128 During step (1) we might fault in a TyCon defined in another module, and it might
129 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
130 knot around type declarations with ARecThing, so that the fault-in code can get
131 the TyCon being defined.
134 %************************************************************************
136 \subsection{Checking types}
138 %************************************************************************
141 tcHsSigType, tcHsSigTypeNC :: UserTypeCtxt -> LHsType Name -> TcM Type
142 -- Do kind checking, and hoist for-alls to the top
143 -- NB: it's important that the foralls that come from the top-level
144 -- HsForAllTy in hs_ty occur *first* in the returned type.
145 -- See Note [Scoped] with TcSigInfo
146 tcHsSigType ctxt hs_ty
147 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
148 tcHsSigTypeNC ctxt hs_ty
150 tcHsSigTypeNC ctxt hs_ty
151 = do { (kinded_ty, _kind) <- kc_lhs_type hs_ty
152 -- The kind is checked by checkValidType, and isn't necessarily
153 -- of kind * in a Template Haskell quote eg [t| Maybe |]
154 ; ty <- tcHsKindedType kinded_ty
155 ; checkValidType ctxt ty
158 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Class, [Type])
159 -- Typecheck an instance head. We can't use
160 -- tcHsSigType, because it's not a valid user type.
161 tcHsInstHead (L loc hs_ty)
162 = setSrcSpan loc $ -- No need for an "In the type..." context
163 -- because that comes from the caller
164 do { kinded_ty <- kc_inst_head hs_ty
165 ; ds_inst_head kinded_ty }
167 kc_inst_head ty@(HsPredTy pred@(HsClassP {}))
168 = do { (pred', kind) <- kc_pred pred
169 ; checkExpectedKind ty kind ekLifted
170 ; return (HsPredTy pred') }
171 kc_inst_head (HsForAllTy exp tv_names context (L loc ty))
172 = kcHsTyVars tv_names $ \ tv_names' ->
173 do { ctxt' <- kcHsContext context
174 ; ty' <- kc_inst_head ty
175 ; return (HsForAllTy exp tv_names' ctxt' (L loc ty')) }
176 kc_inst_head _ = failWithTc (ptext (sLit "Malformed instance type"))
178 ds_inst_head (HsPredTy (HsClassP cls_name tys))
179 = do { clas <- tcLookupClass cls_name
180 ; arg_tys <- dsHsTypes tys
181 ; return ([], [], clas, arg_tys) }
182 ds_inst_head (HsForAllTy _ tvs ctxt (L _ tau))
183 = tcTyVarBndrs tvs $ \ tvs' ->
184 do { ctxt' <- mapM dsHsLPred (unLoc ctxt)
185 ; (tvs_r, ctxt_r, cls, tys) <- ds_inst_head tau
186 ; return (tvs' ++ tvs_r, ctxt' ++ ctxt_r , cls, tys) }
187 ds_inst_head _ = panic "ds_inst_head"
189 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
190 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
191 -- except that we want to keep the tvs separate
192 tcHsQuantifiedType tv_names hs_ty
193 = kcHsTyVars tv_names $ \ tv_names' ->
194 do { kc_ty <- kcHsSigType hs_ty
195 ; tcTyVarBndrs tv_names' $ \ tvs ->
196 do { ty <- dsHsType kc_ty
197 ; return (tvs, ty) } }
199 -- Used for the deriving(...) items
200 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
201 tcHsDeriv = tc_hs_deriv []
203 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
204 -> TcM ([TyVar], Class, [Type])
205 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
206 = kcHsTyVars tv_names $ \ tv_names' ->
207 do { cls_kind <- kcClass cls_name
208 ; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
209 ; tcTyVarBndrs tv_names' $ \ tyvars ->
210 do { arg_tys <- dsHsTypes tys
211 ; cls <- tcLookupClass cls_name
212 ; return (tyvars, cls, arg_tys) }}
214 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
215 = -- Funny newtype deriving form
217 -- where C has arity 2. Hence can't use regular functions
218 tc_hs_deriv (tv_names1 ++ tv_names2) ty
221 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
224 These functions are used during knot-tying in
225 type and class declarations, when we have to
226 separate kind-checking, desugaring, and validity checking
229 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
230 -- Used for type signatures
231 kcHsSigType ty = addKcTypeCtxt ty $ kcTypeType ty
232 kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
234 tcHsKindedType :: LHsType Name -> TcM Type
235 -- Don't do kind checking, nor validity checking.
236 -- This is used in type and class decls, where kinding is
237 -- done in advance, and validity checking is done later
238 -- [Validity checking done later because of knot-tying issues.]
239 tcHsKindedType hs_ty = dsHsType hs_ty
241 tcHsBangType :: LHsType Name -> TcM Type
242 -- Permit a bang, but discard it
243 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
244 tcHsBangType ty = tcHsKindedType ty
246 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
247 -- Used when we are expecting a ClassContext (i.e. no implicit params)
248 -- Does not do validity checking, like tcHsKindedType
249 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
253 %************************************************************************
255 The main kind checker: kcHsType
257 %************************************************************************
259 First a couple of simple wrappers for kcHsType
262 ---------------------------
263 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
264 -- The type ty must be a *lifted* *type*
265 kcLiftedType ty = kc_check_lhs_type ty ekLifted
267 ---------------------------
268 kcTypeType :: LHsType Name -> TcM (LHsType Name)
269 -- The type ty must be a *type*, but it can be lifted or
270 -- unlifted or an unboxed tuple.
271 kcTypeType ty = kc_check_lhs_type ty ekOpen
273 ---------------------------
274 kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
275 kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_check_lhs_type ty kind
278 kc_check_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
279 -- Check that the type has the specified kind
280 -- Be sure to use checkExpectedKind, rather than simply unifying
281 -- with OpenTypeKind, because it gives better error messages
282 kc_check_lhs_type (L span ty) exp_kind
284 do { ty' <- kc_check_hs_type ty exp_kind
285 ; return (L span ty') }
287 kc_check_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
288 kc_check_lhs_types tys_w_kinds
289 = mapM kc_arg tys_w_kinds
291 kc_arg (arg, arg_kind) = kc_check_lhs_type arg arg_kind
294 ---------------------------
295 kc_check_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
297 -- First some special cases for better error messages
298 -- when we know the expected kind
299 kc_check_hs_type (HsParTy ty) exp_kind
300 = do { ty' <- kc_check_lhs_type ty exp_kind; return (HsParTy ty') }
302 kc_check_hs_type ty@(HsAppTy ty1 ty2) exp_kind
303 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 [ty2]
304 ; (fun_ty', fun_kind) <- kc_lhs_type fun_ty
305 ; arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
306 ; return (mkHsAppTys fun_ty' arg_tys') }
308 -- This is the general case: infer the kind and compare
309 kc_check_hs_type ty exp_kind
310 = do { (ty', act_kind) <- kc_hs_type ty
311 -- Add the context round the inner check only
312 -- because checkExpectedKind already mentions
313 -- 'ty' by name in any error message
315 ; checkExpectedKind (strip ty) act_kind exp_kind
318 -- We infer the kind of the type, and then complain if it's
319 -- not right. But we don't want to complain about
320 -- (ty) or !(ty) or forall a. ty
321 -- when the real difficulty is with the 'ty' part.
322 strip (HsParTy (L _ ty)) = strip ty
323 strip (HsBangTy _ (L _ ty)) = strip ty
324 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
328 Here comes the main function
331 kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
332 -- Called from outside: set the context
333 kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type ty)
335 kc_lhs_type :: LHsType Name -> TcM (LHsType Name, TcKind)
336 kc_lhs_type (L span ty)
338 do { (ty', kind) <- kc_hs_type ty
339 ; return (L span ty', kind) }
341 -- kc_hs_type *returns* the kind of the type, rather than taking an expected
342 -- kind as argument as tcExpr does.
344 -- (a) the kind of (->) is
345 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
346 -- so we'd need to generate huge numbers of bx variables.
347 -- (b) kinds are so simple that the error messages are fine
349 -- The translated type has explicitly-kinded type-variable binders
351 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
352 kc_hs_type (HsParTy ty) = do
353 (ty', kind) <- kc_lhs_type ty
354 return (HsParTy ty', kind)
356 kc_hs_type (HsTyVar name) = do
358 return (HsTyVar name, kind)
360 kc_hs_type (HsListTy ty) = do
361 ty' <- kcLiftedType ty
362 return (HsListTy ty', liftedTypeKind)
364 kc_hs_type (HsPArrTy ty) = do
365 ty' <- kcLiftedType ty
366 return (HsPArrTy ty', liftedTypeKind)
368 kc_hs_type (HsModalBoxType ecn ty) = do
369 kc_check_hs_type (HsTyVar ecn) (EK ecKind EkUnk)
370 ty' <- kcLiftedType ty
371 return (HsModalBoxType ecn ty', liftedTypeKind)
373 kc_hs_type (HsKindSig ty k) = do
374 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
375 return (HsKindSig ty' k, k)
377 kc_hs_type (HsTupleTy Boxed tys) = do
378 tys' <- mapM kcLiftedType tys
379 return (HsTupleTy Boxed tys', liftedTypeKind)
381 kc_hs_type (HsTupleTy Unboxed tys) = do
382 tys' <- mapM kcTypeType tys
383 return (HsTupleTy Unboxed tys', ubxTupleKind)
385 kc_hs_type (HsFunTy ty1 ty2) = do
386 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
387 ty2' <- kcTypeType ty2
388 return (HsFunTy ty1' ty2', liftedTypeKind)
390 kc_hs_type (HsOpTy ty1 op ty2) = do
391 op_kind <- addLocM kcTyVar op
392 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
393 return (HsOpTy ty1' op ty2', res_kind)
395 kc_hs_type (HsAppTy ty1 ty2) = do
396 let (fun_ty, arg_tys) = splitHsAppTys ty1 [ty2]
397 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
398 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
399 return (mkHsAppTys fun_ty' arg_tys', res_kind)
401 kc_hs_type (HsPredTy pred)
404 kc_hs_type (HsCoreTy ty)
405 = return (HsCoreTy ty, typeKind ty)
407 kc_hs_type (HsForAllTy exp tv_names context ty)
408 = kcHsTyVars tv_names $ \ tv_names' ->
409 do { ctxt' <- kcHsContext context
410 ; ty' <- kcLiftedType ty
411 -- The body of a forall is usually a type, but in principle
412 -- there's no reason to prohibit *unlifted* types.
413 -- In fact, GHC can itself construct a function with an
414 -- unboxed tuple inside a for-all (via CPR analyis; see
415 -- typecheck/should_compile/tc170)
417 -- Still, that's only for internal interfaces, which aren't
418 -- kind-checked, so we only allow liftedTypeKind here
420 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
422 kc_hs_type (HsBangTy b ty)
423 = do { (ty', kind) <- kc_lhs_type ty
424 ; return (HsBangTy b ty', kind) }
426 kc_hs_type ty@(HsRecTy _)
427 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
428 -- Record types (which only show up temporarily in constructor signatures)
429 -- should have been removed by now
431 #ifdef GHCI /* Only if bootstrapped */
432 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
434 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
437 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
439 -- remove the doc nodes here, no need to worry about the location since
440 -- its the same for a doc node and it's child type node
441 kc_hs_type (HsDocTy ty _)
442 = kc_hs_type (unLoc ty)
444 ---------------------------
445 kcApps :: Outputable a
447 -> TcKind -- Function kind
448 -> [LHsType Name] -- Arg types
449 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
450 kcApps the_fun fun_kind args
451 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
452 ; args' <- kc_check_lhs_types args_w_kinds
453 ; return (args', res_kind) }
455 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
456 -> HsType Name -- The type being checked (for err messages only)
457 -> ExpKind -- Expected kind
458 -> TcM [LHsType Name]
459 kcCheckApps the_fun fun_kind args ty exp_kind
460 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
461 ; checkExpectedKind ty res_kind exp_kind
462 -- Check the result kind *before* checking argument kinds
463 -- This improves error message; Trac #2994
464 ; kc_check_lhs_types args_w_kinds }
467 ---------------------------
468 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
469 splitFunKind _ _ fk [] = return ([], fk)
470 splitFunKind the_fun arg_no fk (arg:args)
471 = do { mb_fk <- matchExpectedFunKind fk
473 Nothing -> failWithTc too_many_args
474 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
475 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
477 too_many_args = quotes the_fun <+>
478 ptext (sLit "is applied to too many type arguments")
480 ---------------------------
481 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
482 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
484 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
485 kcHsLPred = wrapLocM kcHsPred
487 kcHsPred :: HsPred Name -> TcM (HsPred Name)
488 kcHsPred pred = do -- Checks that the result is a type kind
489 (pred', kind) <- kc_pred pred
490 checkExpectedKind pred kind ekOpen
493 ---------------------------
494 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
495 -- Does *not* check for a saturated
496 -- application (reason: used from TcDeriv)
497 kc_pred (HsIParam name ty)
498 = do { (ty', kind) <- kc_lhs_type ty
499 ; return (HsIParam name ty', kind) }
500 kc_pred (HsClassP cls tys)
501 = do { kind <- kcClass cls
502 ; (tys', res_kind) <- kcApps cls kind tys
503 ; return (HsClassP cls tys', res_kind) }
504 kc_pred (HsEqualP ty1 ty2)
505 = do { (ty1', kind1) <- kc_lhs_type ty1
506 ; (ty2', kind2) <- kc_lhs_type ty2
507 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
508 ; return (HsEqualP ty1' ty2', unliftedTypeKind) }
510 ---------------------------
511 kcTyVar :: Name -> TcM TcKind
512 kcTyVar name = do -- Could be a tyvar or a tycon
513 traceTc "lk1" (ppr name)
514 thing <- tcLookup name
515 traceTc "lk2" (ppr name <+> ppr thing)
517 ATyVar _ ty -> return (typeKind ty)
518 AThing kind -> return kind
519 AGlobal (ATyCon tc) -> return (tyConKind tc)
520 _ -> wrongThingErr "type" thing name
522 kcClass :: Name -> TcM TcKind
523 kcClass cls = do -- Must be a class
524 thing <- tcLookup cls
526 AThing kind -> return kind
527 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
528 _ -> wrongThingErr "class" thing cls
532 %************************************************************************
536 %************************************************************************
540 * Transforms from HsType to Type
543 It cannot fail, and does no validity checking, except for
544 structural matters, such as
545 (a) spurious ! annotations.
546 (b) a class used as a type
549 dsHsType :: LHsType Name -> TcM Type
550 -- All HsTyVarBndrs in the intput type are kind-annotated
551 dsHsType ty = ds_type (unLoc ty)
553 ds_type :: HsType Name -> TcM Type
554 ds_type ty@(HsTyVar _)
557 ds_type (HsParTy ty) -- Remove the parentheses markers
560 ds_type ty@(HsBangTy {}) -- No bangs should be here
561 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
563 ds_type ty@(HsRecTy {}) -- No bangs should be here
564 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
566 ds_type (HsKindSig ty _)
567 = dsHsType ty -- Kind checking done already
569 ds_type (HsListTy ty) = do
570 tau_ty <- dsHsType ty
571 checkWiredInTyCon listTyCon
572 return (mkListTy tau_ty)
574 ds_type (HsPArrTy ty) = do
575 tau_ty <- dsHsType ty
576 checkWiredInTyCon parrTyCon
577 return (mkPArrTy tau_ty)
579 ds_type (HsModalBoxType ecn ty) = do
580 tau_ty <- dsHsType ty
581 checkWiredInTyCon hetMetCodeTypeTyCon
582 return (mkHetMetCodeTypeTy (mkTyVar ecn ecKind) tau_ty)
584 ds_type (HsTupleTy boxity tys) = do
585 tau_tys <- dsHsTypes tys
586 checkWiredInTyCon tycon
587 return (mkTyConApp tycon tau_tys)
589 tycon = tupleTyCon boxity (length tys)
591 ds_type (HsFunTy ty1 ty2) = do
592 tau_ty1 <- dsHsType ty1
593 tau_ty2 <- dsHsType ty2
594 return (mkFunTy tau_ty1 tau_ty2)
596 ds_type (HsOpTy ty1 (L span op) ty2) = do
597 tau_ty1 <- dsHsType ty1
598 tau_ty2 <- dsHsType ty2
599 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
601 ds_type ty@(HsAppTy _ _)
604 ds_type (HsPredTy pred) = do
605 pred' <- dsHsPred pred
606 return (mkPredTy pred')
608 ds_type (HsForAllTy _ tv_names ctxt ty)
609 = tcTyVarBndrs tv_names $ \ tyvars -> do
610 theta <- mapM dsHsLPred (unLoc ctxt)
612 return (mkSigmaTy tyvars theta tau)
614 ds_type (HsDocTy ty _) -- Remove the doc comment
617 ds_type (HsSpliceTy _ _ kind)
618 = do { kind' <- zonkTcKindToKind kind
619 ; newFlexiTyVarTy kind' }
621 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
622 ds_type (HsCoreTy ty) = return ty
624 dsHsTypes :: [LHsType Name] -> TcM [Type]
625 dsHsTypes arg_tys = mapM dsHsType arg_tys
628 Help functions for type applications
629 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
632 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
633 ds_app (HsAppTy ty1 ty2) tys
634 = ds_app (unLoc ty1) (ty2:tys)
637 arg_tys <- dsHsTypes tys
639 HsTyVar fun -> ds_var_app fun arg_tys
640 _ -> do fun_ty <- ds_type ty
641 return (mkAppTys fun_ty arg_tys)
643 ds_var_app :: Name -> [Type] -> TcM Type
644 ds_var_app name arg_tys = do
645 thing <- tcLookup name
647 ATyVar _ ty -> return (mkAppTys ty arg_tys)
648 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
649 _ -> wrongThingErr "type" thing name
657 dsHsLPred :: LHsPred Name -> TcM PredType
658 dsHsLPred pred = dsHsPred (unLoc pred)
660 dsHsPred :: HsPred Name -> TcM PredType
661 dsHsPred (HsClassP class_name tys)
662 = do { arg_tys <- dsHsTypes tys
663 ; clas <- tcLookupClass class_name
664 ; return (ClassP clas arg_tys)
666 dsHsPred (HsEqualP ty1 ty2)
667 = do { arg_ty1 <- dsHsType ty1
668 ; arg_ty2 <- dsHsType ty2
669 ; return (EqPred arg_ty1 arg_ty2)
671 dsHsPred (HsIParam name ty)
672 = do { arg_ty <- dsHsType ty
673 ; return (IParam name arg_ty)
678 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
679 -- Wrap a context around only if we want to show that contexts.
680 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
681 -- Omit invisble ones and ones user's won't grok (HsPred p).
682 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
684 typeCtxt :: HsType Name -> SDoc
685 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
688 %************************************************************************
690 Type-variable binders
692 %************************************************************************
696 kcHsTyVars :: [LHsTyVarBndr Name]
697 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
698 -- They scope over the thing inside
700 kcHsTyVars tvs thing_inside
701 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
702 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
704 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
705 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
706 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
707 kcHsTyVar tv@(KindedTyVar {}) = return tv
710 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
711 -> ([TyVar] -> TcM r)
713 -- Used when type-checking types/classes/type-decls
714 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
715 tcTyVarBndrs bndrs thing_inside = do
716 tyvars <- mapM (zonk . unLoc) bndrs
717 tcExtendTyVarEnv tyvars (thing_inside tyvars)
719 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
720 ; return (mkTyVar name kind') }
721 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
723 -----------------------------------
724 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
725 -- GADT decls can have a (perhaps partial) kind signature
726 -- e.g. data T :: * -> * -> * where ...
727 -- This function makes up suitable (kinded) type variables for
728 -- the argument kinds, and checks that the result kind is indeed *.
729 -- We use it also to make up argument type variables for for data instances.
730 tcDataKindSig Nothing = return []
731 tcDataKindSig (Just kind)
732 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
733 ; span <- getSrcSpanM
734 ; us <- newUniqueSupply
735 ; let uniqs = uniqsFromSupply us
736 ; return [ mk_tv span uniq str kind
737 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
739 (arg_kinds, res_kind) = splitKindFunTys kind
740 mk_tv loc uniq str kind = mkTyVar name kind
742 name = mkInternalName uniq occ loc
743 occ = mkOccName tvName str
745 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
748 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
750 badKindSig :: Kind -> SDoc
752 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
756 Note [Avoid name clashes for associated data types]
757 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
758 Consider class C a b where
760 When typechecking the decl for D, we'll invent an extra type variable for D,
761 to fill out its kind. We *don't* want this type variable to be 'a', because
762 in an .hi file we'd get
765 which makes it look as if there are *two* type indices. But there aren't!
766 So we use $a instead, which cannot clash with a user-written type variable.
767 Remember that type variable binders in interface files are just FastStrings,
770 (The tidying phase can't help here because we don't tidy TyCons. Another
771 alternative would be to record the number of indexing parameters in the
775 %************************************************************************
777 Scoped type variables
779 %************************************************************************
782 tcAddScopedTyVars is used for scoped type variables added by pattern
784 e.g. \ ((x::a), (y::a)) -> x+y
785 They never have explicit kinds (because this is source-code only)
786 They are mutable (because they can get bound to a more specific type).
788 Usually we kind-infer and expand type splices, and then
789 tupecheck/desugar the type. That doesn't work well for scoped type
790 variables, because they scope left-right in patterns. (e.g. in the
791 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
793 The current not-very-good plan is to
794 * find all the types in the patterns
795 * find their free tyvars
797 * bring the kinded type vars into scope
798 * BUT throw away the kind-checked type
799 (we'll kind-check it again when we type-check the pattern)
801 This is bad because throwing away the kind checked type throws away
802 its splices. But too bad for now. [July 03]
805 We no longer specify that these type variables must be univerally
806 quantified (lots of email on the subject). If you want to put that
808 a) Do a checkSigTyVars after thing_inside
809 b) More insidiously, don't pass in expected_ty, else
810 we unify with it too early and checkSigTyVars barfs
811 Instead you have to pass in a fresh ty var, and unify
812 it with expected_ty afterwards
815 tcHsPatSigType :: UserTypeCtxt
816 -> LHsType Name -- The type signature
817 -> TcM ([TyVar], -- Newly in-scope type variables
818 Type) -- The signature
819 -- Used for type-checking type signatures in
820 -- (a) patterns e.g f (x::Int) = e
821 -- (b) result signatures e.g. g x :: Int = e
822 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
824 tcHsPatSigType ctxt hs_ty
825 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
826 do { -- Find the type variables that are mentioned in the type
827 -- but not already in scope. These are the ones that
828 -- should be bound by the pattern signature
829 in_scope <- getInLocalScope
830 ; let span = getLoc hs_ty
831 sig_tvs = userHsTyVarBndrs $ map (L span) $
833 nameSetToList (extractHsTyVars hs_ty)
835 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
836 ; checkValidType ctxt sig_ty
837 ; return (tyvars, sig_ty)
840 tcPatSig :: UserTypeCtxt
843 -> TcM (TcType, -- The type to use for "inside" the signature
844 [(Name, TcType)], -- The new bit of type environment, binding
845 -- the scoped type variables
846 HsWrapper) -- Coercion due to unification with actual ty
847 -- Of shape: res_ty ~ sig_ty
848 tcPatSig ctxt sig res_ty
849 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
850 -- sig_tvs are the type variables free in 'sig',
851 -- and not already in scope. These are the ones
852 -- that should be brought into scope
854 ; if null sig_tvs then do {
855 -- The type signature binds no type variables,
856 -- and hence is rigid, so use it to zap the res_ty
857 wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty
858 ; return (sig_ty, [], wrap)
860 -- Type signature binds at least one scoped type variable
862 -- A pattern binding cannot bind scoped type variables
863 -- The renamer fails with a name-out-of-scope error
864 -- if a pattern binding tries to bind a type variable,
865 -- So we just have an ASSERT here
866 ; let in_pat_bind = case ctxt of
867 BindPatSigCtxt -> True
869 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
871 -- Check that all newly-in-scope tyvars are in fact
872 -- constrained by the pattern. This catches tiresome
876 -- f (x :: T a) = ...
877 -- Here 'a' doesn't get a binding. Sigh
878 ; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
879 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
881 -- Now do a subsumption check of the pattern signature against res_ty
882 ; sig_tvs' <- tcInstSigTyVars sig_tvs
883 ; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
884 sig_tv_tys' = mkTyVarTys sig_tvs'
885 ; wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty'
887 -- Check that each is bound to a distinct type variable,
888 -- and one that is not already in scope
889 ; binds_in_scope <- getScopedTyVarBinds
890 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
891 ; check binds_in_scope tv_binds
894 ; return (sig_ty', tv_binds, wrap)
897 check _ [] = return ()
898 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
899 ; check ((n,ty):in_scope) rest }
901 check_one in_scope n ty
902 = checkTc (null dups) (dupInScope n (head dups) ty)
903 -- Must not bind to the same type variable
904 -- as some other in-scope type variable
906 dups = [n' | (n',ty') <- in_scope, eqType ty' ty]
910 %************************************************************************
914 %************************************************************************
916 We would like to get a decent error message from
917 (a) Under-applied type constructors
919 (b) Over-applied type constructors
923 -- The ExpKind datatype means "expected kind" and contains
924 -- some info about just why that kind is expected, to improve
925 -- the error message on a mis-match
926 data ExpKind = EK TcKind EkCtxt
927 data EkCtxt = EkUnk -- Unknown context
928 | EkEqPred -- Second argument of an equality predicate
929 | EkKindSig -- Kind signature
930 | EkArg SDoc Int -- Function, arg posn, expected kind
933 ekLifted, ekOpen :: ExpKind
934 ekLifted = EK liftedTypeKind EkUnk
935 ekOpen = EK openTypeKind EkUnk
937 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
938 -- A fancy wrapper for 'unifyKind', which tries
939 -- to give decent error messages.
940 -- (checkExpectedKind ty act_kind exp_kind)
941 -- checks that the actual kind act_kind is compatible
942 -- with the expected kind exp_kind
943 -- The first argument, ty, is used only in the error message generation
944 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
945 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
948 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
950 Just _ -> return () -- Unification succeeded
953 -- So there's definitely an error
954 -- Now to find out what sort
955 exp_kind <- zonkTcKind exp_kind
956 act_kind <- zonkTcKind act_kind
958 env0 <- tcInitTidyEnv
959 let (exp_as, _) = splitKindFunTys exp_kind
960 (act_as, _) = splitKindFunTys act_kind
961 n_exp_as = length exp_as
962 n_act_as = length act_as
964 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
965 (env2, tidy_act_kind) = tidyKind env1 act_kind
967 err | n_exp_as < n_act_as -- E.g. [Maybe]
968 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
970 -- Now n_exp_as >= n_act_as. In the next two cases,
971 -- n_exp_as == 0, and hence so is n_act_as
972 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
973 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
974 <+> ptext (sLit "is unlifted")
976 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
977 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
978 <+> ptext (sLit "is lifted")
980 | otherwise -- E.g. Monad [Int]
981 = ptext (sLit "Kind mis-match")
983 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
984 <+> quotes (pprKind tidy_exp_kind) <> comma,
985 ptext (sLit "but") <+> quotes (ppr ty) <+>
986 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
988 expected_herald EkUnk = ptext (sLit "Expected")
989 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
990 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
991 expected_herald (EkArg fun arg_no)
992 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
993 <+> quotes fun <+> ptext (sLit ("should have"))
995 failWithTcM (env2, err $$ more_info)
998 %************************************************************************
1000 Scoped type variables
1002 %************************************************************************
1005 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1006 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1007 nest 2 (pp_sig ctxt) ]
1009 pp_sig (FunSigCtxt n) = pp_n_colon n
1010 pp_sig (ConArgCtxt n) = pp_n_colon n
1011 pp_sig (ForSigCtxt n) = pp_n_colon n
1012 pp_sig _ = ppr (unLoc hs_ty)
1014 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1016 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1017 badPatSigTvs sig_ty bad_tvs
1018 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1019 quotes (pprWithCommas ppr bad_tvs),
1020 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1021 ptext (sLit "but are actually discarded by a type synonym") ]
1022 , ptext (sLit "To fix this, expand the type synonym")
1023 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1025 dupInScope :: Name -> Name -> Type -> SDoc
1027 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1028 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1029 ptext (sLit "Distinct scoped type variables must be distinct")])
1031 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1032 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)