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 {- 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 (HsNumTy n)
369 = return (HsNumTy n, liftedTypeKind)
371 kc_hs_type (HsKindSig ty k) = do
372 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
373 return (HsKindSig ty' k, k)
375 kc_hs_type (HsTupleTy Boxed tys) = do
376 tys' <- mapM kcLiftedType tys
377 return (HsTupleTy Boxed tys', liftedTypeKind)
379 kc_hs_type (HsTupleTy Unboxed tys) = do
380 tys' <- mapM kcTypeType tys
381 return (HsTupleTy Unboxed tys', ubxTupleKind)
383 kc_hs_type (HsFunTy ty1 ty2) = do
384 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
385 ty2' <- kcTypeType ty2
386 return (HsFunTy ty1' ty2', liftedTypeKind)
388 kc_hs_type (HsOpTy ty1 op ty2) = do
389 op_kind <- addLocM kcTyVar op
390 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
391 return (HsOpTy ty1' op ty2', res_kind)
393 kc_hs_type (HsAppTy ty1 ty2) = do
394 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
395 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
396 return (mkHsAppTys fun_ty' arg_tys', res_kind)
398 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
400 kc_hs_type (HsPredTy pred)
403 kc_hs_type (HsCoreTy ty)
404 = return (HsCoreTy ty, typeKind ty)
406 kc_hs_type (HsForAllTy exp tv_names context ty)
407 = kcHsTyVars tv_names $ \ tv_names' ->
408 do { ctxt' <- kcHsContext context
409 ; ty' <- kcLiftedType ty
410 -- The body of a forall is usually a type, but in principle
411 -- there's no reason to prohibit *unlifted* types.
412 -- In fact, GHC can itself construct a function with an
413 -- unboxed tuple inside a for-all (via CPR analyis; see
414 -- typecheck/should_compile/tc170)
416 -- Still, that's only for internal interfaces, which aren't
417 -- kind-checked, so we only allow liftedTypeKind here
419 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
421 kc_hs_type (HsBangTy b ty)
422 = do { (ty', kind) <- kc_lhs_type ty
423 ; return (HsBangTy b ty', kind) }
425 kc_hs_type ty@(HsRecTy _)
426 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
427 -- Record types (which only show up temporarily in constructor signatures)
428 -- should have been removed by now
430 #ifdef GHCI /* Only if bootstrapped */
431 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
433 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
436 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
438 -- remove the doc nodes here, no need to worry about the location since
439 -- its the same for a doc node and it's child type node
440 kc_hs_type (HsDocTy ty _)
441 = kc_hs_type (unLoc ty)
443 ---------------------------
444 kcApps :: Outputable a
446 -> TcKind -- Function kind
447 -> [LHsType Name] -- Arg types
448 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
449 kcApps the_fun fun_kind args
450 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
451 ; args' <- kc_check_lhs_types args_w_kinds
452 ; return (args', res_kind) }
454 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
455 -> HsType Name -- The type being checked (for err messages only)
456 -> ExpKind -- Expected kind
457 -> TcM [LHsType Name]
458 kcCheckApps the_fun fun_kind args ty exp_kind
459 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
460 ; checkExpectedKind ty res_kind exp_kind
461 -- Check the result kind *before* checking argument kinds
462 -- This improves error message; Trac #2994
463 ; kc_check_lhs_types args_w_kinds }
465 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
466 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
468 split (L _ (HsAppTy f a)) as = split f (a:as)
471 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
472 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
473 mkHsAppTys fun_ty (arg_ty:arg_tys)
474 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
476 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
477 -- the application; they are
480 ---------------------------
481 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
482 splitFunKind _ _ fk [] = return ([], fk)
483 splitFunKind the_fun arg_no fk (arg:args)
484 = do { mb_fk <- matchExpectedFunKind fk
486 Nothing -> failWithTc too_many_args
487 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
488 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
490 too_many_args = quotes the_fun <+>
491 ptext (sLit "is applied to too many type arguments")
493 ---------------------------
494 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
495 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
497 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
498 kcHsLPred = wrapLocM kcHsPred
500 kcHsPred :: HsPred Name -> TcM (HsPred Name)
501 kcHsPred pred = do -- Checks that the result is a type kind
502 (pred', kind) <- kc_pred pred
503 checkExpectedKind pred kind ekOpen
506 ---------------------------
507 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
508 -- Does *not* check for a saturated
509 -- application (reason: used from TcDeriv)
510 kc_pred (HsIParam name ty)
511 = do { (ty', kind) <- kc_lhs_type ty
512 ; return (HsIParam name ty', kind) }
513 kc_pred (HsClassP cls tys)
514 = do { kind <- kcClass cls
515 ; (tys', res_kind) <- kcApps cls kind tys
516 ; return (HsClassP cls tys', res_kind) }
517 kc_pred (HsEqualP ty1 ty2)
518 = do { (ty1', kind1) <- kc_lhs_type ty1
519 ; (ty2', kind2) <- kc_lhs_type ty2
520 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
521 ; return (HsEqualP ty1' ty2', unliftedTypeKind) }
523 ---------------------------
524 kcTyVar :: Name -> TcM TcKind
525 kcTyVar name = do -- Could be a tyvar or a tycon
526 traceTc "lk1" (ppr name)
527 thing <- tcLookup name
528 traceTc "lk2" (ppr name <+> ppr thing)
530 ATyVar _ ty -> return (typeKind ty)
531 AThing kind -> return kind
532 AGlobal (ATyCon tc) -> return (tyConKind tc)
533 _ -> wrongThingErr "type" thing name
535 kcClass :: Name -> TcM TcKind
536 kcClass cls = do -- Must be a class
537 thing <- tcLookup cls
539 AThing kind -> return kind
540 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
541 _ -> wrongThingErr "class" thing cls
545 %************************************************************************
549 %************************************************************************
553 * Transforms from HsType to Type
556 It cannot fail, and does no validity checking, except for
557 structural matters, such as
558 (a) spurious ! annotations.
559 (b) a class used as a type
562 dsHsType :: LHsType Name -> TcM Type
563 -- All HsTyVarBndrs in the intput type are kind-annotated
564 dsHsType ty = ds_type (unLoc ty)
566 ds_type :: HsType Name -> TcM Type
567 ds_type ty@(HsTyVar _)
570 ds_type (HsParTy ty) -- Remove the parentheses markers
573 ds_type ty@(HsBangTy {}) -- No bangs should be here
574 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
576 ds_type ty@(HsRecTy {}) -- No bangs should be here
577 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
579 ds_type (HsKindSig ty _)
580 = dsHsType ty -- Kind checking done already
582 ds_type (HsListTy ty) = do
583 tau_ty <- dsHsType ty
584 checkWiredInTyCon listTyCon
585 return (mkListTy tau_ty)
587 ds_type (HsPArrTy ty) = do
588 tau_ty <- dsHsType ty
589 checkWiredInTyCon parrTyCon
590 return (mkPArrTy tau_ty)
592 ds_type (HsTupleTy boxity tys) = do
593 tau_tys <- dsHsTypes tys
594 checkWiredInTyCon tycon
595 return (mkTyConApp tycon tau_tys)
597 tycon = tupleTyCon boxity (length tys)
599 ds_type (HsFunTy ty1 ty2) = do
600 tau_ty1 <- dsHsType ty1
601 tau_ty2 <- dsHsType ty2
602 return (mkFunTy tau_ty1 tau_ty2)
604 ds_type (HsOpTy ty1 (L span op) ty2) = do
605 tau_ty1 <- dsHsType ty1
606 tau_ty2 <- dsHsType ty2
607 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
611 tc <- tcLookupTyCon genUnitTyConName
612 return (mkTyConApp tc [])
614 ds_type ty@(HsAppTy _ _)
617 ds_type (HsPredTy pred) = do
618 pred' <- dsHsPred pred
619 return (mkPredTy pred')
621 ds_type (HsForAllTy _ tv_names ctxt ty)
622 = tcTyVarBndrs tv_names $ \ tyvars -> do
623 theta <- mapM dsHsLPred (unLoc ctxt)
625 return (mkSigmaTy tyvars theta tau)
627 ds_type (HsDocTy ty _) -- Remove the doc comment
630 ds_type (HsSpliceTy _ _ kind)
631 = do { kind' <- zonkTcKindToKind kind
632 ; newFlexiTyVarTy kind' }
634 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
635 ds_type (HsCoreTy ty) = return ty
637 dsHsTypes :: [LHsType Name] -> TcM [Type]
638 dsHsTypes arg_tys = mapM dsHsType arg_tys
641 Help functions for type applications
642 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
645 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
646 ds_app (HsAppTy ty1 ty2) tys
647 = ds_app (unLoc ty1) (ty2:tys)
650 arg_tys <- dsHsTypes tys
652 HsTyVar fun -> ds_var_app fun arg_tys
653 _ -> do fun_ty <- ds_type ty
654 return (mkAppTys fun_ty arg_tys)
656 ds_var_app :: Name -> [Type] -> TcM Type
657 ds_var_app name arg_tys = do
658 thing <- tcLookup name
660 ATyVar _ ty -> return (mkAppTys ty arg_tys)
661 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
662 _ -> wrongThingErr "type" thing name
670 dsHsLPred :: LHsPred Name -> TcM PredType
671 dsHsLPred pred = dsHsPred (unLoc pred)
673 dsHsPred :: HsPred Name -> TcM PredType
674 dsHsPred (HsClassP class_name tys)
675 = do { arg_tys <- dsHsTypes tys
676 ; clas <- tcLookupClass class_name
677 ; return (ClassP clas arg_tys)
679 dsHsPred (HsEqualP ty1 ty2)
680 = do { arg_ty1 <- dsHsType ty1
681 ; arg_ty2 <- dsHsType ty2
682 ; return (EqPred arg_ty1 arg_ty2)
684 dsHsPred (HsIParam name ty)
685 = do { arg_ty <- dsHsType ty
686 ; return (IParam name arg_ty)
691 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
692 -- Wrap a context around only if we want to show that contexts.
693 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
694 -- Omit invisble ones and ones user's won't grok (HsPred p).
695 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
697 typeCtxt :: HsType Name -> SDoc
698 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
701 %************************************************************************
703 Type-variable binders
705 %************************************************************************
709 kcHsTyVars :: [LHsTyVarBndr Name]
710 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
711 -- They scope over the thing inside
713 kcHsTyVars tvs thing_inside
714 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
715 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
717 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
718 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
719 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
720 kcHsTyVar tv@(KindedTyVar {}) = return tv
723 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
724 -> ([TyVar] -> TcM r)
726 -- Used when type-checking types/classes/type-decls
727 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
728 tcTyVarBndrs bndrs thing_inside = do
729 tyvars <- mapM (zonk . unLoc) bndrs
730 tcExtendTyVarEnv tyvars (thing_inside tyvars)
732 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
733 ; return (mkTyVar name kind') }
734 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
736 -----------------------------------
737 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
738 -- GADT decls can have a (perhaps partial) kind signature
739 -- e.g. data T :: * -> * -> * where ...
740 -- This function makes up suitable (kinded) type variables for
741 -- the argument kinds, and checks that the result kind is indeed *.
742 -- We use it also to make up argument type variables for for data instances.
743 tcDataKindSig Nothing = return []
744 tcDataKindSig (Just kind)
745 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
746 ; span <- getSrcSpanM
747 ; us <- newUniqueSupply
748 ; let uniqs = uniqsFromSupply us
749 ; return [ mk_tv span uniq str kind
750 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
752 (arg_kinds, res_kind) = splitKindFunTys kind
753 mk_tv loc uniq str kind = mkTyVar name kind
755 name = mkInternalName uniq occ loc
756 occ = mkOccName tvName str
758 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
761 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
763 badKindSig :: Kind -> SDoc
765 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
769 Note [Avoid name clashes for associated data types]
770 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
771 Consider class C a b where
773 When typechecking the decl for D, we'll invent an extra type variable for D,
774 to fill out its kind. We *don't* want this type variable to be 'a', because
775 in an .hi file we'd get
778 which makes it look as if there are *two* type indices. But there aren't!
779 So we use $a instead, which cannot clash with a user-written type variable.
780 Remember that type variable binders in interface files are just FastStrings,
783 (The tidying phase can't help here because we don't tidy TyCons. Another
784 alternative would be to record the number of indexing parameters in the
788 %************************************************************************
790 Scoped type variables
792 %************************************************************************
795 tcAddScopedTyVars is used for scoped type variables added by pattern
797 e.g. \ ((x::a), (y::a)) -> x+y
798 They never have explicit kinds (because this is source-code only)
799 They are mutable (because they can get bound to a more specific type).
801 Usually we kind-infer and expand type splices, and then
802 tupecheck/desugar the type. That doesn't work well for scoped type
803 variables, because they scope left-right in patterns. (e.g. in the
804 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
806 The current not-very-good plan is to
807 * find all the types in the patterns
808 * find their free tyvars
810 * bring the kinded type vars into scope
811 * BUT throw away the kind-checked type
812 (we'll kind-check it again when we type-check the pattern)
814 This is bad because throwing away the kind checked type throws away
815 its splices. But too bad for now. [July 03]
818 We no longer specify that these type variables must be univerally
819 quantified (lots of email on the subject). If you want to put that
821 a) Do a checkSigTyVars after thing_inside
822 b) More insidiously, don't pass in expected_ty, else
823 we unify with it too early and checkSigTyVars barfs
824 Instead you have to pass in a fresh ty var, and unify
825 it with expected_ty afterwards
828 tcHsPatSigType :: UserTypeCtxt
829 -> LHsType Name -- The type signature
830 -> TcM ([TyVar], -- Newly in-scope type variables
831 Type) -- The signature
832 -- Used for type-checking type signatures in
833 -- (a) patterns e.g f (x::Int) = e
834 -- (b) result signatures e.g. g x :: Int = e
835 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
837 tcHsPatSigType ctxt hs_ty
838 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
839 do { -- Find the type variables that are mentioned in the type
840 -- but not already in scope. These are the ones that
841 -- should be bound by the pattern signature
842 in_scope <- getInLocalScope
843 ; let span = getLoc hs_ty
844 sig_tvs = userHsTyVarBndrs $ map (L span) $
846 nameSetToList (extractHsTyVars hs_ty)
848 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
849 ; checkValidType ctxt sig_ty
850 ; return (tyvars, sig_ty)
853 tcPatSig :: UserTypeCtxt
856 -> TcM (TcType, -- The type to use for "inside" the signature
857 [(Name, TcType)], -- The new bit of type environment, binding
858 -- the scoped type variables
859 HsWrapper) -- Coercion due to unification with actual ty
860 -- Of shape: res_ty ~ sig_ty
861 tcPatSig ctxt sig res_ty
862 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
863 -- sig_tvs are the type variables free in 'sig',
864 -- and not already in scope. These are the ones
865 -- that should be brought into scope
867 ; if null sig_tvs then do {
868 -- The type signature binds no type variables,
869 -- and hence is rigid, so use it to zap the res_ty
870 wrap <- tcSubType PatSigOrigin (SigSkol ctxt) res_ty sig_ty
871 ; return (sig_ty, [], wrap)
874 -- Type signature binds at least one scoped type variable
876 -- A pattern binding cannot bind scoped type variables
877 -- The renamer fails with a name-out-of-scope error
878 -- if a pattern binding tries to bind a type variable,
879 -- So we just have an ASSERT here
880 ; let in_pat_bind = case ctxt of
881 BindPatSigCtxt -> True
883 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
885 -- Check that all newly-in-scope tyvars are in fact
886 -- constrained by the pattern. This catches tiresome
890 -- f (x :: T a) = ...
891 -- Here 'a' doesn't get a binding. Sigh
892 ; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
893 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
895 -- Now do a subsumption check of the pattern signature against res_ty
896 ; sig_tvs' <- tcInstSigTyVars sig_tvs
897 ; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
898 sig_tv_tys' = mkTyVarTys sig_tvs'
899 ; wrap <- tcSubType PatSigOrigin (SigSkol ctxt) res_ty sig_ty'
901 -- Check that each is bound to a distinct type variable,
902 -- and one that is not already in scope
903 ; binds_in_scope <- getScopedTyVarBinds
904 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
905 ; check binds_in_scope tv_binds
908 ; return (sig_ty', tv_binds, wrap)
911 check _ [] = return ()
912 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
913 ; check ((n,ty):in_scope) rest }
915 check_one in_scope n ty
916 = checkTc (null dups) (dupInScope n (head dups) ty)
917 -- Must not bind to the same type variable
918 -- as some other in-scope type variable
920 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
924 %************************************************************************
928 %************************************************************************
930 We would like to get a decent error message from
931 (a) Under-applied type constructors
933 (b) Over-applied type constructors
937 -- The ExpKind datatype means "expected kind" and contains
938 -- some info about just why that kind is expected, to improve
939 -- the error message on a mis-match
940 data ExpKind = EK TcKind EkCtxt
941 data EkCtxt = EkUnk -- Unknown context
942 | EkEqPred -- Second argument of an equality predicate
943 | EkKindSig -- Kind signature
944 | EkArg SDoc Int -- Function, arg posn, expected kind
947 ekLifted, ekOpen :: ExpKind
948 ekLifted = EK liftedTypeKind EkUnk
949 ekOpen = EK openTypeKind EkUnk
951 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
952 -- A fancy wrapper for 'unifyKind', which tries
953 -- to give decent error messages.
954 -- (checkExpectedKind ty act_kind exp_kind)
955 -- checks that the actual kind act_kind is compatible
956 -- with the expected kind exp_kind
957 -- The first argument, ty, is used only in the error message generation
958 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
959 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
962 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
964 Just _ -> return () -- Unification succeeded
967 -- So there's definitely an error
968 -- Now to find out what sort
969 exp_kind <- zonkTcKind exp_kind
970 act_kind <- zonkTcKind act_kind
972 env0 <- tcInitTidyEnv
973 let (exp_as, _) = splitKindFunTys exp_kind
974 (act_as, _) = splitKindFunTys act_kind
975 n_exp_as = length exp_as
976 n_act_as = length act_as
978 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
979 (env2, tidy_act_kind) = tidyKind env1 act_kind
981 err | n_exp_as < n_act_as -- E.g. [Maybe]
982 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
984 -- Now n_exp_as >= n_act_as. In the next two cases,
985 -- n_exp_as == 0, and hence so is n_act_as
986 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
987 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
988 <+> ptext (sLit "is unlifted")
990 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
991 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
992 <+> ptext (sLit "is lifted")
994 | otherwise -- E.g. Monad [Int]
995 = ptext (sLit "Kind mis-match")
997 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
998 <+> quotes (pprKind tidy_exp_kind) <> comma,
999 ptext (sLit "but") <+> quotes (ppr ty) <+>
1000 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
1002 expected_herald EkUnk = ptext (sLit "Expected")
1003 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
1004 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
1005 expected_herald (EkArg fun arg_no)
1006 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
1007 <+> quotes fun <+> ptext (sLit ("should have"))
1009 failWithTcM (env2, err $$ more_info)
1012 %************************************************************************
1014 Scoped type variables
1016 %************************************************************************
1019 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1020 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1021 nest 2 (pp_sig ctxt) ]
1023 pp_sig (FunSigCtxt n) = pp_n_colon n
1024 pp_sig (ConArgCtxt n) = pp_n_colon n
1025 pp_sig (ForSigCtxt n) = pp_n_colon n
1026 pp_sig _ = ppr (unLoc hs_ty)
1028 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1030 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1031 badPatSigTvs sig_ty bad_tvs
1032 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1033 quotes (pprWithCommas ppr bad_tvs),
1034 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1035 ptext (sLit "but are actually discarded by a type synonym") ]
1036 , ptext (sLit "To fix this, expand the type synonym")
1037 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1039 dupInScope :: Name -> Name -> Type -> SDoc
1041 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1042 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1043 ptext (sLit "Distinct scoped type variables must be distinct")])
1045 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1046 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)