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 (HsModalBoxType ecn ty) = do
369 ty' <- kcLiftedType ty
370 return (HsModalBoxType ecn ty', liftedTypeKind)
372 kc_hs_type (HsNumTy n)
373 = return (HsNumTy n, liftedTypeKind)
375 kc_hs_type (HsKindSig ty k) = do
376 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
377 return (HsKindSig ty' k, k)
379 kc_hs_type (HsTupleTy Boxed tys) = do
380 tys' <- mapM kcLiftedType tys
381 return (HsTupleTy Boxed tys', liftedTypeKind)
383 kc_hs_type (HsTupleTy Unboxed tys) = do
384 tys' <- mapM kcTypeType tys
385 return (HsTupleTy Unboxed tys', ubxTupleKind)
387 kc_hs_type (HsFunTy ty1 ty2) = do
388 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
389 ty2' <- kcTypeType ty2
390 return (HsFunTy ty1' ty2', liftedTypeKind)
392 kc_hs_type (HsOpTy ty1 op ty2) = do
393 op_kind <- addLocM kcTyVar op
394 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
395 return (HsOpTy ty1' op ty2', res_kind)
397 kc_hs_type (HsAppTy ty1 ty2) = do
398 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
399 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
400 return (mkHsAppTys fun_ty' arg_tys', res_kind)
402 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
404 kc_hs_type (HsPredTy pred)
407 kc_hs_type (HsCoreTy ty)
408 = return (HsCoreTy ty, typeKind ty)
410 kc_hs_type (HsForAllTy exp tv_names context ty)
411 = kcHsTyVars tv_names $ \ tv_names' ->
412 do { ctxt' <- kcHsContext context
413 ; ty' <- kcLiftedType ty
414 -- The body of a forall is usually a type, but in principle
415 -- there's no reason to prohibit *unlifted* types.
416 -- In fact, GHC can itself construct a function with an
417 -- unboxed tuple inside a for-all (via CPR analyis; see
418 -- typecheck/should_compile/tc170)
420 -- Still, that's only for internal interfaces, which aren't
421 -- kind-checked, so we only allow liftedTypeKind here
423 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
425 kc_hs_type (HsBangTy b ty)
426 = do { (ty', kind) <- kc_lhs_type ty
427 ; return (HsBangTy b ty', kind) }
429 kc_hs_type ty@(HsRecTy _)
430 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
431 -- Record types (which only show up temporarily in constructor signatures)
432 -- should have been removed by now
434 #ifdef GHCI /* Only if bootstrapped */
435 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
437 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
440 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
442 -- remove the doc nodes here, no need to worry about the location since
443 -- its the same for a doc node and it's child type node
444 kc_hs_type (HsDocTy ty _)
445 = kc_hs_type (unLoc ty)
447 ---------------------------
448 kcApps :: Outputable a
450 -> TcKind -- Function kind
451 -> [LHsType Name] -- Arg types
452 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
453 kcApps the_fun fun_kind args
454 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
455 ; args' <- kc_check_lhs_types args_w_kinds
456 ; return (args', res_kind) }
458 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
459 -> HsType Name -- The type being checked (for err messages only)
460 -> ExpKind -- Expected kind
461 -> TcM [LHsType Name]
462 kcCheckApps the_fun fun_kind args ty exp_kind
463 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
464 ; checkExpectedKind ty res_kind exp_kind
465 -- Check the result kind *before* checking argument kinds
466 -- This improves error message; Trac #2994
467 ; kc_check_lhs_types args_w_kinds }
469 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
470 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
472 split (L _ (HsAppTy f a)) as = split f (a:as)
475 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
476 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
477 mkHsAppTys fun_ty (arg_ty:arg_tys)
478 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
480 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
481 -- the application; they are
484 ---------------------------
485 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
486 splitFunKind _ _ fk [] = return ([], fk)
487 splitFunKind the_fun arg_no fk (arg:args)
488 = do { mb_fk <- matchExpectedFunKind fk
490 Nothing -> failWithTc too_many_args
491 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
492 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
494 too_many_args = quotes the_fun <+>
495 ptext (sLit "is applied to too many type arguments")
497 ---------------------------
498 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
499 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
501 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
502 kcHsLPred = wrapLocM kcHsPred
504 kcHsPred :: HsPred Name -> TcM (HsPred Name)
505 kcHsPred pred = do -- Checks that the result is a type kind
506 (pred', kind) <- kc_pred pred
507 checkExpectedKind pred kind ekOpen
510 ---------------------------
511 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
512 -- Does *not* check for a saturated
513 -- application (reason: used from TcDeriv)
514 kc_pred (HsIParam name ty)
515 = do { (ty', kind) <- kc_lhs_type ty
516 ; return (HsIParam name ty', kind) }
517 kc_pred (HsClassP cls tys)
518 = do { kind <- kcClass cls
519 ; (tys', res_kind) <- kcApps cls kind tys
520 ; return (HsClassP cls tys', res_kind) }
521 kc_pred (HsEqualP ty1 ty2)
522 = do { (ty1', kind1) <- kc_lhs_type ty1
523 ; (ty2', kind2) <- kc_lhs_type ty2
524 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
525 ; return (HsEqualP ty1' ty2', unliftedTypeKind) }
527 ---------------------------
528 kcTyVar :: Name -> TcM TcKind
529 kcTyVar name = do -- Could be a tyvar or a tycon
530 traceTc "lk1" (ppr name)
531 thing <- tcLookup name
532 traceTc "lk2" (ppr name <+> ppr thing)
534 ATyVar _ ty -> return (typeKind ty)
535 AThing kind -> return kind
536 AGlobal (ATyCon tc) -> return (tyConKind tc)
537 _ -> wrongThingErr "type" thing name
539 kcClass :: Name -> TcM TcKind
540 kcClass cls = do -- Must be a class
541 thing <- tcLookup cls
543 AThing kind -> return kind
544 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
545 _ -> wrongThingErr "class" thing cls
549 %************************************************************************
553 %************************************************************************
557 * Transforms from HsType to Type
560 It cannot fail, and does no validity checking, except for
561 structural matters, such as
562 (a) spurious ! annotations.
563 (b) a class used as a type
566 dsHsType :: LHsType Name -> TcM Type
567 -- All HsTyVarBndrs in the intput type are kind-annotated
568 dsHsType ty = ds_type (unLoc ty)
570 ds_type :: HsType Name -> TcM Type
571 ds_type ty@(HsTyVar _)
574 ds_type (HsParTy ty) -- Remove the parentheses markers
577 ds_type ty@(HsBangTy {}) -- No bangs should be here
578 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
580 ds_type ty@(HsRecTy {}) -- No bangs should be here
581 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
583 ds_type (HsKindSig ty _)
584 = dsHsType ty -- Kind checking done already
586 ds_type (HsListTy ty) = do
587 tau_ty <- dsHsType ty
588 checkWiredInTyCon listTyCon
589 return (mkListTy tau_ty)
591 ds_type (HsPArrTy ty) = do
592 tau_ty <- dsHsType ty
593 checkWiredInTyCon parrTyCon
594 return (mkPArrTy tau_ty)
596 ds_type (HsModalBoxType ecn ty) = do
597 ecn' <- ds_app (HsTyVar ecn) []
598 tau_ty <- dsHsType ty
599 checkWiredInTyCon hetMetCodeTypeTyCon
600 return (mkHetMetCodeTypeTy (tcGetTyVar "totally bogus, dude" ecn') tau_ty)
603 ds_type (HsTupleTy boxity tys) = do
604 tau_tys <- dsHsTypes tys
605 checkWiredInTyCon tycon
606 return (mkTyConApp tycon tau_tys)
608 tycon = tupleTyCon boxity (length tys)
610 ds_type (HsFunTy ty1 ty2) = do
611 tau_ty1 <- dsHsType ty1
612 tau_ty2 <- dsHsType ty2
613 return (mkFunTy tau_ty1 tau_ty2)
615 ds_type (HsOpTy ty1 (L span op) ty2) = do
616 tau_ty1 <- dsHsType ty1
617 tau_ty2 <- dsHsType ty2
618 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
622 tc <- tcLookupTyCon genUnitTyConName
623 return (mkTyConApp tc [])
625 ds_type ty@(HsAppTy _ _)
628 ds_type (HsPredTy pred) = do
629 pred' <- dsHsPred pred
630 return (mkPredTy pred')
632 ds_type (HsForAllTy _ tv_names ctxt ty)
633 = tcTyVarBndrs tv_names $ \ tyvars -> do
634 theta <- mapM dsHsLPred (unLoc ctxt)
636 return (mkSigmaTy tyvars theta tau)
638 ds_type (HsDocTy ty _) -- Remove the doc comment
641 ds_type (HsSpliceTy _ _ kind)
642 = do { kind' <- zonkTcKindToKind kind
643 ; newFlexiTyVarTy kind' }
645 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
646 ds_type (HsCoreTy ty) = return ty
648 dsHsTypes :: [LHsType Name] -> TcM [Type]
649 dsHsTypes arg_tys = mapM dsHsType arg_tys
652 Help functions for type applications
653 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
656 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
657 ds_app (HsAppTy ty1 ty2) tys
658 = ds_app (unLoc ty1) (ty2:tys)
661 arg_tys <- dsHsTypes tys
663 HsTyVar fun -> ds_var_app fun arg_tys
664 _ -> do fun_ty <- ds_type ty
665 return (mkAppTys fun_ty arg_tys)
667 ds_var_app :: Name -> [Type] -> TcM Type
668 ds_var_app name arg_tys = do
669 thing <- tcLookup name
671 ATyVar _ ty -> return (mkAppTys ty arg_tys)
672 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
673 _ -> wrongThingErr "type" thing name
681 dsHsLPred :: LHsPred Name -> TcM PredType
682 dsHsLPred pred = dsHsPred (unLoc pred)
684 dsHsPred :: HsPred Name -> TcM PredType
685 dsHsPred (HsClassP class_name tys)
686 = do { arg_tys <- dsHsTypes tys
687 ; clas <- tcLookupClass class_name
688 ; return (ClassP clas arg_tys)
690 dsHsPred (HsEqualP ty1 ty2)
691 = do { arg_ty1 <- dsHsType ty1
692 ; arg_ty2 <- dsHsType ty2
693 ; return (EqPred arg_ty1 arg_ty2)
695 dsHsPred (HsIParam name ty)
696 = do { arg_ty <- dsHsType ty
697 ; return (IParam name arg_ty)
702 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
703 -- Wrap a context around only if we want to show that contexts.
704 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
705 -- Omit invisble ones and ones user's won't grok (HsPred p).
706 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
708 typeCtxt :: HsType Name -> SDoc
709 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
712 %************************************************************************
714 Type-variable binders
716 %************************************************************************
720 kcHsTyVars :: [LHsTyVarBndr Name]
721 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
722 -- They scope over the thing inside
724 kcHsTyVars tvs thing_inside
725 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
726 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
728 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
729 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
730 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
731 kcHsTyVar tv@(KindedTyVar {}) = return tv
734 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
735 -> ([TyVar] -> TcM r)
737 -- Used when type-checking types/classes/type-decls
738 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
739 tcTyVarBndrs bndrs thing_inside = do
740 tyvars <- mapM (zonk . unLoc) bndrs
741 tcExtendTyVarEnv tyvars (thing_inside tyvars)
743 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
744 ; return (mkTyVar name kind') }
745 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
747 -----------------------------------
748 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
749 -- GADT decls can have a (perhaps partial) kind signature
750 -- e.g. data T :: * -> * -> * where ...
751 -- This function makes up suitable (kinded) type variables for
752 -- the argument kinds, and checks that the result kind is indeed *.
753 -- We use it also to make up argument type variables for for data instances.
754 tcDataKindSig Nothing = return []
755 tcDataKindSig (Just kind)
756 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
757 ; span <- getSrcSpanM
758 ; us <- newUniqueSupply
759 ; let uniqs = uniqsFromSupply us
760 ; return [ mk_tv span uniq str kind
761 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
763 (arg_kinds, res_kind) = splitKindFunTys kind
764 mk_tv loc uniq str kind = mkTyVar name kind
766 name = mkInternalName uniq occ loc
767 occ = mkOccName tvName str
769 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
772 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
774 badKindSig :: Kind -> SDoc
776 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
780 Note [Avoid name clashes for associated data types]
781 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
782 Consider class C a b where
784 When typechecking the decl for D, we'll invent an extra type variable for D,
785 to fill out its kind. We *don't* want this type variable to be 'a', because
786 in an .hi file we'd get
789 which makes it look as if there are *two* type indices. But there aren't!
790 So we use $a instead, which cannot clash with a user-written type variable.
791 Remember that type variable binders in interface files are just FastStrings,
794 (The tidying phase can't help here because we don't tidy TyCons. Another
795 alternative would be to record the number of indexing parameters in the
799 %************************************************************************
801 Scoped type variables
803 %************************************************************************
806 tcAddScopedTyVars is used for scoped type variables added by pattern
808 e.g. \ ((x::a), (y::a)) -> x+y
809 They never have explicit kinds (because this is source-code only)
810 They are mutable (because they can get bound to a more specific type).
812 Usually we kind-infer and expand type splices, and then
813 tupecheck/desugar the type. That doesn't work well for scoped type
814 variables, because they scope left-right in patterns. (e.g. in the
815 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
817 The current not-very-good plan is to
818 * find all the types in the patterns
819 * find their free tyvars
821 * bring the kinded type vars into scope
822 * BUT throw away the kind-checked type
823 (we'll kind-check it again when we type-check the pattern)
825 This is bad because throwing away the kind checked type throws away
826 its splices. But too bad for now. [July 03]
829 We no longer specify that these type variables must be univerally
830 quantified (lots of email on the subject). If you want to put that
832 a) Do a checkSigTyVars after thing_inside
833 b) More insidiously, don't pass in expected_ty, else
834 we unify with it too early and checkSigTyVars barfs
835 Instead you have to pass in a fresh ty var, and unify
836 it with expected_ty afterwards
839 tcHsPatSigType :: UserTypeCtxt
840 -> LHsType Name -- The type signature
841 -> TcM ([TyVar], -- Newly in-scope type variables
842 Type) -- The signature
843 -- Used for type-checking type signatures in
844 -- (a) patterns e.g f (x::Int) = e
845 -- (b) result signatures e.g. g x :: Int = e
846 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
848 tcHsPatSigType ctxt hs_ty
849 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
850 do { -- Find the type variables that are mentioned in the type
851 -- but not already in scope. These are the ones that
852 -- should be bound by the pattern signature
853 in_scope <- getInLocalScope
854 ; let span = getLoc hs_ty
855 sig_tvs = userHsTyVarBndrs $ map (L span) $
857 nameSetToList (extractHsTyVars hs_ty)
859 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
860 ; checkValidType ctxt sig_ty
861 ; return (tyvars, sig_ty)
864 tcPatSig :: UserTypeCtxt
867 -> TcM (TcType, -- The type to use for "inside" the signature
868 [(Name, TcType)], -- The new bit of type environment, binding
869 -- the scoped type variables
870 HsWrapper) -- Coercion due to unification with actual ty
871 -- Of shape: res_ty ~ sig_ty
872 tcPatSig ctxt sig res_ty
873 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
874 -- sig_tvs are the type variables free in 'sig',
875 -- and not already in scope. These are the ones
876 -- that should be brought into scope
878 ; if null sig_tvs then do {
879 -- The type signature binds no type variables,
880 -- and hence is rigid, so use it to zap the res_ty
881 wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty
882 ; return (sig_ty, [], wrap)
885 -- Type signature binds at least one scoped type variable
887 -- A pattern binding cannot bind scoped type variables
888 -- The renamer fails with a name-out-of-scope error
889 -- if a pattern binding tries to bind a type variable,
890 -- So we just have an ASSERT here
891 ; let in_pat_bind = case ctxt of
892 BindPatSigCtxt -> True
894 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
896 -- Check that all newly-in-scope tyvars are in fact
897 -- constrained by the pattern. This catches tiresome
901 -- f (x :: T a) = ...
902 -- Here 'a' doesn't get a binding. Sigh
903 ; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
904 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
906 -- Now do a subsumption check of the pattern signature against res_ty
907 ; sig_tvs' <- tcInstSigTyVars sig_tvs
908 ; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
909 sig_tv_tys' = mkTyVarTys sig_tvs'
910 ; wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty'
912 -- Check that each is bound to a distinct type variable,
913 -- and one that is not already in scope
914 ; binds_in_scope <- getScopedTyVarBinds
915 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
916 ; check binds_in_scope tv_binds
919 ; return (sig_ty', tv_binds, wrap)
922 check _ [] = return ()
923 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
924 ; check ((n,ty):in_scope) rest }
926 check_one in_scope n ty
927 = checkTc (null dups) (dupInScope n (head dups) ty)
928 -- Must not bind to the same type variable
929 -- as some other in-scope type variable
931 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
935 %************************************************************************
939 %************************************************************************
941 We would like to get a decent error message from
942 (a) Under-applied type constructors
944 (b) Over-applied type constructors
948 -- The ExpKind datatype means "expected kind" and contains
949 -- some info about just why that kind is expected, to improve
950 -- the error message on a mis-match
951 data ExpKind = EK TcKind EkCtxt
952 data EkCtxt = EkUnk -- Unknown context
953 | EkEqPred -- Second argument of an equality predicate
954 | EkKindSig -- Kind signature
955 | EkArg SDoc Int -- Function, arg posn, expected kind
958 ekLifted, ekOpen :: ExpKind
959 ekLifted = EK liftedTypeKind EkUnk
960 ekOpen = EK openTypeKind EkUnk
962 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
963 -- A fancy wrapper for 'unifyKind', which tries
964 -- to give decent error messages.
965 -- (checkExpectedKind ty act_kind exp_kind)
966 -- checks that the actual kind act_kind is compatible
967 -- with the expected kind exp_kind
968 -- The first argument, ty, is used only in the error message generation
969 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
970 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
973 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
975 Just _ -> return () -- Unification succeeded
978 -- So there's definitely an error
979 -- Now to find out what sort
980 exp_kind <- zonkTcKind exp_kind
981 act_kind <- zonkTcKind act_kind
983 env0 <- tcInitTidyEnv
984 let (exp_as, _) = splitKindFunTys exp_kind
985 (act_as, _) = splitKindFunTys act_kind
986 n_exp_as = length exp_as
987 n_act_as = length act_as
989 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
990 (env2, tidy_act_kind) = tidyKind env1 act_kind
992 err | n_exp_as < n_act_as -- E.g. [Maybe]
993 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
995 -- Now n_exp_as >= n_act_as. In the next two cases,
996 -- n_exp_as == 0, and hence so is n_act_as
997 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
998 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
999 <+> ptext (sLit "is unlifted")
1001 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
1002 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
1003 <+> ptext (sLit "is lifted")
1005 | otherwise -- E.g. Monad [Int]
1006 = ptext (sLit "Kind mis-match")
1008 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
1009 <+> quotes (pprKind tidy_exp_kind) <> comma,
1010 ptext (sLit "but") <+> quotes (ppr ty) <+>
1011 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
1013 expected_herald EkUnk = ptext (sLit "Expected")
1014 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
1015 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
1016 expected_herald (EkArg fun arg_no)
1017 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
1018 <+> quotes fun <+> ptext (sLit ("should have"))
1020 failWithTcM (env2, err $$ more_info)
1023 %************************************************************************
1025 Scoped type variables
1027 %************************************************************************
1030 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1031 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1032 nest 2 (pp_sig ctxt) ]
1034 pp_sig (FunSigCtxt n) = pp_n_colon n
1035 pp_sig (ConArgCtxt n) = pp_n_colon n
1036 pp_sig (ForSigCtxt n) = pp_n_colon n
1037 pp_sig _ = ppr (unLoc hs_ty)
1039 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1041 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1042 badPatSigTvs sig_ty bad_tvs
1043 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1044 quotes (pprWithCommas ppr bad_tvs),
1045 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1046 ptext (sLit "but are actually discarded by a type synonym") ]
1047 , ptext (sLit "To fix this, expand the type synonym")
1048 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1050 dupInScope :: Name -> Name -> Type -> SDoc
1052 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1053 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1054 ptext (sLit "Distinct scoped type variables must be distinct")])
1056 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1057 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)