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,
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
59 ----------------------------
61 ----------------------------
63 Generally speaking we now type-check types in three phases
65 1. kcHsType: kind check the HsType
66 *includes* performing any TH type splices;
67 so it returns a translated, and kind-annotated, type
69 2. dsHsType: convert from HsType to Type:
71 expand type synonyms [mkGenTyApps]
72 hoist the foralls [tcHsType]
74 3. checkValidType: check the validity of the resulting type
76 Often these steps are done one after the other (tcHsSigType).
77 But in mutually recursive groups of type and class decls we do
78 1 kind-check the whole group
79 2 build TyCons/Classes in a knot-tied way
80 3 check the validity of types in the now-unknotted TyCons/Classes
82 For example, when we find
83 (forall a m. m a -> m a)
84 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
85 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
86 an environment that binds a and m suitably.
88 The kind checker passed to tcHsTyVars needs to look at enough to
89 establish the kind of the tyvar:
90 * For a group of type and class decls, it's just the group, not
91 the rest of the program
92 * For a tyvar bound in a pattern type signature, its the types
93 mentioned in the other type signatures in that bunch of patterns
94 * For a tyvar bound in a RULE, it's the type signatures on other
95 universally quantified variables in the rule
97 Note that this may occasionally give surprising results. For example:
99 data T a b = MkT (a b)
101 Here we deduce a::*->*, b::*
102 But equally valid would be a::(*->*)-> *, b::*->*
107 Some of the validity check could in principle be done by the kind checker,
110 - During desugaring, we normalise by expanding type synonyms. Only
111 after this step can we check things like type-synonym saturation
112 e.g. type T k = k Int
114 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
115 and then S is saturated. This is a GHC extension.
117 - Similarly, also a GHC extension, we look through synonyms before complaining
118 about the form of a class or instance declaration
120 - Ambiguity checks involve functional dependencies, and it's easier to wait
121 until knots have been resolved before poking into them
123 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
124 finished building the loop. So to keep things simple, we postpone most validity
125 checking until step (3).
129 During step (1) we might fault in a TyCon defined in another module, and it might
130 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
131 knot around type declarations with ARecThing, so that the fault-in code can get
132 the TyCon being defined.
135 %************************************************************************
137 \subsection{Checking types}
139 %************************************************************************
142 tcHsSigType, tcHsSigTypeNC :: UserTypeCtxt -> LHsType Name -> TcM Type
143 -- Do kind checking, and hoist for-alls to the top
144 -- NB: it's important that the foralls that come from the top-level
145 -- HsForAllTy in hs_ty occur *first* in the returned type.
146 -- See Note [Scoped] with TcSigInfo
147 tcHsSigType ctxt hs_ty
148 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
149 tcHsSigTypeNC ctxt hs_ty
151 tcHsSigTypeNC ctxt hs_ty
152 = do { (kinded_ty, _kind) <- kc_lhs_type hs_ty
153 -- The kind is checked by checkValidType, and isn't necessarily
154 -- of kind * in a Template Haskell quote eg [t| Maybe |]
155 ; ty <- tcHsKindedType kinded_ty
156 ; checkValidType ctxt ty
159 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Type)
160 -- Typecheck an instance head. We can't use
161 -- tcHsSigType, because it's not a valid user type.
162 tcHsInstHead (L loc ty)
163 = setSrcSpan loc $ -- No need for an "In the type..." context
164 tc_inst_head ty -- because that comes from the caller
166 -- tc_inst_head expects HsPredTy, which isn't usually even allowed
167 tc_inst_head (HsPredTy pred)
168 = do { pred' <- kcHsPred pred
169 ; pred'' <- dsHsPred pred'
170 ; return ([], [], mkPredTy pred'') }
172 tc_inst_head (HsForAllTy _ tvs ctxt (L _ (HsPredTy pred)))
173 = kcHsTyVars tvs $ \ tvs' ->
174 do { ctxt' <- kcHsContext ctxt
175 ; pred' <- kcHsPred pred
176 ; tcTyVarBndrs tvs' $ \ tvs'' ->
177 do { ctxt'' <- mapM dsHsLPred (unLoc ctxt')
178 ; pred'' <- dsHsPred pred'
179 ; return (tvs'', ctxt'', mkPredTy pred'') } }
181 tc_inst_head _ = failWithTc (ptext (sLit "Malformed instance type"))
183 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
184 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
185 -- except that we want to keep the tvs separate
186 tcHsQuantifiedType tv_names hs_ty
187 = kcHsTyVars tv_names $ \ tv_names' ->
188 do { kc_ty <- kcHsSigType hs_ty
189 ; tcTyVarBndrs tv_names' $ \ tvs ->
190 do { ty <- dsHsType kc_ty
191 ; return (tvs, ty) } }
193 -- Used for the deriving(...) items
194 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
195 tcHsDeriv = tc_hs_deriv []
197 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
198 -> TcM ([TyVar], Class, [Type])
199 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
200 = kcHsTyVars tv_names $ \ tv_names' ->
201 do { cls_kind <- kcClass cls_name
202 ; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
203 ; tcTyVarBndrs tv_names' $ \ tyvars ->
204 do { arg_tys <- dsHsTypes tys
205 ; cls <- tcLookupClass cls_name
206 ; return (tyvars, cls, arg_tys) }}
208 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
209 = -- Funny newtype deriving form
211 -- where C has arity 2. Hence can't use regular functions
212 tc_hs_deriv (tv_names1 ++ tv_names2) ty
215 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
218 These functions are used during knot-tying in
219 type and class declarations, when we have to
220 separate kind-checking, desugaring, and validity checking
223 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
224 -- Used for type signatures
225 kcHsSigType ty = addKcTypeCtxt ty $ kcTypeType ty
226 kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
228 tcHsKindedType :: LHsType Name -> TcM Type
229 -- Don't do kind checking, nor validity checking.
230 -- This is used in type and class decls, where kinding is
231 -- done in advance, and validity checking is done later
232 -- [Validity checking done later because of knot-tying issues.]
233 tcHsKindedType hs_ty = dsHsType hs_ty
235 tcHsBangType :: LHsType Name -> TcM Type
236 -- Permit a bang, but discard it
237 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
238 tcHsBangType ty = tcHsKindedType ty
240 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
241 -- Used when we are expecting a ClassContext (i.e. no implicit params)
242 -- Does not do validity checking, like tcHsKindedType
243 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
247 %************************************************************************
249 The main kind checker: kcHsType
251 %************************************************************************
253 First a couple of simple wrappers for kcHsType
256 ---------------------------
257 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
258 -- The type ty must be a *lifted* *type*
259 kcLiftedType ty = kc_check_lhs_type ty ekLifted
261 ---------------------------
262 kcTypeType :: LHsType Name -> TcM (LHsType Name)
263 -- The type ty must be a *type*, but it can be lifted or
264 -- unlifted or an unboxed tuple.
265 kcTypeType ty = kc_check_lhs_type ty ekOpen
267 ---------------------------
268 kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
269 kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_check_lhs_type ty kind
272 kc_check_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
273 -- Check that the type has the specified kind
274 -- Be sure to use checkExpectedKind, rather than simply unifying
275 -- with OpenTypeKind, because it gives better error messages
276 kc_check_lhs_type (L span ty) exp_kind
278 do { ty' <- kc_check_hs_type ty exp_kind
279 ; return (L span ty') }
281 kc_check_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
282 kc_check_lhs_types tys_w_kinds
283 = mapM kc_arg tys_w_kinds
285 kc_arg (arg, arg_kind) = kc_check_lhs_type arg arg_kind
288 ---------------------------
289 kc_check_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
291 -- First some special cases for better error messages
292 -- when we know the expected kind
293 kc_check_hs_type (HsParTy ty) exp_kind
294 = do { ty' <- kc_check_lhs_type ty exp_kind; return (HsParTy ty') }
296 kc_check_hs_type ty@(HsAppTy ty1 ty2) exp_kind
297 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
298 ; (fun_ty', fun_kind) <- kc_lhs_type fun_ty
299 ; arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
300 ; return (mkHsAppTys fun_ty' arg_tys') }
302 -- This is the general case: infer the kind and compare
303 kc_check_hs_type ty exp_kind
304 = do { (ty', act_kind) <- kc_hs_type ty
305 -- Add the context round the inner check only
306 -- because checkExpectedKind already mentions
307 -- 'ty' by name in any error message
309 ; checkExpectedKind (strip ty) act_kind exp_kind
312 -- We infer the kind of the type, and then complain if it's
313 -- not right. But we don't want to complain about
314 -- (ty) or !(ty) or forall a. ty
315 -- when the real difficulty is with the 'ty' part.
316 strip (HsParTy (L _ ty)) = strip ty
317 strip (HsBangTy _ (L _ ty)) = strip ty
318 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
322 Here comes the main function
325 kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
326 -- Called from outside: set the context
327 kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type ty)
329 kc_lhs_type :: LHsType Name -> TcM (LHsType Name, TcKind)
330 kc_lhs_type (L span ty)
332 do { (ty', kind) <- kc_hs_type ty
333 ; return (L span ty', kind) }
335 -- kc_hs_type *returns* the kind of the type, rather than taking an expected
336 -- kind as argument as tcExpr does.
338 -- (a) the kind of (->) is
339 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
340 -- so we'd need to generate huge numbers of bx variables.
341 -- (b) kinds are so simple that the error messages are fine
343 -- The translated type has explicitly-kinded type-variable binders
345 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
346 kc_hs_type (HsParTy ty) = do
347 (ty', kind) <- kc_lhs_type ty
348 return (HsParTy ty', kind)
350 kc_hs_type (HsTyVar name) = do
352 return (HsTyVar name, kind)
354 kc_hs_type (HsListTy ty) = do
355 ty' <- kcLiftedType ty
356 return (HsListTy ty', liftedTypeKind)
358 kc_hs_type (HsPArrTy ty) = do
359 ty' <- kcLiftedType ty
360 return (HsPArrTy ty', liftedTypeKind)
362 kc_hs_type (HsNumTy n)
363 = return (HsNumTy n, liftedTypeKind)
365 kc_hs_type (HsKindSig ty k) = do
366 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
367 return (HsKindSig ty' k, k)
369 kc_hs_type (HsTupleTy Boxed tys) = do
370 tys' <- mapM kcLiftedType tys
371 return (HsTupleTy Boxed tys', liftedTypeKind)
373 kc_hs_type (HsTupleTy Unboxed tys) = do
374 tys' <- mapM kcTypeType tys
375 return (HsTupleTy Unboxed tys', ubxTupleKind)
377 kc_hs_type (HsFunTy ty1 ty2) = do
378 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
379 ty2' <- kcTypeType ty2
380 return (HsFunTy ty1' ty2', liftedTypeKind)
382 kc_hs_type (HsOpTy ty1 op ty2) = do
383 op_kind <- addLocM kcTyVar op
384 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
385 return (HsOpTy ty1' op ty2', res_kind)
387 kc_hs_type (HsAppTy ty1 ty2) = do
388 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
389 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
390 return (mkHsAppTys fun_ty' arg_tys', res_kind)
392 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
394 kc_hs_type (HsPredTy pred)
397 kc_hs_type (HsCoreTy ty)
398 = return (HsCoreTy ty, typeKind ty)
400 kc_hs_type (HsForAllTy exp tv_names context ty)
401 = kcHsTyVars tv_names $ \ tv_names' ->
402 do { ctxt' <- kcHsContext context
403 ; ty' <- kcLiftedType ty
404 -- The body of a forall is usually a type, but in principle
405 -- there's no reason to prohibit *unlifted* types.
406 -- In fact, GHC can itself construct a function with an
407 -- unboxed tuple inside a for-all (via CPR analyis; see
408 -- typecheck/should_compile/tc170)
410 -- Still, that's only for internal interfaces, which aren't
411 -- kind-checked, so we only allow liftedTypeKind here
413 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
415 kc_hs_type (HsBangTy b ty)
416 = do { (ty', kind) <- kc_lhs_type ty
417 ; return (HsBangTy b ty', kind) }
419 kc_hs_type ty@(HsRecTy _)
420 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
421 -- Record types (which only show up temporarily in constructor signatures)
422 -- should have been removed by now
424 #ifdef GHCI /* Only if bootstrapped */
425 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
427 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
430 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
432 -- remove the doc nodes here, no need to worry about the location since
433 -- its the same for a doc node and it's child type node
434 kc_hs_type (HsDocTy ty _)
435 = kc_hs_type (unLoc ty)
437 ---------------------------
438 kcApps :: Outputable a
440 -> TcKind -- Function kind
441 -> [LHsType Name] -- Arg types
442 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
443 kcApps the_fun fun_kind args
444 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
445 ; args' <- kc_check_lhs_types args_w_kinds
446 ; return (args', res_kind) }
448 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
449 -> HsType Name -- The type being checked (for err messages only)
450 -> ExpKind -- Expected kind
451 -> TcM [LHsType Name]
452 kcCheckApps the_fun fun_kind args ty exp_kind
453 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
454 ; checkExpectedKind ty res_kind exp_kind
455 -- Check the result kind *before* checking argument kinds
456 -- This improves error message; Trac #2994
457 ; kc_check_lhs_types args_w_kinds }
459 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
460 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
462 split (L _ (HsAppTy f a)) as = split f (a:as)
465 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
466 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
467 mkHsAppTys fun_ty (arg_ty:arg_tys)
468 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
470 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
471 -- the application; they are
474 ---------------------------
475 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
476 splitFunKind _ _ fk [] = return ([], fk)
477 splitFunKind the_fun arg_no fk (arg:args)
478 = do { mb_fk <- unifyFunKind fk
480 Nothing -> failWithTc too_many_args
481 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
482 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
484 too_many_args = quotes the_fun <+>
485 ptext (sLit "is applied to too many type arguments")
487 ---------------------------
488 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
489 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
491 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
492 kcHsLPred = wrapLocM kcHsPred
494 kcHsPred :: HsPred Name -> TcM (HsPred Name)
495 kcHsPred pred = do -- Checks that the result is of kind liftedType
496 (pred', kind) <- kc_pred pred
497 checkExpectedKind pred kind ekLifted
500 ---------------------------
501 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
502 -- Does *not* check for a saturated
503 -- application (reason: used from TcDeriv)
504 kc_pred (HsIParam name ty)
505 = do { (ty', kind) <- kc_lhs_type ty
506 ; return (HsIParam name ty', kind)
508 kc_pred (HsClassP cls tys)
509 = do { kind <- kcClass cls
510 ; (tys', res_kind) <- kcApps cls kind tys
511 ; return (HsClassP cls tys', res_kind)
513 kc_pred (HsEqualP ty1 ty2)
514 = do { (ty1', kind1) <- kc_lhs_type ty1
515 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
516 ; (ty2', kind2) <- kc_lhs_type ty2
517 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
518 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
519 ; return (HsEqualP ty1' ty2', liftedTypeKind)
522 ---------------------------
523 kcTyVar :: Name -> TcM TcKind
524 kcTyVar name = do -- Could be a tyvar or a tycon
525 traceTc (text "lk1" <+> ppr name)
526 thing <- tcLookup name
527 traceTc (text "lk2" <+> ppr name <+> ppr thing)
529 ATyVar _ ty -> return (typeKind ty)
530 AThing kind -> return kind
531 AGlobal (ATyCon tc) -> return (tyConKind tc)
532 _ -> wrongThingErr "type" thing name
534 kcClass :: Name -> TcM TcKind
535 kcClass cls = do -- Must be a class
536 thing <- tcLookup cls
538 AThing kind -> return kind
539 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
540 _ -> wrongThingErr "class" thing cls
544 %************************************************************************
548 %************************************************************************
552 * Transforms from HsType to Type
555 It cannot fail, and does no validity checking, except for
556 structural matters, such as
557 (a) spurious ! annotations.
558 (b) a class used as a type
561 dsHsType :: LHsType Name -> TcM Type
562 -- All HsTyVarBndrs in the intput type are kind-annotated
563 dsHsType ty = ds_type (unLoc ty)
565 ds_type :: HsType Name -> TcM Type
566 ds_type ty@(HsTyVar _)
569 ds_type (HsParTy ty) -- Remove the parentheses markers
572 ds_type ty@(HsBangTy {}) -- No bangs should be here
573 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
575 ds_type ty@(HsRecTy {}) -- No bangs should be here
576 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
578 ds_type (HsKindSig ty _)
579 = dsHsType ty -- Kind checking done already
581 ds_type (HsListTy ty) = do
582 tau_ty <- dsHsType ty
583 checkWiredInTyCon listTyCon
584 return (mkListTy tau_ty)
586 ds_type (HsPArrTy ty) = do
587 tau_ty <- dsHsType ty
588 checkWiredInTyCon parrTyCon
589 return (mkPArrTy tau_ty)
591 ds_type (HsTupleTy boxity tys) = do
592 tau_tys <- dsHsTypes tys
593 checkWiredInTyCon tycon
594 return (mkTyConApp tycon tau_tys)
596 tycon = tupleTyCon boxity (length tys)
598 ds_type (HsFunTy ty1 ty2) = do
599 tau_ty1 <- dsHsType ty1
600 tau_ty2 <- dsHsType ty2
601 return (mkFunTy tau_ty1 tau_ty2)
603 ds_type (HsOpTy ty1 (L span op) ty2) = do
604 tau_ty1 <- dsHsType ty1
605 tau_ty2 <- dsHsType ty2
606 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
610 tc <- tcLookupTyCon genUnitTyConName
611 return (mkTyConApp tc [])
613 ds_type ty@(HsAppTy _ _)
616 ds_type (HsPredTy pred) = do
617 pred' <- dsHsPred pred
618 return (mkPredTy pred')
620 ds_type (HsForAllTy _ tv_names ctxt ty)
621 = tcTyVarBndrs tv_names $ \ tyvars -> do
622 theta <- mapM dsHsLPred (unLoc ctxt)
624 return (mkSigmaTy tyvars theta tau)
626 ds_type (HsDocTy ty _) -- Remove the doc comment
629 ds_type (HsSpliceTy _ _ kind)
630 = do { kind' <- zonkTcKindToKind kind
631 ; newFlexiTyVarTy kind' }
633 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
634 ds_type (HsCoreTy ty) = return ty
636 dsHsTypes :: [LHsType Name] -> TcM [Type]
637 dsHsTypes arg_tys = mapM dsHsType arg_tys
640 Help functions for type applications
641 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
644 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
645 ds_app (HsAppTy ty1 ty2) tys
646 = ds_app (unLoc ty1) (ty2:tys)
649 arg_tys <- dsHsTypes tys
651 HsTyVar fun -> ds_var_app fun arg_tys
652 _ -> do fun_ty <- ds_type ty
653 return (mkAppTys fun_ty arg_tys)
655 ds_var_app :: Name -> [Type] -> TcM Type
656 ds_var_app name arg_tys = do
657 thing <- tcLookup name
659 ATyVar _ ty -> return (mkAppTys ty arg_tys)
660 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
661 _ -> wrongThingErr "type" thing name
669 dsHsLPred :: LHsPred Name -> TcM PredType
670 dsHsLPred pred = dsHsPred (unLoc pred)
672 dsHsPred :: HsPred Name -> TcM PredType
673 dsHsPred (HsClassP class_name tys)
674 = do { arg_tys <- dsHsTypes tys
675 ; clas <- tcLookupClass class_name
676 ; return (ClassP clas arg_tys)
678 dsHsPred (HsEqualP ty1 ty2)
679 = do { arg_ty1 <- dsHsType ty1
680 ; arg_ty2 <- dsHsType ty2
681 ; return (EqPred arg_ty1 arg_ty2)
683 dsHsPred (HsIParam name ty)
684 = do { arg_ty <- dsHsType ty
685 ; return (IParam name arg_ty)
690 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
691 -- Wrap a context around only if we want to show that contexts.
692 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
693 -- Omit invisble ones and ones user's won't grok (HsPred p).
694 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
696 typeCtxt :: HsType Name -> SDoc
697 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
700 %************************************************************************
702 Type-variable binders
704 %************************************************************************
708 kcHsTyVars :: [LHsTyVarBndr Name]
709 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
710 -- They scope over the thing inside
712 kcHsTyVars tvs thing_inside
713 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
714 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
716 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
717 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
718 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
719 kcHsTyVar tv@(KindedTyVar {}) = return tv
722 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
723 -> ([TyVar] -> TcM r)
725 -- Used when type-checking types/classes/type-decls
726 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
727 tcTyVarBndrs bndrs thing_inside = do
728 tyvars <- mapM (zonk . unLoc) bndrs
729 tcExtendTyVarEnv tyvars (thing_inside tyvars)
731 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
732 ; return (mkTyVar name kind') }
733 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
735 -----------------------------------
736 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
737 -- GADT decls can have a (perhaps partial) kind signature
738 -- e.g. data T :: * -> * -> * where ...
739 -- This function makes up suitable (kinded) type variables for
740 -- the argument kinds, and checks that the result kind is indeed *.
741 -- We use it also to make up argument type variables for for data instances.
742 tcDataKindSig Nothing = return []
743 tcDataKindSig (Just kind)
744 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
745 ; span <- getSrcSpanM
746 ; us <- newUniqueSupply
747 ; let uniqs = uniqsFromSupply us
748 ; return [ mk_tv span uniq str kind
749 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
751 (arg_kinds, res_kind) = splitKindFunTys kind
752 mk_tv loc uniq str kind = mkTyVar name kind
754 name = mkInternalName uniq occ loc
755 occ = mkOccName tvName str
757 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
760 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
762 badKindSig :: Kind -> SDoc
764 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
768 Note [Avoid name clashes for associated data types]
769 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
770 Consider class C a b where
772 When typechecking the decl for D, we'll invent an extra type variable for D,
773 to fill out its kind. We *don't* want this type variable to be 'a', because
774 in an .hi file we'd get
777 which makes it look as if there are *two* type indices. But there aren't!
778 So we use $a instead, which cannot clash with a user-written type variable.
779 Remember that type variable binders in interface files are just FastStrings,
782 (The tidying phase can't help here because we don't tidy TyCons. Another
783 alternative would be to record the number of indexing parameters in the
787 %************************************************************************
789 Scoped type variables
791 %************************************************************************
794 tcAddScopedTyVars is used for scoped type variables added by pattern
796 e.g. \ ((x::a), (y::a)) -> x+y
797 They never have explicit kinds (because this is source-code only)
798 They are mutable (because they can get bound to a more specific type).
800 Usually we kind-infer and expand type splices, and then
801 tupecheck/desugar the type. That doesn't work well for scoped type
802 variables, because they scope left-right in patterns. (e.g. in the
803 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
805 The current not-very-good plan is to
806 * find all the types in the patterns
807 * find their free tyvars
809 * bring the kinded type vars into scope
810 * BUT throw away the kind-checked type
811 (we'll kind-check it again when we type-check the pattern)
813 This is bad because throwing away the kind checked type throws away
814 its splices. But too bad for now. [July 03]
817 We no longer specify that these type variables must be univerally
818 quantified (lots of email on the subject). If you want to put that
820 a) Do a checkSigTyVars after thing_inside
821 b) More insidiously, don't pass in expected_ty, else
822 we unify with it too early and checkSigTyVars barfs
823 Instead you have to pass in a fresh ty var, and unify
824 it with expected_ty afterwards
827 tcHsPatSigType :: UserTypeCtxt
828 -> LHsType Name -- The type signature
829 -> TcM ([TyVar], -- Newly in-scope type variables
830 Type) -- The signature
831 -- Used for type-checking type signatures in
832 -- (a) patterns e.g f (x::Int) = e
833 -- (b) result signatures e.g. g x :: Int = e
834 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
836 tcHsPatSigType ctxt hs_ty
837 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
838 do { -- Find the type variables that are mentioned in the type
839 -- but not already in scope. These are the ones that
840 -- should be bound by the pattern signature
841 in_scope <- getInLocalScope
842 ; let span = getLoc hs_ty
843 sig_tvs = userHsTyVarBndrs $ map (L span) $
845 nameSetToList (extractHsTyVars hs_ty)
847 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
848 ; checkValidType ctxt sig_ty
849 ; return (tyvars, sig_ty)
852 tcPatSig :: UserTypeCtxt
855 -> TcM (TcType, -- The type to use for "inside" the signature
856 [(Name, TcType)], -- The new bit of type environment, binding
857 -- the scoped type variables
858 CoercionI) -- Coercion due to unification with actual ty
859 tcPatSig ctxt sig res_ty
860 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
862 ; if null sig_tvs then do {
863 -- The type signature binds no type variables,
864 -- and hence is rigid, so use it to zap the res_ty
865 coi <- boxyUnify sig_ty res_ty
866 ; return (sig_ty, [], coi)
869 -- Type signature binds at least one scoped type variable
871 -- A pattern binding cannot bind scoped type variables
872 -- The renamer fails with a name-out-of-scope error
873 -- if a pattern binding tries to bind a type variable,
874 -- So we just have an ASSERT here
875 ; let in_pat_bind = case ctxt of
876 BindPatSigCtxt -> True
878 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
880 -- Check that pat_ty is rigid
881 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
883 -- Check that all newly-in-scope tyvars are in fact
884 -- constrained by the pattern. This catches tiresome
888 -- f (x :: T a) = ...
889 -- Here 'a' doesn't get a binding. Sigh
890 ; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
891 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
893 -- Now match the pattern signature against res_ty
894 -- For convenience, and uniform-looking error messages
895 -- we do the matching by allocating meta type variables,
896 -- unifying, and reading out the results.
897 -- This is a strictly local operation.
898 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
899 ; coi <- boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty)
901 ; sig_tv_tys <- mapM readFilledBox box_tvs
903 -- Check that each is bound to a distinct type variable,
904 -- and one that is not already in scope
905 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
906 ; binds_in_scope <- getScopedTyVarBinds
907 ; check binds_in_scope tv_binds
910 ; return (res_ty, tv_binds, coi)
913 check _ [] = return ()
914 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
915 ; check ((n,ty):in_scope) rest }
917 check_one in_scope n ty
918 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
919 -- Must bind to a type variable
921 ; checkTc (null dups) (dupInScope n (head dups) ty)
922 -- Must not bind to the same type variable
923 -- as some other in-scope type variable
927 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
931 %************************************************************************
935 %************************************************************************
937 We would like to get a decent error message from
938 (a) Under-applied type constructors
940 (b) Over-applied type constructors
944 -- The ExpKind datatype means "expected kind" and contains
945 -- some info about just why that kind is expected, to improve
946 -- the error message on a mis-match
947 data ExpKind = EK TcKind EkCtxt
948 data EkCtxt = EkUnk -- Unknown context
949 | EkEqPred -- Second argument of an equality predicate
950 | EkKindSig -- Kind signature
951 | EkArg SDoc Int -- Function, arg posn, expected kind
954 ekLifted, ekOpen :: ExpKind
955 ekLifted = EK liftedTypeKind EkUnk
956 ekOpen = EK openTypeKind EkUnk
958 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
959 -- A fancy wrapper for 'unifyKind', which tries
960 -- to give decent error messages.
961 -- (checkExpectedKind ty act_kind exp_kind)
962 -- checks that the actual kind act_kind is compatible
963 -- with the expected kind exp_kind
964 -- The first argument, ty, is used only in the error message generation
965 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
966 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
969 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
971 Just _ -> return () -- Unification succeeded
974 -- So there's definitely an error
975 -- Now to find out what sort
976 exp_kind <- zonkTcKind exp_kind
977 act_kind <- zonkTcKind act_kind
979 env0 <- tcInitTidyEnv
980 let (exp_as, _) = splitKindFunTys exp_kind
981 (act_as, _) = splitKindFunTys act_kind
982 n_exp_as = length exp_as
983 n_act_as = length act_as
985 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
986 (env2, tidy_act_kind) = tidyKind env1 act_kind
988 err | n_exp_as < n_act_as -- E.g. [Maybe]
989 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
991 -- Now n_exp_as >= n_act_as. In the next two cases,
992 -- n_exp_as == 0, and hence so is n_act_as
993 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
994 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
995 <+> ptext (sLit "is unlifted")
997 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
998 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
999 <+> ptext (sLit "is lifted")
1001 | otherwise -- E.g. Monad [Int]
1002 = ptext (sLit "Kind mis-match")
1004 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
1005 <+> quotes (pprKind tidy_exp_kind) <> comma,
1006 ptext (sLit "but") <+> quotes (ppr ty) <+>
1007 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
1009 expected_herald EkUnk = ptext (sLit "Expected")
1010 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
1011 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
1012 expected_herald (EkArg fun arg_no)
1013 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
1014 <+> quotes fun <+> ptext (sLit ("should have"))
1016 failWithTcM (env2, err $$ more_info)
1019 %************************************************************************
1021 Scoped type variables
1023 %************************************************************************
1026 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1027 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1028 nest 2 (pp_sig ctxt) ]
1030 pp_sig (FunSigCtxt n) = pp_n_colon n
1031 pp_sig (ConArgCtxt n) = pp_n_colon n
1032 pp_sig (ForSigCtxt n) = pp_n_colon n
1033 pp_sig _ = ppr (unLoc hs_ty)
1035 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1037 wobblyPatSig :: [Var] -> SDoc
1038 wobblyPatSig sig_tvs
1039 = hang (ptext (sLit "A pattern type signature cannot bind scoped type variables")
1040 <+> pprQuotedList sig_tvs)
1041 2 (ptext (sLit "unless the pattern has a rigid type context"))
1043 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1044 badPatSigTvs sig_ty bad_tvs
1045 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1046 quotes (pprWithCommas ppr bad_tvs),
1047 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1048 ptext (sLit "but are actually discarded by a type synonym") ]
1049 , ptext (sLit "To fix this, expand the type synonym")
1050 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1052 scopedNonVar :: Name -> Type -> SDoc
1054 = vcat [sep [ptext (sLit "The scoped type variable") <+> quotes (ppr n),
1055 nest 2 (ptext (sLit "is bound to the type") <+> quotes (ppr ty))],
1056 nest 2 (ptext (sLit "You can only bind scoped type variables to type variables"))]
1058 dupInScope :: Name -> Name -> Type -> SDoc
1060 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1061 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1062 ptext (sLit "Distinct scoped type variables must be distinct")])
1064 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1065 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)