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
57 ----------------------------
59 ----------------------------
61 Generally speaking we now type-check types in three phases
63 1. kcHsType: kind check the HsType
64 *includes* performing any TH type splices;
65 so it returns a translated, and kind-annotated, type
67 2. dsHsType: convert from HsType to Type:
69 expand type synonyms [mkGenTyApps]
70 hoist the foralls [tcHsType]
72 3. checkValidType: check the validity of the resulting type
74 Often these steps are done one after the other (tcHsSigType).
75 But in mutually recursive groups of type and class decls we do
76 1 kind-check the whole group
77 2 build TyCons/Classes in a knot-tied way
78 3 check the validity of types in the now-unknotted TyCons/Classes
80 For example, when we find
81 (forall a m. m a -> m a)
82 we bind a,m to kind varibles and kind-check (m a -> m a). This makes
83 a get kind *, and m get kind *->*. Now we typecheck (m a -> m a) in
84 an environment that binds a and m suitably.
86 The kind checker passed to tcHsTyVars needs to look at enough to
87 establish the kind of the tyvar:
88 * For a group of type and class decls, it's just the group, not
89 the rest of the program
90 * For a tyvar bound in a pattern type signature, its the types
91 mentioned in the other type signatures in that bunch of patterns
92 * For a tyvar bound in a RULE, it's the type signatures on other
93 universally quantified variables in the rule
95 Note that this may occasionally give surprising results. For example:
97 data T a b = MkT (a b)
99 Here we deduce a::*->*, b::*
100 But equally valid would be a::(*->*)-> *, b::*->*
105 Some of the validity check could in principle be done by the kind checker,
108 - During desugaring, we normalise by expanding type synonyms. Only
109 after this step can we check things like type-synonym saturation
110 e.g. type T k = k Int
112 Then (T S) is ok, because T is saturated; (T S) expands to (S Int);
113 and then S is saturated. This is a GHC extension.
115 - Similarly, also a GHC extension, we look through synonyms before complaining
116 about the form of a class or instance declaration
118 - Ambiguity checks involve functional dependencies, and it's easier to wait
119 until knots have been resolved before poking into them
121 Also, in a mutually recursive group of types, we can't look at the TyCon until we've
122 finished building the loop. So to keep things simple, we postpone most validity
123 checking until step (3).
127 During step (1) we might fault in a TyCon defined in another module, and it might
128 (via a loop) refer back to a TyCon defined in this module. So when we tie a big
129 knot around type declarations with ARecThing, so that the fault-in code can get
130 the TyCon being defined.
133 %************************************************************************
135 \subsection{Checking types}
137 %************************************************************************
140 tcHsSigType, tcHsSigTypeNC :: UserTypeCtxt -> LHsType Name -> TcM Type
141 -- Do kind checking, and hoist for-alls to the top
142 -- NB: it's important that the foralls that come from the top-level
143 -- HsForAllTy in hs_ty occur *first* in the returned type.
144 -- See Note [Scoped] with TcSigInfo
145 tcHsSigType ctxt hs_ty
146 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
147 tcHsSigTypeNC ctxt hs_ty
149 tcHsSigTypeNC ctxt hs_ty
150 = do { (kinded_ty, _kind) <- kc_lhs_type hs_ty
151 -- The kind is checked by checkValidType, and isn't necessarily
152 -- of kind * in a Template Haskell quote eg [t| Maybe |]
153 ; ty <- tcHsKindedType kinded_ty
154 ; checkValidType ctxt ty
157 tcHsInstHead :: LHsType Name -> TcM ([TyVar], ThetaType, Class, [Type])
158 -- Typecheck an instance head. We can't use
159 -- tcHsSigType, because it's not a valid user type.
160 tcHsInstHead (L loc hs_ty)
161 = setSrcSpan loc $ -- No need for an "In the type..." context
162 -- because that comes from the caller
163 do { kinded_ty <- kc_inst_head hs_ty
164 ; ds_inst_head kinded_ty }
166 kc_inst_head ty@(HsPredTy pred@(HsClassP {}))
167 = do { (pred', kind) <- kc_pred pred
168 ; checkExpectedKind ty kind ekLifted
169 ; return (HsPredTy pred') }
170 kc_inst_head (HsForAllTy exp tv_names context (L loc ty))
171 = kcHsTyVars tv_names $ \ tv_names' ->
172 do { ctxt' <- kcHsContext context
173 ; ty' <- kc_inst_head ty
174 ; return (HsForAllTy exp tv_names' ctxt' (L loc ty')) }
175 kc_inst_head _ = failWithTc (ptext (sLit "Malformed instance type"))
177 ds_inst_head (HsPredTy (HsClassP cls_name tys))
178 = do { clas <- tcLookupClass cls_name
179 ; arg_tys <- dsHsTypes tys
180 ; return ([], [], clas, arg_tys) }
181 ds_inst_head (HsForAllTy _ tvs ctxt (L _ tau))
182 = tcTyVarBndrs tvs $ \ tvs' ->
183 do { ctxt' <- mapM dsHsLPred (unLoc ctxt)
184 ; (tvs_r, ctxt_r, cls, tys) <- ds_inst_head tau
185 ; return (tvs' ++ tvs_r, ctxt' ++ ctxt_r , cls, tys) }
186 ds_inst_head _ = panic "ds_inst_head"
188 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
189 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
190 -- except that we want to keep the tvs separate
191 tcHsQuantifiedType tv_names hs_ty
192 = kcHsTyVars tv_names $ \ tv_names' ->
193 do { kc_ty <- kcHsSigType hs_ty
194 ; tcTyVarBndrs tv_names' $ \ tvs ->
195 do { ty <- dsHsType kc_ty
196 ; return (tvs, ty) } }
198 -- Used for the deriving(...) items
199 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
200 tcHsDeriv = tc_hs_deriv []
202 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
203 -> TcM ([TyVar], Class, [Type])
204 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
205 = kcHsTyVars tv_names $ \ tv_names' ->
206 do { cls_kind <- kcClass cls_name
207 ; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
208 ; tcTyVarBndrs tv_names' $ \ tyvars ->
209 do { arg_tys <- dsHsTypes tys
210 ; cls <- tcLookupClass cls_name
211 ; return (tyvars, cls, arg_tys) }}
213 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
214 = -- Funny newtype deriving form
216 -- where C has arity 2. Hence can't use regular functions
217 tc_hs_deriv (tv_names1 ++ tv_names2) ty
220 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
223 These functions are used during knot-tying in
224 type and class declarations, when we have to
225 separate kind-checking, desugaring, and validity checking
228 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
229 -- Used for type signatures
230 kcHsSigType ty = addKcTypeCtxt ty $ kcTypeType ty
231 kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
233 tcHsKindedType :: LHsType Name -> TcM Type
234 -- Don't do kind checking, nor validity checking.
235 -- This is used in type and class decls, where kinding is
236 -- done in advance, and validity checking is done later
237 -- [Validity checking done later because of knot-tying issues.]
238 tcHsKindedType hs_ty = dsHsType hs_ty
240 tcHsBangType :: LHsType Name -> TcM Type
241 -- Permit a bang, but discard it
242 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
243 tcHsBangType ty = tcHsKindedType ty
245 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
246 -- Used when we are expecting a ClassContext (i.e. no implicit params)
247 -- Does not do validity checking, like tcHsKindedType
248 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
252 %************************************************************************
254 The main kind checker: kcHsType
256 %************************************************************************
258 First a couple of simple wrappers for kcHsType
261 ---------------------------
262 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
263 -- The type ty must be a *lifted* *type*
264 kcLiftedType ty = kc_check_lhs_type ty ekLifted
266 ---------------------------
267 kcTypeType :: LHsType Name -> TcM (LHsType Name)
268 -- The type ty must be a *type*, but it can be lifted or
269 -- unlifted or an unboxed tuple.
270 kcTypeType ty = kc_check_lhs_type ty ekOpen
272 ---------------------------
273 kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
274 kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_check_lhs_type ty kind
277 kc_check_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
278 -- Check that the type has the specified kind
279 -- Be sure to use checkExpectedKind, rather than simply unifying
280 -- with OpenTypeKind, because it gives better error messages
281 kc_check_lhs_type (L span ty) exp_kind
283 do { ty' <- kc_check_hs_type ty exp_kind
284 ; return (L span ty') }
286 kc_check_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
287 kc_check_lhs_types tys_w_kinds
288 = mapM kc_arg tys_w_kinds
290 kc_arg (arg, arg_kind) = kc_check_lhs_type arg arg_kind
293 ---------------------------
294 kc_check_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
296 -- First some special cases for better error messages
297 -- when we know the expected kind
298 kc_check_hs_type (HsParTy ty) exp_kind
299 = do { ty' <- kc_check_lhs_type ty exp_kind; return (HsParTy ty') }
301 kc_check_hs_type ty@(HsAppTy ty1 ty2) exp_kind
302 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
303 ; (fun_ty', fun_kind) <- kc_lhs_type fun_ty
304 ; arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
305 ; return (mkHsAppTys fun_ty' arg_tys') }
307 -- This is the general case: infer the kind and compare
308 kc_check_hs_type ty exp_kind
309 = do { (ty', act_kind) <- kc_hs_type ty
310 -- Add the context round the inner check only
311 -- because checkExpectedKind already mentions
312 -- 'ty' by name in any error message
314 ; checkExpectedKind (strip ty) act_kind exp_kind
317 -- We infer the kind of the type, and then complain if it's
318 -- not right. But we don't want to complain about
319 -- (ty) or !(ty) or forall a. ty
320 -- when the real difficulty is with the 'ty' part.
321 strip (HsParTy (L _ ty)) = strip ty
322 strip (HsBangTy _ (L _ ty)) = strip ty
323 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
327 Here comes the main function
330 kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
331 -- Called from outside: set the context
332 kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type ty)
334 kc_lhs_type :: LHsType Name -> TcM (LHsType Name, TcKind)
335 kc_lhs_type (L span ty)
337 do { (ty', kind) <- kc_hs_type ty
338 ; return (L span ty', kind) }
340 -- kc_hs_type *returns* the kind of the type, rather than taking an expected
341 -- kind as argument as tcExpr does.
343 -- (a) the kind of (->) is
344 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
345 -- so we'd need to generate huge numbers of bx variables.
346 -- (b) kinds are so simple that the error messages are fine
348 -- The translated type has explicitly-kinded type-variable binders
350 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
351 kc_hs_type (HsParTy ty) = do
352 (ty', kind) <- kc_lhs_type ty
353 return (HsParTy ty', kind)
355 kc_hs_type (HsTyVar name) = do
357 return (HsTyVar name, kind)
359 kc_hs_type (HsListTy ty) = do
360 ty' <- kcLiftedType ty
361 return (HsListTy ty', liftedTypeKind)
363 kc_hs_type (HsPArrTy ty) = do
364 ty' <- kcLiftedType ty
365 return (HsPArrTy ty', liftedTypeKind)
367 kc_hs_type (HsKindSig ty k) = do
368 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
369 return (HsKindSig ty' k, k)
371 kc_hs_type (HsTupleTy Boxed tys) = do
372 tys' <- mapM kcLiftedType tys
373 return (HsTupleTy Boxed tys', liftedTypeKind)
375 kc_hs_type (HsTupleTy Unboxed tys) = do
376 tys' <- mapM kcTypeType tys
377 return (HsTupleTy Unboxed tys', ubxTupleKind)
379 kc_hs_type (HsFunTy ty1 ty2) = do
380 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
381 ty2' <- kcTypeType ty2
382 return (HsFunTy ty1' ty2', liftedTypeKind)
384 kc_hs_type (HsOpTy ty1 op ty2) = do
385 op_kind <- addLocM kcTyVar op
386 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
387 return (HsOpTy ty1' op ty2', res_kind)
389 kc_hs_type (HsAppTy ty1 ty2) = do
390 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
391 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
392 return (mkHsAppTys fun_ty' arg_tys', res_kind)
394 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
396 kc_hs_type (HsPredTy pred)
399 kc_hs_type (HsCoreTy ty)
400 = return (HsCoreTy ty, typeKind ty)
402 kc_hs_type (HsForAllTy exp tv_names context ty)
403 = kcHsTyVars tv_names $ \ tv_names' ->
404 do { ctxt' <- kcHsContext context
405 ; ty' <- kcLiftedType ty
406 -- The body of a forall is usually a type, but in principle
407 -- there's no reason to prohibit *unlifted* types.
408 -- In fact, GHC can itself construct a function with an
409 -- unboxed tuple inside a for-all (via CPR analyis; see
410 -- typecheck/should_compile/tc170)
412 -- Still, that's only for internal interfaces, which aren't
413 -- kind-checked, so we only allow liftedTypeKind here
415 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
417 kc_hs_type (HsBangTy b ty)
418 = do { (ty', kind) <- kc_lhs_type ty
419 ; return (HsBangTy b ty', kind) }
421 kc_hs_type ty@(HsRecTy _)
422 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
423 -- Record types (which only show up temporarily in constructor signatures)
424 -- should have been removed by now
426 #ifdef GHCI /* Only if bootstrapped */
427 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
429 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
432 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
434 -- remove the doc nodes here, no need to worry about the location since
435 -- its the same for a doc node and it's child type node
436 kc_hs_type (HsDocTy ty _)
437 = kc_hs_type (unLoc ty)
439 ---------------------------
440 kcApps :: Outputable a
442 -> TcKind -- Function kind
443 -> [LHsType Name] -- Arg types
444 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
445 kcApps the_fun fun_kind args
446 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
447 ; args' <- kc_check_lhs_types args_w_kinds
448 ; return (args', res_kind) }
450 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
451 -> HsType Name -- The type being checked (for err messages only)
452 -> ExpKind -- Expected kind
453 -> TcM [LHsType Name]
454 kcCheckApps the_fun fun_kind args ty exp_kind
455 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
456 ; checkExpectedKind ty res_kind exp_kind
457 -- Check the result kind *before* checking argument kinds
458 -- This improves error message; Trac #2994
459 ; kc_check_lhs_types args_w_kinds }
461 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
462 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
464 split (L _ (HsAppTy f a)) as = split f (a:as)
467 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
468 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
469 mkHsAppTys fun_ty (arg_ty:arg_tys)
470 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
472 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
473 -- the application; they are
476 ---------------------------
477 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
478 splitFunKind _ _ fk [] = return ([], fk)
479 splitFunKind the_fun arg_no fk (arg:args)
480 = do { mb_fk <- matchExpectedFunKind fk
482 Nothing -> failWithTc too_many_args
483 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
484 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
486 too_many_args = quotes the_fun <+>
487 ptext (sLit "is applied to too many type arguments")
489 ---------------------------
490 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
491 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
493 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
494 kcHsLPred = wrapLocM kcHsPred
496 kcHsPred :: HsPred Name -> TcM (HsPred Name)
497 kcHsPred pred = do -- Checks that the result is a type kind
498 (pred', kind) <- kc_pred pred
499 checkExpectedKind pred kind ekOpen
502 ---------------------------
503 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
504 -- Does *not* check for a saturated
505 -- application (reason: used from TcDeriv)
506 kc_pred (HsIParam name ty)
507 = do { (ty', kind) <- kc_lhs_type ty
508 ; return (HsIParam name ty', kind) }
509 kc_pred (HsClassP cls tys)
510 = do { kind <- kcClass cls
511 ; (tys', res_kind) <- kcApps cls kind tys
512 ; return (HsClassP cls tys', res_kind) }
513 kc_pred (HsEqualP ty1 ty2)
514 = do { (ty1', kind1) <- kc_lhs_type ty1
515 ; (ty2', kind2) <- kc_lhs_type ty2
516 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
517 ; return (HsEqualP ty1' ty2', unliftedTypeKind) }
519 ---------------------------
520 kcTyVar :: Name -> TcM TcKind
521 kcTyVar name = do -- Could be a tyvar or a tycon
522 traceTc "lk1" (ppr name)
523 thing <- tcLookup name
524 traceTc "lk2" (ppr name <+> ppr thing)
526 ATyVar _ ty -> return (typeKind ty)
527 AThing kind -> return kind
528 AGlobal (ATyCon tc) -> return (tyConKind tc)
529 _ -> wrongThingErr "type" thing name
531 kcClass :: Name -> TcM TcKind
532 kcClass cls = do -- Must be a class
533 thing <- tcLookup cls
535 AThing kind -> return kind
536 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
537 _ -> wrongThingErr "class" thing cls
541 %************************************************************************
545 %************************************************************************
549 * Transforms from HsType to Type
552 It cannot fail, and does no validity checking, except for
553 structural matters, such as
554 (a) spurious ! annotations.
555 (b) a class used as a type
558 dsHsType :: LHsType Name -> TcM Type
559 -- All HsTyVarBndrs in the intput type are kind-annotated
560 dsHsType ty = ds_type (unLoc ty)
562 ds_type :: HsType Name -> TcM Type
563 ds_type ty@(HsTyVar _)
566 ds_type (HsParTy ty) -- Remove the parentheses markers
569 ds_type ty@(HsBangTy {}) -- No bangs should be here
570 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
572 ds_type ty@(HsRecTy {}) -- No bangs should be here
573 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
575 ds_type (HsKindSig ty _)
576 = dsHsType ty -- Kind checking done already
578 ds_type (HsListTy ty) = do
579 tau_ty <- dsHsType ty
580 checkWiredInTyCon listTyCon
581 return (mkListTy tau_ty)
583 ds_type (HsPArrTy ty) = do
584 tau_ty <- dsHsType ty
585 checkWiredInTyCon parrTyCon
586 return (mkPArrTy tau_ty)
588 ds_type (HsTupleTy boxity tys) = do
589 tau_tys <- dsHsTypes tys
590 checkWiredInTyCon tycon
591 return (mkTyConApp tycon tau_tys)
593 tycon = tupleTyCon boxity (length tys)
595 ds_type (HsFunTy ty1 ty2) = do
596 tau_ty1 <- dsHsType ty1
597 tau_ty2 <- dsHsType ty2
598 return (mkFunTy tau_ty1 tau_ty2)
600 ds_type (HsOpTy ty1 (L span op) ty2) = do
601 tau_ty1 <- dsHsType ty1
602 tau_ty2 <- dsHsType ty2
603 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
605 ds_type ty@(HsAppTy _ _)
608 ds_type (HsPredTy pred) = do
609 pred' <- dsHsPred pred
610 return (mkPredTy pred')
612 ds_type (HsForAllTy _ tv_names ctxt ty)
613 = tcTyVarBndrs tv_names $ \ tyvars -> do
614 theta <- mapM dsHsLPred (unLoc ctxt)
616 return (mkSigmaTy tyvars theta tau)
618 ds_type (HsDocTy ty _) -- Remove the doc comment
621 ds_type (HsSpliceTy _ _ kind)
622 = do { kind' <- zonkTcKindToKind kind
623 ; newFlexiTyVarTy kind' }
625 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
626 ds_type (HsCoreTy ty) = return ty
628 dsHsTypes :: [LHsType Name] -> TcM [Type]
629 dsHsTypes arg_tys = mapM dsHsType arg_tys
632 Help functions for type applications
633 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
636 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
637 ds_app (HsAppTy ty1 ty2) tys
638 = ds_app (unLoc ty1) (ty2:tys)
641 arg_tys <- dsHsTypes tys
643 HsTyVar fun -> ds_var_app fun arg_tys
644 _ -> do fun_ty <- ds_type ty
645 return (mkAppTys fun_ty arg_tys)
647 ds_var_app :: Name -> [Type] -> TcM Type
648 ds_var_app name arg_tys = do
649 thing <- tcLookup name
651 ATyVar _ ty -> return (mkAppTys ty arg_tys)
652 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
653 _ -> wrongThingErr "type" thing name
661 dsHsLPred :: LHsPred Name -> TcM PredType
662 dsHsLPred pred = dsHsPred (unLoc pred)
664 dsHsPred :: HsPred Name -> TcM PredType
665 dsHsPred (HsClassP class_name tys)
666 = do { arg_tys <- dsHsTypes tys
667 ; clas <- tcLookupClass class_name
668 ; return (ClassP clas arg_tys)
670 dsHsPred (HsEqualP ty1 ty2)
671 = do { arg_ty1 <- dsHsType ty1
672 ; arg_ty2 <- dsHsType ty2
673 ; return (EqPred arg_ty1 arg_ty2)
675 dsHsPred (HsIParam name ty)
676 = do { arg_ty <- dsHsType ty
677 ; return (IParam name arg_ty)
682 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
683 -- Wrap a context around only if we want to show that contexts.
684 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
685 -- Omit invisble ones and ones user's won't grok (HsPred p).
686 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
688 typeCtxt :: HsType Name -> SDoc
689 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
692 %************************************************************************
694 Type-variable binders
696 %************************************************************************
700 kcHsTyVars :: [LHsTyVarBndr Name]
701 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
702 -- They scope over the thing inside
704 kcHsTyVars tvs thing_inside
705 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
706 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
708 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
709 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
710 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
711 kcHsTyVar tv@(KindedTyVar {}) = return tv
714 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
715 -> ([TyVar] -> TcM r)
717 -- Used when type-checking types/classes/type-decls
718 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
719 tcTyVarBndrs bndrs thing_inside = do
720 tyvars <- mapM (zonk . unLoc) bndrs
721 tcExtendTyVarEnv tyvars (thing_inside tyvars)
723 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
724 ; return (mkTyVar name kind') }
725 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
727 -----------------------------------
728 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
729 -- GADT decls can have a (perhaps partial) kind signature
730 -- e.g. data T :: * -> * -> * where ...
731 -- This function makes up suitable (kinded) type variables for
732 -- the argument kinds, and checks that the result kind is indeed *.
733 -- We use it also to make up argument type variables for for data instances.
734 tcDataKindSig Nothing = return []
735 tcDataKindSig (Just kind)
736 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
737 ; span <- getSrcSpanM
738 ; us <- newUniqueSupply
739 ; let uniqs = uniqsFromSupply us
740 ; return [ mk_tv span uniq str kind
741 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
743 (arg_kinds, res_kind) = splitKindFunTys kind
744 mk_tv loc uniq str kind = mkTyVar name kind
746 name = mkInternalName uniq occ loc
747 occ = mkOccName tvName str
749 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
752 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
754 badKindSig :: Kind -> SDoc
756 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
760 Note [Avoid name clashes for associated data types]
761 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
762 Consider class C a b where
764 When typechecking the decl for D, we'll invent an extra type variable for D,
765 to fill out its kind. We *don't* want this type variable to be 'a', because
766 in an .hi file we'd get
769 which makes it look as if there are *two* type indices. But there aren't!
770 So we use $a instead, which cannot clash with a user-written type variable.
771 Remember that type variable binders in interface files are just FastStrings,
774 (The tidying phase can't help here because we don't tidy TyCons. Another
775 alternative would be to record the number of indexing parameters in the
779 %************************************************************************
781 Scoped type variables
783 %************************************************************************
786 tcAddScopedTyVars is used for scoped type variables added by pattern
788 e.g. \ ((x::a), (y::a)) -> x+y
789 They never have explicit kinds (because this is source-code only)
790 They are mutable (because they can get bound to a more specific type).
792 Usually we kind-infer and expand type splices, and then
793 tupecheck/desugar the type. That doesn't work well for scoped type
794 variables, because they scope left-right in patterns. (e.g. in the
795 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
797 The current not-very-good plan is to
798 * find all the types in the patterns
799 * find their free tyvars
801 * bring the kinded type vars into scope
802 * BUT throw away the kind-checked type
803 (we'll kind-check it again when we type-check the pattern)
805 This is bad because throwing away the kind checked type throws away
806 its splices. But too bad for now. [July 03]
809 We no longer specify that these type variables must be univerally
810 quantified (lots of email on the subject). If you want to put that
812 a) Do a checkSigTyVars after thing_inside
813 b) More insidiously, don't pass in expected_ty, else
814 we unify with it too early and checkSigTyVars barfs
815 Instead you have to pass in a fresh ty var, and unify
816 it with expected_ty afterwards
819 tcHsPatSigType :: UserTypeCtxt
820 -> LHsType Name -- The type signature
821 -> TcM ([TyVar], -- Newly in-scope type variables
822 Type) -- The signature
823 -- Used for type-checking type signatures in
824 -- (a) patterns e.g f (x::Int) = e
825 -- (b) result signatures e.g. g x :: Int = e
826 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
828 tcHsPatSigType ctxt hs_ty
829 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
830 do { -- Find the type variables that are mentioned in the type
831 -- but not already in scope. These are the ones that
832 -- should be bound by the pattern signature
833 in_scope <- getInLocalScope
834 ; let span = getLoc hs_ty
835 sig_tvs = userHsTyVarBndrs $ map (L span) $
837 nameSetToList (extractHsTyVars hs_ty)
839 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
840 ; checkValidType ctxt sig_ty
841 ; return (tyvars, sig_ty)
844 tcPatSig :: UserTypeCtxt
847 -> TcM (TcType, -- The type to use for "inside" the signature
848 [(Name, TcType)], -- The new bit of type environment, binding
849 -- the scoped type variables
850 HsWrapper) -- Coercion due to unification with actual ty
851 -- Of shape: res_ty ~ sig_ty
852 tcPatSig ctxt sig res_ty
853 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
854 -- sig_tvs are the type variables free in 'sig',
855 -- and not already in scope. These are the ones
856 -- that should be brought into scope
858 ; if null sig_tvs then do {
859 -- The type signature binds no type variables,
860 -- and hence is rigid, so use it to zap the res_ty
861 wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty
862 ; return (sig_ty, [], wrap)
865 -- Type signature binds at least one scoped type variable
867 -- A pattern binding cannot bind scoped type variables
868 -- The renamer fails with a name-out-of-scope error
869 -- if a pattern binding tries to bind a type variable,
870 -- So we just have an ASSERT here
871 ; let in_pat_bind = case ctxt of
872 BindPatSigCtxt -> True
874 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
876 -- Check that all newly-in-scope tyvars are in fact
877 -- constrained by the pattern. This catches tiresome
881 -- f (x :: T a) = ...
882 -- Here 'a' doesn't get a binding. Sigh
883 ; let bad_tvs = filterOut (`elemVarSet` exactTyVarsOfType sig_ty) sig_tvs
884 ; checkTc (null bad_tvs) (badPatSigTvs sig_ty bad_tvs)
886 -- Now do a subsumption check of the pattern signature against res_ty
887 ; sig_tvs' <- tcInstSigTyVars sig_tvs
888 ; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
889 sig_tv_tys' = mkTyVarTys sig_tvs'
890 ; wrap <- tcSubType PatSigOrigin ctxt res_ty sig_ty'
892 -- Check that each is bound to a distinct type variable,
893 -- and one that is not already in scope
894 ; binds_in_scope <- getScopedTyVarBinds
895 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
896 ; check binds_in_scope tv_binds
899 ; return (sig_ty', tv_binds, wrap)
902 check _ [] = return ()
903 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
904 ; check ((n,ty):in_scope) rest }
906 check_one in_scope n ty
907 = checkTc (null dups) (dupInScope n (head dups) ty)
908 -- Must not bind to the same type variable
909 -- as some other in-scope type variable
911 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
915 %************************************************************************
919 %************************************************************************
921 We would like to get a decent error message from
922 (a) Under-applied type constructors
924 (b) Over-applied type constructors
928 -- The ExpKind datatype means "expected kind" and contains
929 -- some info about just why that kind is expected, to improve
930 -- the error message on a mis-match
931 data ExpKind = EK TcKind EkCtxt
932 data EkCtxt = EkUnk -- Unknown context
933 | EkEqPred -- Second argument of an equality predicate
934 | EkKindSig -- Kind signature
935 | EkArg SDoc Int -- Function, arg posn, expected kind
938 ekLifted, ekOpen :: ExpKind
939 ekLifted = EK liftedTypeKind EkUnk
940 ekOpen = EK openTypeKind EkUnk
942 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
943 -- A fancy wrapper for 'unifyKind', which tries
944 -- to give decent error messages.
945 -- (checkExpectedKind ty act_kind exp_kind)
946 -- checks that the actual kind act_kind is compatible
947 -- with the expected kind exp_kind
948 -- The first argument, ty, is used only in the error message generation
949 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
950 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
953 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
955 Just _ -> return () -- Unification succeeded
958 -- So there's definitely an error
959 -- Now to find out what sort
960 exp_kind <- zonkTcKind exp_kind
961 act_kind <- zonkTcKind act_kind
963 env0 <- tcInitTidyEnv
964 let (exp_as, _) = splitKindFunTys exp_kind
965 (act_as, _) = splitKindFunTys act_kind
966 n_exp_as = length exp_as
967 n_act_as = length act_as
969 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
970 (env2, tidy_act_kind) = tidyKind env1 act_kind
972 err | n_exp_as < n_act_as -- E.g. [Maybe]
973 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
975 -- Now n_exp_as >= n_act_as. In the next two cases,
976 -- n_exp_as == 0, and hence so is n_act_as
977 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
978 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
979 <+> ptext (sLit "is unlifted")
981 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
982 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
983 <+> ptext (sLit "is lifted")
985 | otherwise -- E.g. Monad [Int]
986 = ptext (sLit "Kind mis-match")
988 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
989 <+> quotes (pprKind tidy_exp_kind) <> comma,
990 ptext (sLit "but") <+> quotes (ppr ty) <+>
991 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
993 expected_herald EkUnk = ptext (sLit "Expected")
994 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
995 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
996 expected_herald (EkArg fun arg_no)
997 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
998 <+> quotes fun <+> ptext (sLit ("should have"))
1000 failWithTcM (env2, err $$ more_info)
1003 %************************************************************************
1005 Scoped type variables
1007 %************************************************************************
1010 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1011 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1012 nest 2 (pp_sig ctxt) ]
1014 pp_sig (FunSigCtxt n) = pp_n_colon n
1015 pp_sig (ConArgCtxt n) = pp_n_colon n
1016 pp_sig (ForSigCtxt n) = pp_n_colon n
1017 pp_sig _ = ppr (unLoc hs_ty)
1019 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1021 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1022 badPatSigTvs sig_ty bad_tvs
1023 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1024 quotes (pprWithCommas ppr bad_tvs),
1025 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1026 ptext (sLit "but are actually discarded by a type synonym") ]
1027 , ptext (sLit "To fix this, expand the type synonym")
1028 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1030 dupInScope :: Name -> Name -> Type -> SDoc
1032 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1033 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1034 ptext (sLit "Distinct scoped type variables must be distinct")])
1036 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1037 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)