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, Type)
159 -- Typecheck an instance head. We can't use
160 -- tcHsSigType, because it's not a valid user type.
161 tcHsInstHead (L loc ty)
162 = setSrcSpan loc $ -- No need for an "In the type..." context
163 tc_inst_head ty -- because that comes from the caller
165 -- tc_inst_head expects HsPredTy, which isn't usually even allowed
166 tc_inst_head (HsPredTy pred)
167 = do { pred' <- kcHsPred pred
168 ; pred'' <- dsHsPred pred'
169 ; return ([], [], mkPredTy pred'') }
171 tc_inst_head (HsForAllTy _ tvs ctxt (L _ (HsPredTy pred)))
172 = kcHsTyVars tvs $ \ tvs' ->
173 do { ctxt' <- kcHsContext ctxt
174 ; pred' <- kcHsPred pred
175 ; tcTyVarBndrs tvs' $ \ tvs'' ->
176 do { ctxt'' <- mapM dsHsLPred (unLoc ctxt')
177 ; pred'' <- dsHsPred pred'
178 ; return (tvs'', ctxt'', mkPredTy pred'') } }
180 tc_inst_head _ = failWithTc (ptext (sLit "Malformed instance type"))
182 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
183 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
184 -- except that we want to keep the tvs separate
185 tcHsQuantifiedType tv_names hs_ty
186 = kcHsTyVars tv_names $ \ tv_names' ->
187 do { kc_ty <- kcHsSigType hs_ty
188 ; tcTyVarBndrs tv_names' $ \ tvs ->
189 do { ty <- dsHsType kc_ty
190 ; return (tvs, ty) } }
192 -- Used for the deriving(...) items
193 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
194 tcHsDeriv = tc_hs_deriv []
196 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
197 -> TcM ([TyVar], Class, [Type])
198 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
199 = kcHsTyVars tv_names $ \ tv_names' ->
200 do { cls_kind <- kcClass cls_name
201 ; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
202 ; tcTyVarBndrs tv_names' $ \ tyvars ->
203 do { arg_tys <- dsHsTypes tys
204 ; cls <- tcLookupClass cls_name
205 ; return (tyvars, cls, arg_tys) }}
207 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
208 = -- Funny newtype deriving form
210 -- where C has arity 2. Hence can't use regular functions
211 tc_hs_deriv (tv_names1 ++ tv_names2) ty
214 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
217 These functions are used during knot-tying in
218 type and class declarations, when we have to
219 separate kind-checking, desugaring, and validity checking
222 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
223 -- Used for type signatures
224 kcHsSigType ty = addKcTypeCtxt ty $ kcTypeType ty
225 kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
227 tcHsKindedType :: LHsType Name -> TcM Type
228 -- Don't do kind checking, nor validity checking.
229 -- This is used in type and class decls, where kinding is
230 -- done in advance, and validity checking is done later
231 -- [Validity checking done later because of knot-tying issues.]
232 tcHsKindedType hs_ty = dsHsType hs_ty
234 tcHsBangType :: LHsType Name -> TcM Type
235 -- Permit a bang, but discard it
236 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
237 tcHsBangType ty = tcHsKindedType ty
239 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
240 -- Used when we are expecting a ClassContext (i.e. no implicit params)
241 -- Does not do validity checking, like tcHsKindedType
242 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
246 %************************************************************************
248 The main kind checker: kcHsType
250 %************************************************************************
252 First a couple of simple wrappers for kcHsType
255 ---------------------------
256 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
257 -- The type ty must be a *lifted* *type*
258 kcLiftedType ty = kc_check_lhs_type ty ekLifted
260 ---------------------------
261 kcTypeType :: LHsType Name -> TcM (LHsType Name)
262 -- The type ty must be a *type*, but it can be lifted or
263 -- unlifted or an unboxed tuple.
264 kcTypeType ty = kc_check_lhs_type ty ekOpen
266 ---------------------------
267 kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
268 kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_check_lhs_type ty kind
271 kc_check_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
272 -- Check that the type has the specified kind
273 -- Be sure to use checkExpectedKind, rather than simply unifying
274 -- with OpenTypeKind, because it gives better error messages
275 kc_check_lhs_type (L span ty) exp_kind
277 do { ty' <- kc_check_hs_type ty exp_kind
278 ; return (L span ty') }
280 kc_check_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
281 kc_check_lhs_types tys_w_kinds
282 = mapM kc_arg tys_w_kinds
284 kc_arg (arg, arg_kind) = kc_check_lhs_type arg arg_kind
287 ---------------------------
288 kc_check_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
290 -- First some special cases for better error messages
291 -- when we know the expected kind
292 kc_check_hs_type (HsParTy ty) exp_kind
293 = do { ty' <- kc_check_lhs_type ty exp_kind; return (HsParTy ty') }
295 kc_check_hs_type ty@(HsAppTy ty1 ty2) exp_kind
296 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
297 ; (fun_ty', fun_kind) <- kc_lhs_type fun_ty
298 ; arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
299 ; return (mkHsAppTys fun_ty' arg_tys') }
301 -- This is the general case: infer the kind and compare
302 kc_check_hs_type ty exp_kind
303 = do { (ty', act_kind) <- kc_hs_type ty
304 -- Add the context round the inner check only
305 -- because checkExpectedKind already mentions
306 -- 'ty' by name in any error message
308 ; checkExpectedKind (strip ty) act_kind exp_kind
311 -- We infer the kind of the type, and then complain if it's
312 -- not right. But we don't want to complain about
313 -- (ty) or !(ty) or forall a. ty
314 -- when the real difficulty is with the 'ty' part.
315 strip (HsParTy (L _ ty)) = strip ty
316 strip (HsBangTy _ (L _ ty)) = strip ty
317 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
321 Here comes the main function
324 kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
325 -- Called from outside: set the context
326 kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type ty)
328 kc_lhs_type :: LHsType Name -> TcM (LHsType Name, TcKind)
329 kc_lhs_type (L span ty)
331 do { (ty', kind) <- kc_hs_type ty
332 ; return (L span ty', kind) }
334 -- kc_hs_type *returns* the kind of the type, rather than taking an expected
335 -- kind as argument as tcExpr does.
337 -- (a) the kind of (->) is
338 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
339 -- so we'd need to generate huge numbers of bx variables.
340 -- (b) kinds are so simple that the error messages are fine
342 -- The translated type has explicitly-kinded type-variable binders
344 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
345 kc_hs_type (HsParTy ty) = do
346 (ty', kind) <- kc_lhs_type ty
347 return (HsParTy ty', kind)
349 kc_hs_type (HsTyVar name) = do
351 return (HsTyVar name, kind)
353 kc_hs_type (HsListTy ty) = do
354 ty' <- kcLiftedType ty
355 return (HsListTy ty', liftedTypeKind)
357 kc_hs_type (HsPArrTy ty) = do
358 ty' <- kcLiftedType ty
359 return (HsPArrTy ty', liftedTypeKind)
361 kc_hs_type (HsNumTy n)
362 = return (HsNumTy n, liftedTypeKind)
364 kc_hs_type (HsKindSig ty k) = do
365 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
366 return (HsKindSig ty' k, k)
368 kc_hs_type (HsTupleTy Boxed tys) = do
369 tys' <- mapM kcLiftedType tys
370 return (HsTupleTy Boxed tys', liftedTypeKind)
372 kc_hs_type (HsTupleTy Unboxed tys) = do
373 tys' <- mapM kcTypeType tys
374 return (HsTupleTy Unboxed tys', ubxTupleKind)
376 kc_hs_type (HsFunTy ty1 ty2) = do
377 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
378 ty2' <- kcTypeType ty2
379 return (HsFunTy ty1' ty2', liftedTypeKind)
381 kc_hs_type (HsOpTy ty1 op ty2) = do
382 op_kind <- addLocM kcTyVar op
383 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
384 return (HsOpTy ty1' op ty2', res_kind)
386 kc_hs_type (HsAppTy ty1 ty2) = do
387 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
388 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
389 return (mkHsAppTys fun_ty' arg_tys', res_kind)
391 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
393 kc_hs_type (HsPredTy pred)
396 kc_hs_type (HsCoreTy ty)
397 = return (HsCoreTy ty, typeKind ty)
399 kc_hs_type (HsForAllTy exp tv_names context ty)
400 = kcHsTyVars tv_names $ \ tv_names' ->
401 do { ctxt' <- kcHsContext context
402 ; ty' <- kcLiftedType ty
403 -- The body of a forall is usually a type, but in principle
404 -- there's no reason to prohibit *unlifted* types.
405 -- In fact, GHC can itself construct a function with an
406 -- unboxed tuple inside a for-all (via CPR analyis; see
407 -- typecheck/should_compile/tc170)
409 -- Still, that's only for internal interfaces, which aren't
410 -- kind-checked, so we only allow liftedTypeKind here
412 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
414 kc_hs_type (HsBangTy b ty)
415 = do { (ty', kind) <- kc_lhs_type ty
416 ; return (HsBangTy b ty', kind) }
418 kc_hs_type ty@(HsRecTy _)
419 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
420 -- Record types (which only show up temporarily in constructor signatures)
421 -- should have been removed by now
423 #ifdef GHCI /* Only if bootstrapped */
424 kc_hs_type (HsSpliceTy sp fvs _) = kcSpliceType sp fvs
426 kc_hs_type ty@(HsSpliceTy {}) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
429 kc_hs_type (HsQuasiQuoteTy {}) = panic "kc_hs_type" -- Eliminated by renamer
431 -- remove the doc nodes here, no need to worry about the location since
432 -- its the same for a doc node and it's child type node
433 kc_hs_type (HsDocTy ty _)
434 = kc_hs_type (unLoc ty)
436 ---------------------------
437 kcApps :: Outputable a
439 -> TcKind -- Function kind
440 -> [LHsType Name] -- Arg types
441 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
442 kcApps the_fun fun_kind args
443 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
444 ; args' <- kc_check_lhs_types args_w_kinds
445 ; return (args', res_kind) }
447 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
448 -> HsType Name -- The type being checked (for err messages only)
449 -> ExpKind -- Expected kind
450 -> TcM [LHsType Name]
451 kcCheckApps the_fun fun_kind args ty exp_kind
452 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
453 ; checkExpectedKind ty res_kind exp_kind
454 -- Check the result kind *before* checking argument kinds
455 -- This improves error message; Trac #2994
456 ; kc_check_lhs_types args_w_kinds }
458 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
459 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
461 split (L _ (HsAppTy f a)) as = split f (a:as)
464 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
465 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
466 mkHsAppTys fun_ty (arg_ty:arg_tys)
467 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
469 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
470 -- the application; they are
473 ---------------------------
474 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
475 splitFunKind _ _ fk [] = return ([], fk)
476 splitFunKind the_fun arg_no fk (arg:args)
477 = do { mb_fk <- matchExpectedFunKind fk
479 Nothing -> failWithTc too_many_args
480 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
481 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
483 too_many_args = quotes the_fun <+>
484 ptext (sLit "is applied to too many type arguments")
486 ---------------------------
487 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
488 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
490 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
491 kcHsLPred = wrapLocM kcHsPred
493 kcHsPred :: HsPred Name -> TcM (HsPred Name)
494 kcHsPred pred = do -- Checks that the result is of kind liftedType
495 (pred', kind) <- kc_pred pred
496 checkExpectedKind pred kind ekLifted
499 ---------------------------
500 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
501 -- Does *not* check for a saturated
502 -- application (reason: used from TcDeriv)
503 kc_pred (HsIParam name ty)
504 = do { (ty', kind) <- kc_lhs_type ty
505 ; return (HsIParam name ty', kind)
507 kc_pred (HsClassP cls tys)
508 = do { kind <- kcClass cls
509 ; (tys', res_kind) <- kcApps cls kind tys
510 ; return (HsClassP cls tys', res_kind)
512 kc_pred (HsEqualP ty1 ty2)
513 = do { (ty1', kind1) <- kc_lhs_type ty1
514 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
515 ; (ty2', kind2) <- kc_lhs_type ty2
516 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
517 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
518 ; return (HsEqualP ty1' ty2', liftedTypeKind)
521 ---------------------------
522 kcTyVar :: Name -> TcM TcKind
523 kcTyVar name = do -- Could be a tyvar or a tycon
524 traceTc "lk1" (ppr name)
525 thing <- tcLookup name
526 traceTc "lk2" (ppr name <+> ppr thing)
528 ATyVar _ ty -> return (typeKind ty)
529 AThing kind -> return kind
530 AGlobal (ATyCon tc) -> return (tyConKind tc)
531 _ -> wrongThingErr "type" thing name
533 kcClass :: Name -> TcM TcKind
534 kcClass cls = do -- Must be a class
535 thing <- tcLookup cls
537 AThing kind -> return kind
538 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
539 _ -> wrongThingErr "class" thing cls
543 %************************************************************************
547 %************************************************************************
551 * Transforms from HsType to Type
554 It cannot fail, and does no validity checking, except for
555 structural matters, such as
556 (a) spurious ! annotations.
557 (b) a class used as a type
560 dsHsType :: LHsType Name -> TcM Type
561 -- All HsTyVarBndrs in the intput type are kind-annotated
562 dsHsType ty = ds_type (unLoc ty)
564 ds_type :: HsType Name -> TcM Type
565 ds_type ty@(HsTyVar _)
568 ds_type (HsParTy ty) -- Remove the parentheses markers
571 ds_type ty@(HsBangTy {}) -- No bangs should be here
572 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
574 ds_type ty@(HsRecTy {}) -- No bangs should be here
575 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
577 ds_type (HsKindSig ty _)
578 = dsHsType ty -- Kind checking done already
580 ds_type (HsListTy ty) = do
581 tau_ty <- dsHsType ty
582 checkWiredInTyCon listTyCon
583 return (mkListTy tau_ty)
585 ds_type (HsPArrTy ty) = do
586 tau_ty <- dsHsType ty
587 checkWiredInTyCon parrTyCon
588 return (mkPArrTy tau_ty)
590 ds_type (HsTupleTy boxity tys) = do
591 tau_tys <- dsHsTypes tys
592 checkWiredInTyCon tycon
593 return (mkTyConApp tycon tau_tys)
595 tycon = tupleTyCon boxity (length tys)
597 ds_type (HsFunTy ty1 ty2) = do
598 tau_ty1 <- dsHsType ty1
599 tau_ty2 <- dsHsType ty2
600 return (mkFunTy tau_ty1 tau_ty2)
602 ds_type (HsOpTy ty1 (L span op) ty2) = do
603 tau_ty1 <- dsHsType ty1
604 tau_ty2 <- dsHsType ty2
605 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
609 tc <- tcLookupTyCon genUnitTyConName
610 return (mkTyConApp tc [])
612 ds_type ty@(HsAppTy _ _)
615 ds_type (HsPredTy pred) = do
616 pred' <- dsHsPred pred
617 return (mkPredTy pred')
619 ds_type (HsForAllTy _ tv_names ctxt ty)
620 = tcTyVarBndrs tv_names $ \ tyvars -> do
621 theta <- mapM dsHsLPred (unLoc ctxt)
623 return (mkSigmaTy tyvars theta tau)
625 ds_type (HsDocTy ty _) -- Remove the doc comment
628 ds_type (HsSpliceTy _ _ kind)
629 = do { kind' <- zonkTcKindToKind kind
630 ; newFlexiTyVarTy kind' }
632 ds_type (HsQuasiQuoteTy {}) = panic "ds_type" -- Eliminated by renamer
633 ds_type (HsCoreTy ty) = return ty
635 dsHsTypes :: [LHsType Name] -> TcM [Type]
636 dsHsTypes arg_tys = mapM dsHsType arg_tys
639 Help functions for type applications
640 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
643 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
644 ds_app (HsAppTy ty1 ty2) tys
645 = ds_app (unLoc ty1) (ty2:tys)
648 arg_tys <- dsHsTypes tys
650 HsTyVar fun -> ds_var_app fun arg_tys
651 _ -> do fun_ty <- ds_type ty
652 return (mkAppTys fun_ty arg_tys)
654 ds_var_app :: Name -> [Type] -> TcM Type
655 ds_var_app name arg_tys = do
656 thing <- tcLookup name
658 ATyVar _ ty -> return (mkAppTys ty arg_tys)
659 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
660 _ -> wrongThingErr "type" thing name
668 dsHsLPred :: LHsPred Name -> TcM PredType
669 dsHsLPred pred = dsHsPred (unLoc pred)
671 dsHsPred :: HsPred Name -> TcM PredType
672 dsHsPred (HsClassP class_name tys)
673 = do { arg_tys <- dsHsTypes tys
674 ; clas <- tcLookupClass class_name
675 ; return (ClassP clas arg_tys)
677 dsHsPred (HsEqualP ty1 ty2)
678 = do { arg_ty1 <- dsHsType ty1
679 ; arg_ty2 <- dsHsType ty2
680 ; return (EqPred arg_ty1 arg_ty2)
682 dsHsPred (HsIParam name ty)
683 = do { arg_ty <- dsHsType ty
684 ; return (IParam name arg_ty)
689 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
690 -- Wrap a context around only if we want to show that contexts.
691 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
692 -- Omit invisble ones and ones user's won't grok (HsPred p).
693 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
695 typeCtxt :: HsType Name -> SDoc
696 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
699 %************************************************************************
701 Type-variable binders
703 %************************************************************************
707 kcHsTyVars :: [LHsTyVarBndr Name]
708 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
709 -- They scope over the thing inside
711 kcHsTyVars tvs thing_inside
712 = do { kinded_tvs <- mapM (wrapLocM kcHsTyVar) tvs
713 ; tcExtendKindEnvTvs kinded_tvs thing_inside }
715 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
716 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
717 kcHsTyVar (UserTyVar name _) = UserTyVar name <$> newKindVar
718 kcHsTyVar tv@(KindedTyVar {}) = return tv
721 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
722 -> ([TyVar] -> TcM r)
724 -- Used when type-checking types/classes/type-decls
725 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
726 tcTyVarBndrs bndrs thing_inside = do
727 tyvars <- mapM (zonk . unLoc) bndrs
728 tcExtendTyVarEnv tyvars (thing_inside tyvars)
730 zonk (UserTyVar name kind) = do { kind' <- zonkTcKindToKind kind
731 ; return (mkTyVar name kind') }
732 zonk (KindedTyVar name kind) = return (mkTyVar name kind)
734 -----------------------------------
735 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
736 -- GADT decls can have a (perhaps partial) kind signature
737 -- e.g. data T :: * -> * -> * where ...
738 -- This function makes up suitable (kinded) type variables for
739 -- the argument kinds, and checks that the result kind is indeed *.
740 -- We use it also to make up argument type variables for for data instances.
741 tcDataKindSig Nothing = return []
742 tcDataKindSig (Just kind)
743 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
744 ; span <- getSrcSpanM
745 ; us <- newUniqueSupply
746 ; let uniqs = uniqsFromSupply us
747 ; return [ mk_tv span uniq str kind
748 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
750 (arg_kinds, res_kind) = splitKindFunTys kind
751 mk_tv loc uniq str kind = mkTyVar name kind
753 name = mkInternalName uniq occ loc
754 occ = mkOccName tvName str
756 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
759 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
761 badKindSig :: Kind -> SDoc
763 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
767 Note [Avoid name clashes for associated data types]
768 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
769 Consider class C a b where
771 When typechecking the decl for D, we'll invent an extra type variable for D,
772 to fill out its kind. We *don't* want this type variable to be 'a', because
773 in an .hi file we'd get
776 which makes it look as if there are *two* type indices. But there aren't!
777 So we use $a instead, which cannot clash with a user-written type variable.
778 Remember that type variable binders in interface files are just FastStrings,
781 (The tidying phase can't help here because we don't tidy TyCons. Another
782 alternative would be to record the number of indexing parameters in the
786 %************************************************************************
788 Scoped type variables
790 %************************************************************************
793 tcAddScopedTyVars is used for scoped type variables added by pattern
795 e.g. \ ((x::a), (y::a)) -> x+y
796 They never have explicit kinds (because this is source-code only)
797 They are mutable (because they can get bound to a more specific type).
799 Usually we kind-infer and expand type splices, and then
800 tupecheck/desugar the type. That doesn't work well for scoped type
801 variables, because they scope left-right in patterns. (e.g. in the
802 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
804 The current not-very-good plan is to
805 * find all the types in the patterns
806 * find their free tyvars
808 * bring the kinded type vars into scope
809 * BUT throw away the kind-checked type
810 (we'll kind-check it again when we type-check the pattern)
812 This is bad because throwing away the kind checked type throws away
813 its splices. But too bad for now. [July 03]
816 We no longer specify that these type variables must be univerally
817 quantified (lots of email on the subject). If you want to put that
819 a) Do a checkSigTyVars after thing_inside
820 b) More insidiously, don't pass in expected_ty, else
821 we unify with it too early and checkSigTyVars barfs
822 Instead you have to pass in a fresh ty var, and unify
823 it with expected_ty afterwards
826 tcHsPatSigType :: UserTypeCtxt
827 -> LHsType Name -- The type signature
828 -> TcM ([TyVar], -- Newly in-scope type variables
829 Type) -- The signature
830 -- Used for type-checking type signatures in
831 -- (a) patterns e.g f (x::Int) = e
832 -- (b) result signatures e.g. g x :: Int = e
833 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
835 tcHsPatSigType ctxt hs_ty
836 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
837 do { -- Find the type variables that are mentioned in the type
838 -- but not already in scope. These are the ones that
839 -- should be bound by the pattern signature
840 in_scope <- getInLocalScope
841 ; let span = getLoc hs_ty
842 sig_tvs = userHsTyVarBndrs $ map (L span) $
844 nameSetToList (extractHsTyVars hs_ty)
846 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
847 ; checkValidType ctxt sig_ty
848 ; return (tyvars, sig_ty)
851 tcPatSig :: UserTypeCtxt
854 -> TcM (TcType, -- The type to use for "inside" the signature
855 [(Name, TcType)], -- The new bit of type environment, binding
856 -- the scoped type variables
857 HsWrapper) -- Coercion due to unification with actual ty
858 -- Of shape: res_ty ~ sig_ty
859 tcPatSig ctxt sig res_ty
860 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
861 -- sig_tvs are the type variables free in 'sig',
862 -- and not already in scope. These are the ones
863 -- that should be brought into scope
865 ; if null sig_tvs then do {
866 -- The type signature binds no type variables,
867 -- and hence is rigid, so use it to zap the res_ty
868 wrap <- tcSubType PatSigOrigin (SigSkol ctxt) res_ty sig_ty
869 ; return (sig_ty, [], wrap)
872 -- Type signature binds at least one scoped type variable
874 -- A pattern binding cannot bind scoped type variables
875 -- The renamer fails with a name-out-of-scope error
876 -- if a pattern binding tries to bind a type variable,
877 -- So we just have an ASSERT here
878 ; let in_pat_bind = case ctxt of
879 BindPatSigCtxt -> True
881 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
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 do a subsumption check of the pattern signature against res_ty
894 ; sig_tvs' <- tcInstSigTyVars sig_tvs
895 ; let sig_ty' = substTyWith sig_tvs sig_tv_tys' sig_ty
896 sig_tv_tys' = mkTyVarTys sig_tvs'
897 ; wrap <- tcSubType PatSigOrigin (SigSkol ctxt) res_ty sig_ty'
899 -- Check that each is bound to a distinct type variable,
900 -- and one that is not already in scope
901 ; binds_in_scope <- getScopedTyVarBinds
902 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys'
903 ; check binds_in_scope tv_binds
906 ; return (sig_ty', tv_binds, wrap)
909 check _ [] = return ()
910 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
911 ; check ((n,ty):in_scope) rest }
913 check_one in_scope n ty
914 = checkTc (null dups) (dupInScope n (head dups) ty)
915 -- Must not bind to the same type variable
916 -- as some other in-scope type variable
918 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
922 %************************************************************************
926 %************************************************************************
928 We would like to get a decent error message from
929 (a) Under-applied type constructors
931 (b) Over-applied type constructors
935 -- The ExpKind datatype means "expected kind" and contains
936 -- some info about just why that kind is expected, to improve
937 -- the error message on a mis-match
938 data ExpKind = EK TcKind EkCtxt
939 data EkCtxt = EkUnk -- Unknown context
940 | EkEqPred -- Second argument of an equality predicate
941 | EkKindSig -- Kind signature
942 | EkArg SDoc Int -- Function, arg posn, expected kind
945 ekLifted, ekOpen :: ExpKind
946 ekLifted = EK liftedTypeKind EkUnk
947 ekOpen = EK openTypeKind EkUnk
949 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
950 -- A fancy wrapper for 'unifyKind', which tries
951 -- to give decent error messages.
952 -- (checkExpectedKind ty act_kind exp_kind)
953 -- checks that the actual kind act_kind is compatible
954 -- with the expected kind exp_kind
955 -- The first argument, ty, is used only in the error message generation
956 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
957 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
960 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
962 Just _ -> return () -- Unification succeeded
965 -- So there's definitely an error
966 -- Now to find out what sort
967 exp_kind <- zonkTcKind exp_kind
968 act_kind <- zonkTcKind act_kind
970 env0 <- tcInitTidyEnv
971 let (exp_as, _) = splitKindFunTys exp_kind
972 (act_as, _) = splitKindFunTys act_kind
973 n_exp_as = length exp_as
974 n_act_as = length act_as
976 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
977 (env2, tidy_act_kind) = tidyKind env1 act_kind
979 err | n_exp_as < n_act_as -- E.g. [Maybe]
980 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
982 -- Now n_exp_as >= n_act_as. In the next two cases,
983 -- n_exp_as == 0, and hence so is n_act_as
984 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
985 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
986 <+> ptext (sLit "is unlifted")
988 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
989 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
990 <+> ptext (sLit "is lifted")
992 | otherwise -- E.g. Monad [Int]
993 = ptext (sLit "Kind mis-match")
995 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
996 <+> quotes (pprKind tidy_exp_kind) <> comma,
997 ptext (sLit "but") <+> quotes (ppr ty) <+>
998 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
1000 expected_herald EkUnk = ptext (sLit "Expected")
1001 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
1002 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
1003 expected_herald (EkArg fun arg_no)
1004 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
1005 <+> quotes fun <+> ptext (sLit ("should have"))
1007 failWithTcM (env2, err $$ more_info)
1010 %************************************************************************
1012 Scoped type variables
1014 %************************************************************************
1017 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1018 pprHsSigCtxt ctxt hs_ty = sep [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1019 nest 2 (pp_sig ctxt) ]
1021 pp_sig (FunSigCtxt n) = pp_n_colon n
1022 pp_sig (ConArgCtxt n) = pp_n_colon n
1023 pp_sig (ForSigCtxt n) = pp_n_colon n
1024 pp_sig _ = ppr (unLoc hs_ty)
1026 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1028 badPatSigTvs :: TcType -> [TyVar] -> SDoc
1029 badPatSigTvs sig_ty bad_tvs
1030 = vcat [ fsep [ptext (sLit "The type variable") <> plural bad_tvs,
1031 quotes (pprWithCommas ppr bad_tvs),
1032 ptext (sLit "should be bound by the pattern signature") <+> quotes (ppr sig_ty),
1033 ptext (sLit "but are actually discarded by a type synonym") ]
1034 , ptext (sLit "To fix this, expand the type synonym")
1035 , ptext (sLit "[Note: I hope to lift this restriction in due course]") ]
1037 dupInScope :: Name -> Name -> Type -> SDoc
1039 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1040 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1041 ptext (sLit "Distinct scoped type variables must be distinct")])
1043 wrongPredErr :: HsPred Name -> TcM (HsType Name, TcKind)
1044 wrongPredErr pred = failWithTc (text "Predicate used as a type:" <+> ppr pred)