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, tcLHsConResTy,
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, Type)
158 -- Typecheck an instance head. We can't use
159 -- tcHsSigType, because it's not a valid user type.
161 = do { kinded_ty <- kcHsSigType hs_ty
162 ; poly_ty <- tcHsKindedType kinded_ty
163 ; return (tcSplitSigmaTy poly_ty) }
165 tcHsQuantifiedType :: [LHsTyVarBndr Name] -> LHsType Name -> TcM ([TyVar], Type)
166 -- Behave very like type-checking (HsForAllTy sig_tvs hs_ty),
167 -- except that we want to keep the tvs separate
168 tcHsQuantifiedType tv_names hs_ty
169 = kcHsTyVars tv_names $ \ tv_names' ->
170 do { kc_ty <- kcHsSigType hs_ty
171 ; tcTyVarBndrs tv_names' $ \ tvs ->
172 do { ty <- dsHsType kc_ty
173 ; return (tvs, ty) } }
175 -- Used for the deriving(...) items
176 tcHsDeriv :: HsType Name -> TcM ([TyVar], Class, [Type])
177 tcHsDeriv = tc_hs_deriv []
179 tc_hs_deriv :: [LHsTyVarBndr Name] -> HsType Name
180 -> TcM ([TyVar], Class, [Type])
181 tc_hs_deriv tv_names (HsPredTy (HsClassP cls_name hs_tys))
182 = kcHsTyVars tv_names $ \ tv_names' ->
183 do { cls_kind <- kcClass cls_name
184 ; (tys, _res_kind) <- kcApps cls_name cls_kind hs_tys
185 ; tcTyVarBndrs tv_names' $ \ tyvars ->
186 do { arg_tys <- dsHsTypes tys
187 ; cls <- tcLookupClass cls_name
188 ; return (tyvars, cls, arg_tys) }}
190 tc_hs_deriv tv_names1 (HsForAllTy _ tv_names2 (L _ []) (L _ ty))
191 = -- Funny newtype deriving form
193 -- where C has arity 2. Hence can't use regular functions
194 tc_hs_deriv (tv_names1 ++ tv_names2) ty
197 = failWithTc (ptext (sLit "Illegal deriving item") <+> ppr other)
200 These functions are used during knot-tying in
201 type and class declarations, when we have to
202 separate kind-checking, desugaring, and validity checking
205 kcHsSigType, kcHsLiftedSigType :: LHsType Name -> TcM (LHsType Name)
206 -- Used for type signatures
207 kcHsSigType ty = addKcTypeCtxt ty $ kcTypeType ty
208 kcHsLiftedSigType ty = addKcTypeCtxt ty $ kcLiftedType ty
210 tcHsKindedType :: LHsType Name -> TcM Type
211 -- Don't do kind checking, nor validity checking.
212 -- This is used in type and class decls, where kinding is
213 -- done in advance, and validity checking is done later
214 -- [Validity checking done later because of knot-tying issues.]
215 tcHsKindedType hs_ty = dsHsType hs_ty
217 tcHsBangType :: LHsType Name -> TcM Type
218 -- Permit a bang, but discard it
219 tcHsBangType (L _ (HsBangTy _ ty)) = tcHsKindedType ty
220 tcHsBangType ty = tcHsKindedType ty
222 tcHsKindedContext :: LHsContext Name -> TcM ThetaType
223 -- Used when we are expecting a ClassContext (i.e. no implicit params)
224 -- Does not do validity checking, like tcHsKindedType
225 tcHsKindedContext hs_theta = addLocM (mapM dsHsLPred) hs_theta
229 %************************************************************************
231 The main kind checker: kcHsType
233 %************************************************************************
235 First a couple of simple wrappers for kcHsType
238 ---------------------------
239 kcLiftedType :: LHsType Name -> TcM (LHsType Name)
240 -- The type ty must be a *lifted* *type*
241 kcLiftedType ty = kc_check_lhs_type ty ekLifted
243 ---------------------------
244 kcTypeType :: LHsType Name -> TcM (LHsType Name)
245 -- The type ty must be a *type*, but it can be lifted or
246 -- unlifted or an unboxed tuple.
247 kcTypeType ty = kc_check_lhs_type ty ekOpen
249 ---------------------------
250 kcCheckLHsType :: LHsType Name -> ExpKind -> TcM (LHsType Name)
251 kcCheckLHsType ty kind = addKcTypeCtxt ty $ kc_check_lhs_type ty kind
254 kc_check_lhs_type :: LHsType Name -> ExpKind -> TcM (LHsType Name)
255 -- Check that the type has the specified kind
256 -- Be sure to use checkExpectedKind, rather than simply unifying
257 -- with OpenTypeKind, because it gives better error messages
258 kc_check_lhs_type (L span ty) exp_kind
260 do { ty' <- kc_check_hs_type ty exp_kind
261 ; return (L span ty') }
263 kc_check_lhs_types :: [(LHsType Name, ExpKind)] -> TcM [LHsType Name]
264 kc_check_lhs_types tys_w_kinds
265 = mapM kc_arg tys_w_kinds
267 kc_arg (arg, arg_kind) = kc_check_lhs_type arg arg_kind
270 ---------------------------
271 kc_check_hs_type :: HsType Name -> ExpKind -> TcM (HsType Name)
273 -- First some special cases for better error messages
274 -- when we know the expected kind
275 kc_check_hs_type (HsParTy ty) exp_kind
276 = do { ty' <- kc_check_lhs_type ty exp_kind; return (HsParTy ty') }
278 kc_check_hs_type ty@(HsAppTy ty1 ty2) exp_kind
279 = do { let (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
280 ; (fun_ty', fun_kind) <- kc_lhs_type fun_ty
281 ; arg_tys' <- kcCheckApps fun_ty fun_kind arg_tys ty exp_kind
282 ; return (mkHsAppTys fun_ty' arg_tys') }
284 kc_check_hs_type ty@(HsPredTy (HsClassP cls tys)) exp_kind
285 = do { cls_kind <- kcClass cls
286 ; tys' <- kcCheckApps cls cls_kind tys ty exp_kind
287 ; return (HsPredTy (HsClassP cls tys')) }
289 -- This is the general case: infer the kind and compare
290 kc_check_hs_type ty exp_kind
291 = do { (ty', act_kind) <- kc_hs_type ty
292 -- Add the context round the inner check only
293 -- because checkExpectedKind already mentions
294 -- 'ty' by name in any error message
296 ; checkExpectedKind (strip ty) act_kind exp_kind
299 -- We infer the kind of the type, and then complain if it's
300 -- not right. But we don't want to complain about
301 -- (ty) or !(ty) or forall a. ty
302 -- when the real difficulty is with the 'ty' part.
303 strip (HsParTy (L _ ty)) = strip ty
304 strip (HsBangTy _ (L _ ty)) = strip ty
305 strip (HsForAllTy _ _ _ (L _ ty)) = strip ty
310 Here comes the main function
313 kcLHsType :: LHsType Name -> TcM (LHsType Name, TcKind)
314 -- Called from outside: set the context
315 kcLHsType ty = addKcTypeCtxt ty (kc_lhs_type ty)
317 kc_lhs_type :: LHsType Name -> TcM (LHsType Name, TcKind)
318 kc_lhs_type (L span ty)
320 do { (ty', kind) <- kc_hs_type ty
321 ; return (L span ty', kind) }
323 -- kc_hs_type *returns* the kind of the type, rather than taking an expected
324 -- kind as argument as tcExpr does.
326 -- (a) the kind of (->) is
327 -- forall bx1 bx2. Type bx1 -> Type bx2 -> Type Boxed
328 -- so we'd need to generate huge numbers of bx variables.
329 -- (b) kinds are so simple that the error messages are fine
331 -- The translated type has explicitly-kinded type-variable binders
333 kc_hs_type :: HsType Name -> TcM (HsType Name, TcKind)
334 kc_hs_type (HsParTy ty) = do
335 (ty', kind) <- kc_lhs_type ty
336 return (HsParTy ty', kind)
338 kc_hs_type (HsTyVar name) = do
340 return (HsTyVar name, kind)
342 kc_hs_type (HsListTy ty) = do
343 ty' <- kcLiftedType ty
344 return (HsListTy ty', liftedTypeKind)
346 kc_hs_type (HsPArrTy ty) = do
347 ty' <- kcLiftedType ty
348 return (HsPArrTy ty', liftedTypeKind)
350 kc_hs_type (HsNumTy n)
351 = return (HsNumTy n, liftedTypeKind)
353 kc_hs_type (HsKindSig ty k) = do
354 ty' <- kc_check_lhs_type ty (EK k EkKindSig)
355 return (HsKindSig ty' k, k)
357 kc_hs_type (HsTupleTy Boxed tys) = do
358 tys' <- mapM kcLiftedType tys
359 return (HsTupleTy Boxed tys', liftedTypeKind)
361 kc_hs_type (HsTupleTy Unboxed tys) = do
362 tys' <- mapM kcTypeType tys
363 return (HsTupleTy Unboxed tys', ubxTupleKind)
365 kc_hs_type (HsFunTy ty1 ty2) = do
366 ty1' <- kc_check_lhs_type ty1 (EK argTypeKind EkUnk)
367 ty2' <- kcTypeType ty2
368 return (HsFunTy ty1' ty2', liftedTypeKind)
370 kc_hs_type (HsOpTy ty1 op ty2) = do
371 op_kind <- addLocM kcTyVar op
372 ([ty1',ty2'], res_kind) <- kcApps op op_kind [ty1,ty2]
373 return (HsOpTy ty1' op ty2', res_kind)
375 kc_hs_type (HsAppTy ty1 ty2) = do
376 (fun_ty', fun_kind) <- kc_lhs_type fun_ty
377 (arg_tys', res_kind) <- kcApps fun_ty fun_kind arg_tys
378 return (mkHsAppTys fun_ty' arg_tys', res_kind)
380 (fun_ty, arg_tys) = splitHsAppTys ty1 ty2
382 kc_hs_type (HsPredTy (HsEqualP _ _))
385 kc_hs_type (HsPredTy pred) = do
386 pred' <- kcHsPred pred
387 return (HsPredTy pred', liftedTypeKind)
389 kc_hs_type (HsForAllTy exp tv_names context ty)
390 = kcHsTyVars tv_names $ \ tv_names' ->
391 do { ctxt' <- kcHsContext context
392 ; ty' <- kcLiftedType ty
393 -- The body of a forall is usually a type, but in principle
394 -- there's no reason to prohibit *unlifted* types.
395 -- In fact, GHC can itself construct a function with an
396 -- unboxed tuple inside a for-all (via CPR analyis; see
397 -- typecheck/should_compile/tc170)
399 -- Still, that's only for internal interfaces, which aren't
400 -- kind-checked, so we only allow liftedTypeKind here
402 ; return (HsForAllTy exp tv_names' ctxt' ty', liftedTypeKind) }
404 kc_hs_type (HsBangTy b ty)
405 = do { (ty', kind) <- kc_lhs_type ty
406 ; return (HsBangTy b ty', kind) }
408 kc_hs_type ty@(HsRecTy _)
409 = failWithTc (ptext (sLit "Unexpected record type") <+> ppr ty)
410 -- Record types (which only show up temporarily in constructor signatures)
411 -- should have been removed by now
413 #ifdef GHCI /* Only if bootstrapped */
414 kc_hs_type (HsSpliceTy sp) = kcSpliceType sp
416 kc_hs_type ty@(HsSpliceTy _) = failWithTc (ptext (sLit "Unexpected type splice:") <+> ppr ty)
419 -- remove the doc nodes here, no need to worry about the location since
420 -- its the same for a doc node and it's child type node
421 kc_hs_type (HsDocTy ty _)
422 = kc_hs_type (unLoc ty)
424 ---------------------------
425 kcApps :: Outputable a
427 -> TcKind -- Function kind
428 -> [LHsType Name] -- Arg types
429 -> TcM ([LHsType Name], TcKind) -- Kind-checked args
430 kcApps the_fun fun_kind args
431 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
432 ; args' <- kc_check_lhs_types args_w_kinds
433 ; return (args', res_kind) }
435 kcCheckApps :: Outputable a => a -> TcKind -> [LHsType Name]
436 -> HsType Name -- The type being checked (for err messages only)
437 -> ExpKind -- Expected kind
438 -> TcM [LHsType Name]
439 kcCheckApps the_fun fun_kind args ty exp_kind
440 = do { (args_w_kinds, res_kind) <- splitFunKind (ppr the_fun) 1 fun_kind args
441 ; checkExpectedKind ty res_kind exp_kind
442 -- Check the result kind *before* checking argument kinds
443 -- This improves error message; Trac #2994
444 ; kc_check_lhs_types args_w_kinds }
446 splitHsAppTys :: LHsType Name -> LHsType Name -> (LHsType Name, [LHsType Name])
447 splitHsAppTys fun_ty arg_ty = split fun_ty [arg_ty]
449 split (L _ (HsAppTy f a)) as = split f (a:as)
452 mkHsAppTys :: LHsType Name -> [LHsType Name] -> HsType Name
453 mkHsAppTys fun_ty [] = pprPanic "mkHsAppTys" (ppr fun_ty)
454 mkHsAppTys fun_ty (arg_ty:arg_tys)
455 = foldl mk_app (HsAppTy fun_ty arg_ty) arg_tys
457 mk_app fun arg = HsAppTy (noLoc fun) arg -- Add noLocs for inner nodes of
458 -- the application; they are
461 ---------------------------
462 splitFunKind :: SDoc -> Int -> TcKind -> [b] -> TcM ([(b,ExpKind)], TcKind)
463 splitFunKind _ _ fk [] = return ([], fk)
464 splitFunKind the_fun arg_no fk (arg:args)
465 = do { mb_fk <- unifyFunKind fk
467 Nothing -> failWithTc too_many_args
468 Just (ak,fk') -> do { (aks, rk) <- splitFunKind the_fun (arg_no+1) fk' args
469 ; return ((arg, EK ak (EkArg the_fun arg_no)):aks, rk) } }
471 too_many_args = quotes the_fun <+>
472 ptext (sLit "is applied to too many type arguments")
474 ---------------------------
475 kcHsContext :: LHsContext Name -> TcM (LHsContext Name)
476 kcHsContext ctxt = wrapLocM (mapM kcHsLPred) ctxt
478 kcHsLPred :: LHsPred Name -> TcM (LHsPred Name)
479 kcHsLPred = wrapLocM kcHsPred
481 kcHsPred :: HsPred Name -> TcM (HsPred Name)
482 kcHsPred pred = do -- Checks that the result is of kind liftedType
483 (pred', kind) <- kc_pred pred
484 checkExpectedKind pred kind ekLifted
487 ---------------------------
488 kc_pred :: HsPred Name -> TcM (HsPred Name, TcKind)
489 -- Does *not* check for a saturated
490 -- application (reason: used from TcDeriv)
491 kc_pred (HsIParam name ty)
492 = do { (ty', kind) <- kc_lhs_type ty
493 ; return (HsIParam name ty', kind)
495 kc_pred (HsClassP cls tys)
496 = do { kind <- kcClass cls
497 ; (tys', res_kind) <- kcApps cls kind tys
498 ; return (HsClassP cls tys', res_kind)
500 kc_pred (HsEqualP ty1 ty2)
501 = do { (ty1', kind1) <- kc_lhs_type ty1
502 -- ; checkExpectedKind ty1 kind1 liftedTypeKind
503 ; (ty2', kind2) <- kc_lhs_type ty2
504 -- ; checkExpectedKind ty2 kind2 liftedTypeKind
505 ; checkExpectedKind ty2 kind2 (EK kind1 EkEqPred)
506 ; return (HsEqualP ty1' ty2', liftedTypeKind)
509 ---------------------------
510 kcTyVar :: Name -> TcM TcKind
511 kcTyVar name = do -- Could be a tyvar or a tycon
512 traceTc (text "lk1" <+> ppr name)
513 thing <- tcLookup name
514 traceTc (text "lk2" <+> ppr name <+> ppr thing)
516 ATyVar _ ty -> return (typeKind ty)
517 AThing kind -> return kind
518 AGlobal (ATyCon tc) -> return (tyConKind tc)
519 _ -> wrongThingErr "type" thing name
521 kcClass :: Name -> TcM TcKind
522 kcClass cls = do -- Must be a class
523 thing <- tcLookup cls
525 AThing kind -> return kind
526 AGlobal (AClass cls) -> return (tyConKind (classTyCon cls))
527 _ -> wrongThingErr "class" thing cls
531 %************************************************************************
535 %************************************************************************
539 * Transforms from HsType to Type
542 It cannot fail, and does no validity checking, except for
543 structural matters, such as
544 (a) spurious ! annotations.
545 (b) a class used as a type
548 dsHsType :: LHsType Name -> TcM Type
549 -- All HsTyVarBndrs in the intput type are kind-annotated
550 dsHsType ty = ds_type (unLoc ty)
552 ds_type :: HsType Name -> TcM Type
553 ds_type ty@(HsTyVar _)
556 ds_type (HsParTy ty) -- Remove the parentheses markers
559 ds_type ty@(HsBangTy {}) -- No bangs should be here
560 = failWithTc (ptext (sLit "Unexpected strictness annotation:") <+> ppr ty)
562 ds_type ty@(HsRecTy {}) -- No bangs should be here
563 = failWithTc (ptext (sLit "Unexpected record type:") <+> ppr ty)
565 ds_type (HsKindSig ty _)
566 = dsHsType ty -- Kind checking done already
568 ds_type (HsListTy ty) = do
569 tau_ty <- dsHsType ty
570 checkWiredInTyCon listTyCon
571 return (mkListTy tau_ty)
573 ds_type (HsPArrTy ty) = do
574 tau_ty <- dsHsType ty
575 checkWiredInTyCon parrTyCon
576 return (mkPArrTy tau_ty)
578 ds_type (HsTupleTy boxity tys) = do
579 tau_tys <- dsHsTypes tys
580 checkWiredInTyCon tycon
581 return (mkTyConApp tycon tau_tys)
583 tycon = tupleTyCon boxity (length tys)
585 ds_type (HsFunTy ty1 ty2) = do
586 tau_ty1 <- dsHsType ty1
587 tau_ty2 <- dsHsType ty2
588 return (mkFunTy tau_ty1 tau_ty2)
590 ds_type (HsOpTy ty1 (L span op) ty2) = do
591 tau_ty1 <- dsHsType ty1
592 tau_ty2 <- dsHsType ty2
593 setSrcSpan span (ds_var_app op [tau_ty1,tau_ty2])
597 tc <- tcLookupTyCon genUnitTyConName
598 return (mkTyConApp tc [])
600 ds_type ty@(HsAppTy _ _)
603 ds_type (HsPredTy pred) = do
604 pred' <- dsHsPred pred
605 return (mkPredTy pred')
607 ds_type (HsForAllTy _ tv_names ctxt ty)
608 = tcTyVarBndrs tv_names $ \ tyvars -> do
609 theta <- mapM dsHsLPred (unLoc ctxt)
611 return (mkSigmaTy tyvars theta tau)
613 ds_type (HsSpliceTy {}) = panic "ds_type: HsSpliceTy"
615 ds_type (HsDocTy ty _) -- Remove the doc comment
618 dsHsTypes :: [LHsType Name] -> TcM [Type]
619 dsHsTypes arg_tys = mapM dsHsType arg_tys
622 Help functions for type applications
623 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
626 ds_app :: HsType Name -> [LHsType Name] -> TcM Type
627 ds_app (HsAppTy ty1 ty2) tys
628 = ds_app (unLoc ty1) (ty2:tys)
631 arg_tys <- dsHsTypes tys
633 HsTyVar fun -> ds_var_app fun arg_tys
634 _ -> do fun_ty <- ds_type ty
635 return (mkAppTys fun_ty arg_tys)
637 ds_var_app :: Name -> [Type] -> TcM Type
638 ds_var_app name arg_tys = do
639 thing <- tcLookup name
641 ATyVar _ ty -> return (mkAppTys ty arg_tys)
642 AGlobal (ATyCon tc) -> return (mkTyConApp tc arg_tys)
643 _ -> wrongThingErr "type" thing name
651 dsHsLPred :: LHsPred Name -> TcM PredType
652 dsHsLPred pred = dsHsPred (unLoc pred)
654 dsHsPred :: HsPred Name -> TcM PredType
655 dsHsPred (HsClassP class_name tys)
656 = do { arg_tys <- dsHsTypes tys
657 ; clas <- tcLookupClass class_name
658 ; return (ClassP clas arg_tys)
660 dsHsPred (HsEqualP ty1 ty2)
661 = do { arg_ty1 <- dsHsType ty1
662 ; arg_ty2 <- dsHsType ty2
663 ; return (EqPred arg_ty1 arg_ty2)
665 dsHsPred (HsIParam name ty)
666 = do { arg_ty <- dsHsType ty
667 ; return (IParam name arg_ty)
671 GADT constructor signatures
674 tcLHsConResTy :: LHsType Name -> TcM (TyCon, [TcType])
675 tcLHsConResTy (L span res_ty)
677 case get_args res_ty [] of
678 (HsTyVar tc_name, args)
679 -> do { args' <- mapM dsHsType args
680 ; thing <- tcLookup tc_name
682 AGlobal (ATyCon tc) -> return (tc, args')
683 _ -> failWithTc (badGadtDecl res_ty) }
684 _ -> failWithTc (badGadtDecl res_ty)
686 -- We can't call dsHsType on res_ty, and then do tcSplitTyConApp_maybe
687 -- because that causes a black hole, and for good reason. Building
688 -- the type means expanding type synonyms, and we can't do that
689 -- inside the "knot". So we have to work by steam.
690 get_args (HsAppTy (L _ fun) arg) args = get_args fun (arg:args)
691 get_args (HsParTy (L _ ty)) args = get_args ty args
692 get_args (HsOpTy ty1 (L _ tc) ty2) args = (HsTyVar tc, ty1:ty2:args)
693 get_args ty args = (ty, args)
695 badGadtDecl :: HsType Name -> SDoc
697 = hang (ptext (sLit "Malformed constructor result type:"))
700 addKcTypeCtxt :: LHsType Name -> TcM a -> TcM a
701 -- Wrap a context around only if we want to show that contexts.
702 addKcTypeCtxt (L _ (HsPredTy _)) thing = thing
703 -- Omit invisble ones and ones user's won't grok (HsPred p).
704 addKcTypeCtxt (L _ other_ty) thing = addErrCtxt (typeCtxt other_ty) thing
706 typeCtxt :: HsType Name -> SDoc
707 typeCtxt ty = ptext (sLit "In the type") <+> quotes (ppr ty)
710 %************************************************************************
712 Type-variable binders
714 %************************************************************************
718 kcHsTyVars :: [LHsTyVarBndr Name]
719 -> ([LHsTyVarBndr Name] -> TcM r) -- These binders are kind-annotated
720 -- They scope over the thing inside
722 kcHsTyVars tvs thing_inside = do
723 bndrs <- mapM (wrapLocM kcHsTyVar) tvs
724 tcExtendKindEnvTvs bndrs (thing_inside bndrs)
726 kcHsTyVar :: HsTyVarBndr Name -> TcM (HsTyVarBndr Name)
727 -- Return a *kind-annotated* binder, and a tyvar with a mutable kind in it
728 kcHsTyVar (UserTyVar name) = KindedTyVar name <$> newKindVar
729 kcHsTyVar (KindedTyVar name kind) = return (KindedTyVar name kind)
732 tcTyVarBndrs :: [LHsTyVarBndr Name] -- Kind-annotated binders, which need kind-zonking
733 -> ([TyVar] -> TcM r)
735 -- Used when type-checking types/classes/type-decls
736 -- Brings into scope immutable TyVars, not mutable ones that require later zonking
737 tcTyVarBndrs bndrs thing_inside = do
738 tyvars <- mapM (zonk . unLoc) bndrs
739 tcExtendTyVarEnv tyvars (thing_inside tyvars)
741 zonk (KindedTyVar name kind) = do { kind' <- zonkTcKindToKind kind
742 ; return (mkTyVar name kind') }
743 zonk (UserTyVar name) = WARN( True, ptext (sLit "Un-kinded tyvar") <+> ppr name )
744 return (mkTyVar name liftedTypeKind)
746 -----------------------------------
747 tcDataKindSig :: Maybe Kind -> TcM [TyVar]
748 -- GADT decls can have a (perhaps partial) kind signature
749 -- e.g. data T :: * -> * -> * where ...
750 -- This function makes up suitable (kinded) type variables for
751 -- the argument kinds, and checks that the result kind is indeed *.
752 -- We use it also to make up argument type variables for for data instances.
753 tcDataKindSig Nothing = return []
754 tcDataKindSig (Just kind)
755 = do { checkTc (isLiftedTypeKind res_kind) (badKindSig kind)
756 ; span <- getSrcSpanM
757 ; us <- newUniqueSupply
758 ; let uniqs = uniqsFromSupply us
759 ; return [ mk_tv span uniq str kind
760 | ((kind, str), uniq) <- arg_kinds `zip` dnames `zip` uniqs ] }
762 (arg_kinds, res_kind) = splitKindFunTys kind
763 mk_tv loc uniq str kind = mkTyVar name kind
765 name = mkInternalName uniq occ loc
766 occ = mkOccName tvName str
768 dnames = map ('$' :) names -- Note [Avoid name clashes for associated data types]
771 names = [ c:cs | cs <- "" : names, c <- ['a'..'z'] ]
773 badKindSig :: Kind -> SDoc
775 = hang (ptext (sLit "Kind signature on data type declaration has non-* return kind"))
779 Note [Avoid name clashes for associated data types]
780 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
781 Consider class C a b where
783 When typechecking the decl for D, we'll invent an extra type variable for D,
784 to fill out its kind. We *don't* want this type variable to be 'a', because
785 in an .hi file we'd get
788 which makes it look as if there are *two* type indices. But there aren't!
789 So we use $a instead, which cannot clash with a user-written type variable.
790 Remember that type variable binders in interface files are just FastStrings,
793 (The tidying phase can't help here because we don't tidy TyCons. Another
794 alternative would be to record the number of indexing parameters in the
798 %************************************************************************
800 Scoped type variables
802 %************************************************************************
805 tcAddScopedTyVars is used for scoped type variables added by pattern
807 e.g. \ ((x::a), (y::a)) -> x+y
808 They never have explicit kinds (because this is source-code only)
809 They are mutable (because they can get bound to a more specific type).
811 Usually we kind-infer and expand type splices, and then
812 tupecheck/desugar the type. That doesn't work well for scoped type
813 variables, because they scope left-right in patterns. (e.g. in the
814 example above, the 'a' in (y::a) is bound by the 'a' in (x::a).
816 The current not-very-good plan is to
817 * find all the types in the patterns
818 * find their free tyvars
820 * bring the kinded type vars into scope
821 * BUT throw away the kind-checked type
822 (we'll kind-check it again when we type-check the pattern)
824 This is bad because throwing away the kind checked type throws away
825 its splices. But too bad for now. [July 03]
828 We no longer specify that these type variables must be univerally
829 quantified (lots of email on the subject). If you want to put that
831 a) Do a checkSigTyVars after thing_inside
832 b) More insidiously, don't pass in expected_ty, else
833 we unify with it too early and checkSigTyVars barfs
834 Instead you have to pass in a fresh ty var, and unify
835 it with expected_ty afterwards
838 tcHsPatSigType :: UserTypeCtxt
839 -> LHsType Name -- The type signature
840 -> TcM ([TyVar], -- Newly in-scope type variables
841 Type) -- The signature
842 -- Used for type-checking type signatures in
843 -- (a) patterns e.g f (x::Int) = e
844 -- (b) result signatures e.g. g x :: Int = e
845 -- (c) RULE forall bndrs e.g. forall (x::Int). f x = x
847 tcHsPatSigType ctxt hs_ty
848 = addErrCtxt (pprHsSigCtxt ctxt hs_ty) $
849 do { -- Find the type variables that are mentioned in the type
850 -- but not already in scope. These are the ones that
851 -- should be bound by the pattern signature
852 in_scope <- getInLocalScope
853 ; let span = getLoc hs_ty
854 sig_tvs = [ L span (UserTyVar n)
855 | n <- nameSetToList (extractHsTyVars hs_ty),
858 ; (tyvars, sig_ty) <- tcHsQuantifiedType sig_tvs hs_ty
859 ; checkValidType ctxt sig_ty
860 ; return (tyvars, sig_ty)
863 tcPatSig :: UserTypeCtxt
866 -> TcM (TcType, -- The type to use for "inside" the signature
867 [(Name, TcType)], -- The new bit of type environment, binding
868 -- the scoped type variables
869 CoercionI) -- Coercion due to unification with actual ty
870 tcPatSig ctxt sig res_ty
871 = do { (sig_tvs, sig_ty) <- tcHsPatSigType ctxt sig
873 ; if null sig_tvs then do {
874 -- The type signature binds no type variables,
875 -- and hence is rigid, so use it to zap the res_ty
876 coi <- boxyUnify sig_ty res_ty
877 ; return (sig_ty, [], coi)
880 -- Type signature binds at least one scoped type variable
882 -- A pattern binding cannot bind scoped type variables
883 -- The renamer fails with a name-out-of-scope error
884 -- if a pattern binding tries to bind a type variable,
885 -- So we just have an ASSERT here
886 ; let in_pat_bind = case ctxt of
887 BindPatSigCtxt -> True
889 ; ASSERT( not in_pat_bind || null sig_tvs ) return ()
891 -- Check that pat_ty is rigid
892 ; checkTc (isRigidTy res_ty) (wobblyPatSig sig_tvs)
894 -- Now match the pattern signature against res_ty
895 -- For convenience, and uniform-looking error messages
896 -- we do the matching by allocating meta type variables,
897 -- unifying, and reading out the results.
898 -- This is a strictly local operation.
899 ; box_tvs <- mapM tcInstBoxyTyVar sig_tvs
900 ; coi <- boxyUnify (substTyWith sig_tvs (mkTyVarTys box_tvs) sig_ty)
902 ; sig_tv_tys <- mapM readFilledBox box_tvs
904 -- Check that each is bound to a distinct type variable,
905 -- and one that is not already in scope
906 ; let tv_binds = map tyVarName sig_tvs `zip` sig_tv_tys
907 ; binds_in_scope <- getScopedTyVarBinds
908 ; check binds_in_scope tv_binds
911 ; return (res_ty, tv_binds, coi)
914 check _ [] = return ()
915 check in_scope ((n,ty):rest) = do { check_one in_scope n ty
916 ; check ((n,ty):in_scope) rest }
918 check_one in_scope n ty
919 = do { checkTc (tcIsTyVarTy ty) (scopedNonVar n ty)
920 -- Must bind to a type variable
922 ; checkTc (null dups) (dupInScope n (head dups) ty)
923 -- Must not bind to the same type variable
924 -- as some other in-scope type variable
928 dups = [n' | (n',ty') <- in_scope, tcEqType ty' ty]
932 %************************************************************************
936 %************************************************************************
938 We would like to get a decent error message from
939 (a) Under-applied type constructors
941 (b) Over-applied type constructors
945 -- The ExpKind datatype means "expected kind" and contains
946 -- some info about just why that kind is expected, to improve
947 -- the error message on a mis-match
948 data ExpKind = EK TcKind EkCtxt
949 data EkCtxt = EkUnk -- Unknown context
950 | EkEqPred -- Second argument of an equality predicate
951 | EkKindSig -- Kind signature
952 | EkArg SDoc Int -- Function, arg posn, expected kind
955 ekLifted, ekOpen :: ExpKind
956 ekLifted = EK liftedTypeKind EkUnk
957 ekOpen = EK openTypeKind EkUnk
959 checkExpectedKind :: Outputable a => a -> TcKind -> ExpKind -> TcM ()
960 -- A fancy wrapper for 'unifyKind', which tries
961 -- to give decent error messages.
962 -- (checkExpectedKind ty act_kind exp_kind)
963 -- checks that the actual kind act_kind is compatible
964 -- with the expected kind exp_kind
965 -- The first argument, ty, is used only in the error message generation
966 checkExpectedKind ty act_kind (EK exp_kind ek_ctxt)
967 | act_kind `isSubKind` exp_kind -- Short cut for a very common case
970 (_errs, mb_r) <- tryTc (unifyKind exp_kind act_kind)
972 Just _ -> return () -- Unification succeeded
975 -- So there's definitely an error
976 -- Now to find out what sort
977 exp_kind <- zonkTcKind exp_kind
978 act_kind <- zonkTcKind act_kind
980 env0 <- tcInitTidyEnv
981 let (exp_as, _) = splitKindFunTys exp_kind
982 (act_as, _) = splitKindFunTys act_kind
983 n_exp_as = length exp_as
984 n_act_as = length act_as
986 (env1, tidy_exp_kind) = tidyKind env0 exp_kind
987 (env2, tidy_act_kind) = tidyKind env1 act_kind
989 err | n_exp_as < n_act_as -- E.g. [Maybe]
990 = quotes (ppr ty) <+> ptext (sLit "is not applied to enough type arguments")
992 -- Now n_exp_as >= n_act_as. In the next two cases,
993 -- n_exp_as == 0, and hence so is n_act_as
994 | isLiftedTypeKind exp_kind && isUnliftedTypeKind act_kind
995 = ptext (sLit "Expecting a lifted type, but") <+> quotes (ppr ty)
996 <+> ptext (sLit "is unlifted")
998 | isUnliftedTypeKind exp_kind && isLiftedTypeKind act_kind
999 = ptext (sLit "Expecting an unlifted type, but") <+> quotes (ppr ty)
1000 <+> ptext (sLit "is lifted")
1002 | otherwise -- E.g. Monad [Int]
1003 = ptext (sLit "Kind mis-match")
1005 more_info = sep [ expected_herald ek_ctxt <+> ptext (sLit "kind")
1006 <+> quotes (pprKind tidy_exp_kind) <> comma,
1007 ptext (sLit "but") <+> quotes (ppr ty) <+>
1008 ptext (sLit "has kind") <+> quotes (pprKind tidy_act_kind)]
1010 expected_herald EkUnk = ptext (sLit "Expected")
1011 expected_herald EkKindSig = ptext (sLit "An enclosing kind signature specified")
1012 expected_herald EkEqPred = ptext (sLit "The left argument of the equality predicate had")
1013 expected_herald (EkArg fun arg_no)
1014 = ptext (sLit "The") <+> speakNth arg_no <+> ptext (sLit "argument of")
1015 <+> quotes fun <+> ptext (sLit ("should have"))
1017 failWithTcM (env2, err $$ more_info)
1020 %************************************************************************
1022 Scoped type variables
1024 %************************************************************************
1027 pprHsSigCtxt :: UserTypeCtxt -> LHsType Name -> SDoc
1028 pprHsSigCtxt ctxt hs_ty = vcat [ ptext (sLit "In") <+> pprUserTypeCtxt ctxt <> colon,
1029 nest 2 (pp_sig ctxt) ]
1031 pp_sig (FunSigCtxt n) = pp_n_colon n
1032 pp_sig (ConArgCtxt n) = pp_n_colon n
1033 pp_sig (ForSigCtxt n) = pp_n_colon n
1034 pp_sig _ = ppr (unLoc hs_ty)
1036 pp_n_colon n = ppr n <+> dcolon <+> ppr (unLoc hs_ty)
1038 wobblyPatSig :: [Var] -> SDoc
1039 wobblyPatSig sig_tvs
1040 = hang (ptext (sLit "A pattern type signature cannot bind scoped type variables")
1041 <+> pprQuotedList sig_tvs)
1042 2 (ptext (sLit "unless the pattern has a rigid type context"))
1044 scopedNonVar :: Name -> Type -> SDoc
1046 = vcat [sep [ptext (sLit "The scoped type variable") <+> quotes (ppr n),
1047 nest 2 (ptext (sLit "is bound to the type") <+> quotes (ppr ty))],
1048 nest 2 (ptext (sLit "You can only bind scoped type variables to type variables"))]
1050 dupInScope :: Name -> Name -> Type -> SDoc
1052 = hang (ptext (sLit "The scoped type variables") <+> quotes (ppr n) <+> ptext (sLit "and") <+> quotes (ppr n'))
1053 2 (vcat [ptext (sLit "are bound to the same type (variable)"),
1054 ptext (sLit "Distinct scoped type variables must be distinct")])
1056 wrongEqualityErr :: TcM (HsType Name, TcKind)
1058 = failWithTc (text "Equality predicate used as a type")