2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcMonoType]{Typechecking user-specified @MonoTypes@}
7 module TcMonoType ( tcHsType, tcHsTypeKind, tcHsTopType, tcHsTopBoxedType,
8 tcContext, tcHsTyVar, kcHsTyVar,
9 tcExtendTyVarScope, tcExtendTopTyVarScope,
10 TcSigInfo(..), tcTySig, mkTcSig, noSigs, maybeSig,
11 checkSigTyVars, sigCtxt, sigPatCtxt
14 #include "HsVersions.h"
16 import HsSyn ( HsType(..), HsTyVar(..), Sig(..), pprClassAssertion, pprParendHsType )
17 import RnHsSyn ( RenamedHsType, RenamedContext, RenamedSig )
18 import TcHsSyn ( TcId )
21 import TcEnv ( tcExtendTyVarEnv, tcLookupTy, tcGetValueEnv, tcGetInScopeTyVars,
22 tcGetGlobalTyVars, TcTyThing(..)
24 import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType,
25 typeToTcType, tcInstTcType, kindToTcKind,
27 zonkTcKindToKind, zonkTcTypeToType, zonkTcTyVars, zonkTcType
29 import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr )
30 import TcUnify ( unifyKind, unifyKinds, unifyTypeKind )
31 import Type ( Type, ThetaType,
32 mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy, zipFunTys,
33 mkSigmaTy, mkDictTy, mkTyConApp, mkAppTys, splitRhoTy,
34 boxedTypeKind, unboxedTypeKind, tyVarsOfType,
35 mkArrowKinds, getTyVar_maybe, getTyVar,
36 tidyOpenType, tidyOpenTypes, tidyTyVar
38 import Id ( mkUserId, idName, idType, idFreeTyVars )
39 import Var ( TyVar, mkTyVar )
42 import Bag ( bagToList )
43 import ErrUtils ( Message )
44 import PrelInfo ( cCallishClassKeys )
45 import TyCon ( TyCon )
46 import Name ( Name, OccName, isLocallyDefined )
47 import TysWiredIn ( mkListTy, mkTupleTy, mkUnboxedTupleTy )
48 import SrcLoc ( SrcLoc )
49 import Unique ( Unique, Uniquable(..) )
50 import UniqFM ( eltsUFM )
51 import Util ( zipWithEqual, zipLazy, mapAccumL )
56 %************************************************************************
58 \subsection{Checking types}
60 %************************************************************************
62 tcHsType and tcHsTypeKind
63 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
65 tcHsType checks that the type really is of kind Type!
68 tcHsType :: RenamedHsType -> TcM s TcType
70 = -- tcAddErrCtxt (typeCtxt ty) $
73 tcHsTypeKind :: RenamedHsType -> TcM s (TcKind, TcType)
75 = -- tcAddErrCtxt (typeCtxt ty) $
78 -- Type-check a type, *and* then lazily zonk it. The important
79 -- point is that this zonks all the uncommitted *kind* variables
80 -- in kinds of any any nested for-all tyvars.
81 -- There won't be any mutable *type* variables at all.
83 -- NOTE the forkNF_Tc. This makes the zonking lazy, which is
84 -- absolutely necessary. During the type-checking of a recursive
85 -- group of tycons/classes (TcTyClsDecls.tcGroup) we use an
86 -- environment in which we aren't allowed to look at the actual
87 -- tycons/classes returned from a lookup. Because tc_app does
88 -- look at the tycon to build the type, we can't look at the type
89 -- either, until we get out of the loop. The fork delays the
90 -- zonking till we've completed the loop. Sigh.
92 tcHsTopType :: RenamedHsType -> TcM s Type
94 = -- tcAddErrCtxt (typeCtxt ty) $
95 tc_type ty `thenTc` \ ty' ->
96 forkNF_Tc (zonkTcTypeToType ty')
98 tcHsTopBoxedType :: RenamedHsType -> TcM s Type
100 = -- tcAddErrCtxt (typeCtxt ty) $
101 tc_boxed_type ty `thenTc` \ ty' ->
102 forkNF_Tc (zonkTcTypeToType ty')
110 tc_boxed_type :: RenamedHsType -> TcM s Type
112 = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) ->
113 tcAddErrCtxt (typeKindCtxt ty)
114 (unifyKind boxedTypeKind actual_kind) `thenTc_`
117 tc_type :: RenamedHsType -> TcM s Type
119 -- The type ty must be a *type*, but it can be boxed
120 -- or unboxed. So we check that is is of form (Type bv)
121 -- using unifyTypeKind
122 = tc_type_kind ty `thenTc` \ (actual_kind, tc_ty) ->
123 tcAddErrCtxt (typeKindCtxt ty)
124 (unifyTypeKind actual_kind) `thenTc_`
127 tc_type_kind :: RenamedHsType -> TcM s (TcKind, Type)
128 tc_type_kind ty@(MonoTyVar name)
131 tc_type_kind (MonoListTy ty)
132 = tc_boxed_type ty `thenTc` \ tau_ty ->
133 returnTc (boxedTypeKind, mkListTy tau_ty)
135 tc_type_kind (MonoTupleTy tys True {-boxed-})
136 = mapTc tc_boxed_type tys `thenTc` \ tau_tys ->
137 returnTc (boxedTypeKind, mkTupleTy (length tys) tau_tys)
139 tc_type_kind (MonoTupleTy tys False {-unboxed-})
140 = mapTc tc_type tys `thenTc` \ tau_tys ->
141 returnTc (unboxedTypeKind, mkUnboxedTupleTy (length tys) tau_tys)
143 tc_type_kind (MonoFunTy ty1 ty2)
144 = tc_type ty1 `thenTc` \ tau_ty1 ->
145 tc_type ty2 `thenTc` \ tau_ty2 ->
146 returnTc (boxedTypeKind, mkFunTy tau_ty1 tau_ty2)
148 tc_type_kind (MonoTyApp ty1 ty2)
151 tc_type_kind (MonoDictTy class_name tys)
152 = tcClassAssertion (class_name, tys) `thenTc` \ (clas, arg_tys) ->
153 returnTc (boxedTypeKind, mkDictTy clas arg_tys)
155 tc_type_kind (HsForAllTy (Just tv_names) context ty)
156 = tcExtendTyVarScope tv_names $ \ tyvars ->
157 tcContext context `thenTc` \ theta ->
158 tc_boxed_type ty `thenTc` \ tau ->
159 -- Body of a for-all is a boxed type!
160 returnTc (boxedTypeKind, mkSigmaTy tyvars theta tau)
163 Help functions for type applications
164 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
167 tc_app (MonoTyApp ty1 ty2) tys
168 = tc_app ty1 (ty2:tys)
175 = tcAddErrCtxt (appKindCtxt pp_app) $
176 mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) ->
177 tc_fun_type ty arg_tys `thenTc` \ (fun_kind, result_ty) ->
179 -- Check argument compatibility
180 newKindVar `thenNF_Tc` \ result_kind ->
181 unifyKind fun_kind (mkArrowKinds arg_kinds result_kind)
183 returnTc (result_kind, result_ty)
185 pp_app = ppr ty <+> sep (map pprParendHsType tys)
187 -- (tc_fun_type ty arg_tys) returns (kind-of ty, mkAppTys ty arg_tys)
188 -- But not quite; for synonyms it checks the correct arity, and builds a SynTy
189 -- hence the rather strange functionality.
191 tc_fun_type (MonoTyVar name) arg_tys
192 = tcLookupTy name `thenTc` \ (tycon_kind, maybe_arity, thing) ->
194 ATyVar tv -> returnTc (tycon_kind, mkAppTys (mkTyVarTy tv) arg_tys)
195 AClass clas -> failWithTc (classAsTyConErr name)
196 ATyCon tc -> case maybe_arity of
197 Nothing -> -- Data or newtype
198 returnTc (tycon_kind, mkTyConApp tc arg_tys)
200 Just arity -> -- Type synonym
201 checkTc (arity <= n_args) err_msg `thenTc_`
202 returnTc (tycon_kind, result_ty)
204 -- It's OK to have an *over-applied* type synonym
205 -- data Tree a b = ...
206 -- type Foo a = Tree [a]
207 -- f :: Foo a b -> ...
208 result_ty = mkAppTys (mkSynTy tc (take arity arg_tys))
210 err_msg = arityErr "type synonym" name arity n_args
211 n_args = length arg_tys
213 tc_fun_type ty arg_tys
214 = tc_type_kind ty `thenTc` \ (fun_kind, fun_ty) ->
215 returnTc (fun_kind, mkAppTys fun_ty arg_tys)
223 tcContext :: RenamedContext -> TcM s ThetaType
225 = --Someone discovered that @CCallable@ and @CReturnable@
226 -- could be used in contexts such as:
227 -- foo :: CCallable a => a -> PrimIO Int
228 -- Doing this utterly wrecks the whole point of introducing these
229 -- classes so we specifically check that this isn't being done.
231 -- We *don't* do this check in tcClassAssertion, because that's
232 -- called when checking a HsDictTy, and we don't want to reject
233 -- instance CCallable Int
235 mapTc check_naughty context `thenTc_`
237 mapTc tcClassAssertion context
240 check_naughty (class_name, _)
241 = checkTc (not (getUnique class_name `elem` cCallishClassKeys))
242 (naughtyCCallContextErr class_name)
244 tcClassAssertion assn@(class_name, tys)
245 = tcAddErrCtxt (appKindCtxt (pprClassAssertion assn)) $
246 mapAndUnzipTc tc_type_kind tys `thenTc` \ (arg_kinds, arg_tys) ->
247 tcLookupTy class_name `thenTc` \ (kind, ~(Just arity), thing) ->
249 ATyVar _ -> failWithTc (tyVarAsClassErr class_name)
250 ATyCon _ -> failWithTc (tyConAsClassErr class_name)
252 -- Check with kind mis-match
253 checkTc (arity == n_tys) err `thenTc_`
254 unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind) `thenTc_`
255 returnTc (clas, arg_tys)
258 err = arityErr "Class" class_name arity n_tys
262 %************************************************************************
264 \subsection{Type variables, with knot tying!}
266 %************************************************************************
269 tcExtendTopTyVarScope :: TcKind -> [HsTyVar Name]
270 -> ([TcTyVar] -> TcKind -> TcM s a)
272 tcExtendTopTyVarScope kind tyvar_names thing_inside
274 (tyvars_w_kinds, result_kind) = zipFunTys tyvar_names kind
275 tyvars = map mk_tv tyvars_w_kinds
277 tcExtendTyVarEnv tyvars (thing_inside tyvars result_kind)
279 mk_tv (UserTyVar name, kind) = mkTyVar name kind
280 mk_tv (IfaceTyVar name _, kind) = mkTyVar name kind
281 -- NB: immutable tyvars, but perhaps with mutable kinds
283 tcExtendTyVarScope :: [HsTyVar Name]
284 -> ([TcTyVar] -> TcM s a) -> TcM s a
285 tcExtendTyVarScope tv_names thing_inside
286 = mapNF_Tc tcHsTyVar tv_names `thenNF_Tc` \ tyvars ->
287 tcExtendTyVarEnv tyvars $
290 tcHsTyVar :: HsTyVar Name -> NF_TcM s TcTyVar
291 tcHsTyVar (UserTyVar name) = newKindVar `thenNF_Tc` \ kind ->
292 tcNewMutTyVar name kind
293 -- NB: mutable kind => mutable tyvar, so that zonking can bind
294 -- the tyvar to its immutable form
296 tcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (mkTyVar name (kindToTcKind kind))
298 kcHsTyVar :: HsTyVar name -> NF_TcM s TcKind
299 kcHsTyVar (UserTyVar name) = newKindVar
300 kcHsTyVar (IfaceTyVar name kind) = returnNF_Tc (kindToTcKind kind)
304 %************************************************************************
306 \subsection{Signatures}
308 %************************************************************************
310 @tcSigs@ checks the signatures for validity, and returns a list of
311 {\em freshly-instantiated} signatures. That is, the types are already
312 split up, and have fresh type variables installed. All non-type-signature
313 "RenamedSigs" are ignored.
315 The @TcSigInfo@ contains @TcTypes@ because they are unified with
316 the variable's type, and after that checked to see whether they've
322 Name -- N, the Name in corresponding binding
324 TcId -- *Polymorphic* binder for this value...
331 TcId -- *Monomorphic* binder for this value
332 -- Does *not* have name = N
335 Inst -- Empty if theta is null, or
336 -- (method mono_id) otherwise
338 SrcLoc -- Of the signature
341 maybeSig :: [TcSigInfo] -> Name -> Maybe (TcSigInfo)
342 -- Search for a particular signature
343 maybeSig [] name = Nothing
344 maybeSig (sig@(TySigInfo sig_name _ _ _ _ _ _ _) : sigs) name
345 | name == sig_name = Just sig
346 | otherwise = maybeSig sigs name
348 -- This little helper is useful to pass to tcPat
349 noSigs :: Name -> Maybe TcId
350 noSigs name = Nothing
355 tcTySig :: RenamedSig -> TcM s TcSigInfo
357 tcTySig (Sig v ty src_loc)
358 = tcAddSrcLoc src_loc $
359 tcHsType ty `thenTc` \ sigma_tc_ty ->
360 mkTcSig (mkUserId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
363 mkTcSig :: TcId -> SrcLoc -> NF_TcM s TcSigInfo
364 mkTcSig poly_id src_loc
365 = -- Instantiate this type
366 -- It's important to do this even though in the error-free case
367 -- we could just split the sigma_tc_ty (since the tyvars don't
368 -- unified with anything). But in the case of an error, when
369 -- the tyvars *do* get unified with something, we want to carry on
370 -- typechecking the rest of the program with the function bound
371 -- to a pristine type, namely sigma_tc_ty
372 tcInstTcType (idType poly_id) `thenNF_Tc` \ (tyvars, rho) ->
374 (theta, tau) = splitRhoTy rho
375 -- This splitSigmaTy tries hard to make sure that tau' is a type synonym
376 -- wherever possible, which can improve interface files.
378 newMethodWithGivenTy SignatureOrigin
381 theta tau `thenNF_Tc` \ inst ->
382 -- We make a Method even if it's not overloaded; no harm
384 returnNF_Tc (TySigInfo name poly_id tyvars theta tau (instToIdBndr inst) inst src_loc)
386 name = idName poly_id
391 %************************************************************************
393 \subsection{Checking signature type variables}
395 %************************************************************************
397 @checkSigTyVars@ is used after the type in a type signature has been unified with
398 the actual type found. It then checks that the type variables of the type signature
400 (a) Still all type variables
401 eg matching signature [a] against inferred type [(p,q)]
402 [then a will be unified to a non-type variable]
404 (b) Still all distinct
405 eg matching signature [(a,b)] against inferred type [(p,p)]
406 [then a and b will be unified together]
408 (c) Not mentioned in the environment
409 eg the signature for f in this:
415 Here, f is forced to be monorphic by the free occurence of x.
417 (d) Not (unified with another type variable that is) in scope.
418 eg f x :: (r->r) = (\y->y) :: forall a. a->r
419 when checking the expression type signature, we find that
420 even though there is nothing in scope whose type mentions r,
421 nevertheless the type signature for the expression isn't right.
423 Another example is in a class or instance declaration:
425 op :: forall b. a -> b
427 Here, b gets unified with a
429 Before doing this, the substitution is applied to the signature type variable.
431 We used to have the notion of a "DontBind" type variable, which would
432 only be bound to itself or nothing. Then points (a) and (b) were
433 self-checking. But it gave rise to bogus consequential error messages.
436 f = (*) -- Monomorphic
441 Here, we get a complaint when checking the type signature for g,
442 that g isn't polymorphic enough; but then we get another one when
443 dealing with the (Num x) context arising from f's definition;
444 we try to unify x with Int (to default it), but find that x has already
445 been unified with the DontBind variable "a" from g's signature.
446 This is really a problem with side-effecting unification; we'd like to
447 undo g's effects when its type signature fails, but unification is done
448 by side effect, so we can't (easily).
450 So we revert to ordinary type variables for signatures, and try to
451 give a helpful message in checkSigTyVars.
454 checkSigTyVars :: [TcTyVar] -- The original signature type variables
455 -> TcM s [TcTyVar] -- Zonked signature type variables
457 checkSigTyVars [] = returnTc []
459 checkSigTyVars sig_tyvars
460 = zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys ->
461 tcGetGlobalTyVars `thenNF_Tc` \ globals ->
463 checkTcM (all_ok sig_tys globals)
464 (complain sig_tys globals) `thenTc_`
466 returnTc (map (getTyVar "checkSigTyVars") sig_tys)
470 all_ok (ty:tys) acc = case getTyVar_maybe ty of
471 Nothing -> False -- Point (a)
472 Just tv | tv `elemVarSet` acc -> False -- Point (b) or (c)
473 | otherwise -> all_ok tys (acc `extendVarSet` tv)
476 complain sig_tys globals
477 = -- For the in-scope ones, zonk them and construct a map
478 -- from the zonked tyvar to the in-scope one
479 -- If any of the in-scope tyvars zonk to a type, then ignore them;
480 -- that'll be caught later when we back up to their type sig
481 tcGetInScopeTyVars `thenNF_Tc` \ in_scope_tvs ->
482 zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys ->
484 in_scope_assoc = [ (zonked_tv, in_scope_tv)
485 | (z_ty, in_scope_tv) <- in_scope_tys `zip` in_scope_tvs,
486 Just zonked_tv <- [getTyVar_maybe z_ty]
488 in_scope_env = mkVarEnv in_scope_assoc
491 -- "check" checks each sig tyvar in turn
493 (env2, in_scope_env, [])
494 (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) ->
496 failWithTcM (env3, main_msg $$ nest 4 (vcat msgs))
498 (env1, tidy_tvs) = mapAccumL tidyTyVar emptyTidyEnv sig_tyvars
499 (env2, tidy_tys) = tidyOpenTypes env1 sig_tys
501 main_msg = ptext SLIT("Inferred type is less polymorphic than expected")
503 check (env, acc, msgs) (sig_tyvar,ty)
504 -- sig_tyvar is from the signature;
505 -- ty is what you get if you zonk sig_tyvar and then tidy it
507 -- acc maps a zonked type variable back to a signature type variable
508 = case getTyVar_maybe ty of {
509 Nothing -> -- Error (a)!
510 returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ;
514 case lookupVarEnv acc tv of {
515 Just sig_tyvar' -> -- Error (b) or (d)!
516 returnNF_Tc (env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ;
520 if tv `elemVarSet` globals -- Error (c)! Type variable escapes
521 -- The least comprehensible, so put it last
522 then tcGetValueEnv `thenNF_Tc` \ ve ->
523 find_globals tv env (eltsUFM ve) `thenNF_Tc` \ (env1, globs) ->
524 returnNF_Tc (env1, acc, escape_msg sig_tyvar tv globs : msgs)
527 returnNF_Tc (env, extendVarEnv acc tv sig_tyvar, msgs)
530 -- find_globals looks at the value environment and finds values
531 -- whose types mention the offending type variable. It has to be
532 -- careful to zonk the Id's type first, so it has to be in the monad.
533 -- We must be careful to pass it a zonked type variable, too.
534 find_globals tv tidy_env ids
536 = returnNF_Tc (tidy_env, [])
538 find_globals tv tidy_env (id:ids)
539 | not (isLocallyDefined id) ||
540 isEmptyVarSet (idFreeTyVars id)
541 = find_globals tv tidy_env ids
544 = zonkTcType (idType id) `thenNF_Tc` \ id_ty ->
545 if tv `elemVarSet` tyVarsOfType id_ty then
547 (tidy_env', id_ty') = tidyOpenType tidy_env id_ty
549 find_globals tv tidy_env' ids `thenNF_Tc` \ (tidy_env'', globs) ->
550 returnNF_Tc (tidy_env'', (idName id, id_ty') : globs)
552 find_globals tv tidy_env ids
554 escape_msg sig_tv tv globs
555 = vcat [mk_msg sig_tv <+> ptext SLIT("escapes"),
557 ptext SLIT("The following variables in the environment mention") <+> quotes (ppr tv),
558 nest 4 (vcat_first 10 [ppr name <+> dcolon <+> ppr ty | (name,ty) <- globs])
561 pp_escape | sig_tv /= tv = ptext SLIT("It unifies with") <+>
562 quotes (ppr tv) <> comma <+>
563 ptext SLIT("which is mentioned in the environment")
564 | otherwise = ptext SLIT("It is mentioned in the environment")
566 vcat_first :: Int -> [SDoc] -> SDoc
567 vcat_first n [] = empty
568 vcat_first 0 (x:xs) = text "...others omitted..."
569 vcat_first n (x:xs) = x $$ vcat_first (n-1) xs
571 unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing
572 mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
575 These two context are used with checkSigTyVars
578 sigCtxt :: (Type -> Message) -> Type
579 -> TidyEnv -> NF_TcM s (TidyEnv, Message)
580 sigCtxt mk_msg sig_ty tidy_env
582 (env1, tidy_sig_ty) = tidyOpenType tidy_env sig_ty
584 returnNF_Tc (env1, mk_msg tidy_sig_ty)
586 sigPatCtxt bound_tvs bound_ids tidy_env
588 sep [ptext SLIT("When checking a pattern that binds"),
589 nest 4 (vcat (zipWith ppr_id show_ids tidy_tys))])
591 show_ids = filter is_interesting bound_ids
592 is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs
594 (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids)
595 ppr_id id ty = ppr id <+> dcolon <+> ppr ty
596 -- Don't zonk the types so we get the separate, un-unified versions
600 %************************************************************************
602 \subsection{Errors and contexts}
604 %************************************************************************
607 naughtyCCallContextErr clas_name
608 = sep [ptext SLIT("Can't use class") <+> quotes (ppr clas_name),
609 ptext SLIT("in a context")]
611 typeCtxt ty = ptext SLIT("In the type") <+> quotes (ppr ty)
613 typeKindCtxt :: RenamedHsType -> Message
614 typeKindCtxt ty = sep [ptext SLIT("When checking that"),
615 nest 2 (quotes (ppr ty)),
616 ptext SLIT("is a type")]
618 appKindCtxt :: SDoc -> Message
619 appKindCtxt pp = ptext SLIT("When checking kinds in") <+> quotes pp
622 = ptext SLIT("Class used as a type constructor:") <+> ppr name
625 = ptext SLIT("Type constructor used as a class:") <+> ppr name
628 = ptext SLIT("Type variable used as a class:") <+> ppr name