2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( kcClassDecl, tcClassDecl1, tcClassDecls2, mkImplicitClassBinds,
8 tcMethodBind, checkFromThisClass
11 #include "HsVersions.h"
13 import HsSyn ( HsDecl(..), TyClDecl(..), Sig(..), MonoBinds(..),
14 InPat(..), HsBinds(..), GRHSs(..),
15 HsExpr(..), HsLit(..), HsType(..), HsPred(..),
17 andMonoBinds, andMonoBindList, getTyVarName,
18 isClassDecl, isClassOpSig, isPragSig, collectMonoBinders
20 import HsPragmas ( ClassPragmas(..) )
21 import BasicTypes ( NewOrData(..), TopLevelFlag(..), RecFlag(..) )
22 import RnHsSyn ( RenamedTyClDecl, RenamedClassPragmas,
23 RenamedClassOpSig, RenamedMonoBinds,
24 RenamedContext, RenamedHsDecl, RenamedSig
26 import TcHsSyn ( TcMonoBinds, idsToMonoBinds )
28 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs, newDicts, newMethod )
29 import TcEnv ( TcId, ValueEnv, TcTyThing(..), tcAddImportedIdInfo,
30 tcLookupTy, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcTyDecls ( mkNewTyConRep )
35 import TcUnify ( unifyKinds )
37 import TcMonoType ( kcHsType, tcHsTopType, tcExtendTopTyVarScope,
38 tcContext, checkSigTyVars, sigCtxt, mkTcSig
40 import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
41 import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcTyVarBndr, tcGetTyVar )
42 import TcInstUtil ( classDataCon )
43 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
44 import FieldLabel ( firstFieldLabelTag )
45 import Bag ( unionManyBags, bagToList )
46 import Class ( mkClass, classBigSig, classSelIds, Class, ClassOpItem )
47 import CmdLineOpts ( opt_GlasgowExts, opt_WarnMissingMethods )
48 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
49 import DataCon ( mkDataCon, dataConId, dataConWrapId, notMarkedStrict )
50 import Id ( Id, setInlinePragma, idUnfolding, idType, idName )
51 import CoreUnfold ( unfoldingTemplate )
53 import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..) )
54 import NameSet ( emptyNameSet )
56 import Type ( Type, ThetaType, ClassContext,
57 mkFunTy, mkTyVarTy, mkTyVarTys, mkDictTy, mkDictTys,
58 mkSigmaTy, mkForAllTys, mkClassPred, classesOfPreds,
59 boxedTypeKind, mkArrowKind
61 import Var ( tyVarKind, TyVar )
62 import VarSet ( mkVarSet, emptyVarSet )
63 import TyCon ( AlgTyConFlavour(..), mkClassTyCon )
64 import Unique ( Unique, Uniquable(..) )
66 import Maybes ( seqMaybe )
67 import FiniteMap ( lookupWithDefaultFM )
74 Every class implicitly declares a new data type, corresponding to dictionaries
75 of that class. So, for example:
77 class (D a) => C a where
79 op2 :: forall b. Ord b => a -> b -> b
81 would implicitly declare
83 data CDict a = CDict (D a)
85 (forall b. Ord b => a -> b -> b)
87 (We could use a record decl, but that means changing more of the existing apparatus.
90 For classes with just one superclass+method, we use a newtype decl instead:
93 op :: forallb. a -> b -> b
97 newtype CDict a = CDict (forall b. a -> b -> b)
99 Now DictTy in Type is just a form of type synomym:
100 DictTy c t = TyConTy CDict `AppTy` t
102 Death to "ExpandingDicts".
105 %************************************************************************
107 \subsection{Kind checking}
109 %************************************************************************
112 kcClassDecl (ClassDecl context class_name
113 tyvar_names fundeps class_sigs def_methods pragmas
115 = -- CHECK ARITY 1 FOR HASKELL 1.4
116 checkTc (opt_GlasgowExts || length tyvar_names == 1)
117 (classArityErr class_name) `thenTc_`
119 -- Get the (mutable) class kind
120 tcLookupTy class_name `thenNF_Tc` \ (kind, _) ->
122 -- Make suitable tyvars and do kind checking
123 -- The net effect is to mutate the class kind
124 tcExtendTopTyVarScope kind tyvar_names $ \ _ _ ->
125 tcContext context `thenTc_`
126 mapTc kc_sig the_class_sigs `thenTc_`
130 the_class_sigs = filter isClassOpSig class_sigs
132 kc_sig (ClassOpSig _ _ _ op_ty loc) = tcAddSrcLoc loc (kcHsType op_ty)
136 %************************************************************************
138 \subsection{Type checking}
140 %************************************************************************
143 tcClassDecl1 rec_env rec_vrcs
144 (ClassDecl context class_name
145 tyvar_names fundeps class_sigs def_methods pragmas
146 tycon_name datacon_name datacon_wkr_name sc_sel_names src_loc)
147 = -- LOOK THINGS UP IN THE ENVIRONMENT
148 tcLookupTy class_name `thenTc` \ (class_kind, AClass rec_class arity) ->
149 tcExtendTopTyVarScope class_kind tyvar_names $ \ tyvars _ ->
150 -- The class kind is by now immutable
153 -- traceTc (text "tcClassCtxt" <+> ppr class_name) `thenTc_`
154 tcClassContext class_name rec_class tyvars context sc_sel_names
155 `thenTc` \ (sc_theta, sc_tys, sc_sel_ids) ->
156 -- traceTc (text "tcClassCtxt done" <+> ppr class_name) `thenTc_`
158 -- CHECK THE FUNCTIONAL DEPENDENCIES,
159 tcFundeps fundeps `thenTc` \ fds ->
161 -- CHECK THE CLASS SIGNATURES,
162 mapTc (tcClassSig rec_env rec_class tyvars)
163 (filter isClassOpSig class_sigs)
164 `thenTc` \ sig_stuff ->
166 -- MAKE THE CLASS OBJECT ITSELF
168 (op_tys, op_items) = unzip sig_stuff
169 clas = mkClass class_name tyvars fds
170 sc_theta sc_sel_ids op_items
173 dict_component_tys = sc_tys ++ op_tys
174 new_or_data = case dict_component_tys of
175 [_] -> NewTyCon (mkNewTyConRep tycon)
178 dict_con = mkDataCon datacon_name
179 [notMarkedStrict | _ <- dict_component_tys]
180 [{- No labelled fields -}]
183 [{-No existential tyvars-}] [{-Or context-}]
185 tycon dict_con_id dict_wrap_id
187 dict_con_id = mkDataConId datacon_wkr_name dict_con
188 dict_wrap_id = mkDataConWrapId dict_con
190 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
194 tycon = mkClassTyCon tycon_name
198 dict_con -- Constructors
199 clas -- Yes! It's a dictionary
202 returnTc (class_name, AClass clas arity)
206 tcFundeps = mapTc tc_fundep
208 mapTc tc_fd_tyvar us `thenTc` \ us' ->
209 mapTc tc_fd_tyvar vs `thenTc` \ vs' ->
212 tcLookupTy v `thenTc` \(_, ATyVar tv) ->
217 tcClassContext :: Name -> Class -> [TyVar]
218 -> RenamedContext -- class context
219 -> [Name] -- Names for superclass selectors
220 -> TcM s (ClassContext, -- the superclass context
221 [Type], -- types of the superclass dictionaries
222 [Id]) -- superclass selector Ids
224 tcClassContext class_name rec_class rec_tyvars context sc_sel_names
225 = -- Check the context.
226 -- The renamer has already checked that the context mentions
227 -- only the type variable of the class decl.
229 -- For std Haskell check that the context constrains only tyvars
230 (if opt_GlasgowExts then
233 mapTc check_constraint context
236 tcContext context `thenTc` \ sc_theta ->
239 sc_theta' = classesOfPreds sc_theta
240 sc_tys = mkDictTys sc_theta'
241 sc_sel_ids = [mkDictSelId sc_name rec_class | sc_name <- sc_sel_names]
244 returnTc (sc_theta', sc_tys, sc_sel_ids)
247 check_constraint sc@(HsPClass c tys) = checkTc (all is_tyvar tys)
248 (superClassErr class_name sc)
250 is_tyvar (HsTyVar _) = True
251 is_tyvar other = False
254 tcClassSig :: ValueEnv -- Knot tying only!
255 -> Class -- ...ditto...
256 -> [TyVar] -- The class type variable, used for error check only
258 -> TcM s (Type, -- Type of the method
259 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
262 tcClassSig rec_env rec_clas rec_clas_tyvars
263 (ClassOpSig op_name dm_name explicit_dm
265 = tcAddSrcLoc src_loc $
267 -- Check the type signature. NB that the envt *already has*
268 -- bindings for the type variables; see comments in TcTyAndClassDcls.
270 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
271 -- and that it is not constrained by theta
272 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
273 tcHsTopType op_ty `thenTc` \ local_ty ->
275 global_ty = mkSigmaTy rec_clas_tyvars
276 [mkClassPred rec_clas (mkTyVarTys rec_clas_tyvars)]
279 -- Build the selector id and default method id
280 sel_id = mkDictSelId op_name rec_clas
281 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
282 final_dm_id = tcAddImportedIdInfo rec_env dm_id
284 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
285 returnTc (local_ty, (sel_id, final_dm_id, explicit_dm))
289 %************************************************************************
291 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
293 %************************************************************************
295 The purpose of pass 2 is
298 to beat on the explicitly-provided default-method decls (if any),
299 using them to produce a complete set of default-method decls.
300 (Omitted ones elicit an error message.)
302 to produce a definition for the selector function for each method
303 and superclass dictionary.
306 Pass~2 only applies to locally-defined class declarations.
308 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
309 each local class decl.
312 tcClassDecls2 :: [RenamedHsDecl]
313 -> NF_TcM s (LIE, TcMonoBinds)
317 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
318 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
320 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
321 tc2 `thenNF_Tc` \ (lie2, binds2) ->
322 returnNF_Tc (lie1 `plusLIE` lie2,
323 binds1 `AndMonoBinds` binds2)
326 @tcClassDecl2@ is the business end of things.
329 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
330 -> NF_TcM s (LIE, TcMonoBinds)
332 tcClassDecl2 (ClassDecl context class_name
333 tyvar_names _ class_sigs default_binds pragmas _ _ _ _ src_loc)
335 | not (isLocallyDefined class_name)
336 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
338 | otherwise -- It is locally defined
339 = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
340 tcAddSrcLoc src_loc $
341 tcLookupTy class_name `thenNF_Tc` \ (_, AClass clas _) ->
342 tcDefaultMethodBinds clas default_binds class_sigs
346 mkImplicitClassBinds :: [Class] -> NF_TcM s ([Id], TcMonoBinds)
347 mkImplicitClassBinds classes
348 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
349 -- The selector binds are already in the selector Id's unfoldings
351 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
353 mk_implicit clas = (all_cls_ids, binds)
355 dict_con = classDataCon clas
356 all_cls_ids = dataConId dict_con : cls_ids
357 cls_ids = dataConWrapId dict_con : classSelIds clas
359 -- The wrapper and selectors get bindings, the worker does not
360 binds | isLocallyDefined clas = idsToMonoBinds cls_ids
361 | otherwise = EmptyMonoBinds
364 %************************************************************************
366 \subsection[Default methods]{Default methods}
368 %************************************************************************
370 The default methods for a class are each passed a dictionary for the
371 class, so that they get access to the other methods at the same type.
372 So, given the class decl
376 op2 :: Ord b => a -> b -> b -> b
379 op2 x y z = if (op1 x) && (y < z) then y else z
381 we get the default methods:
383 defm.Foo.op1 :: forall a. Foo a => a -> Bool
384 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
386 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
387 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
388 if (op1 a dfoo x) && (< b dord y z) then y else z
391 When we come across an instance decl, we may need to use the default
394 instance Foo Int where {}
398 const.Foo.Int.op1 :: Int -> Bool
399 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
401 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
402 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
404 dfun.Foo.Int :: Foo Int
405 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
407 Notice that, as with method selectors above, we assume that dictionary
408 application is curried, so there's no need to mention the Ord dictionary
409 in const.Foo.Int.op2 (or the type variable).
412 instance Foo a => Foo [a] where {}
414 dfun.Foo.List :: forall a. Foo a -> Foo [a]
416 = /\ a -> \ dfoo_a ->
418 op1 = defm.Foo.op1 [a] dfoo_list
419 op2 = defm.Foo.op2 [a] dfoo_list
420 dfoo_list = (op1, op2)
430 -> TcM s (LIE, TcMonoBinds)
432 tcDefaultMethodBinds clas default_binds sigs
433 = -- Check that the default bindings come from this class
434 checkFromThisClass clas op_items default_binds `thenNF_Tc_`
436 -- Do each default method separately
437 -- For Hugs compatibility we make a default-method for every
438 -- class op, regardless of whether or not the programmer supplied an
439 -- explicit default decl for the class. GHC will actually never
440 -- call the default method for such operations, because it'll whip up
441 -- a more-informative default method at each instance decl.
442 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
444 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
446 prags = filter isPragSig sigs
448 (tyvars, _, _, op_items) = classBigSig clas
450 origin = ClassDeclOrigin
452 -- We make a separate binding for each default method.
453 -- At one time I used a single AbsBinds for all of them, thus
454 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
455 -- But that desugars into
456 -- ds = \d -> (..., ..., ...)
457 -- dm1 = \d -> case ds d of (a,b,c) -> a
458 -- And since ds is big, it doesn't get inlined, so we don't get good
459 -- default methods. Better to make separate AbsBinds for each
461 tc_dm op_item@(_, dm_id, _)
462 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
464 theta = [(mkClassPred clas inst_tys)]
466 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
468 avail_insts = this_dict
470 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
471 tcMethodBind clas origin clas_tyvars inst_tys theta
472 default_binds prags False
474 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
476 tcAddErrCtxt (defltMethCtxt clas) $
478 -- tcMethodBind has checked that the class_tyvars havn't
479 -- been unified with each other or another type, but we must
480 -- still zonk them before passing them to tcSimplifyAndCheck
481 mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
485 (ptext SLIT("class") <+> ppr clas)
486 (mkVarSet clas_tyvars')
488 insts_needed `thenTc` \ (const_lie, dict_binds) ->
494 [(clas_tyvars', dm_id, local_dm_id)]
495 emptyNameSet -- No inlines (yet)
496 (dict_binds `andMonoBinds` defm_bind)
498 returnTc (full_bind, const_lie)
502 checkFromThisClass :: Class -> [ClassOpItem] -> RenamedMonoBinds -> NF_TcM s ()
503 checkFromThisClass clas op_items mono_binds
504 = mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
507 check_from_this_class (bndr, loc)
508 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
509 | otherwise = tcAddSrcLoc loc $
510 addErrTc (badMethodErr bndr clas)
511 sel_names = [getOccName sel_id | (sel_id,_,_) <- op_items]
512 bndrs = bagToList (collectMonoBinders mono_binds)
516 @tcMethodBind@ is used to type-check both default-method and
517 instance-decl method declarations. We must type-check methods one at a
518 time, because their signatures may have different contexts and
525 -> [TcTyVar] -- Instantiated type variables for the
526 -- enclosing class/instance decl.
527 -- They'll be signature tyvars, and we
528 -- want to check that they don't get bound
529 -> [TcType] -- Instance types
530 -> TcThetaType -- Available theta; this could be used to check
531 -- the method signature, but actually that's done by
532 -- the caller; here, it's just used for the error message
533 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
534 -> [RenamedSig] -- Pramgas (just for this one)
535 -> Bool -- True <=> This method is from an instance declaration
536 -> ClassOpItem -- The method selector and default-method Id
537 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
539 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
540 meth_binds prags is_inst_decl
541 (sel_id, dm_id, explicit_dm)
542 = tcGetSrcLoc `thenNF_Tc` \ loc ->
544 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
545 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
548 meth_name = idName meth_id
549 maybe_user_bind = find_bind meth_name meth_binds
551 no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
553 meth_bind = case maybe_user_bind of
555 Nothing -> mk_default_bind meth_name loc
557 meth_prags = find_prags meth_name prags
560 -- Warn if no method binding, only if -fwarn-missing-methods
561 warnTc (is_inst_decl && opt_WarnMissingMethods && no_user_bind && not explicit_dm)
562 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
564 -- Check the bindings; first add inst_tyvars to the envt
565 -- so that we don't quantify over them in nested places
566 -- The *caller* put the class/inst decl tyvars into the envt
567 tcExtendGlobalTyVars (mkVarSet inst_tyvars) (
568 tcAddErrCtxt (methodCtxt sel_id) $
569 tcBindWithSigs NotTopLevel meth_bind
570 [sig_info] meth_prags NonRecursive
571 ) `thenTc` \ (binds, insts, _) ->
574 tcExtendLocalValEnv [(meth_name, meth_id)] (
575 tcSpecSigs meth_prags
576 ) `thenTc` \ (prag_binds1, prag_lie) ->
578 -- The prag_lie for a SPECIALISE pragma will mention the function
579 -- itself, so we have to simplify them away right now lest they float
581 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
584 -- Now check that the instance type variables
585 -- (or, in the case of a class decl, the class tyvars)
586 -- have not been unified with anything in the environment
587 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
588 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
590 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
591 insts `plusLIE` prag_lie',
594 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_name
596 sel_name = idName sel_id
598 -- The renamer just puts the selector ID as the binder in the method binding
599 -- but we must use the method name; so we substitute it here. Crude but simple.
600 find_bind meth_name (FunMonoBind op_name fix matches loc)
601 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
602 find_bind meth_name (AndMonoBinds b1 b2)
603 = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
604 find_bind meth_name other = Nothing -- Default case
607 -- Find the prags for this method, and replace the
608 -- selector name with the method name
609 find_prags meth_name [] = []
610 find_prags meth_name (SpecSig name ty loc : prags)
611 | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
612 find_prags meth_name (InlineSig name phase loc : prags)
613 | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
614 find_prags meth_name (NoInlineSig name phase loc : prags)
615 | name == sel_name = NoInlineSig meth_name phase loc : find_prags meth_name prags
616 find_prags meth_name (prag:prags) = find_prags meth_name prags
618 mk_default_bind local_meth_name loc
619 = FunMonoBind local_meth_name
620 False -- Not infix decl
621 [mkSimpleMatch [] (default_expr loc) Nothing loc]
625 | explicit_dm = HsVar (getName dm_id) -- There's a default method
626 | otherwise = error_expr loc -- No default method
628 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
629 (HsLit (HsString (_PK_ (error_msg loc))))
631 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
637 classArityErr class_name
638 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
640 superClassErr class_name sc
641 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
642 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
644 defltMethCtxt class_name
645 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
648 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
650 badMethodErr bndr clas
651 = hsep [ptext SLIT("Class"), quotes (ppr clas),
652 ptext SLIT("does not have a method"), quotes (ppr bndr)]
654 omittedMethodWarn sel_id clas
655 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
656 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]