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_inst_mapper 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 rec_class_inst_env = rec_inst_mapper rec_class
170 clas = mkClass class_name tyvars fds
171 sc_theta sc_sel_ids op_items
175 dict_component_tys = sc_tys ++ op_tys
176 new_or_data = case dict_component_tys of
177 [_] -> NewTyCon (mkNewTyConRep tycon)
180 dict_con = mkDataCon datacon_name
181 [notMarkedStrict | _ <- dict_component_tys]
182 [{- No labelled fields -}]
185 [{-No existential tyvars-}] [{-Or context-}]
187 tycon dict_con_id dict_wrap_id
189 dict_con_id = mkDataConId datacon_wkr_name dict_con
190 dict_wrap_id = mkDataConWrapId dict_con
192 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
196 tycon = mkClassTyCon tycon_name
200 dict_con -- Constructors
201 clas -- Yes! It's a dictionary
204 returnTc (class_name, AClass clas arity)
208 tcFundeps = mapTc tc_fundep
210 mapTc tc_fd_tyvar us `thenTc` \ us' ->
211 mapTc tc_fd_tyvar vs `thenTc` \ vs' ->
214 tcLookupTy v `thenTc` \(_, ATyVar tv) ->
219 tcClassContext :: Name -> Class -> [TyVar]
220 -> RenamedContext -- class context
221 -> [Name] -- Names for superclass selectors
222 -> TcM s (ClassContext, -- the superclass context
223 [Type], -- types of the superclass dictionaries
224 [Id]) -- superclass selector Ids
226 tcClassContext class_name rec_class rec_tyvars context sc_sel_names
227 = -- Check the context.
228 -- The renamer has already checked that the context mentions
229 -- only the type variable of the class decl.
231 -- For std Haskell check that the context constrains only tyvars
232 (if opt_GlasgowExts then
235 mapTc check_constraint context
238 tcContext context `thenTc` \ sc_theta ->
241 sc_theta' = classesOfPreds sc_theta
242 sc_tys = mkDictTys sc_theta'
243 sc_sel_ids = [mkDictSelId sc_name rec_class | sc_name <- sc_sel_names]
246 returnTc (sc_theta', sc_tys, sc_sel_ids)
249 check_constraint sc@(HsPClass c tys) = checkTc (all is_tyvar tys)
250 (superClassErr class_name sc)
252 is_tyvar (HsTyVar _) = True
253 is_tyvar other = False
256 tcClassSig :: ValueEnv -- Knot tying only!
257 -> Class -- ...ditto...
258 -> [TyVar] -- The class type variable, used for error check only
260 -> TcM s (Type, -- Type of the method
261 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
264 tcClassSig rec_env rec_clas rec_clas_tyvars
265 (ClassOpSig op_name dm_name explicit_dm
267 = tcAddSrcLoc src_loc $
269 -- Check the type signature. NB that the envt *already has*
270 -- bindings for the type variables; see comments in TcTyAndClassDcls.
272 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
273 -- and that it is not constrained by theta
274 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
275 tcHsTopType op_ty `thenTc` \ local_ty ->
277 global_ty = mkSigmaTy rec_clas_tyvars
278 [mkClassPred rec_clas (mkTyVarTys rec_clas_tyvars)]
281 -- Build the selector id and default method id
282 sel_id = mkDictSelId op_name rec_clas
283 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
284 final_dm_id = tcAddImportedIdInfo rec_env dm_id
286 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
287 returnTc (local_ty, (sel_id, final_dm_id, explicit_dm))
291 %************************************************************************
293 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
295 %************************************************************************
297 The purpose of pass 2 is
300 to beat on the explicitly-provided default-method decls (if any),
301 using them to produce a complete set of default-method decls.
302 (Omitted ones elicit an error message.)
304 to produce a definition for the selector function for each method
305 and superclass dictionary.
308 Pass~2 only applies to locally-defined class declarations.
310 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
311 each local class decl.
314 tcClassDecls2 :: [RenamedHsDecl]
315 -> NF_TcM s (LIE, TcMonoBinds)
319 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
320 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
322 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
323 tc2 `thenNF_Tc` \ (lie2, binds2) ->
324 returnNF_Tc (lie1 `plusLIE` lie2,
325 binds1 `AndMonoBinds` binds2)
328 @tcClassDecl2@ is the business end of things.
331 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
332 -> NF_TcM s (LIE, TcMonoBinds)
334 tcClassDecl2 (ClassDecl context class_name
335 tyvar_names _ class_sigs default_binds pragmas _ _ _ _ src_loc)
337 | not (isLocallyDefined class_name)
338 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
340 | otherwise -- It is locally defined
341 = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
342 tcAddSrcLoc src_loc $
343 tcLookupTy class_name `thenNF_Tc` \ (_, AClass clas _) ->
344 tcDefaultMethodBinds clas default_binds class_sigs
348 mkImplicitClassBinds :: [Class] -> NF_TcM s ([Id], TcMonoBinds)
349 mkImplicitClassBinds classes
350 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
351 -- The selector binds are already in the selector Id's unfoldings
353 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
355 mk_implicit clas = (all_cls_ids, binds)
357 dict_con = classDataCon clas
358 all_cls_ids = dataConId dict_con : cls_ids
359 cls_ids = dataConWrapId dict_con : classSelIds clas
361 -- The wrapper and selectors get bindings, the worker does not
362 binds | isLocallyDefined clas = idsToMonoBinds cls_ids
363 | otherwise = EmptyMonoBinds
366 %************************************************************************
368 \subsection[Default methods]{Default methods}
370 %************************************************************************
372 The default methods for a class are each passed a dictionary for the
373 class, so that they get access to the other methods at the same type.
374 So, given the class decl
378 op2 :: Ord b => a -> b -> b -> b
381 op2 x y z = if (op1 x) && (y < z) then y else z
383 we get the default methods:
385 defm.Foo.op1 :: forall a. Foo a => a -> Bool
386 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
388 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
389 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
390 if (op1 a dfoo x) && (< b dord y z) then y else z
393 When we come across an instance decl, we may need to use the default
396 instance Foo Int where {}
400 const.Foo.Int.op1 :: Int -> Bool
401 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
403 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
404 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
406 dfun.Foo.Int :: Foo Int
407 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
409 Notice that, as with method selectors above, we assume that dictionary
410 application is curried, so there's no need to mention the Ord dictionary
411 in const.Foo.Int.op2 (or the type variable).
414 instance Foo a => Foo [a] where {}
416 dfun.Foo.List :: forall a. Foo a -> Foo [a]
418 = /\ a -> \ dfoo_a ->
420 op1 = defm.Foo.op1 [a] dfoo_list
421 op2 = defm.Foo.op2 [a] dfoo_list
422 dfoo_list = (op1, op2)
432 -> TcM s (LIE, TcMonoBinds)
434 tcDefaultMethodBinds clas default_binds sigs
435 = -- Check that the default bindings come from this class
436 checkFromThisClass clas op_items default_binds `thenNF_Tc_`
438 -- Do each default method separately
439 -- For Hugs compatibility we make a default-method for every
440 -- class op, regardless of whether or not the programmer supplied an
441 -- explicit default decl for the class. GHC will actually never
442 -- call the default method for such operations, because it'll whip up
443 -- a more-informative default method at each instance decl.
444 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
446 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
448 prags = filter isPragSig sigs
450 (tyvars, _, _, op_items) = classBigSig clas
452 origin = ClassDeclOrigin
454 -- We make a separate binding for each default method.
455 -- At one time I used a single AbsBinds for all of them, thus
456 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
457 -- But that desugars into
458 -- ds = \d -> (..., ..., ...)
459 -- dm1 = \d -> case ds d of (a,b,c) -> a
460 -- And since ds is big, it doesn't get inlined, so we don't get good
461 -- default methods. Better to make separate AbsBinds for each
463 tc_dm op_item@(_, dm_id, _)
464 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
466 theta = [(mkClassPred clas inst_tys)]
468 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
470 avail_insts = this_dict
472 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
473 tcMethodBind clas origin clas_tyvars inst_tys theta
474 default_binds prags False
476 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
478 tcAddErrCtxt (defltMethCtxt clas) $
480 -- tcMethodBind has checked that the class_tyvars havn't
481 -- been unified with each other or another type, but we must
482 -- still zonk them before passing them to tcSimplifyAndCheck
483 mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
487 (ptext SLIT("class") <+> ppr clas)
488 (mkVarSet clas_tyvars')
490 insts_needed `thenTc` \ (const_lie, dict_binds) ->
496 [(clas_tyvars', dm_id, local_dm_id)]
497 emptyNameSet -- No inlines (yet)
498 (dict_binds `andMonoBinds` defm_bind)
500 returnTc (full_bind, const_lie)
504 checkFromThisClass :: Class -> [ClassOpItem] -> RenamedMonoBinds -> NF_TcM s ()
505 checkFromThisClass clas op_items mono_binds
506 = mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
509 check_from_this_class (bndr, loc)
510 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
511 | otherwise = tcAddSrcLoc loc $
512 addErrTc (badMethodErr bndr clas)
513 sel_names = [getOccName sel_id | (sel_id,_,_) <- op_items]
514 bndrs = bagToList (collectMonoBinders mono_binds)
518 @tcMethodBind@ is used to type-check both default-method and
519 instance-decl method declarations. We must type-check methods one at a
520 time, because their signatures may have different contexts and
527 -> [TcTyVar] -- Instantiated type variables for the
528 -- enclosing class/instance decl.
529 -- They'll be signature tyvars, and we
530 -- want to check that they don't get bound
531 -> [TcType] -- Instance types
532 -> TcThetaType -- Available theta; this could be used to check
533 -- the method signature, but actually that's done by
534 -- the caller; here, it's just used for the error message
535 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
536 -> [RenamedSig] -- Pramgas (just for this one)
537 -> Bool -- True <=> This method is from an instance declaration
538 -> ClassOpItem -- The method selector and default-method Id
539 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
541 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
542 meth_binds prags is_inst_decl
543 (sel_id, dm_id, explicit_dm)
544 = tcGetSrcLoc `thenNF_Tc` \ loc ->
546 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
547 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
550 meth_name = idName meth_id
551 maybe_user_bind = find_bind meth_name meth_binds
553 no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
555 meth_bind = case maybe_user_bind of
557 Nothing -> mk_default_bind meth_name loc
559 meth_prags = find_prags meth_name prags
562 -- Warn if no method binding, only if -fwarn-missing-methods
563 warnTc (is_inst_decl && opt_WarnMissingMethods && no_user_bind && not explicit_dm)
564 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
566 -- Check the bindings; first add inst_tyvars to the envt
567 -- so that we don't quantify over them in nested places
568 -- The *caller* put the class/inst decl tyvars into the envt
569 tcExtendGlobalTyVars (mkVarSet inst_tyvars) (
570 tcAddErrCtxt (methodCtxt sel_id) $
571 tcBindWithSigs NotTopLevel meth_bind
572 [sig_info] meth_prags NonRecursive
573 ) `thenTc` \ (binds, insts, _) ->
576 tcExtendLocalValEnv [(meth_name, meth_id)] (
577 tcSpecSigs meth_prags
578 ) `thenTc` \ (prag_binds1, prag_lie) ->
580 -- The prag_lie for a SPECIALISE pragma will mention the function
581 -- itself, so we have to simplify them away right now lest they float
583 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
586 -- Now check that the instance type variables
587 -- (or, in the case of a class decl, the class tyvars)
588 -- have not been unified with anything in the environment
589 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
590 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
592 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
593 insts `plusLIE` prag_lie',
596 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_name
598 sel_name = idName sel_id
600 -- The renamer just puts the selector ID as the binder in the method binding
601 -- but we must use the method name; so we substitute it here. Crude but simple.
602 find_bind meth_name (FunMonoBind op_name fix matches loc)
603 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
604 find_bind meth_name (AndMonoBinds b1 b2)
605 = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
606 find_bind meth_name other = Nothing -- Default case
609 -- Find the prags for this method, and replace the
610 -- selector name with the method name
611 find_prags meth_name [] = []
612 find_prags meth_name (SpecSig name ty loc : prags)
613 | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
614 find_prags meth_name (InlineSig name phase loc : prags)
615 | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
616 find_prags meth_name (NoInlineSig name phase loc : prags)
617 | name == sel_name = NoInlineSig meth_name phase loc : find_prags meth_name prags
618 find_prags meth_name (prag:prags) = find_prags meth_name prags
620 mk_default_bind local_meth_name loc
621 = FunMonoBind local_meth_name
622 False -- Not infix decl
623 [mkSimpleMatch [] (default_expr loc) Nothing loc]
627 | explicit_dm = HsVar (getName dm_id) -- There's a default method
628 | otherwise = error_expr loc -- No default method
630 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
631 (HsLit (HsString (_PK_ (error_msg loc))))
633 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
639 classArityErr class_name
640 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
642 superClassErr class_name sc
643 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
644 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
646 defltMethCtxt class_name
647 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
650 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
652 badMethodErr bndr clas
653 = hsep [ptext SLIT("Class"), quotes (ppr clas),
654 ptext SLIT("does not have a method"), quotes (ppr bndr)]
656 omittedMethodWarn sel_id clas
657 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
658 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]