2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( kcClassDecl, tcClassDecl1, tcClassDecls2,
8 tcMethodBind, checkFromThisClass
11 #include "HsVersions.h"
13 import HsSyn ( HsDecl(..), TyClDecl(..), Sig(..), MonoBinds(..),
14 InPat(..), HsBinds(..), GRHSs(..),
15 HsExpr(..), HsLit(..), HsType(..), pprClassAssertion,
16 unguardedRHS, andMonoBinds, andMonoBindList, getTyVarName,
17 isClassDecl, isClassOpSig, collectMonoBinders
19 import HsPragmas ( ClassPragmas(..) )
20 import BasicTypes ( NewOrData(..), TopLevelFlag(..), RecFlag(..) )
21 import RnHsSyn ( RenamedTyClDecl, RenamedClassPragmas,
22 RenamedClassOpSig, RenamedMonoBinds,
23 RenamedContext, RenamedHsDecl, RenamedSig
25 import TcHsSyn ( TcMonoBinds )
27 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, newDicts, newMethod )
28 import TcEnv ( TcId, ValueEnv, TcTyThing(..), tcAddImportedIdInfo,
29 tcLookupClass, tcLookupTy, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
32 import TcBinds ( tcBindWithSigs, tcSpecSigs )
33 import TcUnify ( unifyKinds )
35 import TcMonoType ( tcHsType, tcHsTopType, tcExtendTopTyVarScope,
36 tcContext, checkSigTyVars, sigCtxt, mkTcSig
38 import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
39 import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcTyVarBndr, tcGetTyVar )
40 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
41 import FieldLabel ( firstFieldLabelTag )
42 import Bag ( unionManyBags, bagToList )
43 import Class ( mkClass, classBigSig, Class )
44 import CmdLineOpts ( opt_GlasgowExts, opt_WarnMissingMethods )
45 import MkId ( mkDictSelId, mkDataConId, mkDefaultMethodId )
46 import DataCon ( mkDataCon, notMarkedStrict )
48 getIdUnfolding, idType, idName
50 import CoreUnfold ( getUnfoldingTemplate )
52 import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..) )
53 import NameSet ( emptyNameSet )
55 import Type ( mkFunTy, mkTyVarTy, mkTyVarTys, mkDictTy,
56 mkSigmaTy, mkForAllTys, Type, ThetaType,
57 boxedTypeKind, mkArrowKind
59 import Var ( tyVarKind, TyVar )
60 import VarSet ( mkVarSet )
61 import TyCon ( mkAlgTyCon )
62 import Unique ( Unique, Uniquable(..) )
64 import Maybes ( seqMaybe )
65 import FiniteMap ( lookupWithDefaultFM )
72 Every class implicitly declares a new data type, corresponding to dictionaries
73 of that class. So, for example:
75 class (D a) => C a where
77 op2 :: forall b. Ord b => a -> b -> b
79 would implicitly declare
81 data CDict a = CDict (D a)
83 (forall b. Ord b => a -> b -> b)
85 (We could use a record decl, but that means changing more of the existing apparatus.
88 For classes with just one superclass+method, we use a newtype decl instead:
91 op :: forallb. a -> b -> b
95 newtype CDict a = CDict (forall b. a -> b -> b)
97 Now DictTy in Type is just a form of type synomym:
98 DictTy c t = TyConTy CDict `AppTy` t
100 Death to "ExpandingDicts".
103 %************************************************************************
105 \subsection{Kind checking}
107 %************************************************************************
110 kcClassDecl (ClassDecl context class_name
111 tyvar_names class_sigs def_methods pragmas
112 tycon_name datacon_name sc_sel_names src_loc)
113 = -- CHECK ARITY 1 FOR HASKELL 1.4
114 checkTc (opt_GlasgowExts || length tyvar_names == 1)
115 (classArityErr class_name) `thenTc_`
117 -- Get the (mutable) class kind
118 tcLookupTy class_name `thenNF_Tc` \ (kind, _, _) ->
120 -- Make suitable tyvars and do kind checking
121 -- The net effect is to mutate the class kind
122 tcExtendTopTyVarScope kind tyvar_names $ \ _ _ ->
123 tcContext context `thenTc_`
124 mapTc kc_sig the_class_sigs `thenTc_`
128 the_class_sigs = filter isClassOpSig class_sigs
130 kc_sig (ClassOpSig _ _ op_ty loc) = tcAddSrcLoc loc (tcHsType op_ty)
134 %************************************************************************
136 \subsection{Type checking}
138 %************************************************************************
141 tcClassDecl1 rec_env rec_inst_mapper rec_vrcs
142 (ClassDecl context class_name
143 tyvar_names class_sigs def_methods pragmas
144 tycon_name datacon_name sc_sel_names src_loc)
145 = -- LOOK THINGS UP IN THE ENVIRONMENT
146 tcLookupTy class_name `thenTc` \ (class_kind, _, AClass rec_class) ->
147 tcExtendTopTyVarScope class_kind tyvar_names $ \ tyvars _ ->
148 -- The class kind is by now immutable
151 -- traceTc (text "tcClassCtxt" <+> ppr class_name) `thenTc_`
152 tcClassContext class_name rec_class tyvars context sc_sel_names
153 `thenTc` \ (sc_theta, sc_tys, sc_sel_ids) ->
154 -- traceTc (text "tcClassCtxt done" <+> ppr class_name) `thenTc_`
156 -- CHECK THE CLASS SIGNATURES,
157 mapTc (tcClassSig rec_env rec_class tyvars)
158 (filter isClassOpSig class_sigs)
159 `thenTc` \ sig_stuff ->
161 -- MAKE THE CLASS OBJECT ITSELF
163 (op_tys, op_sel_ids, defm_ids) = unzip3 sig_stuff
164 rec_class_inst_env = rec_inst_mapper rec_class
165 clas = mkClass class_name tyvars
166 sc_theta sc_sel_ids op_sel_ids defm_ids
170 dict_component_tys = sc_tys ++ op_tys
171 new_or_data = case dict_component_tys of
175 dict_con = mkDataCon datacon_name
176 [notMarkedStrict | _ <- dict_component_tys]
177 [{- No labelled fields -}]
180 [{-No existential tyvars-}] [{-Or context-}]
183 dict_con_id = mkDataConId dict_con
185 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
189 tycon = mkAlgTyCon tycon_name
194 [dict_con] -- Constructors
196 (Just clas) -- Yes! It's a dictionary
205 tcClassContext :: Name -> Class -> [TyVar]
206 -> RenamedContext -- class context
207 -> [Name] -- Names for superclass selectors
208 -> TcM s (ThetaType, -- the superclass context
209 [Type], -- types of the superclass dictionaries
210 [Id]) -- superclass selector Ids
212 tcClassContext class_name rec_class rec_tyvars context sc_sel_names
213 = -- Check the context.
214 -- The renamer has already checked that the context mentions
215 -- only the type variable of the class decl.
217 -- For std Haskell check that the context constrains only tyvars
218 (if opt_GlasgowExts then
221 mapTc check_constraint context
224 tcContext context `thenTc` \ sc_theta ->
227 sc_tys = [mkDictTy sc tys | (sc,tys) <- sc_theta]
228 sc_sel_ids = zipWithEqual "tcClassContext" mk_super_id sc_sel_names sc_tys
231 returnTc (sc_theta, sc_tys, sc_sel_ids)
234 rec_tyvar_tys = mkTyVarTys rec_tyvars
236 mk_super_id name dict_ty
237 = mkDictSelId name rec_class ty
239 ty = mkForAllTys rec_tyvars $
240 mkFunTy (mkDictTy rec_class rec_tyvar_tys) dict_ty
242 check_constraint (c, tys) = checkTc (all is_tyvar tys)
243 (superClassErr class_name (c, tys))
245 is_tyvar (MonoTyVar _) = True
246 is_tyvar other = False
249 tcClassSig :: ValueEnv -- Knot tying only!
250 -> Class -- ...ditto...
251 -> [TyVar] -- The class type variable, used for error check only
253 -> TcM s (Type, -- Type of the method
255 Maybe Id) -- default-method ids
257 tcClassSig rec_env rec_clas rec_clas_tyvars
258 (ClassOpSig op_name maybe_dm_name
261 = tcAddSrcLoc src_loc $
263 -- Check the type signature. NB that the envt *already has*
264 -- bindings for the type variables; see comments in TcTyAndClassDcls.
266 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
267 -- and that it is not constrained by theta
268 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
269 tcHsTopType op_ty `thenTc` \ local_ty ->
271 global_ty = mkSigmaTy rec_clas_tyvars
272 [(rec_clas, mkTyVarTys rec_clas_tyvars)]
275 -- Build the selector id and default method id
276 sel_id = mkDictSelId op_name rec_clas global_ty
277 maybe_dm_id = case maybe_dm_name of
280 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
282 Just (tcAddImportedIdInfo rec_env dm_id)
284 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
285 returnTc (local_ty, sel_id, maybe_dm_id)
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 $
342 -- Get the relevant class
343 tcLookupClass class_name `thenNF_Tc` \ clas ->
345 (tyvars, sc_theta, sc_sel_ids, op_sel_ids, defm_ids) = classBigSig clas
347 -- The selector binds are already in the selector Id's unfoldings
348 sel_binds = [ CoreMonoBind sel_id (getUnfoldingTemplate (getIdUnfolding sel_id))
349 | sel_id <- sc_sel_ids ++ op_sel_ids
352 -- Generate bindings for the default methods
353 tcDefaultMethodBinds clas default_binds `thenTc` \ (const_insts, meth_binds) ->
355 returnTc (const_insts,
356 meth_binds `AndMonoBinds` andMonoBindList sel_binds)
359 %************************************************************************
361 \subsection[Default methods]{Default methods}
363 %************************************************************************
365 The default methods for a class are each passed a dictionary for the
366 class, so that they get access to the other methods at the same type.
367 So, given the class decl
371 op2 :: Ord b => a -> b -> b -> b
374 op2 x y z = if (op1 x) && (y < z) then y else z
376 we get the default methods:
378 defm.Foo.op1 :: forall a. Foo a => a -> Bool
379 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
381 ====================== OLD ==================
383 defm.Foo.op2 :: forall a, b. (Foo a, Ord b) => a -> b -> b -> b
384 defm.Foo.op2 = /\ a b -> \ dfoo dord -> \x y z ->
385 if (op1 a dfoo x) && (< b dord y z) then y else z
387 Notice that, like all ids, the foralls of defm.Foo.op2 are at the top.
388 ====================== END OF OLD ===================
392 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
393 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
394 if (op1 a dfoo x) && (< b dord y z) then y else z
398 When we come across an instance decl, we may need to use the default
401 instance Foo Int where {}
405 const.Foo.Int.op1 :: Int -> Bool
406 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
408 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
409 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
411 dfun.Foo.Int :: Foo Int
412 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
414 Notice that, as with method selectors above, we assume that dictionary
415 application is curried, so there's no need to mention the Ord dictionary
416 in const.Foo.Int.op2 (or the type variable).
419 instance Foo a => Foo [a] where {}
421 dfun.Foo.List :: forall a. Foo a -> Foo [a]
423 = /\ a -> \ dfoo_a ->
425 op1 = defm.Foo.op1 [a] dfoo_list
426 op2 = defm.Foo.op2 [a] dfoo_list
427 dfoo_list = (op1, op2)
436 -> TcM s (LIE, TcMonoBinds)
438 tcDefaultMethodBinds clas default_binds
439 = -- Construct suitable signatures
440 tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
442 -- Check that the default bindings come from this class
443 checkFromThisClass clas op_sel_ids default_binds `thenNF_Tc_`
445 -- Typecheck the default bindings
447 theta = [(clas,inst_tys)]
448 tc_dm sel_id_w_dm@(_, Just dm_id)
449 = tcMethodBind clas origin clas_tyvars inst_tys theta
450 default_binds [{-no prags-}] False
451 sel_id_w_dm `thenTc` \ (bind, insts, (_, local_dm_id)) ->
452 returnTc (bind, insts, (clas_tyvars, dm_id, local_dm_id))
454 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
455 mapAndUnzip3Tc tc_dm sel_ids_w_dms
456 ) `thenTc` \ (defm_binds, insts_needed, abs_bind_stuff) ->
460 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
462 avail_insts = this_dict
464 tcAddErrCtxt (defltMethCtxt clas) $
466 -- tcMethodBind has checked that the class_tyvars havn't
467 -- been unified with each other or another type, but we must
468 -- still zonk them before passing them to tcSimplifyAndCheck
469 mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
472 (ptext SLIT("class") <+> ppr clas)
473 (mkVarSet clas_tyvars')
475 (unionManyBags insts_needed) `thenTc` \ (const_lie, dict_binds) ->
478 full_binds = AbsBinds
482 emptyNameSet -- No inlines (yet)
483 (dict_binds `andMonoBinds` andMonoBindList defm_binds)
485 returnTc (const_lie, full_binds)
488 (tyvars, sc_theta, sc_sel_ids, op_sel_ids, defm_ids) = classBigSig clas
490 sel_ids_w_dms = [pair | pair@(_, Just _) <- op_sel_ids `zip` defm_ids]
491 -- Just the ones for which there is an explicit
492 -- user default declaration
494 origin = ClassDeclOrigin
498 checkFromThisClass :: Class -> [Id] -> RenamedMonoBinds -> NF_TcM s ()
499 checkFromThisClass clas op_sel_ids mono_binds
500 = mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
503 check_from_this_class (bndr, loc)
504 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
505 | otherwise = tcAddSrcLoc loc $
506 addErrTc (badMethodErr bndr clas)
507 sel_names = map getOccName op_sel_ids
508 bndrs = bagToList (collectMonoBinders mono_binds)
512 @tcMethodBind@ is used to type-check both default-method and
513 instance-decl method declarations. We must type-check methods one at a
514 time, because their signatures may have different contexts and
521 -> [TcTyVar] -- Instantiated type variables for the
522 -- enclosing class/instance decl.
523 -- They'll be signature tyvars, and we
524 -- want to check that they don't get bound
525 -> [TcType] -- Instance types
526 -> TcThetaType -- Available theta; this could be used to check
527 -- the method signature, but actually that's done by
528 -- the caller; here, it's just used for the error message
529 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
530 -> [RenamedSig] -- Pramgas (just for this one)
531 -> Bool -- True <=> supply default decl if no explicit decl
532 -- This is true for instance decls,
533 -- false for class decls
534 -> (Id, Maybe Id) -- The method selector and default-method Id
535 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
537 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
538 meth_binds prags supply_default_bind
539 (sel_id, maybe_dm_id)
540 = tcGetSrcLoc `thenNF_Tc` \ loc ->
542 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
543 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
546 meth_name = idName meth_id
547 maybe_user_bind = find_bind meth_name meth_binds
549 no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
550 no_user_default = case maybe_dm_id of {Nothing -> True; other -> False}
552 meth_bind = case maybe_user_bind of
554 Nothing -> mk_default_bind meth_name loc
556 meth_prags = find_prags meth_name prags
559 -- Warn if no method binding, only if -fwarn-missing-methods
560 if no_user_bind && not supply_default_bind then
561 pprPanic "tcMethodBind" (ppr clas <+> ppr inst_tys)
563 warnTc (opt_WarnMissingMethods && no_user_bind && no_user_default)
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 (mkSigmaTy inst_tyvars inst_theta (idType meth_id))) $
590 checkSigTyVars inst_tyvars `thenTc_`
592 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
593 insts `plusLIE` prag_lie',
596 sig_msg ty = sep [ptext SLIT("When checking the expected type for"),
597 nest 4 (ppr sel_name <+> dcolon <+> ppr ty)]
599 sel_name = idName sel_id
601 -- The renamer just puts the selector ID as the binder in the method binding
602 -- but we must use the method name; so we substitute it here. Crude but simple.
603 find_bind meth_name (FunMonoBind op_name fix matches loc)
604 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
605 find_bind meth_name (PatMonoBind (VarPatIn op_name) grhss loc)
606 | op_name == sel_name = Just (PatMonoBind (VarPatIn meth_name) grhss loc)
607 find_bind meth_name (AndMonoBinds b1 b2)
608 = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
609 find_bind meth_name other = Nothing -- Default case
612 -- Find the prags for this method, and replace the
613 -- selector name with the method name
614 find_prags meth_name [] = []
615 find_prags meth_name (SpecSig name ty loc : prags)
616 | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
617 find_prags meth_name (InlineSig name loc : prags)
618 | name == sel_name = InlineSig meth_name loc : find_prags meth_name prags
619 find_prags meth_name (NoInlineSig name loc : prags)
620 | name == sel_name = NoInlineSig meth_name loc : find_prags meth_name prags
621 find_prags meth_name (prag:prags) = find_prags meth_name prags
623 mk_default_bind local_meth_name loc
624 = PatMonoBind (VarPatIn local_meth_name)
625 (GRHSs (unguardedRHS (default_expr loc) loc) EmptyBinds Nothing)
629 = case maybe_dm_id of
630 Just dm_id -> HsVar (getName dm_id) -- There's a default method
631 Nothing -> error_expr loc -- No default method
633 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
634 (HsLit (HsString (_PK_ (error_msg loc))))
636 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
642 classArityErr class_name
643 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
645 superClassErr class_name sc
646 = ptext SLIT("Illegal superclass constraint") <+> quotes (pprClassAssertion sc)
647 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
649 defltMethCtxt class_name
650 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
653 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
655 badMethodErr bndr clas
656 = hsep [ptext SLIT("Class"), quotes (ppr clas),
657 ptext SLIT("does not have a method"), quotes (ppr bndr)]
659 omittedMethodWarn sel_id clas
660 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
661 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]