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(..), HsPred(..),
16 pprHsClassAssertion, unguardedRHS,
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 )
28 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs, newDicts, newMethod )
29 import TcEnv ( TcId, ValueEnv, TcTyThing(..), tcAddImportedIdInfo,
30 tcLookupClass, tcLookupTy, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcUnify ( unifyKinds )
36 import TcMonoType ( tcHsType, tcHsTopType, tcExtendTopTyVarScope,
37 tcContext, checkSigTyVars, sigCtxt, mkTcSig
39 import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
40 import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcTyVarBndr, tcGetTyVar )
41 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
42 import FieldLabel ( firstFieldLabelTag )
43 import Bag ( unionManyBags, bagToList )
44 import Class ( mkClass, classBigSig, classSelIds, Class, ClassOpItem )
45 import CmdLineOpts ( opt_GlasgowExts, opt_WarnMissingMethods )
46 import MkId ( mkDictSelId, mkDataConId, mkDefaultMethodId )
47 import DataCon ( mkDataCon, notMarkedStrict )
48 import Id ( Id, setInlinePragma, getIdUnfolding, idType, idName )
49 import CoreUnfold ( unfoldingTemplate )
51 import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..) )
52 import NameSet ( emptyNameSet )
54 import Type ( Type, ThetaType, ClassContext,
55 mkFunTy, mkTyVarTy, mkTyVarTys, mkDictTy,
56 mkSigmaTy, mkForAllTys, mkClassPred, classesOfPreds,
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 fundeps 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 fundeps 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 FUNCTIONAL DEPENDENCIES,
157 tcFundeps fundeps `thenTc` \ fds ->
159 -- CHECK THE CLASS SIGNATURES,
160 mapTc (tcClassSig rec_env rec_class tyvars)
161 (filter isClassOpSig class_sigs)
162 `thenTc` \ sig_stuff ->
164 -- MAKE THE CLASS OBJECT ITSELF
166 (op_tys, op_items) = unzip sig_stuff
167 rec_class_inst_env = rec_inst_mapper rec_class
168 clas = mkClass class_name tyvars fds
169 sc_theta sc_sel_ids op_items
173 dict_component_tys = sc_tys ++ op_tys
174 new_or_data = case dict_component_tys of
178 dict_con = mkDataCon datacon_name
179 [notMarkedStrict | _ <- dict_component_tys]
180 [{- No labelled fields -}]
183 [{-No existential tyvars-}] [{-Or context-}]
187 dict_con_id = mkDataConId dict_con
189 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
193 tycon = mkAlgTyCon tycon_name
198 [dict_con] -- Constructors
200 (Just clas) -- Yes! It's a dictionary
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` \(_, _, thing) ->
216 ATyVar tv -> returnTc tv
217 -- ZZ else should fail more gracefully
221 tcClassContext :: Name -> Class -> [TyVar]
222 -> RenamedContext -- class context
223 -> [Name] -- Names for superclass selectors
224 -> TcM s (ClassContext, -- the superclass context
225 [Type], -- types of the superclass dictionaries
226 [Id]) -- superclass selector Ids
228 tcClassContext class_name rec_class rec_tyvars context sc_sel_names
229 = -- Check the context.
230 -- The renamer has already checked that the context mentions
231 -- only the type variable of the class decl.
233 -- For std Haskell check that the context constrains only tyvars
234 (if opt_GlasgowExts then
237 mapTc check_constraint context
240 tcContext context `thenTc` \ sc_theta ->
243 sc_theta' = classesOfPreds sc_theta
244 sc_tys = [mkDictTy sc tys | (sc,tys) <- sc_theta']
245 sc_sel_ids = zipWithEqual "tcClassContext" mk_super_id sc_sel_names sc_tys
248 returnTc (sc_theta', sc_tys, sc_sel_ids)
251 rec_tyvar_tys = mkTyVarTys rec_tyvars
253 mk_super_id name dict_ty
254 = mkDictSelId name rec_class ty
256 ty = mkForAllTys rec_tyvars $
257 mkFunTy (mkDictTy rec_class rec_tyvar_tys) dict_ty
259 check_constraint (HsPClass c tys) = checkTc (all is_tyvar tys)
260 (superClassErr class_name (c, tys))
262 is_tyvar (MonoTyVar _) = True
263 is_tyvar other = False
266 tcClassSig :: ValueEnv -- Knot tying only!
267 -> Class -- ...ditto...
268 -> [TyVar] -- The class type variable, used for error check only
270 -> TcM s (Type, -- Type of the method
271 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
274 tcClassSig rec_env rec_clas rec_clas_tyvars
275 (ClassOpSig op_name dm_name explicit_dm
277 = tcAddSrcLoc src_loc $
279 -- Check the type signature. NB that the envt *already has*
280 -- bindings for the type variables; see comments in TcTyAndClassDcls.
282 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
283 -- and that it is not constrained by theta
284 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
285 tcHsTopType op_ty `thenTc` \ local_ty ->
287 global_ty = mkSigmaTy rec_clas_tyvars
288 [mkClassPred rec_clas (mkTyVarTys rec_clas_tyvars)]
291 -- Build the selector id and default method id
292 sel_id = mkDictSelId op_name rec_clas global_ty
293 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
294 final_dm_id = tcAddImportedIdInfo rec_env dm_id
296 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
297 returnTc (local_ty, (sel_id, final_dm_id, explicit_dm))
301 %************************************************************************
303 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
305 %************************************************************************
307 The purpose of pass 2 is
310 to beat on the explicitly-provided default-method decls (if any),
311 using them to produce a complete set of default-method decls.
312 (Omitted ones elicit an error message.)
314 to produce a definition for the selector function for each method
315 and superclass dictionary.
318 Pass~2 only applies to locally-defined class declarations.
320 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
321 each local class decl.
324 tcClassDecls2 :: [RenamedHsDecl]
325 -> NF_TcM s (LIE, TcMonoBinds)
329 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
330 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
332 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
333 tc2 `thenNF_Tc` \ (lie2, binds2) ->
334 returnNF_Tc (lie1 `plusLIE` lie2,
335 binds1 `AndMonoBinds` binds2)
338 @tcClassDecl2@ is the business end of things.
341 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
342 -> NF_TcM s (LIE, TcMonoBinds)
344 tcClassDecl2 (ClassDecl context class_name
345 tyvar_names _ class_sigs default_binds pragmas _ _ _ src_loc)
347 | not (isLocallyDefined class_name)
348 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
350 | otherwise -- It is locally defined
351 = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
352 tcAddSrcLoc src_loc $
354 -- Get the relevant class
355 tcLookupClass class_name `thenNF_Tc` \ clas ->
357 -- The selector binds are already in the selector Id's unfoldings
358 sel_binds = [ CoreMonoBind sel_id (unfoldingTemplate (getIdUnfolding sel_id))
359 | sel_id <- classSelIds clas
362 -- Generate bindings for the default methods
363 tcDefaultMethodBinds clas default_binds class_sigs `thenTc` \ (const_insts, meth_binds) ->
365 returnTc (const_insts,
366 meth_binds `AndMonoBinds` andMonoBindList sel_binds)
369 %************************************************************************
371 \subsection[Default methods]{Default methods}
373 %************************************************************************
375 The default methods for a class are each passed a dictionary for the
376 class, so that they get access to the other methods at the same type.
377 So, given the class decl
381 op2 :: Ord b => a -> b -> b -> b
384 op2 x y z = if (op1 x) && (y < z) then y else z
386 we get the default methods:
388 defm.Foo.op1 :: forall a. Foo a => a -> Bool
389 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
391 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
392 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
393 if (op1 a dfoo x) && (< b dord y z) then y else z
396 When we come across an instance decl, we may need to use the default
399 instance Foo Int where {}
403 const.Foo.Int.op1 :: Int -> Bool
404 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
406 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
407 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
409 dfun.Foo.Int :: Foo Int
410 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
412 Notice that, as with method selectors above, we assume that dictionary
413 application is curried, so there's no need to mention the Ord dictionary
414 in const.Foo.Int.op2 (or the type variable).
417 instance Foo a => Foo [a] where {}
419 dfun.Foo.List :: forall a. Foo a -> Foo [a]
421 = /\ a -> \ dfoo_a ->
423 op1 = defm.Foo.op1 [a] dfoo_list
424 op2 = defm.Foo.op2 [a] dfoo_list
425 dfoo_list = (op1, op2)
435 -> TcM s (LIE, TcMonoBinds)
437 tcDefaultMethodBinds clas default_binds sigs
438 = -- Check that the default bindings come from this class
439 checkFromThisClass clas op_items default_binds `thenNF_Tc_`
441 -- Do each default method separately
442 -- For Hugs compatibility we make a default-method for every
443 -- class op, regardless of whether or not the programmer supplied an
444 -- explicit default decl for the class. GHC will actually never
445 -- call the default method for such operations, because it'll whip up
446 -- a more-informative default method at each instance decl.
447 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
449 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
451 prags = filter isPragSig sigs
453 (tyvars, _, _, op_items) = classBigSig clas
455 origin = ClassDeclOrigin
457 -- We make a separate binding for each default method.
458 -- At one time I used a single AbsBinds for all of them, thus
459 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
460 -- But that desugars into
461 -- ds = \d -> (..., ..., ...)
462 -- dm1 = \d -> case ds d of (a,b,c) -> a
463 -- And since ds is big, it doesn't get inlined, so we don't get good
464 -- default methods. Better to make separate AbsBinds for each
466 tc_dm op_item@(_, dm_id, _)
467 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
469 theta = [(mkClassPred clas inst_tys)]
471 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
473 avail_insts = this_dict
475 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
476 tcMethodBind clas origin clas_tyvars inst_tys theta
477 default_binds prags False
479 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
481 tcAddErrCtxt (defltMethCtxt clas) $
483 -- tcMethodBind has checked that the class_tyvars havn't
484 -- been unified with each other or another type, but we must
485 -- still zonk them before passing them to tcSimplifyAndCheck
486 mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
490 (ptext SLIT("class") <+> ppr clas)
491 (mkVarSet clas_tyvars')
493 insts_needed `thenTc` \ (const_lie, dict_binds) ->
499 [(clas_tyvars', dm_id, local_dm_id)]
500 emptyNameSet -- No inlines (yet)
501 (dict_binds `andMonoBinds` defm_bind)
503 returnTc (full_bind, const_lie)
507 checkFromThisClass :: Class -> [ClassOpItem] -> RenamedMonoBinds -> NF_TcM s ()
508 checkFromThisClass clas op_items mono_binds
509 = mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
512 check_from_this_class (bndr, loc)
513 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
514 | otherwise = tcAddSrcLoc loc $
515 addErrTc (badMethodErr bndr clas)
516 sel_names = [getOccName sel_id | (sel_id,_,_) <- op_items]
517 bndrs = bagToList (collectMonoBinders mono_binds)
521 @tcMethodBind@ is used to type-check both default-method and
522 instance-decl method declarations. We must type-check methods one at a
523 time, because their signatures may have different contexts and
530 -> [TcTyVar] -- Instantiated type variables for the
531 -- enclosing class/instance decl.
532 -- They'll be signature tyvars, and we
533 -- want to check that they don't get bound
534 -> [TcType] -- Instance types
535 -> TcThetaType -- Available theta; this could be used to check
536 -- the method signature, but actually that's done by
537 -- the caller; here, it's just used for the error message
538 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
539 -> [RenamedSig] -- Pramgas (just for this one)
540 -> Bool -- True <=> This method is from an instance declaration
541 -> ClassOpItem -- The method selector and default-method Id
542 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
544 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
545 meth_binds prags is_inst_decl
546 (sel_id, dm_id, explicit_dm)
547 = tcGetSrcLoc `thenNF_Tc` \ loc ->
549 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
550 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
553 meth_name = idName meth_id
554 maybe_user_bind = find_bind meth_name meth_binds
556 no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
558 meth_bind = case maybe_user_bind of
560 Nothing -> mk_default_bind meth_name loc
562 meth_prags = find_prags meth_name prags
565 -- Warn if no method binding, only if -fwarn-missing-methods
566 warnTc (is_inst_decl && opt_WarnMissingMethods && no_user_bind && not explicit_dm)
567 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
569 -- Check the bindings; first add inst_tyvars to the envt
570 -- so that we don't quantify over them in nested places
571 -- The *caller* put the class/inst decl tyvars into the envt
572 tcExtendGlobalTyVars (mkVarSet inst_tyvars) (
573 tcAddErrCtxt (methodCtxt sel_id) $
574 tcBindWithSigs NotTopLevel meth_bind
575 [sig_info] meth_prags NonRecursive
576 ) `thenTc` \ (binds, insts, _) ->
579 tcExtendLocalValEnv [(meth_name, meth_id)] (
580 tcSpecSigs meth_prags
581 ) `thenTc` \ (prag_binds1, prag_lie) ->
583 -- The prag_lie for a SPECIALISE pragma will mention the function
584 -- itself, so we have to simplify them away right now lest they float
586 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
589 -- Now check that the instance type variables
590 -- (or, in the case of a class decl, the class tyvars)
591 -- have not been unified with anything in the environment
592 tcAddErrCtxtM (sigCtxt sig_msg (mkSigmaTy inst_tyvars inst_theta (idType meth_id))) $
593 checkSigTyVars inst_tyvars `thenTc_`
595 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
596 insts `plusLIE` prag_lie',
599 sig_msg ty = sep [ptext SLIT("When checking the expected type for"),
600 nest 4 (ppr sel_name <+> dcolon <+> ppr ty)]
602 sel_name = idName sel_id
604 -- The renamer just puts the selector ID as the binder in the method binding
605 -- but we must use the method name; so we substitute it here. Crude but simple.
606 find_bind meth_name (FunMonoBind op_name fix matches loc)
607 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
608 find_bind meth_name (PatMonoBind (VarPatIn op_name) grhss loc)
609 | op_name == sel_name = Just (PatMonoBind (VarPatIn meth_name) grhss loc)
610 find_bind meth_name (AndMonoBinds b1 b2)
611 = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
612 find_bind meth_name other = Nothing -- Default case
615 -- Find the prags for this method, and replace the
616 -- selector name with the method name
617 find_prags meth_name [] = []
618 find_prags meth_name (SpecSig name ty loc : prags)
619 | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
620 find_prags meth_name (InlineSig name phase loc : prags)
621 | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
622 find_prags meth_name (NoInlineSig name phase loc : prags)
623 | name == sel_name = NoInlineSig meth_name phase loc : find_prags meth_name prags
624 find_prags meth_name (prag:prags) = find_prags meth_name prags
626 mk_default_bind local_meth_name loc
627 = PatMonoBind (VarPatIn local_meth_name)
628 (GRHSs (unguardedRHS (default_expr loc) loc) EmptyBinds Nothing)
632 | explicit_dm = HsVar (getName dm_id) -- There's a default method
633 | otherwise = error_expr loc -- No default method
635 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
636 (HsLit (HsString (_PK_ (error_msg loc))))
638 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
644 classArityErr class_name
645 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
647 superClassErr class_name sc
648 = ptext SLIT("Illegal superclass constraint") <+> quotes (pprHsClassAssertion sc)
649 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
651 defltMethCtxt class_name
652 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
655 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
657 badMethodErr bndr clas
658 = hsep [ptext SLIT("Class"), quotes (ppr clas),
659 ptext SLIT("does not have a method"), quotes (ppr bndr)]
661 omittedMethodWarn sel_id clas
662 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
663 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]