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, isPragSig, 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, plusLIEs, 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, classSelIds, Class, ClassOpItem )
44 import CmdLineOpts ( opt_GlasgowExts, opt_WarnMissingMethods )
45 import MkId ( mkDictSelId, mkDataConId, mkDefaultMethodId )
46 import DataCon ( mkDataCon, notMarkedStrict )
47 import Id ( Id, setInlinePragma, getIdUnfolding, idType, idName )
48 import CoreUnfold ( unfoldingTemplate )
50 import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..) )
51 import NameSet ( emptyNameSet )
53 import Type ( mkFunTy, mkTyVarTy, mkTyVarTys, mkDictTy,
54 mkSigmaTy, mkForAllTys, Type, ThetaType,
55 boxedTypeKind, mkArrowKind
57 import Var ( tyVarKind, TyVar )
58 import VarSet ( mkVarSet )
59 import TyCon ( mkAlgTyCon )
60 import Unique ( Unique, Uniquable(..) )
62 import Maybes ( seqMaybe )
63 import FiniteMap ( lookupWithDefaultFM )
70 Every class implicitly declares a new data type, corresponding to dictionaries
71 of that class. So, for example:
73 class (D a) => C a where
75 op2 :: forall b. Ord b => a -> b -> b
77 would implicitly declare
79 data CDict a = CDict (D a)
81 (forall b. Ord b => a -> b -> b)
83 (We could use a record decl, but that means changing more of the existing apparatus.
86 For classes with just one superclass+method, we use a newtype decl instead:
89 op :: forallb. a -> b -> b
93 newtype CDict a = CDict (forall b. a -> b -> b)
95 Now DictTy in Type is just a form of type synomym:
96 DictTy c t = TyConTy CDict `AppTy` t
98 Death to "ExpandingDicts".
101 %************************************************************************
103 \subsection{Kind checking}
105 %************************************************************************
108 kcClassDecl (ClassDecl context class_name
109 tyvar_names fundeps class_sigs def_methods pragmas
110 tycon_name datacon_name sc_sel_names src_loc)
111 = -- CHECK ARITY 1 FOR HASKELL 1.4
112 checkTc (opt_GlasgowExts || length tyvar_names == 1)
113 (classArityErr class_name) `thenTc_`
115 -- Get the (mutable) class kind
116 tcLookupTy class_name `thenNF_Tc` \ (kind, _, _) ->
118 -- Make suitable tyvars and do kind checking
119 -- The net effect is to mutate the class kind
120 tcExtendTopTyVarScope kind tyvar_names $ \ _ _ ->
121 tcContext context `thenTc_`
122 mapTc kc_sig the_class_sigs `thenTc_`
126 the_class_sigs = filter isClassOpSig class_sigs
128 kc_sig (ClassOpSig _ _ _ op_ty loc) = tcAddSrcLoc loc (tcHsType op_ty)
132 %************************************************************************
134 \subsection{Type checking}
136 %************************************************************************
139 tcClassDecl1 rec_env rec_inst_mapper rec_vrcs
140 (ClassDecl context class_name
141 tyvar_names fundeps class_sigs def_methods pragmas
142 tycon_name datacon_name sc_sel_names src_loc)
143 = -- LOOK THINGS UP IN THE ENVIRONMENT
144 tcLookupTy class_name `thenTc` \ (class_kind, _, AClass rec_class) ->
145 tcExtendTopTyVarScope class_kind tyvar_names $ \ tyvars _ ->
146 -- The class kind is by now immutable
149 -- traceTc (text "tcClassCtxt" <+> ppr class_name) `thenTc_`
150 tcClassContext class_name rec_class tyvars context sc_sel_names
151 `thenTc` \ (sc_theta, sc_tys, sc_sel_ids) ->
152 -- traceTc (text "tcClassCtxt done" <+> ppr class_name) `thenTc_`
154 -- CHECK THE FUNCTIONAL DEPENDENCIES,
155 tcFundeps fundeps `thenTc` \ fds ->
157 -- CHECK THE CLASS SIGNATURES,
158 mapTc (tcClassSig rec_env rec_class tyvars)
159 (filter isClassOpSig class_sigs)
160 `thenTc` \ sig_stuff ->
162 -- MAKE THE CLASS OBJECT ITSELF
164 (op_tys, op_items) = unzip sig_stuff
165 rec_class_inst_env = rec_inst_mapper rec_class
166 clas = mkClass class_name tyvars fds
167 sc_theta sc_sel_ids op_items
171 dict_component_tys = sc_tys ++ op_tys
172 new_or_data = case dict_component_tys of
176 dict_con = mkDataCon datacon_name
177 [notMarkedStrict | _ <- dict_component_tys]
178 [{- No labelled fields -}]
181 [{-No existential tyvars-}] [{-Or context-}]
185 dict_con_id = mkDataConId dict_con
187 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
191 tycon = mkAlgTyCon tycon_name
196 [dict_con] -- Constructors
198 (Just clas) -- Yes! It's a dictionary
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` \(_, _, thing) ->
214 ATyVar tv -> returnTc tv
215 -- ZZ else should fail more gracefully
219 tcClassContext :: Name -> Class -> [TyVar]
220 -> RenamedContext -- class context
221 -> [Name] -- Names for superclass selectors
222 -> TcM s (ThetaType, -- 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_tys = [mkDictTy sc tys | (sc,tys) <- sc_theta]
242 sc_sel_ids = zipWithEqual "tcClassContext" mk_super_id sc_sel_names sc_tys
245 returnTc (sc_theta, sc_tys, sc_sel_ids)
248 rec_tyvar_tys = mkTyVarTys rec_tyvars
250 mk_super_id name dict_ty
251 = mkDictSelId name rec_class ty
253 ty = mkForAllTys rec_tyvars $
254 mkFunTy (mkDictTy rec_class rec_tyvar_tys) dict_ty
256 check_constraint (c, tys) = checkTc (all is_tyvar tys)
257 (superClassErr class_name (c, tys))
259 is_tyvar (MonoTyVar _) = True
260 is_tyvar other = False
263 tcClassSig :: ValueEnv -- Knot tying only!
264 -> Class -- ...ditto...
265 -> [TyVar] -- The class type variable, used for error check only
267 -> TcM s (Type, -- Type of the method
268 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
271 tcClassSig rec_env rec_clas rec_clas_tyvars
272 (ClassOpSig op_name dm_name explicit_dm
274 = tcAddSrcLoc src_loc $
276 -- Check the type signature. NB that the envt *already has*
277 -- bindings for the type variables; see comments in TcTyAndClassDcls.
279 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
280 -- and that it is not constrained by theta
281 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
282 tcHsTopType op_ty `thenTc` \ local_ty ->
284 global_ty = mkSigmaTy rec_clas_tyvars
285 [(rec_clas, mkTyVarTys rec_clas_tyvars)]
288 -- Build the selector id and default method id
289 sel_id = mkDictSelId op_name rec_clas global_ty
290 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
291 final_dm_id = tcAddImportedIdInfo rec_env dm_id
293 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
294 returnTc (local_ty, (sel_id, final_dm_id, explicit_dm))
298 %************************************************************************
300 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
302 %************************************************************************
304 The purpose of pass 2 is
307 to beat on the explicitly-provided default-method decls (if any),
308 using them to produce a complete set of default-method decls.
309 (Omitted ones elicit an error message.)
311 to produce a definition for the selector function for each method
312 and superclass dictionary.
315 Pass~2 only applies to locally-defined class declarations.
317 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
318 each local class decl.
321 tcClassDecls2 :: [RenamedHsDecl]
322 -> NF_TcM s (LIE, TcMonoBinds)
326 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
327 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
329 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
330 tc2 `thenNF_Tc` \ (lie2, binds2) ->
331 returnNF_Tc (lie1 `plusLIE` lie2,
332 binds1 `AndMonoBinds` binds2)
335 @tcClassDecl2@ is the business end of things.
338 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
339 -> NF_TcM s (LIE, TcMonoBinds)
341 tcClassDecl2 (ClassDecl context class_name
342 tyvar_names _ class_sigs default_binds pragmas _ _ _ src_loc)
344 | not (isLocallyDefined class_name)
345 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
347 | otherwise -- It is locally defined
348 = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
349 tcAddSrcLoc src_loc $
351 -- Get the relevant class
352 tcLookupClass class_name `thenNF_Tc` \ clas ->
354 -- The selector binds are already in the selector Id's unfoldings
355 sel_binds = [ CoreMonoBind sel_id (unfoldingTemplate (getIdUnfolding sel_id))
356 | sel_id <- classSelIds clas
359 -- Generate bindings for the default methods
360 tcDefaultMethodBinds clas default_binds class_sigs `thenTc` \ (const_insts, meth_binds) ->
362 returnTc (const_insts,
363 meth_binds `AndMonoBinds` andMonoBindList sel_binds)
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 = [(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 (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 phase loc : prags)
618 | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
619 find_prags meth_name (NoInlineSig name phase loc : prags)
620 | name == sel_name = NoInlineSig meth_name phase 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 | explicit_dm = HsVar (getName dm_id) -- There's a default method
630 | otherwise = error_expr loc -- No default method
632 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
633 (HsLit (HsString (_PK_ (error_msg loc))))
635 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
641 classArityErr class_name
642 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
644 superClassErr class_name sc
645 = ptext SLIT("Illegal superclass constraint") <+> quotes (pprClassAssertion sc)
646 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
648 defltMethCtxt class_name
649 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
652 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
654 badMethodErr bndr clas
655 = hsep [ptext SLIT("Class"), quotes (ppr clas),
656 ptext SLIT("does not have a method"), quotes (ppr bndr)]
658 omittedMethodWarn sel_id clas
659 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
660 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]