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 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 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 CLASS SIGNATURES,
155 mapTc (tcClassSig rec_env rec_class tyvars)
156 (filter isClassOpSig class_sigs)
157 `thenTc` \ sig_stuff ->
159 -- MAKE THE CLASS OBJECT ITSELF
161 (op_tys, op_items) = unzip sig_stuff
162 rec_class_inst_env = rec_inst_mapper rec_class
163 clas = mkClass class_name tyvars
164 sc_theta sc_sel_ids op_items
168 dict_component_tys = sc_tys ++ op_tys
169 new_or_data = case dict_component_tys of
173 dict_con = mkDataCon datacon_name
174 [notMarkedStrict | _ <- dict_component_tys]
175 [{- No labelled fields -}]
178 [{-No existential tyvars-}] [{-Or context-}]
182 dict_con_id = mkDataConId dict_con
184 argvrcs = lookupWithDefaultFM rec_vrcs (pprPanic "tcClassDecl1: argvrcs:" $
188 tycon = mkAlgTyCon tycon_name
193 [dict_con] -- Constructors
195 (Just clas) -- Yes! It's a dictionary
204 tcClassContext :: Name -> Class -> [TyVar]
205 -> RenamedContext -- class context
206 -> [Name] -- Names for superclass selectors
207 -> TcM s (ThetaType, -- the superclass context
208 [Type], -- types of the superclass dictionaries
209 [Id]) -- superclass selector Ids
211 tcClassContext class_name rec_class rec_tyvars context sc_sel_names
212 = -- Check the context.
213 -- The renamer has already checked that the context mentions
214 -- only the type variable of the class decl.
216 -- For std Haskell check that the context constrains only tyvars
217 (if opt_GlasgowExts then
220 mapTc check_constraint context
223 tcContext context `thenTc` \ sc_theta ->
226 sc_tys = [mkDictTy sc tys | (sc,tys) <- sc_theta]
227 sc_sel_ids = zipWithEqual "tcClassContext" mk_super_id sc_sel_names sc_tys
230 returnTc (sc_theta, sc_tys, sc_sel_ids)
233 rec_tyvar_tys = mkTyVarTys rec_tyvars
235 mk_super_id name dict_ty
236 = mkDictSelId name rec_class ty
238 ty = mkForAllTys rec_tyvars $
239 mkFunTy (mkDictTy rec_class rec_tyvar_tys) dict_ty
241 check_constraint (c, tys) = checkTc (all is_tyvar tys)
242 (superClassErr class_name (c, tys))
244 is_tyvar (MonoTyVar _) = True
245 is_tyvar other = False
248 tcClassSig :: ValueEnv -- Knot tying only!
249 -> Class -- ...ditto...
250 -> [TyVar] -- The class type variable, used for error check only
252 -> TcM s (Type, -- Type of the method
253 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
256 tcClassSig rec_env rec_clas rec_clas_tyvars
257 (ClassOpSig op_name dm_name explicit_dm
259 = tcAddSrcLoc src_loc $
261 -- Check the type signature. NB that the envt *already has*
262 -- bindings for the type variables; see comments in TcTyAndClassDcls.
264 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
265 -- and that it is not constrained by theta
266 -- traceTc (text "tcClassSig" <+> ppr op_name) `thenTc_`
267 tcHsTopType op_ty `thenTc` \ local_ty ->
269 global_ty = mkSigmaTy rec_clas_tyvars
270 [(rec_clas, mkTyVarTys rec_clas_tyvars)]
273 -- Build the selector id and default method id
274 sel_id = mkDictSelId op_name rec_clas global_ty
275 dm_id = mkDefaultMethodId dm_name rec_clas global_ty
276 final_dm_id = tcAddImportedIdInfo rec_env dm_id
278 -- traceTc (text "tcClassSig done" <+> ppr op_name) `thenTc_`
279 returnTc (local_ty, (sel_id, final_dm_id, explicit_dm))
283 %************************************************************************
285 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
287 %************************************************************************
289 The purpose of pass 2 is
292 to beat on the explicitly-provided default-method decls (if any),
293 using them to produce a complete set of default-method decls.
294 (Omitted ones elicit an error message.)
296 to produce a definition for the selector function for each method
297 and superclass dictionary.
300 Pass~2 only applies to locally-defined class declarations.
302 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
303 each local class decl.
306 tcClassDecls2 :: [RenamedHsDecl]
307 -> NF_TcM s (LIE, TcMonoBinds)
311 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
312 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls, isClassDecl cls_decl]
314 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
315 tc2 `thenNF_Tc` \ (lie2, binds2) ->
316 returnNF_Tc (lie1 `plusLIE` lie2,
317 binds1 `AndMonoBinds` binds2)
320 @tcClassDecl2@ is the business end of things.
323 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
324 -> NF_TcM s (LIE, TcMonoBinds)
326 tcClassDecl2 (ClassDecl context class_name
327 tyvar_names class_sigs default_binds pragmas _ _ _ src_loc)
329 | not (isLocallyDefined class_name)
330 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
332 | otherwise -- It is locally defined
333 = recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
334 tcAddSrcLoc src_loc $
336 -- Get the relevant class
337 tcLookupClass class_name `thenNF_Tc` \ clas ->
339 -- The selector binds are already in the selector Id's unfoldings
340 sel_binds = [ CoreMonoBind sel_id (unfoldingTemplate (getIdUnfolding sel_id))
341 | sel_id <- classSelIds clas
344 -- Generate bindings for the default methods
345 tcDefaultMethodBinds clas default_binds class_sigs `thenTc` \ (const_insts, meth_binds) ->
347 returnTc (const_insts,
348 meth_binds `AndMonoBinds` andMonoBindList sel_binds)
351 %************************************************************************
353 \subsection[Default methods]{Default methods}
355 %************************************************************************
357 The default methods for a class are each passed a dictionary for the
358 class, so that they get access to the other methods at the same type.
359 So, given the class decl
363 op2 :: Ord b => a -> b -> b -> b
366 op2 x y z = if (op1 x) && (y < z) then y else z
368 we get the default methods:
370 defm.Foo.op1 :: forall a. Foo a => a -> Bool
371 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
373 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
374 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
375 if (op1 a dfoo x) && (< b dord y z) then y else z
378 When we come across an instance decl, we may need to use the default
381 instance Foo Int where {}
385 const.Foo.Int.op1 :: Int -> Bool
386 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
388 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
389 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
391 dfun.Foo.Int :: Foo Int
392 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
394 Notice that, as with method selectors above, we assume that dictionary
395 application is curried, so there's no need to mention the Ord dictionary
396 in const.Foo.Int.op2 (or the type variable).
399 instance Foo a => Foo [a] where {}
401 dfun.Foo.List :: forall a. Foo a -> Foo [a]
403 = /\ a -> \ dfoo_a ->
405 op1 = defm.Foo.op1 [a] dfoo_list
406 op2 = defm.Foo.op2 [a] dfoo_list
407 dfoo_list = (op1, op2)
417 -> TcM s (LIE, TcMonoBinds)
419 tcDefaultMethodBinds clas default_binds sigs
420 = -- Check that the default bindings come from this class
421 checkFromThisClass clas op_items default_binds `thenNF_Tc_`
423 -- Do each default method separately
424 -- For Hugs compatibility we make a default-method for every
425 -- class op, regardless of whether or not the programmer supplied an
426 -- explicit default decl for the class. GHC will actually never
427 -- call the default method for such operations, because it'll whip up
428 -- a more-informative default method at each instance decl.
429 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
431 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
433 prags = filter isPragSig sigs
435 (tyvars, _, _, op_items) = classBigSig clas
437 origin = ClassDeclOrigin
439 -- We make a separate binding for each default method.
440 -- At one time I used a single AbsBinds for all of them, thus
441 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
442 -- But that desugars into
443 -- ds = \d -> (..., ..., ...)
444 -- dm1 = \d -> case ds d of (a,b,c) -> a
445 -- And since ds is big, it doesn't get inlined, so we don't get good
446 -- default methods. Better to make separate AbsBinds for each
448 tc_dm op_item@(_, dm_id, _)
449 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
451 theta = [(clas,inst_tys)]
453 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
455 avail_insts = this_dict
457 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
458 tcMethodBind clas origin clas_tyvars inst_tys theta
459 default_binds prags False
461 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
463 tcAddErrCtxt (defltMethCtxt clas) $
465 -- tcMethodBind has checked that the class_tyvars havn't
466 -- been unified with each other or another type, but we must
467 -- still zonk them before passing them to tcSimplifyAndCheck
468 mapNF_Tc zonkTcTyVarBndr clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
472 (ptext SLIT("class") <+> ppr clas)
473 (mkVarSet clas_tyvars')
475 insts_needed `thenTc` \ (const_lie, dict_binds) ->
481 [(clas_tyvars', dm_id, local_dm_id)]
482 emptyNameSet -- No inlines (yet)
483 (dict_binds `andMonoBinds` defm_bind)
485 returnTc (full_bind, const_lie)
489 checkFromThisClass :: Class -> [ClassOpItem] -> RenamedMonoBinds -> NF_TcM s ()
490 checkFromThisClass clas op_items mono_binds
491 = mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
494 check_from_this_class (bndr, loc)
495 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
496 | otherwise = tcAddSrcLoc loc $
497 addErrTc (badMethodErr bndr clas)
498 sel_names = [getOccName sel_id | (sel_id,_,_) <- op_items]
499 bndrs = bagToList (collectMonoBinders mono_binds)
503 @tcMethodBind@ is used to type-check both default-method and
504 instance-decl method declarations. We must type-check methods one at a
505 time, because their signatures may have different contexts and
512 -> [TcTyVar] -- Instantiated type variables for the
513 -- enclosing class/instance decl.
514 -- They'll be signature tyvars, and we
515 -- want to check that they don't get bound
516 -> [TcType] -- Instance types
517 -> TcThetaType -- Available theta; this could be used to check
518 -- the method signature, but actually that's done by
519 -- the caller; here, it's just used for the error message
520 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
521 -> [RenamedSig] -- Pramgas (just for this one)
522 -> Bool -- True <=> This method is from an instance declaration
523 -> ClassOpItem -- The method selector and default-method Id
524 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
526 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
527 meth_binds prags is_inst_decl
528 (sel_id, dm_id, explicit_dm)
529 = tcGetSrcLoc `thenNF_Tc` \ loc ->
531 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
532 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
535 meth_name = idName meth_id
536 maybe_user_bind = find_bind meth_name meth_binds
538 no_user_bind = case maybe_user_bind of {Nothing -> True; other -> False}
540 meth_bind = case maybe_user_bind of
542 Nothing -> mk_default_bind meth_name loc
544 meth_prags = find_prags meth_name prags
547 -- Warn if no method binding, only if -fwarn-missing-methods
548 warnTc (is_inst_decl && opt_WarnMissingMethods && no_user_bind && not explicit_dm)
549 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
551 -- Check the bindings; first add inst_tyvars to the envt
552 -- so that we don't quantify over them in nested places
553 -- The *caller* put the class/inst decl tyvars into the envt
554 tcExtendGlobalTyVars (mkVarSet inst_tyvars) (
555 tcAddErrCtxt (methodCtxt sel_id) $
556 tcBindWithSigs NotTopLevel meth_bind
557 [sig_info] meth_prags NonRecursive
558 ) `thenTc` \ (binds, insts, _) ->
561 tcExtendLocalValEnv [(meth_name, meth_id)] (
562 tcSpecSigs meth_prags
563 ) `thenTc` \ (prag_binds1, prag_lie) ->
565 -- The prag_lie for a SPECIALISE pragma will mention the function
566 -- itself, so we have to simplify them away right now lest they float
568 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
571 -- Now check that the instance type variables
572 -- (or, in the case of a class decl, the class tyvars)
573 -- have not been unified with anything in the environment
574 tcAddErrCtxtM (sigCtxt sig_msg (mkSigmaTy inst_tyvars inst_theta (idType meth_id))) $
575 checkSigTyVars inst_tyvars `thenTc_`
577 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
578 insts `plusLIE` prag_lie',
581 sig_msg ty = sep [ptext SLIT("When checking the expected type for"),
582 nest 4 (ppr sel_name <+> dcolon <+> ppr ty)]
584 sel_name = idName sel_id
586 -- The renamer just puts the selector ID as the binder in the method binding
587 -- but we must use the method name; so we substitute it here. Crude but simple.
588 find_bind meth_name (FunMonoBind op_name fix matches loc)
589 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
590 find_bind meth_name (PatMonoBind (VarPatIn op_name) grhss loc)
591 | op_name == sel_name = Just (PatMonoBind (VarPatIn meth_name) grhss loc)
592 find_bind meth_name (AndMonoBinds b1 b2)
593 = find_bind meth_name b1 `seqMaybe` find_bind meth_name b2
594 find_bind meth_name other = Nothing -- Default case
597 -- Find the prags for this method, and replace the
598 -- selector name with the method name
599 find_prags meth_name [] = []
600 find_prags meth_name (SpecSig name ty loc : prags)
601 | name == sel_name = SpecSig meth_name ty loc : find_prags meth_name prags
602 find_prags meth_name (InlineSig name phase loc : prags)
603 | name == sel_name = InlineSig meth_name phase loc : find_prags meth_name prags
604 find_prags meth_name (NoInlineSig name phase loc : prags)
605 | name == sel_name = NoInlineSig meth_name phase loc : find_prags meth_name prags
606 find_prags meth_name (prag:prags) = find_prags meth_name prags
608 mk_default_bind local_meth_name loc
609 = PatMonoBind (VarPatIn local_meth_name)
610 (GRHSs (unguardedRHS (default_expr loc) loc) EmptyBinds Nothing)
614 | explicit_dm = HsVar (getName dm_id) -- There's a default method
615 | otherwise = error_expr loc -- No default method
617 error_expr loc = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
618 (HsLit (HsString (_PK_ (error_msg loc))))
620 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
626 classArityErr class_name
627 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
629 superClassErr class_name sc
630 = ptext SLIT("Illegal superclass constraint") <+> quotes (pprClassAssertion sc)
631 <+> ptext SLIT("in declaration for class") <+> quotes (ppr class_name)
633 defltMethCtxt class_name
634 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr class_name)
637 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
639 badMethodErr bndr clas
640 = hsep [ptext SLIT("Class"), quotes (ppr clas),
641 ptext SLIT("does not have a method"), quotes (ppr bndr)]
643 omittedMethodWarn sel_id clas
644 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
645 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]