2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassSigs, tcClassDecl2,
9 MethodSpec, tcMethodBind, mkMethodBind,
10 tcAddDeclCtxt, badMethodErr
13 #include "HsVersions.h"
16 import BasicTypes ( RecFlag(..), NewOrData(..) )
17 import RnHsSyn ( maybeGenericMatch, extractHsTyVars )
18 import RnExpr ( rnLExpr )
19 import RnEnv ( lookupTopBndrRn, lookupImportedName )
21 import Inst ( Inst, InstOrigin(..), instToId, newDicts, newMethod )
22 import TcEnv ( tcLookupLocatedClass, tcExtendLocalValEnv2,
24 InstInfo(..), pprInstInfoDetails,
25 simpleInstInfoTyCon, simpleInstInfoTy,
26 InstBindings(..), newDFunName
28 import TcBinds ( tcMonoBinds, tcSpecSigs )
29 import TcHsType ( TcSigInfo(..), mkTcSig, tcHsKindedType, tcHsSigType )
30 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
31 import TcUnify ( checkSigTyVars, sigCtxt )
32 import TcMType ( tcInstTyVars, UserTypeCtxt( GenPatCtxt ) )
33 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
34 mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
35 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
36 getClassPredTys_maybe, mkPhiTy, mkTyVarTy
39 import Generics ( mkGenericRhs, validGenericInstanceType )
40 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
41 import Class ( classTyVars, classBigSig,
42 Class, ClassOpItem, DefMeth (..) )
43 import TyCon ( TyCon, tyConName, tyConHasGenerics )
44 import Subst ( substTyWith )
45 import MkId ( mkDefaultMethodId, mkDictFunId )
46 import Id ( Id, idType, idName, mkUserLocal, setInlinePragma )
47 import Name ( Name, NamedThing(..) )
48 import NameEnv ( NameEnv, lookupNameEnv, mkNameEnv )
49 import NameSet ( emptyNameSet, unitNameSet, nameSetToList )
50 import OccName ( reportIfUnused, mkDefaultMethodOcc )
51 import RdrName ( RdrName, mkDerivedRdrName )
54 import PrelNames ( genericTyConNames )
56 import UnicodeUtil ( stringToUtf8 )
57 import ErrUtils ( dumpIfSet_dyn )
58 import Util ( count, lengthIs, isSingleton, lengthExceeds )
59 import Unique ( Uniquable(..) )
60 import ListSetOps ( equivClassesByUniq, minusList )
61 import SrcLoc ( Located(..), srcSpanStart, unLoc, noLoc )
62 import Maybes ( seqMaybe, isJust, mapCatMaybes )
63 import List ( partition )
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 Type-checking the class op signatures
107 %************************************************************************
110 tcClassSigs :: Name -- Name of the class
115 type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
116 -- between tcClassSigs and buildClass
117 tcClassSigs clas sigs def_methods
118 = do { dm_env <- checkDefaultBinds clas op_names def_methods
119 ; mappM (tcClassSig dm_env) op_sigs }
121 op_sigs = [sig | sig@(L _ (Sig _ _)) <- sigs]
122 op_names = [n | sig@(L _ (Sig (L _ n) _)) <- op_sigs]
125 checkDefaultBinds :: Name -> [Name] -> LHsBinds Name -> TcM (NameEnv Bool)
126 -- Check default bindings
127 -- a) must be for a class op for this class
128 -- b) must be all generic or all non-generic
129 -- and return a mapping from class-op to Bool
130 -- where True <=> it's a generic default method
131 checkDefaultBinds clas ops binds
132 = do dm_infos <- mapM (addLocM (checkDefaultBind clas ops)) (bagToList binds)
133 return (mkNameEnv dm_infos)
135 checkDefaultBind clas ops (FunBind (L _ op) _ matches)
136 = do { -- Check that the op is from this class
137 checkTc (op `elem` ops) (badMethodErr clas op)
139 -- Check that all the defns ar generic, or none are
140 ; checkTc (all_generic || none_generic) (mixedGenericErr op)
142 ; returnM (op, all_generic)
145 n_generic = count (isJust . maybeGenericMatch) matches
146 none_generic = n_generic == 0
147 all_generic = matches `lengthIs` n_generic
150 tcClassSig :: NameEnv Bool -- Info about default methods;
154 tcClassSig dm_env (L loc (Sig (L _ op_name) op_hs_ty))
155 = addSrcSpan loc $ do
156 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
157 ; let dm = case lookupNameEnv dm_env op_name of
159 Just False -> DefMeth
160 Just True -> GenDefMeth
161 ; returnM (op_name, dm, op_ty) }
165 %************************************************************************
167 \subsection[Default methods]{Default methods}
169 %************************************************************************
171 The default methods for a class are each passed a dictionary for the
172 class, so that they get access to the other methods at the same type.
173 So, given the class decl
177 op2 :: Ord b => a -> b -> b -> b
180 op2 x y z = if (op1 x) && (y < z) then y else z
182 we get the default methods:
184 defm.Foo.op1 :: forall a. Foo a => a -> Bool
185 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
187 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
188 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
189 if (op1 a dfoo x) && (< b dord y z) then y else z
192 When we come across an instance decl, we may need to use the default
195 instance Foo Int where {}
199 const.Foo.Int.op1 :: Int -> Bool
200 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
202 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
203 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
205 dfun.Foo.Int :: Foo Int
206 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
208 Notice that, as with method selectors above, we assume that dictionary
209 application is curried, so there's no need to mention the Ord dictionary
210 in const.Foo.Int.op2 (or the type variable).
213 instance Foo a => Foo [a] where {}
215 dfun.Foo.List :: forall a. Foo a -> Foo [a]
217 = /\ a -> \ dfoo_a ->
219 op1 = defm.Foo.op1 [a] dfoo_list
220 op2 = defm.Foo.op2 [a] dfoo_list
221 dfoo_list = (op1, op2)
226 @tcClassDecls2@ generates bindings for polymorphic default methods
227 (generic default methods have by now turned into instance declarations)
230 tcClassDecl2 :: LTyClDecl Name -- The class declaration
231 -> TcM (LHsBinds Id, [Id])
233 tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
234 tcdMeths = default_binds}))
235 = recoverM (returnM (emptyBag, [])) $
237 tcLookupLocatedClass class_name `thenM` \ clas ->
239 -- We make a separate binding for each default method.
240 -- At one time I used a single AbsBinds for all of them, thus
241 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
242 -- But that desugars into
243 -- ds = \d -> (..., ..., ...)
244 -- dm1 = \d -> case ds d of (a,b,c) -> a
245 -- And since ds is big, it doesn't get inlined, so we don't get good
246 -- default methods. Better to make separate AbsBinds for each
248 (tyvars, _, _, op_items) = classBigSig clas
249 prags = filter (isPragSig.unLoc) sigs
250 tc_dm = tcDefMeth clas tyvars default_binds prags
252 dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
253 -- Generate code for polymorphic default methods only
254 -- (Generic default methods have turned into instance decls by now.)
255 -- This is incompatible with Hugs, which expects a polymorphic
256 -- default method for every class op, regardless of whether or not
257 -- the programmer supplied an explicit default decl for the class.
258 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
260 mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
261 returnM (listToBag defm_binds, concat dm_ids_s)
263 tcDefMeth clas tyvars binds_in prags sel_id
264 = lookupTopBndrRn (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
265 tcInstTyVars ClsTv tyvars `thenM` \ (clas_tyvars, inst_tys, _) ->
267 dm_ty = idType sel_id -- Same as dict selector!
268 theta = [mkClassPred clas inst_tys]
269 local_dm_id = mkDefaultMethodId dm_name dm_ty
270 xtve = tyvars `zip` clas_tyvars
271 origin = ClassDeclOrigin
273 mkMethodBind origin clas inst_tys
274 binds_in (sel_id, DefMeth) `thenM` \ (_, meth_info) ->
275 newDicts origin theta `thenM` \ [this_dict] ->
276 getLIE (tcMethodBind xtve clas_tyvars theta
277 [this_dict] prags meth_info) `thenM` \ (defm_bind, insts_needed) ->
279 addErrCtxt (defltMethCtxt clas) $
283 (ptext SLIT("class") <+> ppr clas)
286 insts_needed `thenM` \ dict_binds ->
288 -- Simplification can do unification
289 checkSigTyVars clas_tyvars `thenM` \ clas_tyvars' ->
292 (_,dm_inst_id,_) = meth_info
296 [(clas_tyvars', local_dm_id, dm_inst_id)]
297 emptyNameSet -- No inlines (yet)
298 (dict_binds `unionBags` defm_bind)
300 returnM (noLoc full_bind, [local_dm_id])
302 mkDefMethRdrName :: Id -> RdrName
303 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
307 %************************************************************************
309 \subsection{Typechecking a method}
311 %************************************************************************
313 @tcMethodBind@ is used to type-check both default-method and
314 instance-decl method declarations. We must type-check methods one at a
315 time, because their signatures may have different contexts and
319 type MethodSpec = (Id, -- Global selector Id
320 Id, -- Local Id (class tyvars instantiated)
321 LHsBind Name) -- Binding for the method
324 :: [(TyVar,TcTyVar)] -- Bindings for type environment
325 -> [TcTyVar] -- Instantiated type variables for the
326 -- enclosing class/instance decl.
327 -- They'll be signature tyvars, and we
328 -- want to check that they don't get bound
329 -- Always equal the range of the type envt
330 -> TcThetaType -- Available theta; it's just used for the error message
331 -> [Inst] -- Available from context, used to simplify constraints
332 -- from the method body
333 -> [LSig Name] -- Pragmas (e.g. inline pragmas)
334 -> MethodSpec -- Details of this method
337 tcMethodBind xtve inst_tyvars inst_theta avail_insts prags
338 (sel_id, meth_id, meth_bind)
339 = -- Check the bindings; first adding inst_tyvars to the envt
340 -- so that we don't quantify over them in nested places
341 mkTcSig meth_id `thenM` \ meth_sig ->
343 tcExtendTyVarEnv2 xtve (
344 addErrCtxt (methodCtxt sel_id) $
346 tcMonoBinds (unitBag meth_bind) [meth_sig] NonRecursive
347 ) `thenM` \ ((meth_bind,_), meth_lie) ->
349 -- Now do context reduction. We simplify wrt both the local tyvars
350 -- and the ones of the class/instance decl, so that there is
353 -- op :: Eq a => a -> b -> a
355 -- We do this for each method independently to localise error messages
358 TySigInfo { sig_poly_id = meth_id, sig_tvs = meth_tvs,
359 sig_theta = meth_theta, sig_mono_id = local_meth_id } = meth_sig
361 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
362 newDicts SignatureOrigin meth_theta `thenM` \ meth_dicts ->
364 all_tyvars = meth_tvs ++ inst_tyvars
365 all_insts = avail_insts ++ meth_dicts
368 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
369 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
371 checkSigTyVars all_tyvars `thenM` \ all_tyvars' ->
374 sel_name = idName sel_id
375 inline_prags = [ (is_inl, phase)
376 | L _ (InlineSig is_inl (L _ name) phase) <- prags,
379 | prag@(L _ (SpecSig (L _ name) _)) <- prags,
382 -- Attach inline pragmas as appropriate
383 (final_meth_id, inlines)
384 | ((is_inline, phase) : _) <- inline_prags
385 = (meth_id `setInlinePragma` phase,
386 if is_inline then unitNameSet (idName meth_id) else emptyNameSet)
388 = (meth_id, emptyNameSet)
390 meth_tvs' = take (length meth_tvs) all_tyvars'
391 poly_meth_bind = noLoc $ AbsBinds meth_tvs'
392 (map instToId meth_dicts)
393 [(meth_tvs', final_meth_id, local_meth_id)]
395 (lie_binds `unionBags` meth_bind)
398 -- Deal with specialisation pragmas
399 -- The sel_name is what appears in the pragma
400 tcExtendLocalValEnv2 [(sel_name, final_meth_id)] (
401 getLIE (tcSpecSigs spec_prags) `thenM` \ (spec_binds1, prag_lie) ->
403 -- The prag_lie for a SPECIALISE pragma will mention the function itself,
404 -- so we have to simplify them away right now lest they float outwards!
405 bindInstsOfLocalFuns prag_lie [final_meth_id] `thenM` \ spec_binds2 ->
406 returnM (spec_binds1 `unionBags` spec_binds2)
407 ) `thenM` \ spec_binds ->
409 returnM (poly_meth_bind `consBag` spec_binds)
412 mkMethodBind :: InstOrigin
413 -> Class -> [TcType] -- Class and instance types
414 -> LHsBinds Name -- Method binding (pick the right one from in here)
416 -> TcM (Maybe Inst, -- Method inst
418 -- Find the binding for the specified method, or make
419 -- up a suitable default method if it isn't there
421 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
422 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
424 meth_name = idName meth_id
426 -- Figure out what method binding to use
427 -- If the user suppplied one, use it, else construct a default one
428 getSrcSpanM `thenM` \ loc ->
429 (case find_bind (idName sel_id) meth_name meth_binds of
430 Just user_bind -> returnM user_bind
432 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
434 returnM (noLoc $ FunBind (noLoc meth_name) False
435 [mkSimpleMatch [] rhs placeHolderType])
436 ) `thenM` \ meth_bind ->
438 returnM (mb_inst, (sel_id, meth_id, meth_bind))
440 mkMethId :: InstOrigin -> Class
441 -> Id -> [TcType] -- Selector, and instance types
442 -> TcM (Maybe Inst, Id)
444 -- mkMethId instantiates the selector Id at the specified types
445 mkMethId origin clas sel_id inst_tys
447 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
448 rho_ty = ASSERT( length tyvars == length inst_tys )
449 substTyWith tyvars inst_tys rho
450 (preds,tau) = tcSplitPhiTy rho_ty
451 first_pred = head preds
453 -- The first predicate should be of form (C a b)
454 -- where C is the class in question
455 ASSERT( not (null preds) &&
456 case getClassPredTys_maybe first_pred of
457 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
459 if isSingleton preds then
460 -- If it's the only one, make a 'method'
461 getInstLoc origin `thenM` \ inst_loc ->
462 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
463 returnM (Just meth_inst, instToId meth_inst)
465 -- If it's not the only one we need to be careful
466 -- For example, given 'op' defined thus:
468 -- op :: (?x :: String) => a -> a
469 -- (mkMethId op T) should return an Inst with type
470 -- (?x :: String) => T -> T
471 -- That is, the class-op's context is still there.
472 -- BUT: it can't be a Method any more, because it breaks
473 -- INVARIANT 2 of methods. (See the data decl for Inst.)
474 newUnique `thenM` \ uniq ->
475 getSrcSpanM `thenM` \ loc ->
477 real_tau = mkPhiTy (tail preds) tau
478 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
479 (srcSpanStart loc) --TODO
481 returnM (Nothing, meth_id)
483 -- The user didn't supply a method binding,
484 -- so we have to make up a default binding
485 -- The RHS of a default method depends on the default-method info
486 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
487 = -- An polymorphic default method
488 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
489 -- Might not be imported, but will be an OrigName
490 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
491 returnM (nlHsVar dm_name)
493 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
494 = -- No default method
495 -- Warn only if -fwarn-missing-methods
496 doptM Opt_WarnMissingMethods `thenM` \ warn ->
497 warnTc (isInstDecl origin
499 && reportIfUnused (getOccName sel_id))
500 (omittedMethodWarn sel_id) `thenM_`
503 error_rhs = noLoc $ HsLam (mkSimpleMatch wild_pats simple_rhs placeHolderType)
504 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
505 (nlHsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
506 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
508 -- When the type is of form t1 -> t2 -> t3
509 -- make a default method like (\ _ _ -> noMethBind "blah")
510 -- rather than simply (noMethBind "blah")
511 -- Reason: if t1 or t2 are higher-ranked types we get n
512 -- silly ambiguity messages.
513 -- Example: f :: (forall a. Eq a => a -> a) -> Int
515 -- Here, tcSub tries to force (error "urk") to have the right type,
516 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
517 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
519 -- NB: technically this changes the meaning of the default-default
520 -- method slightly, because `seq` can see the lambdas. Oh well.
521 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
522 (_,_,tau2) = tcSplitSigmaTy tau1
523 -- Need two splits because the selector can have a type like
524 -- forall a. Foo a => forall b. Eq b => ...
525 (arg_tys, _) = tcSplitFunTys tau2
526 wild_pats = [wildPat | ty <- arg_tys]
528 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
529 = -- A generic default method
530 -- If the method is defined generically, we can only do the job if the
531 -- instance declaration is for a single-parameter type class with
532 -- a type constructor applied to type arguments in the instance decl
533 -- (checkTc, so False provokes the error)
534 ASSERT( isInstDecl origin ) -- We never get here from a class decl
535 do { checkTc (isJust maybe_tycon)
536 (badGenericInstance sel_id (notSimple inst_tys))
537 ; checkTc (tyConHasGenerics tycon)
538 (badGenericInstance sel_id (notGeneric tycon))
541 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
542 (vcat [ppr clas <+> ppr inst_tys,
543 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
545 -- Rename it before returning it
546 ; (rn_rhs, _) <- rnLExpr rhs
549 rhs = mkGenericRhs sel_id clas_tyvar tycon
551 -- The tycon is only used in the generic case, and in that
552 -- case we require that the instance decl is for a single-parameter
553 -- type class with type variable arguments:
554 -- instance (...) => C (T a b)
555 clas_tyvar = head (classTyVars clas)
556 Just tycon = maybe_tycon
557 maybe_tycon = case inst_tys of
558 [ty] -> case tcSplitTyConApp_maybe ty of
559 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
563 isInstDecl InstanceDeclOrigin = True
564 isInstDecl ClassDeclOrigin = False
569 -- The renamer just puts the selector ID as the binder in the method binding
570 -- but we must use the method name; so we substitute it here. Crude but simple.
571 find_bind sel_name meth_name binds
572 = foldlBag seqMaybe Nothing (mapBag f binds)
574 f (L loc1 (FunBind (L loc2 op_name) fix matches)) | op_name == sel_name
575 = Just (L loc1 (FunBind (L loc2 meth_name) fix matches))
580 %************************************************************************
582 \subsection{Extracting generic instance declaration from class declarations}
584 %************************************************************************
586 @getGenericInstances@ extracts the generic instance declarations from a class
587 declaration. For exmaple
592 op{ x+y } (Inl v) = ...
593 op{ x+y } (Inr v) = ...
594 op{ x*y } (v :*: w) = ...
597 gives rise to the instance declarations
599 instance C (x+y) where
603 instance C (x*y) where
611 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
612 getGenericInstances class_decls
613 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
614 ; let { gen_inst_info = concat gen_inst_infos }
616 -- Return right away if there is no generic stuff
617 ; if null gen_inst_info then returnM []
620 -- Otherwise print it out
622 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
623 (vcat (map pprInstInfoDetails gen_inst_info)))
624 ; returnM gen_inst_info }}
626 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
628 = returnM [] -- The comon case: no generic default methods
630 | otherwise -- A source class decl with generic default methods
631 = recoverM (returnM []) $
633 tcLookupLocatedClass class_name `thenM` \ clas ->
635 -- Group by type, and
636 -- make an InstInfo out of each group
638 groups = groupWith listToBag generic_binds
640 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
642 -- Check that there is only one InstInfo for each type constructor
643 -- The main way this can fail is if you write
644 -- f {| a+b |} ... = ...
645 -- f {| x+y |} ... = ...
646 -- Then at this point we'll have an InstInfo for each
648 tc_inst_infos :: [(TyCon, InstInfo)]
649 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
651 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
652 group `lengthExceeds` 1]
653 get_uniq (tc,_) = getUnique tc
655 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
657 -- Check that there is an InstInfo for each generic type constructor
659 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
661 checkTc (null missing) (missingGenericInstances missing) `thenM_`
665 generic_binds :: [(HsType Name, LHsBind Name)]
666 generic_binds = getGenericBinds def_methods
669 ---------------------------------
670 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
671 -- Takes a group of method bindings, finds the generic ones, and returns
672 -- them in finite map indexed by the type parameter in the definition.
673 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
675 getGenericBind (L loc (FunBind id infixop matches))
676 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
678 wrap ms = L loc (FunBind id infixop ms)
682 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
684 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
687 (this,rest) = partition same_t prs
688 same_t (t',v) = t `eqPatType` t'
690 eqPatLType :: LHsType Name -> LHsType Name -> Bool
691 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
693 eqPatType :: HsType Name -> HsType Name -> Bool
694 -- A very simple equality function, only for
695 -- type patterns in generic function definitions.
696 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
697 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
698 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
699 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
700 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
701 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
702 eqPatType _ _ = False
704 ---------------------------------
705 mkGenericInstance :: Class
706 -> (HsType Name, LHsBinds Name)
709 mkGenericInstance clas (hs_ty, binds)
710 -- Make a generic instance declaration
711 -- For example: instance (C a, C b) => C (a+b) where { binds }
713 = -- Extract the universally quantified type variables
714 -- and wrap them as forall'd tyvars, so that kind inference
715 -- works in the standard way
717 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
718 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
720 -- Type-check the instance type, and check its form
721 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
723 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
725 checkTc (validGenericInstanceType inst_ty)
726 (badGenericInstanceType binds) `thenM_`
728 -- Make the dictionary function.
729 getSrcSpanM `thenM` \ span ->
730 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
732 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
733 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
736 returnM (InstInfo { iDFunId = dfun_id, iBinds = VanillaInst binds [] })
740 %************************************************************************
744 %************************************************************************
747 tcAddDeclCtxt decl thing_inside
748 = addErrCtxt ctxt thing_inside
751 ClassDecl {} -> "class"
752 TySynonym {} -> "type synonym"
753 TyData {tcdND = NewType} -> "newtype"
754 TyData {tcdND = DataType} -> "data type"
756 ctxt = hsep [ptext SLIT("In the"), text thing,
757 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
760 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
763 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
766 = hsep [ptext SLIT("Class"), quotes (ppr clas),
767 ptext SLIT("does not have a method"), quotes (ppr op)]
769 omittedMethodWarn sel_id
770 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
772 badGenericInstance sel_id because
773 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
777 = vcat [ptext SLIT("because the instance type(s)"),
778 nest 2 (ppr inst_tys),
779 ptext SLIT("is not a simple type of form (T a b c)")]
782 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
783 ptext SLIT("was not compiled with -fgenerics")]
785 badGenericInstanceType binds
786 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
789 missingGenericInstances missing
790 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
792 dupGenericInsts tc_inst_infos
793 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
794 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
795 ptext SLIT("All the type patterns for a generic type constructor must be identical")
798 ppr_inst_ty (tc,inst) = ppr tc <+> ppr (simpleInstInfoTy inst)
801 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)