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(..) )
17 import RnHsSyn ( maybeGenericMatch, extractHsTyVars )
18 import RnExpr ( rnLExpr )
19 import RnEnv ( lookupTopBndrRn, lookupImportedName )
21 import Inst ( Inst, InstOrigin(..), instToId, newDicts, newDictsAtLoc, newMethod )
22 import TcEnv ( tcLookupLocatedClass, tcExtendIdEnv2,
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 ( tcSkolSigTyVars, UserTypeCtxt( GenPatCtxt ) )
33 import TcType ( Type, SkolemInfo(ClsSkol, InstSkol),
34 TcType, TcThetaType, TcTyVar, mkTyVarTys,
35 mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
36 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
37 getClassPredTys_maybe, mkPhiTy, mkTyVarTy
40 import Generics ( mkGenericRhs, validGenericInstanceType )
41 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
42 import Class ( classTyVars, classBigSig,
43 Class, ClassOpItem, DefMeth (..) )
44 import TyCon ( TyCon, tyConName, tyConHasGenerics )
45 import Type ( substTyWith )
46 import MkId ( mkDefaultMethodId, mkDictFunId )
47 import Id ( Id, idType, idName, mkUserLocal, setInlinePragma )
48 import Name ( Name, NamedThing(..) )
49 import NameEnv ( NameEnv, lookupNameEnv, mkNameEnv )
50 import NameSet ( emptyNameSet, unitNameSet, nameSetToList )
51 import OccName ( reportIfUnused, mkDefaultMethodOcc )
52 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) _ (MatchGroup 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 = setSrcSpan 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 (emptyLHsBinds, [])) $
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 = do { dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_id)
265 ; let rigid_info = ClsSkol clas
266 clas_tyvars = tcSkolSigTyVars rigid_info tyvars
267 inst_tys = mkTyVarTys clas_tyvars
268 dm_ty = idType sel_id -- Same as dict selector!
269 theta = [mkClassPred clas inst_tys]
270 local_dm_id = mkDefaultMethodId dm_name dm_ty
271 origin = SigOrigin rigid_info
273 ; (_, meth_info) <- mkMethodBind origin clas inst_tys binds_in (sel_id, DefMeth)
274 ; [this_dict] <- newDicts origin theta
275 ; (defm_bind, insts_needed) <- getLIE (tcMethodBind clas_tyvars theta
276 [this_dict] prags meth_info)
278 ; addErrCtxt (defltMethCtxt clas) $ do
281 { dict_binds <- tcSimplifyCheck
282 (ptext SLIT("class") <+> ppr clas)
287 -- Simplification can do unification
288 ; checkSigTyVars clas_tyvars
291 (_,dm_inst_id,_) = meth_info
295 [(clas_tyvars, local_dm_id, dm_inst_id)]
296 emptyNameSet -- No inlines (yet)
297 (dict_binds `unionBags` defm_bind)
298 ; returnM (noLoc full_bind, [local_dm_id]) }}
300 mkDefMethRdrName :: Id -> RdrName
301 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
305 %************************************************************************
307 \subsection{Typechecking a method}
309 %************************************************************************
311 @tcMethodBind@ is used to type-check both default-method and
312 instance-decl method declarations. We must type-check methods one at a
313 time, because their signatures may have different contexts and
317 type MethodSpec = (Id, -- Global selector Id
318 Id, -- Local Id (class tyvars instantiated)
319 LHsBind Name) -- Binding for the method
322 :: [TcTyVar] -- Skolemised type variables for the
323 -- enclosing class/instance decl.
324 -- They'll be signature tyvars, and we
325 -- want to check that they don't get bound
326 -- Also they are scoped, so we bring them into scope
327 -- Always equal the range of the type envt
328 -> TcThetaType -- Available theta; it's just used for the error message
329 -> [Inst] -- Available from context, used to simplify constraints
330 -- from the method body
331 -> [LSig Name] -- Pragmas (e.g. inline pragmas)
332 -> MethodSpec -- Details of this method
335 tcMethodBind inst_tyvars inst_theta avail_insts prags
336 (sel_id, meth_id, meth_bind)
337 = recoverM (returnM emptyLHsBinds) $
338 -- If anything fails, recover returning no bindings.
339 -- This is particularly useful when checking the default-method binding of
340 -- a class decl. If we don't recover, we don't add the default method to
341 -- the type enviroment, and we get a tcLookup failure on $dmeth later.
343 -- Check the bindings; first adding inst_tyvars to the envt
344 -- so that we don't quantify over them in nested places
345 mkTcSig meth_id `thenM` \ meth_sig ->
346 let lookup_sig name = ASSERT( name == idName meth_id )
349 tcExtendTyVarEnv inst_tyvars (
350 addErrCtxt (methodCtxt sel_id) $
352 tcMonoBinds (unitBag meth_bind) lookup_sig NonRecursive
353 ) `thenM` \ ((meth_bind, mono_bind_infos), meth_lie) ->
355 -- Now do context reduction. We simplify wrt both the local tyvars
356 -- and the ones of the class/instance decl, so that there is
359 -- op :: Eq a => a -> b -> a
361 -- We do this for each method independently to localise error messages
363 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
364 newDictsAtLoc (sig_loc meth_sig) (sig_theta meth_sig) `thenM` \ meth_dicts ->
366 meth_tvs = sig_tvs meth_sig
367 all_tyvars = meth_tvs ++ inst_tyvars
368 all_insts = avail_insts ++ meth_dicts
371 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
372 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
374 checkSigTyVars all_tyvars `thenM_`
377 sel_name = idName sel_id
378 inline_prags = [ (is_inl, phase)
379 | L _ (InlineSig is_inl (L _ name) phase) <- prags,
382 | prag@(L _ (SpecSig (L _ name) _)) <- prags,
385 -- Attach inline pragmas as appropriate
386 (final_meth_id, inlines)
387 | ((is_inline, phase) : _) <- inline_prags
388 = (meth_id `setInlinePragma` phase,
389 if is_inline then unitNameSet (idName meth_id) else emptyNameSet)
391 = (meth_id, emptyNameSet)
393 [(_,_,local_meth_id)] = mono_bind_infos
394 poly_meth_bind = noLoc $ AbsBinds meth_tvs
395 (map instToId meth_dicts)
396 [(meth_tvs, final_meth_id, local_meth_id)]
398 (lie_binds `unionBags` meth_bind)
401 -- Deal with specialisation pragmas
402 -- The sel_name is what appears in the pragma
403 tcExtendIdEnv2 [(sel_name, final_meth_id)] (
404 getLIE (tcSpecSigs spec_prags) `thenM` \ (spec_binds1, prag_lie) ->
406 -- The prag_lie for a SPECIALISE pragma will mention the function itself,
407 -- so we have to simplify them away right now lest they float outwards!
408 bindInstsOfLocalFuns prag_lie [final_meth_id] `thenM` \ spec_binds2 ->
409 returnM (spec_binds1 `unionBags` spec_binds2)
410 ) `thenM` \ spec_binds ->
412 returnM (poly_meth_bind `consBag` spec_binds)
415 mkMethodBind :: InstOrigin
416 -> Class -> [TcType] -- Class and instance types
417 -> LHsBinds Name -- Method binding (pick the right one from in here)
419 -> TcM (Maybe Inst, -- Method inst
421 -- Find the binding for the specified method, or make
422 -- up a suitable default method if it isn't there
424 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
425 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
427 meth_name = idName meth_id
429 -- Figure out what method binding to use
430 -- If the user suppplied one, use it, else construct a default one
431 getSrcSpanM `thenM` \ loc ->
432 (case find_bind (idName sel_id) meth_name meth_binds of
433 Just user_bind -> returnM user_bind
435 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
437 returnM (noLoc $ FunBind (noLoc meth_name) False
438 (mkMatchGroup [mkSimpleMatch [] rhs]))
439 ) `thenM` \ meth_bind ->
441 returnM (mb_inst, (sel_id, meth_id, meth_bind))
443 mkMethId :: InstOrigin -> Class
444 -> Id -> [TcType] -- Selector, and instance types
445 -> TcM (Maybe Inst, Id)
447 -- mkMethId instantiates the selector Id at the specified types
448 mkMethId origin clas sel_id inst_tys
450 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
451 rho_ty = ASSERT( length tyvars == length inst_tys )
452 substTyWith tyvars inst_tys rho
453 (preds,tau) = tcSplitPhiTy rho_ty
454 first_pred = head preds
456 -- The first predicate should be of form (C a b)
457 -- where C is the class in question
458 ASSERT( not (null preds) &&
459 case getClassPredTys_maybe first_pred of
460 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
462 if isSingleton preds then
463 -- If it's the only one, make a 'method'
464 getInstLoc origin `thenM` \ inst_loc ->
465 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
466 returnM (Just meth_inst, instToId meth_inst)
468 -- If it's not the only one we need to be careful
469 -- For example, given 'op' defined thus:
471 -- op :: (?x :: String) => a -> a
472 -- (mkMethId op T) should return an Inst with type
473 -- (?x :: String) => T -> T
474 -- That is, the class-op's context is still there.
475 -- BUT: it can't be a Method any more, because it breaks
476 -- INVARIANT 2 of methods. (See the data decl for Inst.)
477 newUnique `thenM` \ uniq ->
478 getSrcSpanM `thenM` \ loc ->
480 real_tau = mkPhiTy (tail preds) tau
481 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
482 (srcSpanStart loc) --TODO
484 returnM (Nothing, meth_id)
486 -- The user didn't supply a method binding,
487 -- so we have to make up a default binding
488 -- The RHS of a default method depends on the default-method info
489 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
490 = -- An polymorphic default method
491 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
492 -- Might not be imported, but will be an OrigName
493 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
494 returnM (nlHsVar dm_name)
496 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
497 = -- No default method
498 -- Warn only if -fwarn-missing-methods
499 doptM Opt_WarnMissingMethods `thenM` \ warn ->
500 warnTc (isInstDecl origin
502 && reportIfUnused (getOccName sel_id))
503 (omittedMethodWarn sel_id) `thenM_`
506 error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
507 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
508 (nlHsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
509 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
511 -- When the type is of form t1 -> t2 -> t3
512 -- make a default method like (\ _ _ -> noMethBind "blah")
513 -- rather than simply (noMethBind "blah")
514 -- Reason: if t1 or t2 are higher-ranked types we get n
515 -- silly ambiguity messages.
516 -- Example: f :: (forall a. Eq a => a -> a) -> Int
518 -- Here, tcSub tries to force (error "urk") to have the right type,
519 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
520 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
522 -- NB: technically this changes the meaning of the default-default
523 -- method slightly, because `seq` can see the lambdas. Oh well.
524 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
525 (_,_,tau2) = tcSplitSigmaTy tau1
526 -- Need two splits because the selector can have a type like
527 -- forall a. Foo a => forall b. Eq b => ...
528 (arg_tys, _) = tcSplitFunTys tau2
529 wild_pats = [nlWildPat | ty <- arg_tys]
531 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
532 = -- A generic default method
533 -- If the method is defined generically, we can only do the job if the
534 -- instance declaration is for a single-parameter type class with
535 -- a type constructor applied to type arguments in the instance decl
536 -- (checkTc, so False provokes the error)
537 ASSERT( isInstDecl origin ) -- We never get here from a class decl
538 do { checkTc (isJust maybe_tycon)
539 (badGenericInstance sel_id (notSimple inst_tys))
540 ; checkTc (tyConHasGenerics tycon)
541 (badGenericInstance sel_id (notGeneric tycon))
544 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
545 (vcat [ppr clas <+> ppr inst_tys,
546 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
548 -- Rename it before returning it
549 ; (rn_rhs, _) <- rnLExpr rhs
552 rhs = mkGenericRhs sel_id clas_tyvar tycon
554 -- The tycon is only used in the generic case, and in that
555 -- case we require that the instance decl is for a single-parameter
556 -- type class with type variable arguments:
557 -- instance (...) => C (T a b)
558 clas_tyvar = head (classTyVars clas)
559 Just tycon = maybe_tycon
560 maybe_tycon = case inst_tys of
561 [ty] -> case tcSplitTyConApp_maybe ty of
562 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
566 isInstDecl (SigOrigin (InstSkol _)) = True
567 isInstDecl (SigOrigin (ClsSkol _)) = False
572 -- The renamer just puts the selector ID as the binder in the method binding
573 -- but we must use the method name; so we substitute it here. Crude but simple.
574 find_bind sel_name meth_name binds
575 = foldlBag seqMaybe Nothing (mapBag f binds)
577 f (L loc1 (FunBind (L loc2 op_name) fix matches)) | op_name == sel_name
578 = Just (L loc1 (FunBind (L loc2 meth_name) fix matches))
583 %************************************************************************
585 \subsection{Extracting generic instance declaration from class declarations}
587 %************************************************************************
589 @getGenericInstances@ extracts the generic instance declarations from a class
590 declaration. For exmaple
595 op{ x+y } (Inl v) = ...
596 op{ x+y } (Inr v) = ...
597 op{ x*y } (v :*: w) = ...
600 gives rise to the instance declarations
602 instance C (x+y) where
606 instance C (x*y) where
614 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
615 getGenericInstances class_decls
616 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
617 ; let { gen_inst_info = concat gen_inst_infos }
619 -- Return right away if there is no generic stuff
620 ; if null gen_inst_info then returnM []
623 -- Otherwise print it out
625 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
626 (vcat (map pprInstInfoDetails gen_inst_info)))
627 ; returnM gen_inst_info }}
629 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
631 = returnM [] -- The comon case: no generic default methods
633 | otherwise -- A source class decl with generic default methods
634 = recoverM (returnM []) $
636 tcLookupLocatedClass class_name `thenM` \ clas ->
638 -- Group by type, and
639 -- make an InstInfo out of each group
641 groups = groupWith listToBag generic_binds
643 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
645 -- Check that there is only one InstInfo for each type constructor
646 -- The main way this can fail is if you write
647 -- f {| a+b |} ... = ...
648 -- f {| x+y |} ... = ...
649 -- Then at this point we'll have an InstInfo for each
651 tc_inst_infos :: [(TyCon, InstInfo)]
652 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
654 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
655 group `lengthExceeds` 1]
656 get_uniq (tc,_) = getUnique tc
658 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
660 -- Check that there is an InstInfo for each generic type constructor
662 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
664 checkTc (null missing) (missingGenericInstances missing) `thenM_`
668 generic_binds :: [(HsType Name, LHsBind Name)]
669 generic_binds = getGenericBinds def_methods
672 ---------------------------------
673 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
674 -- Takes a group of method bindings, finds the generic ones, and returns
675 -- them in finite map indexed by the type parameter in the definition.
676 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
678 getGenericBind (L loc (FunBind id infixop (MatchGroup matches ty)))
679 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
681 wrap ms = L loc (FunBind id infixop (MatchGroup ms ty))
685 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
687 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
690 (this,rest) = partition same_t prs
691 same_t (t',v) = t `eqPatType` t'
693 eqPatLType :: LHsType Name -> LHsType Name -> Bool
694 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
696 eqPatType :: HsType Name -> HsType Name -> Bool
697 -- A very simple equality function, only for
698 -- type patterns in generic function definitions.
699 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
700 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
701 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
702 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
703 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
704 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
705 eqPatType _ _ = False
707 ---------------------------------
708 mkGenericInstance :: Class
709 -> (HsType Name, LHsBinds Name)
712 mkGenericInstance clas (hs_ty, binds)
713 -- Make a generic instance declaration
714 -- For example: instance (C a, C b) => C (a+b) where { binds }
716 = -- Extract the universally quantified type variables
717 -- and wrap them as forall'd tyvars, so that kind inference
718 -- works in the standard way
720 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
721 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
723 -- Type-check the instance type, and check its form
724 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
726 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
728 checkTc (validGenericInstanceType inst_ty)
729 (badGenericInstanceType binds) `thenM_`
731 -- Make the dictionary function.
732 getSrcSpanM `thenM` \ span ->
733 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
735 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
736 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
739 returnM (InstInfo { iDFunId = dfun_id, iBinds = VanillaInst binds [] })
743 %************************************************************************
747 %************************************************************************
750 tcAddDeclCtxt decl thing_inside
751 = addErrCtxt ctxt thing_inside
754 ClassDecl {} -> "class"
755 TySynonym {} -> "type synonym"
756 TyData {tcdND = NewType} -> "newtype"
757 TyData {tcdND = DataType} -> "data type"
759 ctxt = hsep [ptext SLIT("In the"), text thing,
760 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
763 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
766 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
769 = hsep [ptext SLIT("Class"), quotes (ppr clas),
770 ptext SLIT("does not have a method"), quotes (ppr op)]
772 omittedMethodWarn sel_id
773 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
775 badGenericInstance sel_id because
776 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
780 = vcat [ptext SLIT("because the instance type(s)"),
781 nest 2 (ppr inst_tys),
782 ptext SLIT("is not a simple type of form (T a b c)")]
785 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
786 ptext SLIT("was not compiled with -fgenerics")]
788 badGenericInstanceType binds
789 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
792 missingGenericInstances missing
793 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
795 dupGenericInsts tc_inst_infos
796 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
797 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
798 ptext SLIT("All the type patterns for a generic type constructor must be identical")
801 ppr_inst_ty (tc,inst) = ppr tc <+> ppr (simpleInstInfoTy inst)
804 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)