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(..), tcHsKindedType, tcHsSigType )
30 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
31 import TcUnify ( checkSigTyVars, sigCtxt )
32 import TcMType ( tcSkolSigTyVars, UserTypeCtxt( GenPatCtxt ), tcSkolType )
33 import TcType ( Type, SkolemInfo(ClsSkol, InstSkol, SigSkol),
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 isPragLSig 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
347 let -- Fake up a TcSigInfo to pass to tcMonoBinds
348 rigid_info = SigSkol (idName meth_id)
350 tcSkolType rigid_info (idType meth_id) `thenM` \ (tyvars', theta', tau') ->
351 getInstLoc (SigOrigin rigid_info) `thenM` \ loc ->
352 let meth_sig = TcSigInfo { sig_id = meth_id, sig_tvs = tyvars', sig_scoped = [],
353 sig_theta = theta', sig_tau = tau', sig_loc = loc }
354 lookup_sig name = ASSERT( name == idName meth_id )
357 tcExtendTyVarEnv inst_tyvars (
358 addErrCtxt (methodCtxt sel_id) $
360 tcMonoBinds (unitBag meth_bind) lookup_sig NonRecursive
361 ) `thenM` \ ((meth_bind, mono_bind_infos), meth_lie) ->
363 -- Now do context reduction. We simplify wrt both the local tyvars
364 -- and the ones of the class/instance decl, so that there is
367 -- op :: Eq a => a -> b -> a
369 -- We do this for each method independently to localise error messages
371 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
372 newDictsAtLoc (sig_loc meth_sig) (sig_theta meth_sig) `thenM` \ meth_dicts ->
374 meth_tvs = sig_tvs meth_sig
375 all_tyvars = meth_tvs ++ inst_tyvars
376 all_insts = avail_insts ++ meth_dicts
379 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
380 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
382 checkSigTyVars all_tyvars `thenM_`
385 sel_name = idName sel_id
386 inline_prags = [ (is_inl, phase)
387 | L _ (InlineSig is_inl (L _ name) phase) <- prags,
390 | prag@(L _ (SpecSig (L _ name) _)) <- prags,
393 -- Attach inline pragmas as appropriate
394 (final_meth_id, inlines)
395 | ((is_inline, phase) : _) <- inline_prags
396 = (meth_id `setInlinePragma` phase,
397 if is_inline then unitNameSet (idName meth_id) else emptyNameSet)
399 = (meth_id, emptyNameSet)
401 [(_,_,local_meth_id)] = mono_bind_infos
402 poly_meth_bind = noLoc $ AbsBinds meth_tvs
403 (map instToId meth_dicts)
404 [(meth_tvs, final_meth_id, local_meth_id)]
406 (lie_binds `unionBags` meth_bind)
409 -- Deal with specialisation pragmas
410 -- The sel_name is what appears in the pragma
411 tcExtendIdEnv2 [(sel_name, final_meth_id)] (
412 getLIE (tcSpecSigs spec_prags) `thenM` \ (spec_binds1, prag_lie) ->
414 -- The prag_lie for a SPECIALISE pragma will mention the function itself,
415 -- so we have to simplify them away right now lest they float outwards!
416 bindInstsOfLocalFuns prag_lie [final_meth_id] `thenM` \ spec_binds2 ->
417 returnM (spec_binds1 `unionBags` spec_binds2)
418 ) `thenM` \ spec_binds ->
420 returnM (poly_meth_bind `consBag` spec_binds)
423 mkMethodBind :: InstOrigin
424 -> Class -> [TcType] -- Class and instance types
425 -> LHsBinds Name -- Method binding (pick the right one from in here)
427 -> TcM (Maybe Inst, -- Method inst
429 -- Find the binding for the specified method, or make
430 -- up a suitable default method if it isn't there
432 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
433 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
435 meth_name = idName meth_id
437 -- Figure out what method binding to use
438 -- If the user suppplied one, use it, else construct a default one
439 getSrcSpanM `thenM` \ loc ->
440 (case find_bind (idName sel_id) meth_name meth_binds of
441 Just user_bind -> returnM user_bind
443 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
445 returnM (noLoc $ FunBind (noLoc meth_name) False
446 (mkMatchGroup [mkSimpleMatch [] rhs]))
447 ) `thenM` \ meth_bind ->
449 returnM (mb_inst, (sel_id, meth_id, meth_bind))
451 mkMethId :: InstOrigin -> Class
452 -> Id -> [TcType] -- Selector, and instance types
453 -> TcM (Maybe Inst, Id)
455 -- mkMethId instantiates the selector Id at the specified types
456 mkMethId origin clas sel_id inst_tys
458 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
459 rho_ty = ASSERT( length tyvars == length inst_tys )
460 substTyWith tyvars inst_tys rho
461 (preds,tau) = tcSplitPhiTy rho_ty
462 first_pred = head preds
464 -- The first predicate should be of form (C a b)
465 -- where C is the class in question
466 ASSERT( not (null preds) &&
467 case getClassPredTys_maybe first_pred of
468 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
470 if isSingleton preds then
471 -- If it's the only one, make a 'method'
472 getInstLoc origin `thenM` \ inst_loc ->
473 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
474 returnM (Just meth_inst, instToId meth_inst)
476 -- If it's not the only one we need to be careful
477 -- For example, given 'op' defined thus:
479 -- op :: (?x :: String) => a -> a
480 -- (mkMethId op T) should return an Inst with type
481 -- (?x :: String) => T -> T
482 -- That is, the class-op's context is still there.
483 -- BUT: it can't be a Method any more, because it breaks
484 -- INVARIANT 2 of methods. (See the data decl for Inst.)
485 newUnique `thenM` \ uniq ->
486 getSrcSpanM `thenM` \ loc ->
488 real_tau = mkPhiTy (tail preds) tau
489 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
490 (srcSpanStart loc) --TODO
492 returnM (Nothing, meth_id)
494 -- The user didn't supply a method binding,
495 -- so we have to make up a default binding
496 -- The RHS of a default method depends on the default-method info
497 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
498 = -- An polymorphic default method
499 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
500 -- Might not be imported, but will be an OrigName
501 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
502 returnM (nlHsVar dm_name)
504 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
505 = -- No default method
506 -- Warn only if -fwarn-missing-methods
507 doptM Opt_WarnMissingMethods `thenM` \ warn ->
508 warnTc (isInstDecl origin
510 && reportIfUnused (getOccName sel_id))
511 (omittedMethodWarn sel_id) `thenM_`
514 error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
515 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
516 (nlHsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
517 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
519 -- When the type is of form t1 -> t2 -> t3
520 -- make a default method like (\ _ _ -> noMethBind "blah")
521 -- rather than simply (noMethBind "blah")
522 -- Reason: if t1 or t2 are higher-ranked types we get n
523 -- silly ambiguity messages.
524 -- Example: f :: (forall a. Eq a => a -> a) -> Int
526 -- Here, tcSub tries to force (error "urk") to have the right type,
527 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
528 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
530 -- NB: technically this changes the meaning of the default-default
531 -- method slightly, because `seq` can see the lambdas. Oh well.
532 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
533 (_,_,tau2) = tcSplitSigmaTy tau1
534 -- Need two splits because the selector can have a type like
535 -- forall a. Foo a => forall b. Eq b => ...
536 (arg_tys, _) = tcSplitFunTys tau2
537 wild_pats = [nlWildPat | ty <- arg_tys]
539 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
540 = -- A generic default method
541 -- If the method is defined generically, we can only do the job if the
542 -- instance declaration is for a single-parameter type class with
543 -- a type constructor applied to type arguments in the instance decl
544 -- (checkTc, so False provokes the error)
545 ASSERT( isInstDecl origin ) -- We never get here from a class decl
546 do { checkTc (isJust maybe_tycon)
547 (badGenericInstance sel_id (notSimple inst_tys))
548 ; checkTc (tyConHasGenerics tycon)
549 (badGenericInstance sel_id (notGeneric tycon))
552 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
553 (vcat [ppr clas <+> ppr inst_tys,
554 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
556 -- Rename it before returning it
557 ; (rn_rhs, _) <- rnLExpr rhs
560 rhs = mkGenericRhs sel_id clas_tyvar tycon
562 -- The tycon is only used in the generic case, and in that
563 -- case we require that the instance decl is for a single-parameter
564 -- type class with type variable arguments:
565 -- instance (...) => C (T a b)
566 clas_tyvar = head (classTyVars clas)
567 Just tycon = maybe_tycon
568 maybe_tycon = case inst_tys of
569 [ty] -> case tcSplitTyConApp_maybe ty of
570 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
574 isInstDecl (SigOrigin (InstSkol _)) = True
575 isInstDecl (SigOrigin (ClsSkol _)) = False
580 -- The renamer just puts the selector ID as the binder in the method binding
581 -- but we must use the method name; so we substitute it here. Crude but simple.
582 find_bind sel_name meth_name binds
583 = foldlBag seqMaybe Nothing (mapBag f binds)
585 f (L loc1 (FunBind (L loc2 op_name) fix matches)) | op_name == sel_name
586 = Just (L loc1 (FunBind (L loc2 meth_name) fix matches))
591 %************************************************************************
593 \subsection{Extracting generic instance declaration from class declarations}
595 %************************************************************************
597 @getGenericInstances@ extracts the generic instance declarations from a class
598 declaration. For exmaple
603 op{ x+y } (Inl v) = ...
604 op{ x+y } (Inr v) = ...
605 op{ x*y } (v :*: w) = ...
608 gives rise to the instance declarations
610 instance C (x+y) where
614 instance C (x*y) where
622 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
623 getGenericInstances class_decls
624 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
625 ; let { gen_inst_info = concat gen_inst_infos }
627 -- Return right away if there is no generic stuff
628 ; if null gen_inst_info then returnM []
631 -- Otherwise print it out
633 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
634 (vcat (map pprInstInfoDetails gen_inst_info)))
635 ; returnM gen_inst_info }}
637 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
639 = returnM [] -- The comon case: no generic default methods
641 | otherwise -- A source class decl with generic default methods
642 = recoverM (returnM []) $
644 tcLookupLocatedClass class_name `thenM` \ clas ->
646 -- Group by type, and
647 -- make an InstInfo out of each group
649 groups = groupWith listToBag generic_binds
651 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
653 -- Check that there is only one InstInfo for each type constructor
654 -- The main way this can fail is if you write
655 -- f {| a+b |} ... = ...
656 -- f {| x+y |} ... = ...
657 -- Then at this point we'll have an InstInfo for each
659 tc_inst_infos :: [(TyCon, InstInfo)]
660 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
662 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
663 group `lengthExceeds` 1]
664 get_uniq (tc,_) = getUnique tc
666 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
668 -- Check that there is an InstInfo for each generic type constructor
670 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
672 checkTc (null missing) (missingGenericInstances missing) `thenM_`
676 generic_binds :: [(HsType Name, LHsBind Name)]
677 generic_binds = getGenericBinds def_methods
680 ---------------------------------
681 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
682 -- Takes a group of method bindings, finds the generic ones, and returns
683 -- them in finite map indexed by the type parameter in the definition.
684 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
686 getGenericBind (L loc (FunBind id infixop (MatchGroup matches ty)))
687 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
689 wrap ms = L loc (FunBind id infixop (MatchGroup ms ty))
693 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
695 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
698 (this,rest) = partition same_t prs
699 same_t (t',v) = t `eqPatType` t'
701 eqPatLType :: LHsType Name -> LHsType Name -> Bool
702 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
704 eqPatType :: HsType Name -> HsType Name -> Bool
705 -- A very simple equality function, only for
706 -- type patterns in generic function definitions.
707 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
708 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
709 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
710 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
711 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
712 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
713 eqPatType _ _ = False
715 ---------------------------------
716 mkGenericInstance :: Class
717 -> (HsType Name, LHsBinds Name)
720 mkGenericInstance clas (hs_ty, binds)
721 -- Make a generic instance declaration
722 -- For example: instance (C a, C b) => C (a+b) where { binds }
724 = -- Extract the universally quantified type variables
725 -- and wrap them as forall'd tyvars, so that kind inference
726 -- works in the standard way
728 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
729 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
731 -- Type-check the instance type, and check its form
732 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
734 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
736 checkTc (validGenericInstanceType inst_ty)
737 (badGenericInstanceType binds) `thenM_`
739 -- Make the dictionary function.
740 getSrcSpanM `thenM` \ span ->
741 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
743 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
744 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
747 returnM (InstInfo { iDFunId = dfun_id, iBinds = VanillaInst binds [] })
751 %************************************************************************
755 %************************************************************************
758 tcAddDeclCtxt decl thing_inside
759 = addErrCtxt ctxt thing_inside
762 ClassDecl {} -> "class"
763 TySynonym {} -> "type synonym"
764 TyData {tcdND = NewType} -> "newtype"
765 TyData {tcdND = DataType} -> "data type"
767 ctxt = hsep [ptext SLIT("In the"), text thing,
768 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
771 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
774 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
777 = hsep [ptext SLIT("Class"), quotes (ppr clas),
778 ptext SLIT("does not have a method"), quotes (ppr op)]
780 omittedMethodWarn sel_id
781 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
783 badGenericInstance sel_id because
784 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
788 = vcat [ptext SLIT("because the instance type(s)"),
789 nest 2 (ppr inst_tys),
790 ptext SLIT("is not a simple type of form (T a b c)")]
793 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
794 ptext SLIT("was not compiled with -fgenerics")]
796 badGenericInstanceType binds
797 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
800 missingGenericInstances missing
801 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
803 dupGenericInsts tc_inst_infos
804 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
805 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
806 ptext SLIT("All the type patterns for a generic type constructor must be identical")
809 ppr_inst_ty (tc,inst) = ppr tc <+> ppr (simpleInstInfoTy inst)
812 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)