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 RnHsSyn ( maybeGenericMatch, extractHsTyVars )
17 import RnExpr ( rnLExpr )
18 import RnEnv ( lookupTopBndrRn, lookupImportedName )
19 import Inst ( instToId, newDicts, newDictsAtLoc, newMethod, getOverlapFlag )
20 import InstEnv ( mkLocalInstance )
21 import TcEnv ( tcLookupLocatedClass,
22 tcExtendTyVarEnv, tcExtendIdEnv,
23 InstInfo(..), pprInstInfoDetails,
24 simpleInstInfoTyCon, simpleInstInfoTy,
25 InstBindings(..), newDFunName
27 import TcBinds ( TcPragFun, tcMonoBinds, tcPrags, mkPragFun, TcSigInfo(..),
28 TcSigFun, mkTcSigFun )
29 import TcHsType ( tcHsKindedType, tcHsSigType )
30 import TcSimplify ( tcSimplifyCheck )
31 import TcUnify ( checkSigTyVars, sigCtxt )
32 import TcMType ( tcSkolSigTyVars )
33 import TcType ( Type, SkolemInfo(ClsSkol, InstSkol), UserTypeCtxt( GenPatCtxt ),
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 )
48 import Name ( Name, NamedThing(..) )
49 import NameEnv ( NameEnv, lookupNameEnv, mkNameEnv )
50 import NameSet ( nameSetToList )
51 import OccName ( reportIfUnused, mkDefaultMethodOcc )
52 import RdrName ( RdrName, mkDerivedRdrName )
54 import PrelNames ( genericTyConNames )
56 import ErrUtils ( dumpIfSet_dyn )
57 import Util ( count, lengthIs, isSingleton, lengthExceeds )
58 import Unique ( Uniquable(..) )
59 import ListSetOps ( equivClassesByUniq, minusList )
60 import SrcLoc ( Located(..), srcSpanStart, unLoc, noLoc )
61 import Maybes ( seqMaybe, isJust, mapCatMaybes )
62 import List ( partition )
63 import BasicTypes ( RecFlag(..), Boxity(..) )
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 _ (TypeSig _ _)) <- sigs]
122 op_names = [n | sig@(L _ (TypeSig (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 {fun_id = L _ op, fun_matches = 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 (TypeSig (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 prag_fn = mkPragFun sigs
250 sig_fn = mkTcSigFun sigs
251 tc_dm = tcDefMeth clas tyvars default_binds sig_fn prag_fn
253 dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
254 -- Generate code for polymorphic default methods only
255 -- (Generic default methods have turned into instance decls by now.)
256 -- This is incompatible with Hugs, which expects a polymorphic
257 -- default method for every class op, regardless of whether or not
258 -- the programmer supplied an explicit default decl for the class.
259 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
261 mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
262 returnM (listToBag defm_binds, concat dm_ids_s)
264 tcDefMeth clas tyvars binds_in sig_fn prag_fn sel_id
265 = do { dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_id)
266 ; let rigid_info = ClsSkol clas
267 clas_tyvars = tcSkolSigTyVars rigid_info tyvars
268 inst_tys = mkTyVarTys clas_tyvars
269 dm_ty = idType sel_id -- Same as dict selector!
270 theta = [mkClassPred clas inst_tys]
271 local_dm_id = mkDefaultMethodId dm_name dm_ty
272 origin = SigOrigin rigid_info
274 ; (_, meth_info) <- mkMethodBind origin clas inst_tys binds_in (sel_id, DefMeth)
275 ; [this_dict] <- newDicts origin theta
276 ; (defm_bind, insts_needed) <- getLIE (tcMethodBind clas_tyvars theta [this_dict]
277 sig_fn prag_fn meth_info)
279 ; addErrCtxt (defltMethCtxt clas) $ do
282 { dict_binds <- tcSimplifyCheck
283 (ptext SLIT("class") <+> ppr clas)
288 -- Simplification can do unification
289 ; checkSigTyVars clas_tyvars
292 -- We'll have an inline pragma on the local binding, made by tcMethodBind
293 -- but that's not enough; we want one on the global default method too
294 -- Specialisations, on the other hand, belong on the thing inside only, I think
295 ; let (_,dm_inst_id,_) = meth_info
296 sel_name = idName sel_id
297 inline_prags = filter isInlineLSig (prag_fn sel_name)
298 ; prags <- tcPrags dm_inst_id inline_prags
300 ; let full_bind = AbsBinds clas_tyvars
302 [(clas_tyvars, local_dm_id, dm_inst_id, prags)]
303 (dict_binds `unionBags` defm_bind)
304 ; returnM (noLoc full_bind, [local_dm_id]) }}
306 mkDefMethRdrName :: Id -> RdrName
307 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
311 %************************************************************************
313 \subsection{Typechecking a method}
315 %************************************************************************
317 @tcMethodBind@ is used to type-check both default-method and
318 instance-decl method declarations. We must type-check methods one at a
319 time, because their signatures may have different contexts and
323 type MethodSpec = (Id, -- Global selector Id
324 Id, -- Local Id (class tyvars instantiated)
325 LHsBind Name) -- Binding for the method
328 :: [TcTyVar] -- Skolemised type variables for the
329 -- enclosing class/instance decl.
330 -- They'll be signature tyvars, and we
331 -- want to check that they don't get bound
332 -- Also they are scoped, so we bring them into scope
333 -- Always equal the range of the type envt
334 -> TcThetaType -- Available theta; it's just used for the error message
335 -> [Inst] -- Available from context, used to simplify constraints
336 -- from the method body
337 -> TcSigFun -- For scoped tyvars, indexed by sel_name
338 -> TcPragFun -- Pragmas (e.g. inline pragmas), indexed by sel_name
339 -> MethodSpec -- Details of this method
342 tcMethodBind inst_tyvars inst_theta avail_insts sig_fn prag_fn
343 (sel_id, meth_id, meth_bind)
344 = recoverM (returnM emptyLHsBinds) $
345 -- If anything fails, recover returning no bindings.
346 -- This is particularly useful when checking the default-method binding of
347 -- a class decl. If we don't recover, we don't add the default method to
348 -- the type enviroment, and we get a tcLookup failure on $dmeth later.
350 -- Check the bindings; first adding inst_tyvars to the envt
351 -- so that we don't quantify over them in nested places
353 let sel_name = idName sel_id
354 meth_sig_fn meth_name = ASSERT( meth_name == idName meth_id ) sig_fn sel_name
355 -- The meth_bind metions the meth_name, but sig_fn is indexed by sel_name
357 tcExtendTyVarEnv inst_tyvars (
358 tcExtendIdEnv [meth_id] $ -- In scope for tcInstSig
359 addErrCtxt (methodCtxt sel_id) $
361 tcMonoBinds [meth_bind] meth_sig_fn Recursive
362 ) `thenM` \ ((meth_bind, mono_bind_infos), meth_lie) ->
364 -- Now do context reduction. We simplify wrt both the local tyvars
365 -- and the ones of the class/instance decl, so that there is
368 -- op :: Eq a => a -> b -> a
370 -- We do this for each method independently to localise error messages
373 [(_, Just sig, local_meth_id)] = mono_bind_infos
376 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
377 newDictsAtLoc (sig_loc sig) (sig_theta sig) `thenM` \ meth_dicts ->
379 meth_tvs = sig_tvs sig
380 all_tyvars = meth_tvs ++ inst_tyvars
381 all_insts = avail_insts ++ meth_dicts
384 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
385 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
387 checkSigTyVars all_tyvars `thenM_`
389 tcPrags meth_id (prag_fn sel_name) `thenM` \ prags ->
391 poly_meth_bind = noLoc $ AbsBinds meth_tvs
392 (map instToId meth_dicts)
393 [(meth_tvs, meth_id, local_meth_id, prags)]
394 (lie_binds `unionBags` meth_bind)
396 returnM (unitBag poly_meth_bind)
399 mkMethodBind :: InstOrigin
400 -> Class -> [TcType] -- Class and instance types
401 -> LHsBinds Name -- Method binding (pick the right one from in here)
403 -> TcM (Maybe Inst, -- Method inst
405 -- Find the binding for the specified method, or make
406 -- up a suitable default method if it isn't there
408 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
409 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
411 meth_name = idName meth_id
413 -- Figure out what method binding to use
414 -- If the user suppplied one, use it, else construct a default one
415 getSrcSpanM `thenM` \ loc ->
416 (case find_bind (idName sel_id) meth_name meth_binds of
417 Just user_bind -> returnM user_bind
419 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
421 returnM (noLoc $ mkFunBind (noLoc meth_name) [mkSimpleMatch [] rhs])
422 ) `thenM` \ meth_bind ->
424 returnM (mb_inst, (sel_id, meth_id, meth_bind))
426 mkMethId :: InstOrigin -> Class
427 -> Id -> [TcType] -- Selector, and instance types
428 -> TcM (Maybe Inst, Id)
430 -- mkMethId instantiates the selector Id at the specified types
431 mkMethId origin clas sel_id inst_tys
433 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
434 rho_ty = ASSERT( length tyvars == length inst_tys )
435 substTyWith tyvars inst_tys rho
436 (preds,tau) = tcSplitPhiTy rho_ty
437 first_pred = head preds
439 -- The first predicate should be of form (C a b)
440 -- where C is the class in question
441 ASSERT( not (null preds) &&
442 case getClassPredTys_maybe first_pred of
443 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
445 if isSingleton preds then
446 -- If it's the only one, make a 'method'
447 getInstLoc origin `thenM` \ inst_loc ->
448 newMethod inst_loc sel_id inst_tys `thenM` \ meth_inst ->
449 returnM (Just meth_inst, instToId meth_inst)
451 -- If it's not the only one we need to be careful
452 -- For example, given 'op' defined thus:
454 -- op :: (?x :: String) => a -> a
455 -- (mkMethId op T) should return an Inst with type
456 -- (?x :: String) => T -> T
457 -- That is, the class-op's context is still there.
458 -- BUT: it can't be a Method any more, because it breaks
459 -- INVARIANT 2 of methods. (See the data decl for Inst.)
460 newUnique `thenM` \ uniq ->
461 getSrcSpanM `thenM` \ loc ->
463 real_tau = mkPhiTy (tail preds) tau
464 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
465 (srcSpanStart loc) --TODO
467 returnM (Nothing, meth_id)
469 -- The user didn't supply a method binding,
470 -- so we have to make up a default binding
471 -- The RHS of a default method depends on the default-method info
472 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
473 = -- An polymorphic default method
474 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
475 -- Might not be imported, but will be an OrigName
476 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
477 returnM (nlHsVar dm_name)
479 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
480 = -- No default method
481 -- Warn only if -fwarn-missing-methods
482 doptM Opt_WarnMissingMethods `thenM` \ warn ->
483 warnTc (isInstDecl origin
485 && reportIfUnused (getOccName sel_id))
486 (omittedMethodWarn sel_id) `thenM_`
489 error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
490 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
491 (nlHsLit (HsStringPrim (mkFastString error_msg)))
492 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
494 -- When the type is of form t1 -> t2 -> t3
495 -- make a default method like (\ _ _ -> noMethBind "blah")
496 -- rather than simply (noMethBind "blah")
497 -- Reason: if t1 or t2 are higher-ranked types we get n
498 -- silly ambiguity messages.
499 -- Example: f :: (forall a. Eq a => a -> a) -> Int
501 -- Here, tcSub tries to force (error "urk") to have the right type,
502 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
503 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
505 -- NB: technically this changes the meaning of the default-default
506 -- method slightly, because `seq` can see the lambdas. Oh well.
507 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
508 (_,_,tau2) = tcSplitSigmaTy tau1
509 -- Need two splits because the selector can have a type like
510 -- forall a. Foo a => forall b. Eq b => ...
511 (arg_tys, _) = tcSplitFunTys tau2
512 wild_pats = [nlWildPat | ty <- arg_tys]
514 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
515 = -- A generic default method
516 -- If the method is defined generically, we can only do the job if the
517 -- instance declaration is for a single-parameter type class with
518 -- a type constructor applied to type arguments in the instance decl
519 -- (checkTc, so False provokes the error)
520 ASSERT( isInstDecl origin ) -- We never get here from a class decl
521 do { checkTc (isJust maybe_tycon)
522 (badGenericInstance sel_id (notSimple inst_tys))
523 ; checkTc (tyConHasGenerics tycon)
524 (badGenericInstance sel_id (notGeneric tycon))
527 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
528 (vcat [ppr clas <+> ppr inst_tys,
529 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
531 -- Rename it before returning it
532 ; (rn_rhs, _) <- rnLExpr rhs
535 rhs = mkGenericRhs sel_id clas_tyvar tycon
537 -- The tycon is only used in the generic case, and in that
538 -- case we require that the instance decl is for a single-parameter
539 -- type class with type variable arguments:
540 -- instance (...) => C (T a b)
541 clas_tyvar = head (classTyVars clas)
542 Just tycon = maybe_tycon
543 maybe_tycon = case inst_tys of
544 [ty] -> case tcSplitTyConApp_maybe ty of
545 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
549 isInstDecl (SigOrigin (InstSkol _)) = True
550 isInstDecl (SigOrigin (ClsSkol _)) = False
555 -- The renamer just puts the selector ID as the binder in the method binding
556 -- but we must use the method name; so we substitute it here. Crude but simple.
557 find_bind sel_name meth_name binds
558 = foldlBag seqMaybe Nothing (mapBag f binds)
560 f (L loc1 bind@(FunBind { fun_id = L loc2 op_name })) | op_name == sel_name
561 = Just (L loc1 (bind { fun_id = L loc2 meth_name }))
566 %************************************************************************
568 \subsection{Extracting generic instance declaration from class declarations}
570 %************************************************************************
572 @getGenericInstances@ extracts the generic instance declarations from a class
573 declaration. For exmaple
578 op{ x+y } (Inl v) = ...
579 op{ x+y } (Inr v) = ...
580 op{ x*y } (v :*: w) = ...
583 gives rise to the instance declarations
585 instance C (x+y) where
589 instance C (x*y) where
597 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
598 getGenericInstances class_decls
599 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
600 ; let { gen_inst_info = concat gen_inst_infos }
602 -- Return right away if there is no generic stuff
603 ; if null gen_inst_info then returnM []
606 -- Otherwise print it out
608 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
609 (vcat (map pprInstInfoDetails gen_inst_info)))
610 ; returnM gen_inst_info }}
612 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
614 = returnM [] -- The comon case: no generic default methods
616 | otherwise -- A source class decl with generic default methods
617 = recoverM (returnM []) $
619 tcLookupLocatedClass class_name `thenM` \ clas ->
621 -- Group by type, and
622 -- make an InstInfo out of each group
624 groups = groupWith listToBag generic_binds
626 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
628 -- Check that there is only one InstInfo for each type constructor
629 -- The main way this can fail is if you write
630 -- f {| a+b |} ... = ...
631 -- f {| x+y |} ... = ...
632 -- Then at this point we'll have an InstInfo for each
634 tc_inst_infos :: [(TyCon, InstInfo)]
635 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
637 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
638 group `lengthExceeds` 1]
639 get_uniq (tc,_) = getUnique tc
641 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
643 -- Check that there is an InstInfo for each generic type constructor
645 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
647 checkTc (null missing) (missingGenericInstances missing) `thenM_`
651 generic_binds :: [(HsType Name, LHsBind Name)]
652 generic_binds = getGenericBinds def_methods
655 ---------------------------------
656 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
657 -- Takes a group of method bindings, finds the generic ones, and returns
658 -- them in finite map indexed by the type parameter in the definition.
659 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
661 getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
662 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
664 wrap ms = L loc (bind { fun_matches = MatchGroup ms ty })
668 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
670 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
673 (this,rest) = partition same_t prs
674 same_t (t',v) = t `eqPatType` t'
676 eqPatLType :: LHsType Name -> LHsType Name -> Bool
677 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
679 eqPatType :: HsType Name -> HsType Name -> Bool
680 -- A very simple equality function, only for
681 -- type patterns in generic function definitions.
682 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
683 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
684 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
685 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
686 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
687 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
688 eqPatType _ _ = False
690 ---------------------------------
691 mkGenericInstance :: Class
692 -> (HsType Name, LHsBinds Name)
695 mkGenericInstance clas (hs_ty, binds)
696 -- Make a generic instance declaration
697 -- For example: instance (C a, C b) => C (a+b) where { binds }
699 = -- Extract the universally quantified type variables
700 -- and wrap them as forall'd tyvars, so that kind inference
701 -- works in the standard way
703 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
704 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
706 -- Type-check the instance type, and check its form
707 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
709 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
711 checkTc (validGenericInstanceType inst_ty)
712 (badGenericInstanceType binds) `thenM_`
714 -- Make the dictionary function.
715 getSrcSpanM `thenM` \ span ->
716 getOverlapFlag `thenM` \ overlap_flag ->
717 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
719 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
720 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
721 ispec = mkLocalInstance dfun_id overlap_flag
723 returnM (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] })
727 %************************************************************************
731 %************************************************************************
734 tcAddDeclCtxt decl thing_inside
735 = addErrCtxt ctxt thing_inside
738 ClassDecl {} -> "class"
739 TySynonym {} -> "type synonym"
740 TyData {tcdND = NewType} -> "newtype"
741 TyData {tcdND = DataType} -> "data type"
743 ctxt = hsep [ptext SLIT("In the"), text thing,
744 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
747 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
750 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
753 = hsep [ptext SLIT("Class"), quotes (ppr clas),
754 ptext SLIT("does not have a method"), quotes (ppr op)]
756 omittedMethodWarn sel_id
757 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
759 badGenericInstance sel_id because
760 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
764 = vcat [ptext SLIT("because the instance type(s)"),
765 nest 2 (ppr inst_tys),
766 ptext SLIT("is not a simple type of form (T a b c)")]
769 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
770 ptext SLIT("was not compiled with -fgenerics")]
772 badGenericInstanceType binds
773 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
776 missingGenericInstances missing
777 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
779 dupGenericInsts tc_inst_infos
780 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
781 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
782 ptext SLIT("All the type patterns for a generic type constructor must be identical")
785 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
788 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)