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,
23 InstInfo(..), pprInstInfoDetails,
24 simpleInstInfoTyCon, simpleInstInfoTy,
25 InstBindings(..), newDFunName
27 import TcBinds ( TcPragFun, tcMonoBinds, tcPrags, mkPragFun )
28 import TcHsType ( TcSigInfo(..), tcHsKindedType, tcHsSigType )
29 import TcSimplify ( tcSimplifyCheck )
30 import TcUnify ( checkSigTyVars, sigCtxt )
31 import TcMType ( tcSkolSigTyVars, UserTypeCtxt( GenPatCtxt ), tcSkolType )
32 import TcType ( Type, SkolemInfo(ClsSkol, InstSkol, SigSkol),
33 TcType, TcThetaType, TcTyVar, mkTyVarTys,
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 Type ( substTyWith )
45 import MkId ( mkDefaultMethodId, mkDictFunId )
46 import Id ( Id, idType, idName, mkUserLocal )
47 import Name ( Name, NamedThing(..) )
48 import NameEnv ( NameEnv, lookupNameEnv, mkNameEnv )
49 import NameSet ( nameSetToList )
50 import OccName ( reportIfUnused, mkDefaultMethodOcc )
51 import RdrName ( RdrName, mkDerivedRdrName )
53 import PrelNames ( genericTyConNames )
55 import UnicodeUtil ( stringToUtf8 )
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(..) )
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 (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 (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 tc_dm = tcDefMeth clas tyvars default_binds prag_fn
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 prag_fn 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] prag_fn 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, [])]
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 -> TcPragFun -- Pragmas (e.g. inline pragmas)
332 -> MethodSpec -- Details of this method
335 tcMethodBind inst_tyvars inst_theta avail_insts prag_fn
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 [meth_bind] lookup_sig Recursive
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
377 sel_name = idName sel_id
380 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
381 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
383 checkSigTyVars all_tyvars `thenM_`
385 tcPrags meth_id (prag_fn sel_name) `thenM` \ prags ->
387 [(_,_,local_meth_id)] = mono_bind_infos
388 poly_meth_bind = noLoc $ AbsBinds meth_tvs
389 (map instToId meth_dicts)
390 [(meth_tvs, meth_id, local_meth_id, prags)]
391 (lie_binds `unionBags` meth_bind)
393 returnM (unitBag poly_meth_bind)
396 mkMethodBind :: InstOrigin
397 -> Class -> [TcType] -- Class and instance types
398 -> LHsBinds Name -- Method binding (pick the right one from in here)
400 -> TcM (Maybe Inst, -- Method inst
402 -- Find the binding for the specified method, or make
403 -- up a suitable default method if it isn't there
405 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
406 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
408 meth_name = idName meth_id
410 -- Figure out what method binding to use
411 -- If the user suppplied one, use it, else construct a default one
412 getSrcSpanM `thenM` \ loc ->
413 (case find_bind (idName sel_id) meth_name meth_binds of
414 Just user_bind -> returnM user_bind
416 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
418 returnM (noLoc $ FunBind (noLoc meth_name) False
419 (mkMatchGroup [mkSimpleMatch [] rhs])
421 ) `thenM` \ meth_bind ->
423 returnM (mb_inst, (sel_id, meth_id, meth_bind))
425 mkMethId :: InstOrigin -> Class
426 -> Id -> [TcType] -- Selector, and instance types
427 -> TcM (Maybe Inst, Id)
429 -- mkMethId instantiates the selector Id at the specified types
430 mkMethId origin clas sel_id inst_tys
432 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
433 rho_ty = ASSERT( length tyvars == length inst_tys )
434 substTyWith tyvars inst_tys rho
435 (preds,tau) = tcSplitPhiTy rho_ty
436 first_pred = head preds
438 -- The first predicate should be of form (C a b)
439 -- where C is the class in question
440 ASSERT( not (null preds) &&
441 case getClassPredTys_maybe first_pred of
442 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
444 if isSingleton preds then
445 -- If it's the only one, make a 'method'
446 getInstLoc origin `thenM` \ inst_loc ->
447 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
448 returnM (Just meth_inst, instToId meth_inst)
450 -- If it's not the only one we need to be careful
451 -- For example, given 'op' defined thus:
453 -- op :: (?x :: String) => a -> a
454 -- (mkMethId op T) should return an Inst with type
455 -- (?x :: String) => T -> T
456 -- That is, the class-op's context is still there.
457 -- BUT: it can't be a Method any more, because it breaks
458 -- INVARIANT 2 of methods. (See the data decl for Inst.)
459 newUnique `thenM` \ uniq ->
460 getSrcSpanM `thenM` \ loc ->
462 real_tau = mkPhiTy (tail preds) tau
463 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
464 (srcSpanStart loc) --TODO
466 returnM (Nothing, meth_id)
468 -- The user didn't supply a method binding,
469 -- so we have to make up a default binding
470 -- The RHS of a default method depends on the default-method info
471 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
472 = -- An polymorphic default method
473 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
474 -- Might not be imported, but will be an OrigName
475 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
476 returnM (nlHsVar dm_name)
478 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
479 = -- No default method
480 -- Warn only if -fwarn-missing-methods
481 doptM Opt_WarnMissingMethods `thenM` \ warn ->
482 warnTc (isInstDecl origin
484 && reportIfUnused (getOccName sel_id))
485 (omittedMethodWarn sel_id) `thenM_`
488 error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
489 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
490 (nlHsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
491 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
493 -- When the type is of form t1 -> t2 -> t3
494 -- make a default method like (\ _ _ -> noMethBind "blah")
495 -- rather than simply (noMethBind "blah")
496 -- Reason: if t1 or t2 are higher-ranked types we get n
497 -- silly ambiguity messages.
498 -- Example: f :: (forall a. Eq a => a -> a) -> Int
500 -- Here, tcSub tries to force (error "urk") to have the right type,
501 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
502 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
504 -- NB: technically this changes the meaning of the default-default
505 -- method slightly, because `seq` can see the lambdas. Oh well.
506 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
507 (_,_,tau2) = tcSplitSigmaTy tau1
508 -- Need two splits because the selector can have a type like
509 -- forall a. Foo a => forall b. Eq b => ...
510 (arg_tys, _) = tcSplitFunTys tau2
511 wild_pats = [nlWildPat | ty <- arg_tys]
513 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
514 = -- A generic default method
515 -- If the method is defined generically, we can only do the job if the
516 -- instance declaration is for a single-parameter type class with
517 -- a type constructor applied to type arguments in the instance decl
518 -- (checkTc, so False provokes the error)
519 ASSERT( isInstDecl origin ) -- We never get here from a class decl
520 do { checkTc (isJust maybe_tycon)
521 (badGenericInstance sel_id (notSimple inst_tys))
522 ; checkTc (tyConHasGenerics tycon)
523 (badGenericInstance sel_id (notGeneric tycon))
526 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
527 (vcat [ppr clas <+> ppr inst_tys,
528 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
530 -- Rename it before returning it
531 ; (rn_rhs, _) <- rnLExpr rhs
534 rhs = mkGenericRhs sel_id clas_tyvar tycon
536 -- The tycon is only used in the generic case, and in that
537 -- case we require that the instance decl is for a single-parameter
538 -- type class with type variable arguments:
539 -- instance (...) => C (T a b)
540 clas_tyvar = head (classTyVars clas)
541 Just tycon = maybe_tycon
542 maybe_tycon = case inst_tys of
543 [ty] -> case tcSplitTyConApp_maybe ty of
544 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
548 isInstDecl (SigOrigin (InstSkol _)) = True
549 isInstDecl (SigOrigin (ClsSkol _)) = False
554 -- The renamer just puts the selector ID as the binder in the method binding
555 -- but we must use the method name; so we substitute it here. Crude but simple.
556 find_bind sel_name meth_name binds
557 = foldlBag seqMaybe Nothing (mapBag f binds)
559 f (L loc1 (FunBind (L loc2 op_name) fix matches fvs)) | op_name == sel_name
560 = Just (L loc1 (FunBind (L loc2 meth_name) fix matches fvs))
565 %************************************************************************
567 \subsection{Extracting generic instance declaration from class declarations}
569 %************************************************************************
571 @getGenericInstances@ extracts the generic instance declarations from a class
572 declaration. For exmaple
577 op{ x+y } (Inl v) = ...
578 op{ x+y } (Inr v) = ...
579 op{ x*y } (v :*: w) = ...
582 gives rise to the instance declarations
584 instance C (x+y) where
588 instance C (x*y) where
596 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
597 getGenericInstances class_decls
598 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
599 ; let { gen_inst_info = concat gen_inst_infos }
601 -- Return right away if there is no generic stuff
602 ; if null gen_inst_info then returnM []
605 -- Otherwise print it out
607 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
608 (vcat (map pprInstInfoDetails gen_inst_info)))
609 ; returnM gen_inst_info }}
611 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
613 = returnM [] -- The comon case: no generic default methods
615 | otherwise -- A source class decl with generic default methods
616 = recoverM (returnM []) $
618 tcLookupLocatedClass class_name `thenM` \ clas ->
620 -- Group by type, and
621 -- make an InstInfo out of each group
623 groups = groupWith listToBag generic_binds
625 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
627 -- Check that there is only one InstInfo for each type constructor
628 -- The main way this can fail is if you write
629 -- f {| a+b |} ... = ...
630 -- f {| x+y |} ... = ...
631 -- Then at this point we'll have an InstInfo for each
633 tc_inst_infos :: [(TyCon, InstInfo)]
634 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
636 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
637 group `lengthExceeds` 1]
638 get_uniq (tc,_) = getUnique tc
640 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
642 -- Check that there is an InstInfo for each generic type constructor
644 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
646 checkTc (null missing) (missingGenericInstances missing) `thenM_`
650 generic_binds :: [(HsType Name, LHsBind Name)]
651 generic_binds = getGenericBinds def_methods
654 ---------------------------------
655 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
656 -- Takes a group of method bindings, finds the generic ones, and returns
657 -- them in finite map indexed by the type parameter in the definition.
658 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
660 getGenericBind (L loc (FunBind id infixop (MatchGroup matches ty) fvs))
661 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
663 wrap ms = L loc (FunBind id infixop (MatchGroup ms ty) fvs)
667 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
669 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
672 (this,rest) = partition same_t prs
673 same_t (t',v) = t `eqPatType` t'
675 eqPatLType :: LHsType Name -> LHsType Name -> Bool
676 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
678 eqPatType :: HsType Name -> HsType Name -> Bool
679 -- A very simple equality function, only for
680 -- type patterns in generic function definitions.
681 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
682 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
683 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
684 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
685 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
686 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
687 eqPatType _ _ = False
689 ---------------------------------
690 mkGenericInstance :: Class
691 -> (HsType Name, LHsBinds Name)
694 mkGenericInstance clas (hs_ty, binds)
695 -- Make a generic instance declaration
696 -- For example: instance (C a, C b) => C (a+b) where { binds }
698 = -- Extract the universally quantified type variables
699 -- and wrap them as forall'd tyvars, so that kind inference
700 -- works in the standard way
702 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
703 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
705 -- Type-check the instance type, and check its form
706 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
708 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
710 checkTc (validGenericInstanceType inst_ty)
711 (badGenericInstanceType binds) `thenM_`
713 -- Make the dictionary function.
714 getSrcSpanM `thenM` \ span ->
715 getOverlapFlag `thenM` \ overlap_flag ->
716 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
718 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
719 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
720 ispec = mkLocalInstance dfun_id overlap_flag
722 returnM (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] })
726 %************************************************************************
730 %************************************************************************
733 tcAddDeclCtxt decl thing_inside
734 = addErrCtxt ctxt thing_inside
737 ClassDecl {} -> "class"
738 TySynonym {} -> "type synonym"
739 TyData {tcdND = NewType} -> "newtype"
740 TyData {tcdND = DataType} -> "data type"
742 ctxt = hsep [ptext SLIT("In the"), text thing,
743 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
746 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
749 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
752 = hsep [ptext SLIT("Class"), quotes (ppr clas),
753 ptext SLIT("does not have a method"), quotes (ppr op)]
755 omittedMethodWarn sel_id
756 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
758 badGenericInstance sel_id because
759 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
763 = vcat [ptext SLIT("because the instance type(s)"),
764 nest 2 (ppr inst_tys),
765 ptext SLIT("is not a simple type of form (T a b c)")]
768 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
769 ptext SLIT("was not compiled with -fgenerics")]
771 badGenericInstanceType binds
772 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
775 missingGenericInstances missing
776 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
778 dupGenericInsts tc_inst_infos
779 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
780 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
781 ptext SLIT("All the type patterns for a generic type constructor must be identical")
784 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
787 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)