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 )
71 Every class implicitly declares a new data type, corresponding to dictionaries
72 of that class. So, for example:
74 class (D a) => C a where
76 op2 :: forall b. Ord b => a -> b -> b
78 would implicitly declare
80 data CDict a = CDict (D a)
82 (forall b. Ord b => a -> b -> b)
84 (We could use a record decl, but that means changing more of the existing apparatus.
87 For classes with just one superclass+method, we use a newtype decl instead:
90 op :: forallb. a -> b -> b
94 newtype CDict a = CDict (forall b. a -> b -> b)
96 Now DictTy in Type is just a form of type synomym:
97 DictTy c t = TyConTy CDict `AppTy` t
99 Death to "ExpandingDicts".
102 %************************************************************************
104 Type-checking the class op signatures
106 %************************************************************************
109 tcClassSigs :: Name -- Name of the class
114 type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
115 -- between tcClassSigs and buildClass
116 tcClassSigs clas sigs def_methods
117 = do { dm_env <- checkDefaultBinds clas op_names def_methods
118 ; mappM (tcClassSig dm_env) op_sigs }
120 op_sigs = [sig | sig@(L _ (Sig _ _)) <- sigs]
121 op_names = [n | sig@(L _ (Sig (L _ n) _)) <- op_sigs]
124 checkDefaultBinds :: Name -> [Name] -> LHsBinds Name -> TcM (NameEnv Bool)
125 -- Check default bindings
126 -- a) must be for a class op for this class
127 -- b) must be all generic or all non-generic
128 -- and return a mapping from class-op to Bool
129 -- where True <=> it's a generic default method
130 checkDefaultBinds clas ops binds
131 = do dm_infos <- mapM (addLocM (checkDefaultBind clas ops)) (bagToList binds)
132 return (mkNameEnv dm_infos)
134 checkDefaultBind clas ops (FunBind (L _ op) _ (MatchGroup matches _) _)
135 = do { -- Check that the op is from this class
136 checkTc (op `elem` ops) (badMethodErr clas op)
138 -- Check that all the defns ar generic, or none are
139 ; checkTc (all_generic || none_generic) (mixedGenericErr op)
141 ; returnM (op, all_generic)
144 n_generic = count (isJust . maybeGenericMatch) matches
145 none_generic = n_generic == 0
146 all_generic = matches `lengthIs` n_generic
149 tcClassSig :: NameEnv Bool -- Info about default methods;
153 tcClassSig dm_env (L loc (Sig (L _ op_name) op_hs_ty))
154 = setSrcSpan loc $ do
155 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
156 ; let dm = case lookupNameEnv dm_env op_name of
158 Just False -> DefMeth
159 Just True -> GenDefMeth
160 ; returnM (op_name, dm, op_ty) }
164 %************************************************************************
166 \subsection[Default methods]{Default methods}
168 %************************************************************************
170 The default methods for a class are each passed a dictionary for the
171 class, so that they get access to the other methods at the same type.
172 So, given the class decl
176 op2 :: Ord b => a -> b -> b -> b
179 op2 x y z = if (op1 x) && (y < z) then y else z
181 we get the default methods:
183 defm.Foo.op1 :: forall a. Foo a => a -> Bool
184 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
186 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
187 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
188 if (op1 a dfoo x) && (< b dord y z) then y else z
191 When we come across an instance decl, we may need to use the default
194 instance Foo Int where {}
198 const.Foo.Int.op1 :: Int -> Bool
199 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
201 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
202 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
204 dfun.Foo.Int :: Foo Int
205 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
207 Notice that, as with method selectors above, we assume that dictionary
208 application is curried, so there's no need to mention the Ord dictionary
209 in const.Foo.Int.op2 (or the type variable).
212 instance Foo a => Foo [a] where {}
214 dfun.Foo.List :: forall a. Foo a -> Foo [a]
216 = /\ a -> \ dfoo_a ->
218 op1 = defm.Foo.op1 [a] dfoo_list
219 op2 = defm.Foo.op2 [a] dfoo_list
220 dfoo_list = (op1, op2)
225 @tcClassDecls2@ generates bindings for polymorphic default methods
226 (generic default methods have by now turned into instance declarations)
229 tcClassDecl2 :: LTyClDecl Name -- The class declaration
230 -> TcM (LHsBinds Id, [Id])
232 tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
233 tcdMeths = default_binds}))
234 = recoverM (returnM (emptyLHsBinds, [])) $
236 tcLookupLocatedClass class_name `thenM` \ clas ->
238 -- We make a separate binding for each default method.
239 -- At one time I used a single AbsBinds for all of them, thus
240 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
241 -- But that desugars into
242 -- ds = \d -> (..., ..., ...)
243 -- dm1 = \d -> case ds d of (a,b,c) -> a
244 -- And since ds is big, it doesn't get inlined, so we don't get good
245 -- default methods. Better to make separate AbsBinds for each
247 (tyvars, _, _, op_items) = classBigSig clas
248 prag_fn = mkPragFun sigs
249 tc_dm = tcDefMeth clas tyvars default_binds prag_fn
251 dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
252 -- Generate code for polymorphic default methods only
253 -- (Generic default methods have turned into instance decls by now.)
254 -- This is incompatible with Hugs, which expects a polymorphic
255 -- default method for every class op, regardless of whether or not
256 -- the programmer supplied an explicit default decl for the class.
257 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
259 mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
260 returnM (listToBag defm_binds, concat dm_ids_s)
262 tcDefMeth clas tyvars binds_in prag_fn sel_id
263 = do { dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_id)
264 ; let rigid_info = ClsSkol clas
265 clas_tyvars = tcSkolSigTyVars rigid_info tyvars
266 inst_tys = mkTyVarTys clas_tyvars
267 dm_ty = idType sel_id -- Same as dict selector!
268 theta = [mkClassPred clas inst_tys]
269 local_dm_id = mkDefaultMethodId dm_name dm_ty
270 origin = SigOrigin rigid_info
272 ; (_, meth_info) <- mkMethodBind origin clas inst_tys binds_in (sel_id, DefMeth)
273 ; [this_dict] <- newDicts origin theta
274 ; (defm_bind, insts_needed) <- getLIE (tcMethodBind clas_tyvars theta
275 [this_dict] prag_fn meth_info)
277 ; addErrCtxt (defltMethCtxt clas) $ do
280 { dict_binds <- tcSimplifyCheck
281 (ptext SLIT("class") <+> ppr clas)
286 -- Simplification can do unification
287 ; checkSigTyVars clas_tyvars
290 (_,dm_inst_id,_) = meth_info
294 [(clas_tyvars, local_dm_id, dm_inst_id, [])]
296 (dict_binds `unionBags` defm_bind)
297 ; returnM (noLoc full_bind, [local_dm_id]) }}
299 mkDefMethRdrName :: Id -> RdrName
300 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
304 %************************************************************************
306 \subsection{Typechecking a method}
308 %************************************************************************
310 @tcMethodBind@ is used to type-check both default-method and
311 instance-decl method declarations. We must type-check methods one at a
312 time, because their signatures may have different contexts and
316 type MethodSpec = (Id, -- Global selector Id
317 Id, -- Local Id (class tyvars instantiated)
318 LHsBind Name) -- Binding for the method
321 :: [TcTyVar] -- Skolemised type variables for the
322 -- enclosing class/instance decl.
323 -- They'll be signature tyvars, and we
324 -- want to check that they don't get bound
325 -- Also they are scoped, so we bring them into scope
326 -- Always equal the range of the type envt
327 -> TcThetaType -- Available theta; it's just used for the error message
328 -> [Inst] -- Available from context, used to simplify constraints
329 -- from the method body
330 -> TcPragFun -- Pragmas (e.g. inline pragmas)
331 -> MethodSpec -- Details of this method
334 tcMethodBind inst_tyvars inst_theta avail_insts prag_fn
335 (sel_id, meth_id, meth_bind)
336 = recoverM (returnM emptyLHsBinds) $
337 -- If anything fails, recover returning no bindings.
338 -- This is particularly useful when checking the default-method binding of
339 -- a class decl. If we don't recover, we don't add the default method to
340 -- the type enviroment, and we get a tcLookup failure on $dmeth later.
342 -- Check the bindings; first adding inst_tyvars to the envt
343 -- so that we don't quantify over them in nested places
346 let -- Fake up a TcSigInfo to pass to tcMonoBinds
347 rigid_info = SigSkol (idName meth_id)
349 tcSkolType rigid_info (idType meth_id) `thenM` \ (tyvars', theta', tau') ->
350 getInstLoc (SigOrigin rigid_info) `thenM` \ loc ->
351 let meth_sig = TcSigInfo { sig_id = meth_id, sig_tvs = tyvars', sig_scoped = [],
352 sig_theta = theta', sig_tau = tau', sig_loc = loc }
353 lookup_sig name = ASSERT( name == idName meth_id )
356 tcExtendTyVarEnv inst_tyvars (
357 addErrCtxt (methodCtxt sel_id) $
359 tcMonoBinds [meth_bind] lookup_sig True
360 ) `thenM` \ ((meth_bind, mono_bind_infos), meth_lie) ->
362 -- Now do context reduction. We simplify wrt both the local tyvars
363 -- and the ones of the class/instance decl, so that there is
366 -- op :: Eq a => a -> b -> a
368 -- We do this for each method independently to localise error messages
370 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
371 newDictsAtLoc (sig_loc meth_sig) (sig_theta meth_sig) `thenM` \ meth_dicts ->
373 meth_tvs = sig_tvs meth_sig
374 all_tyvars = meth_tvs ++ inst_tyvars
375 all_insts = avail_insts ++ meth_dicts
376 sel_name = idName sel_id
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_`
384 tcPrags meth_id (prag_fn sel_name) `thenM` \ prags ->
386 [(_,_,local_meth_id)] = mono_bind_infos
387 poly_meth_bind = noLoc $ AbsBinds meth_tvs
388 (map instToId meth_dicts)
389 [(meth_tvs, meth_id, local_meth_id, prags)]
390 (lie_binds `unionBags` meth_bind)
392 returnM (unitBag poly_meth_bind)
395 mkMethodBind :: InstOrigin
396 -> Class -> [TcType] -- Class and instance types
397 -> LHsBinds Name -- Method binding (pick the right one from in here)
399 -> TcM (Maybe Inst, -- Method inst
401 -- Find the binding for the specified method, or make
402 -- up a suitable default method if it isn't there
404 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
405 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
407 meth_name = idName meth_id
409 -- Figure out what method binding to use
410 -- If the user suppplied one, use it, else construct a default one
411 getSrcSpanM `thenM` \ loc ->
412 (case find_bind (idName sel_id) meth_name meth_binds of
413 Just user_bind -> returnM user_bind
415 mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
417 returnM (noLoc $ FunBind (noLoc meth_name) False
418 (mkMatchGroup [mkSimpleMatch [] rhs])
420 ) `thenM` \ meth_bind ->
422 returnM (mb_inst, (sel_id, meth_id, meth_bind))
424 mkMethId :: InstOrigin -> Class
425 -> Id -> [TcType] -- Selector, and instance types
426 -> TcM (Maybe Inst, Id)
428 -- mkMethId instantiates the selector Id at the specified types
429 mkMethId origin clas sel_id inst_tys
431 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
432 rho_ty = ASSERT( length tyvars == length inst_tys )
433 substTyWith tyvars inst_tys rho
434 (preds,tau) = tcSplitPhiTy rho_ty
435 first_pred = head preds
437 -- The first predicate should be of form (C a b)
438 -- where C is the class in question
439 ASSERT( not (null preds) &&
440 case getClassPredTys_maybe first_pred of
441 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
443 if isSingleton preds then
444 -- If it's the only one, make a 'method'
445 getInstLoc origin `thenM` \ inst_loc ->
446 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
447 returnM (Just meth_inst, instToId meth_inst)
449 -- If it's not the only one we need to be careful
450 -- For example, given 'op' defined thus:
452 -- op :: (?x :: String) => a -> a
453 -- (mkMethId op T) should return an Inst with type
454 -- (?x :: String) => T -> T
455 -- That is, the class-op's context is still there.
456 -- BUT: it can't be a Method any more, because it breaks
457 -- INVARIANT 2 of methods. (See the data decl for Inst.)
458 newUnique `thenM` \ uniq ->
459 getSrcSpanM `thenM` \ loc ->
461 real_tau = mkPhiTy (tail preds) tau
462 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau
463 (srcSpanStart loc) --TODO
465 returnM (Nothing, meth_id)
467 -- The user didn't supply a method binding,
468 -- so we have to make up a default binding
469 -- The RHS of a default method depends on the default-method info
470 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
471 = -- An polymorphic default method
472 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
473 -- Might not be imported, but will be an OrigName
474 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
475 returnM (nlHsVar dm_name)
477 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
478 = -- No default method
479 -- Warn only if -fwarn-missing-methods
480 doptM Opt_WarnMissingMethods `thenM` \ warn ->
481 warnTc (isInstDecl origin
483 && reportIfUnused (getOccName sel_id))
484 (omittedMethodWarn sel_id) `thenM_`
487 error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
488 simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
489 (nlHsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
490 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
492 -- When the type is of form t1 -> t2 -> t3
493 -- make a default method like (\ _ _ -> noMethBind "blah")
494 -- rather than simply (noMethBind "blah")
495 -- Reason: if t1 or t2 are higher-ranked types we get n
496 -- silly ambiguity messages.
497 -- Example: f :: (forall a. Eq a => a -> a) -> Int
499 -- Here, tcSub tries to force (error "urk") to have the right type,
500 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
501 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
503 -- NB: technically this changes the meaning of the default-default
504 -- method slightly, because `seq` can see the lambdas. Oh well.
505 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
506 (_,_,tau2) = tcSplitSigmaTy tau1
507 -- Need two splits because the selector can have a type like
508 -- forall a. Foo a => forall b. Eq b => ...
509 (arg_tys, _) = tcSplitFunTys tau2
510 wild_pats = [nlWildPat | ty <- arg_tys]
512 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
513 = -- A generic default method
514 -- If the method is defined generically, we can only do the job if the
515 -- instance declaration is for a single-parameter type class with
516 -- a type constructor applied to type arguments in the instance decl
517 -- (checkTc, so False provokes the error)
518 ASSERT( isInstDecl origin ) -- We never get here from a class decl
519 do { checkTc (isJust maybe_tycon)
520 (badGenericInstance sel_id (notSimple inst_tys))
521 ; checkTc (tyConHasGenerics tycon)
522 (badGenericInstance sel_id (notGeneric tycon))
525 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
526 (vcat [ppr clas <+> ppr inst_tys,
527 nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
529 -- Rename it before returning it
530 ; (rn_rhs, _) <- rnLExpr rhs
533 rhs = mkGenericRhs sel_id clas_tyvar tycon
535 -- The tycon is only used in the generic case, and in that
536 -- case we require that the instance decl is for a single-parameter
537 -- type class with type variable arguments:
538 -- instance (...) => C (T a b)
539 clas_tyvar = head (classTyVars clas)
540 Just tycon = maybe_tycon
541 maybe_tycon = case inst_tys of
542 [ty] -> case tcSplitTyConApp_maybe ty of
543 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
547 isInstDecl (SigOrigin (InstSkol _)) = True
548 isInstDecl (SigOrigin (ClsSkol _)) = False
553 -- The renamer just puts the selector ID as the binder in the method binding
554 -- but we must use the method name; so we substitute it here. Crude but simple.
555 find_bind sel_name meth_name binds
556 = foldlBag seqMaybe Nothing (mapBag f binds)
558 f (L loc1 (FunBind (L loc2 op_name) fix matches fvs)) | op_name == sel_name
559 = Just (L loc1 (FunBind (L loc2 meth_name) fix matches fvs))
564 %************************************************************************
566 \subsection{Extracting generic instance declaration from class declarations}
568 %************************************************************************
570 @getGenericInstances@ extracts the generic instance declarations from a class
571 declaration. For exmaple
576 op{ x+y } (Inl v) = ...
577 op{ x+y } (Inr v) = ...
578 op{ x*y } (v :*: w) = ...
581 gives rise to the instance declarations
583 instance C (x+y) where
587 instance C (x*y) where
595 getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
596 getGenericInstances class_decls
597 = do { gen_inst_infos <- mappM (addLocM get_generics) class_decls
598 ; let { gen_inst_info = concat gen_inst_infos }
600 -- Return right away if there is no generic stuff
601 ; if null gen_inst_info then returnM []
604 -- Otherwise print it out
606 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
607 (vcat (map pprInstInfoDetails gen_inst_info)))
608 ; returnM gen_inst_info }}
610 get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
612 = returnM [] -- The comon case: no generic default methods
614 | otherwise -- A source class decl with generic default methods
615 = recoverM (returnM []) $
617 tcLookupLocatedClass class_name `thenM` \ clas ->
619 -- Group by type, and
620 -- make an InstInfo out of each group
622 groups = groupWith listToBag generic_binds
624 mappM (mkGenericInstance clas) groups `thenM` \ inst_infos ->
626 -- Check that there is only one InstInfo for each type constructor
627 -- The main way this can fail is if you write
628 -- f {| a+b |} ... = ...
629 -- f {| x+y |} ... = ...
630 -- Then at this point we'll have an InstInfo for each
632 tc_inst_infos :: [(TyCon, InstInfo)]
633 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
635 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
636 group `lengthExceeds` 1]
637 get_uniq (tc,_) = getUnique tc
639 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
641 -- Check that there is an InstInfo for each generic type constructor
643 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
645 checkTc (null missing) (missingGenericInstances missing) `thenM_`
649 generic_binds :: [(HsType Name, LHsBind Name)]
650 generic_binds = getGenericBinds def_methods
653 ---------------------------------
654 getGenericBinds :: LHsBinds Name -> [(HsType Name, LHsBind Name)]
655 -- Takes a group of method bindings, finds the generic ones, and returns
656 -- them in finite map indexed by the type parameter in the definition.
657 getGenericBinds binds = concat (map getGenericBind (bagToList binds))
659 getGenericBind (L loc (FunBind id infixop (MatchGroup matches ty) fvs))
660 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
662 wrap ms = L loc (FunBind id infixop (MatchGroup ms ty) fvs)
666 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
668 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
671 (this,rest) = partition same_t prs
672 same_t (t',v) = t `eqPatType` t'
674 eqPatLType :: LHsType Name -> LHsType Name -> Bool
675 eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
677 eqPatType :: HsType Name -> HsType Name -> Bool
678 -- A very simple equality function, only for
679 -- type patterns in generic function definitions.
680 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
681 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
682 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
683 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
684 eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
685 eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
686 eqPatType _ _ = False
688 ---------------------------------
689 mkGenericInstance :: Class
690 -> (HsType Name, LHsBinds Name)
693 mkGenericInstance clas (hs_ty, binds)
694 -- Make a generic instance declaration
695 -- For example: instance (C a, C b) => C (a+b) where { binds }
697 = -- Extract the universally quantified type variables
698 -- and wrap them as forall'd tyvars, so that kind inference
699 -- works in the standard way
701 sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
702 hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
704 -- Type-check the instance type, and check its form
705 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
707 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
709 checkTc (validGenericInstanceType inst_ty)
710 (badGenericInstanceType binds) `thenM_`
712 -- Make the dictionary function.
713 getSrcSpanM `thenM` \ span ->
714 getOverlapFlag `thenM` \ overlap_flag ->
715 newDFunName clas [inst_ty] (srcSpanStart span) `thenM` \ dfun_name ->
717 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
718 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
719 ispec = mkLocalInstance dfun_id overlap_flag
721 returnM (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] })
725 %************************************************************************
729 %************************************************************************
732 tcAddDeclCtxt decl thing_inside
733 = addErrCtxt ctxt thing_inside
736 ClassDecl {} -> "class"
737 TySynonym {} -> "type synonym"
738 TyData {tcdND = NewType} -> "newtype"
739 TyData {tcdND = DataType} -> "data type"
741 ctxt = hsep [ptext SLIT("In the"), text thing,
742 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
745 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
748 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
751 = hsep [ptext SLIT("Class"), quotes (ppr clas),
752 ptext SLIT("does not have a method"), quotes (ppr op)]
754 omittedMethodWarn sel_id
755 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
757 badGenericInstance sel_id because
758 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
762 = vcat [ptext SLIT("because the instance type(s)"),
763 nest 2 (ppr inst_tys),
764 ptext SLIT("is not a simple type of form (T a b c)")]
767 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
768 ptext SLIT("was not compiled with -fgenerics")]
770 badGenericInstanceType binds
771 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
774 missingGenericInstances missing
775 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
777 dupGenericInsts tc_inst_infos
778 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
779 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
780 ptext SLIT("All the type patterns for a generic type constructor must be identical")
783 ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
786 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)