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"
15 import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..), HsType(..),
16 HsExpr(..), HsLit(..), Pat(WildPat), HsTyVarBndr(..),
17 mkSimpleMatch, andMonoBinds, andMonoBindList,
18 isPragSig, placeHolderType, mkHsForAllTy
20 import BasicTypes ( RecFlag(..), NewOrData(..) )
21 import RnHsSyn ( RenamedTyClDecl, RenamedSig,
22 RenamedClassOpSig, RenamedMonoBinds,
23 maybeGenericMatch, extractHsTyVars
25 import RnExpr ( rnExpr )
26 import RnEnv ( lookupTopBndrRn, lookupImportedName )
27 import TcHsSyn ( TcMonoBinds )
29 import Inst ( Inst, InstOrigin(..), instToId, newDicts, newMethod )
30 import TcEnv ( tcLookupClass, tcExtendLocalValEnv2, tcExtendTyVarEnv2,
31 InstInfo(..), pprInstInfo, simpleInstInfoTyCon, simpleInstInfoTy,
32 InstBindings(..), newDFunName
34 import TcBinds ( tcMonoBinds, tcSpecSigs )
35 import TcHsType ( TcSigInfo(..), mkTcSig, tcHsKindedType, tcHsSigType )
36 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
37 import TcUnify ( checkSigTyVars, sigCtxt )
38 import TcMType ( tcInstTyVars, UserTypeCtxt( GenPatCtxt ) )
39 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
40 mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
41 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
42 getClassPredTys_maybe, mkPhiTy, mkTyVarTy
45 import Generics ( mkGenericRhs, validGenericInstanceType )
46 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
47 import Class ( classTyVars, classBigSig,
48 Class, ClassOpItem, DefMeth (..) )
49 import TyCon ( TyCon, tyConName, tyConHasGenerics )
50 import Subst ( substTyWith )
51 import MkId ( mkDefaultMethodId, mkDictFunId )
52 import Id ( Id, idType, idName, mkUserLocal, setInlinePragma )
53 import Name ( Name, NamedThing(..) )
54 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
55 import NameSet ( emptyNameSet, unitNameSet, nameSetToList )
56 import OccName ( reportIfUnused, mkDefaultMethodOcc )
57 import RdrName ( RdrName, mkDerivedRdrName )
60 import PrelNames ( genericTyConNames )
62 import UnicodeUtil ( stringToUtf8 )
63 import ErrUtils ( dumpIfSet, dumpIfSet_dyn )
64 import Util ( count, lengthIs, isSingleton, lengthExceeds )
65 import Unique ( Uniquable(..) )
66 import ListSetOps ( equivClassesByUniq, minusList )
67 import SrcLoc ( SrcLoc )
68 import Maybes ( seqMaybe, isJust, mapCatMaybes )
69 import List ( partition )
77 Every class implicitly declares a new data type, corresponding to dictionaries
78 of that class. So, for example:
80 class (D a) => C a where
82 op2 :: forall b. Ord b => a -> b -> b
84 would implicitly declare
86 data CDict a = CDict (D a)
88 (forall b. Ord b => a -> b -> b)
90 (We could use a record decl, but that means changing more of the existing apparatus.
93 For classes with just one superclass+method, we use a newtype decl instead:
96 op :: forallb. a -> b -> b
100 newtype CDict a = CDict (forall b. a -> b -> b)
102 Now DictTy in Type is just a form of type synomym:
103 DictTy c t = TyConTy CDict `AppTy` t
105 Death to "ExpandingDicts".
108 %************************************************************************
110 Type-checking the class op signatures
112 %************************************************************************
115 tcClassSigs :: Name -- Name of the class
116 -> [RenamedClassOpSig]
120 type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
121 -- between tcClassSigs and buildClass
122 tcClassSigs clas sigs def_methods
123 = do { dm_env <- checkDefaultBinds clas op_names def_methods
124 ; mappM (tcClassSig dm_env) op_sigs }
126 op_sigs = [sig | sig@(Sig n _ _) <- sigs]
127 op_names = [n | sig@(Sig n _ _) <- op_sigs]
130 checkDefaultBinds :: Name -> [Name] -> RenamedMonoBinds
131 -> TcM (NameEnv Bool)
132 -- Check default bindings
133 -- a) must be for a class op for this class
134 -- b) must be all generic or all non-generic
135 -- and return a mapping from class-op to Bool
136 -- where True <=> it's a generic default method
138 checkDefaultBinds clas ops EmptyMonoBinds
139 = returnM emptyNameEnv
141 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
142 = do { dm_info1 <- checkDefaultBinds clas ops b1
143 ; dm_info2 <- checkDefaultBinds clas ops b2
144 ; returnM (dm_info1 `plusNameEnv` dm_info2) }
146 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
148 { -- Check that the op is from this class
149 checkTc (op `elem` ops) (badMethodErr clas op)
151 -- Check that all the defns ar generic, or none are
152 ; checkTc (all_generic || none_generic) (mixedGenericErr op)
154 ; returnM (unitNameEnv op all_generic)
157 n_generic = count (isJust . maybeGenericMatch) matches
158 none_generic = n_generic == 0
159 all_generic = matches `lengthIs` n_generic
162 tcClassSig :: NameEnv Bool -- Info about default methods;
166 tcClassSig dm_env (Sig op_name op_hs_ty src_loc)
167 = addSrcLoc src_loc $ do
168 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
169 ; let dm = case lookupNameEnv dm_env op_name of
171 Just False -> DefMeth
172 Just True -> GenDefMeth
173 ; returnM (op_name, dm, op_ty) }
177 %************************************************************************
179 \subsection[Default methods]{Default methods}
181 %************************************************************************
183 The default methods for a class are each passed a dictionary for the
184 class, so that they get access to the other methods at the same type.
185 So, given the class decl
189 op2 :: Ord b => a -> b -> b -> b
192 op2 x y z = if (op1 x) && (y < z) then y else z
194 we get the default methods:
196 defm.Foo.op1 :: forall a. Foo a => a -> Bool
197 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
199 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
200 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
201 if (op1 a dfoo x) && (< b dord y z) then y else z
204 When we come across an instance decl, we may need to use the default
207 instance Foo Int where {}
211 const.Foo.Int.op1 :: Int -> Bool
212 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
214 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
215 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
217 dfun.Foo.Int :: Foo Int
218 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
220 Notice that, as with method selectors above, we assume that dictionary
221 application is curried, so there's no need to mention the Ord dictionary
222 in const.Foo.Int.op2 (or the type variable).
225 instance Foo a => Foo [a] where {}
227 dfun.Foo.List :: forall a. Foo a -> Foo [a]
229 = /\ a -> \ dfoo_a ->
231 op1 = defm.Foo.op1 [a] dfoo_list
232 op2 = defm.Foo.op2 [a] dfoo_list
233 dfoo_list = (op1, op2)
238 @tcClassDecls2@ generates bindings for polymorphic default methods
239 (generic default methods have by now turned into instance declarations)
242 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
243 -> TcM (TcMonoBinds, [Id])
245 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
246 tcdMeths = default_binds, tcdLoc = src_loc})
247 = recoverM (returnM (EmptyMonoBinds, [])) $
249 tcLookupClass class_name `thenM` \ clas ->
251 -- We make a separate binding for each default method.
252 -- At one time I used a single AbsBinds for all of them, thus
253 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
254 -- But that desugars into
255 -- ds = \d -> (..., ..., ...)
256 -- dm1 = \d -> case ds d of (a,b,c) -> a
257 -- And since ds is big, it doesn't get inlined, so we don't get good
258 -- default methods. Better to make separate AbsBinds for each
260 (tyvars, _, _, op_items) = classBigSig clas
261 prags = filter isPragSig sigs
262 tc_dm = tcDefMeth clas tyvars default_binds prags
264 dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
265 -- Generate code for polymorphic default methods only
266 -- (Generic default methods have turned into instance decls by now.)
267 -- This is incompatible with Hugs, which expects a polymorphic
268 -- default method for every class op, regardless of whether or not
269 -- the programmer supplied an explicit default decl for the class.
270 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
272 mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
273 returnM (andMonoBindList defm_binds, concat dm_ids_s)
275 tcDefMeth clas tyvars binds_in prags sel_id
276 = lookupTopBndrRn (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
277 tcInstTyVars ClsTv tyvars `thenM` \ (clas_tyvars, inst_tys, _) ->
279 dm_ty = idType sel_id -- Same as dict selector!
280 theta = [mkClassPred clas inst_tys]
281 local_dm_id = mkDefaultMethodId dm_name dm_ty
282 xtve = tyvars `zip` clas_tyvars
283 origin = ClassDeclOrigin
285 mkMethodBind origin clas inst_tys
286 binds_in (sel_id, DefMeth) `thenM` \ (_, meth_info) ->
287 newDicts origin theta `thenM` \ [this_dict] ->
288 getLIE (tcMethodBind xtve clas_tyvars theta
289 [this_dict] prags meth_info) `thenM` \ (defm_bind, insts_needed) ->
291 addErrCtxt (defltMethCtxt clas) $
295 (ptext SLIT("class") <+> ppr clas)
298 insts_needed `thenM` \ dict_binds ->
300 -- Simplification can do unification
301 checkSigTyVars clas_tyvars `thenM` \ clas_tyvars' ->
304 (_,dm_inst_id,_) = meth_info
308 [(clas_tyvars', local_dm_id, dm_inst_id)]
309 emptyNameSet -- No inlines (yet)
310 (dict_binds `andMonoBinds` defm_bind)
312 returnM (full_bind, [local_dm_id])
314 mkDefMethRdrName :: Id -> RdrName
315 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
319 %************************************************************************
321 \subsection{Typechecking a method}
323 %************************************************************************
325 @tcMethodBind@ is used to type-check both default-method and
326 instance-decl method declarations. We must type-check methods one at a
327 time, because their signatures may have different contexts and
331 type MethodSpec = (Id, -- Global selector Id
332 Id, -- Local Id (class tyvars instantiated)
333 RenamedMonoBinds) -- Binding for the method
336 :: [(TyVar,TcTyVar)] -- Bindings for type environment
337 -> [TcTyVar] -- Instantiated type variables for the
338 -- enclosing class/instance decl.
339 -- They'll be signature tyvars, and we
340 -- want to check that they don't get bound
341 -- Always equal the range of the type envt
342 -> TcThetaType -- Available theta; it's just used for the error message
343 -> [Inst] -- Available from context, used to simplify constraints
344 -- from the method body
345 -> [RenamedSig] -- Pragmas (e.g. inline pragmas)
346 -> MethodSpec -- Details of this method
349 tcMethodBind xtve inst_tyvars inst_theta avail_insts prags
350 (sel_id, meth_id, meth_bind)
351 = -- Check the bindings; first adding inst_tyvars to the envt
352 -- so that we don't quantify over them in nested places
353 mkTcSig meth_id `thenM` \ meth_sig ->
355 tcExtendTyVarEnv2 xtve (
356 addErrCtxt (methodCtxt sel_id) $
358 tcMonoBinds meth_bind [meth_sig] NonRecursive
359 ) `thenM` \ ((meth_bind,_), meth_lie) ->
361 -- Now do context reduction. We simplify wrt both the local tyvars
362 -- and the ones of the class/instance decl, so that there is
365 -- op :: Eq a => a -> b -> a
367 -- We do this for each method independently to localise error messages
370 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
372 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
373 newDicts SignatureOrigin meth_theta `thenM` \ meth_dicts ->
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` \ all_tyvars' ->
385 sel_name = idName sel_id
386 inline_prags = [ (is_inl, phase)
387 | InlineSig is_inl name phase _ <- prags,
390 | prag@(SpecSig 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 meth_tvs' = take (length meth_tvs) all_tyvars'
402 poly_meth_bind = AbsBinds meth_tvs'
403 (map instToId meth_dicts)
404 [(meth_tvs', final_meth_id, local_meth_id)]
406 (lie_binds `andMonoBinds` meth_bind)
409 -- Deal with specialisation pragmas
410 -- The sel_name is what appears in the pragma
411 tcExtendLocalValEnv2 [(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 `andMonoBinds` spec_binds2)
418 ) `thenM` \ spec_binds ->
420 returnM (poly_meth_bind `andMonoBinds` spec_binds)
423 mkMethodBind :: InstOrigin
424 -> Class -> [TcType] -- Class and instance types
425 -> RenamedMonoBinds -- 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 getSrcLocM `thenM` \ loc ->
440 (case find_bind (idName sel_id) meth_name meth_binds of
441 Just user_bind -> returnM user_bind
442 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
443 returnM (FunMonoBind meth_name False -- Not infix decl
444 [mkSimpleMatch [] rhs placeHolderType loc] loc)
445 ) `thenM` \ meth_bind ->
447 returnM (mb_inst, (sel_id, meth_id, meth_bind))
449 mkMethId :: InstOrigin -> Class
450 -> Id -> [TcType] -- Selector, and instance types
451 -> TcM (Maybe Inst, Id)
453 -- mkMethId instantiates the selector Id at the specified types
454 mkMethId origin clas sel_id inst_tys
456 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
457 rho_ty = ASSERT( length tyvars == length inst_tys )
458 substTyWith tyvars inst_tys rho
459 (preds,tau) = tcSplitPhiTy rho_ty
460 first_pred = head preds
462 -- The first predicate should be of form (C a b)
463 -- where C is the class in question
464 ASSERT( not (null preds) &&
465 case getClassPredTys_maybe first_pred of
466 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
468 if isSingleton preds then
469 -- If it's the only one, make a 'method'
470 getInstLoc origin `thenM` \ inst_loc ->
471 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
472 returnM (Just meth_inst, instToId meth_inst)
474 -- If it's not the only one we need to be careful
475 -- For example, given 'op' defined thus:
477 -- op :: (?x :: String) => a -> a
478 -- (mkMethId op T) should return an Inst with type
479 -- (?x :: String) => T -> T
480 -- That is, the class-op's context is still there.
481 -- BUT: it can't be a Method any more, because it breaks
482 -- INVARIANT 2 of methods. (See the data decl for Inst.)
483 newUnique `thenM` \ uniq ->
484 getSrcLocM `thenM` \ loc ->
486 real_tau = mkPhiTy (tail preds) tau
487 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau loc
489 returnM (Nothing, meth_id)
491 -- The user didn't supply a method binding,
492 -- so we have to make up a default binding
493 -- The RHS of a default method depends on the default-method info
494 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
495 = -- An polymorphic default method
496 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
497 -- Might not be imported, but will be an OrigName
498 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
499 returnM (HsVar dm_name)
501 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
502 = -- No default method
503 -- Warn only if -fwarn-missing-methods
504 doptM Opt_WarnMissingMethods `thenM` \ warn ->
505 warnTc (isInstDecl origin
507 && reportIfUnused (getOccName sel_id))
508 (omittedMethodWarn sel_id) `thenM_`
511 error_rhs = HsLam (mkSimpleMatch wild_pats simple_rhs placeHolderType loc)
512 simple_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
513 (HsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
514 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
516 -- When the type is of form t1 -> t2 -> t3
517 -- make a default method like (\ _ _ -> noMethBind "blah")
518 -- rather than simply (noMethBind "blah")
519 -- Reason: if t1 or t2 are higher-ranked types we get n
520 -- silly ambiguity messages.
521 -- Example: f :: (forall a. Eq a => a -> a) -> Int
523 -- Here, tcSub tries to force (error "urk") to have the right type,
524 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
525 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
527 -- NB: technically this changes the meaning of the default-default
528 -- method slightly, because `seq` can see the lambdas. Oh well.
529 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
530 (_,_,tau2) = tcSplitSigmaTy tau1
531 -- Need two splits because the selector can have a type like
532 -- forall a. Foo a => forall b. Eq b => ...
533 (arg_tys, _) = tcSplitFunTys tau2
534 wild_pats = [WildPat placeHolderType | ty <- arg_tys]
536 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
537 = -- A generic default method
538 -- If the method is defined generically, we can only do the job if the
539 -- instance declaration is for a single-parameter type class with
540 -- a type constructor applied to type arguments in the instance decl
541 -- (checkTc, so False provokes the error)
542 ASSERT( isInstDecl origin ) -- We never get here from a class decl
544 checkTc (isJust maybe_tycon)
545 (badGenericInstance sel_id (notSimple inst_tys)) `thenM_`
546 checkTc (tyConHasGenerics tycon)
547 (badGenericInstance sel_id (notGeneric tycon)) `thenM_`
549 ioToTcRn (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenM_`
551 -- Rename it before returning it
552 rnExpr rhs `thenM` \ (rn_rhs, _) ->
555 rhs = mkGenericRhs sel_id clas_tyvar tycon
557 stuff = vcat [ppr clas <+> ppr inst_tys,
558 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
560 -- The tycon is only used in the generic case, and in that
561 -- case we require that the instance decl is for a single-parameter
562 -- type class with type variable arguments:
563 -- instance (...) => C (T a b)
564 clas_tyvar = head (classTyVars clas)
565 Just tycon = maybe_tycon
566 maybe_tycon = case inst_tys of
567 [ty] -> case tcSplitTyConApp_maybe ty of
568 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
572 isInstDecl InstanceDeclOrigin = True
573 isInstDecl ClassDeclOrigin = False
578 -- The renamer just puts the selector ID as the binder in the method binding
579 -- but we must use the method name; so we substitute it here. Crude but simple.
580 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
581 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
582 find_bind sel_name meth_name (AndMonoBinds b1 b2)
583 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
584 find_bind sel_name meth_name other = Nothing -- Default case
588 %************************************************************************
590 \subsection{Extracting generic instance declaration from class declarations}
592 %************************************************************************
594 @getGenericInstances@ extracts the generic instance declarations from a class
595 declaration. For exmaple
600 op{ x+y } (Inl v) = ...
601 op{ x+y } (Inr v) = ...
602 op{ x*y } (v :*: w) = ...
605 gives rise to the instance declarations
607 instance C (x+y) where
611 instance C (x*y) where
619 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
620 getGenericInstances class_decls
621 = do { gen_inst_infos <- mappM get_generics class_decls
622 ; let { gen_inst_info = concat gen_inst_infos }
624 -- Return right away if there is no generic stuff
625 ; if null gen_inst_info then returnM []
628 -- Otherwise print it out
630 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
631 (vcat (map pprInstInfo gen_inst_info)))
632 ; returnM gen_inst_info }}
634 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = def_methods, tcdLoc = loc})
636 = returnM [] -- The comon case: no generic default methods
638 | otherwise -- A source class decl with generic default methods
639 = recoverM (returnM []) $
641 tcLookupClass class_name `thenM` \ clas ->
643 -- Group by type, and
644 -- make an InstInfo out of each group
646 groups = groupWith andMonoBindList generic_binds
648 mappM (mkGenericInstance clas loc) groups `thenM` \ inst_infos ->
650 -- Check that there is only one InstInfo for each type constructor
651 -- The main way this can fail is if you write
652 -- f {| a+b |} ... = ...
653 -- f {| x+y |} ... = ...
654 -- Then at this point we'll have an InstInfo for each
656 tc_inst_infos :: [(TyCon, InstInfo)]
657 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
659 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
660 group `lengthExceeds` 1]
661 get_uniq (tc,_) = getUnique tc
663 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
665 -- Check that there is an InstInfo for each generic type constructor
667 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
669 checkTc (null missing) (missingGenericInstances missing) `thenM_`
674 generic_binds :: [(HsType Name, RenamedMonoBinds)]
675 generic_binds = getGenericBinds def_methods
678 ---------------------------------
679 getGenericBinds :: RenamedMonoBinds -> [(HsType Name, RenamedMonoBinds)]
680 -- Takes a group of method bindings, finds the generic ones, and returns
681 -- them in finite map indexed by the type parameter in the definition.
683 getGenericBinds EmptyMonoBinds = []
684 getGenericBinds (AndMonoBinds m1 m2) = getGenericBinds m1 ++ getGenericBinds m2
686 getGenericBinds (FunMonoBind id infixop matches loc)
687 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
689 wrap ms = FunMonoBind id infixop ms loc
691 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
693 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
696 (this,rest) = partition same_t prs
697 same_t (t',v) = t `eqPatType` t'
699 eqPatType :: HsType Name -> HsType Name -> Bool
700 -- A very simple equality function, only for
701 -- type patterns in generic function definitions.
702 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
703 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatType` s2 && t2 `eqPatType` t2
704 eqPatType _ _ = False
706 ---------------------------------
707 mkGenericInstance :: Class -> SrcLoc
708 -> (HsType Name, RenamedMonoBinds)
711 mkGenericInstance clas loc (hs_ty, binds)
712 -- Make a generic instance declaration
713 -- For example: instance (C a, C b) => C (a+b) where { binds }
715 = -- Extract the universally quantified type variables
716 -- and wrap them as forall'd tyvars, so that kind inference
717 -- works in the standard way
719 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
720 hs_forall_ty = mkHsForAllTy (Just sig_tvs) [] hs_ty
722 -- Type-check the instance type, and check its form
723 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
725 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
727 checkTc (validGenericInstanceType inst_ty)
728 (badGenericInstanceType binds) `thenM_`
730 -- Make the dictionary function.
731 newDFunName clas [inst_ty] loc `thenM` \ dfun_name ->
733 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
734 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
737 returnM (InstInfo { iDFunId = dfun_id, iBinds = VanillaInst binds [] })
741 %************************************************************************
745 %************************************************************************
748 tcAddDeclCtxt decl thing_inside
749 = addSrcLoc (tcdLoc decl) $
754 ClassDecl {} -> "class"
755 TySynonym {} -> "type synonym"
756 TyData {tcdND = NewType} -> "newtype"
757 TyData {tcdND = DataType} -> "data type"
759 ctxt = hsep [ptext SLIT("In the"), text thing,
760 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
763 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
766 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
769 = hsep [ptext SLIT("Class"), quotes (ppr clas),
770 ptext SLIT("does not have a method"), quotes (ppr op)]
772 omittedMethodWarn sel_id
773 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
775 badGenericInstance sel_id because
776 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
780 = vcat [ptext SLIT("because the instance type(s)"),
781 nest 2 (ppr inst_tys),
782 ptext SLIT("is not a simple type of form (T a b c)")]
785 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
786 ptext SLIT("was not compiled with -fgenerics")]
788 badGenericInstanceType binds
789 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
792 missingGenericInstances missing
793 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
795 dupGenericInsts tc_inst_infos
796 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
797 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
798 ptext SLIT("All the type patterns for a generic type constructor must be identical")
801 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
804 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)