2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, tcClassDecls2,
8 MethodSpec, tcMethodBind, mkMethodBind, badMethodErr
11 #include "HsVersions.h"
13 import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..),
14 HsExpr(..), HsLit(..), Pat(WildPat),
15 mkSimpleMatch, andMonoBinds, andMonoBindList,
16 isClassOpSig, isPragSig,
19 import BasicTypes ( RecFlag(..), StrictnessMark(..) )
20 import RnHsSyn ( RenamedTyClDecl, RenamedSig,
21 RenamedClassOpSig, RenamedMonoBinds,
24 import RnEnv ( lookupSysName )
25 import TcHsSyn ( TcMonoBinds )
27 import Inst ( Inst, InstOrigin(..), instToId, newDicts, newMethod )
28 import TcEnv ( TyThingDetails(..),
29 tcLookupClass, tcExtendTyVarEnv2,
32 import TcBinds ( tcMonoBinds )
33 import TcMonoType ( TcSigInfo(..), tcHsType, tcHsTheta, mkTcSig )
34 import TcSimplify ( tcSimplifyCheck )
35 import TcUnify ( checkSigTyVars, sigCtxt )
36 import TcMType ( tcInstTyVars )
37 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
38 mkTyVarTys, mkPredTys, mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
39 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
40 getClassPredTys_maybe, mkPhiTy
43 import Generics ( mkGenericRhs )
44 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
45 import Class ( classTyVars, classBigSig, classTyCon,
46 Class, ClassOpItem, DefMeth (..) )
47 import TyCon ( tyConGenInfo )
48 import Subst ( substTyWith )
49 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
50 import DataCon ( mkDataCon )
51 import Id ( Id, idType, idName, mkUserLocal, setIdLocalExported, setInlinePragma )
52 import Name ( Name, NamedThing(..) )
53 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
54 import NameSet ( emptyNameSet, unitNameSet )
55 import OccName ( mkClassTyConOcc, mkClassDataConOcc, mkWorkerOcc,
56 mkSuperDictSelOcc, reportIfUnused )
60 import UnicodeUtil ( stringToUtf8 )
61 import ErrUtils ( dumpIfSet )
62 import Util ( count, lengthIs, isSingleton )
63 import Maybes ( seqMaybe )
64 import Maybe ( isJust )
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 \subsection{Type checking}
107 %************************************************************************
111 tcClassDecl1 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
112 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
113 tcdTyVars = tyvar_names, tcdFDs = fundeps,
114 tcdSigs = class_sigs, tcdMeths = def_methods,
116 = -- LOOK THINGS UP IN THE ENVIRONMENT
117 tcLookupClass class_name `thenM` \ clas ->
119 tyvars = classTyVars clas
120 op_sigs = filter isClassOpSig class_sigs
121 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
123 tcExtendTyVarEnv tyvars $
125 checkDefaultBinds clas op_names def_methods `thenM` \ mb_dm_env ->
128 -- The renamer has already checked that the context mentions
129 -- only the type variable of the class decl.
130 -- Context is already kind-checked
131 tcHsTheta context `thenM` \ sc_theta ->
133 -- CHECK THE CLASS SIGNATURES,
134 mappM (tcClassSig clas tyvars mb_dm_env) op_sigs `thenM` \ sig_stuff ->
136 -- MAKE THE CLASS DETAILS
137 lookupSysName class_name mkClassDataConOcc `thenM` \ datacon_name ->
138 lookupSysName datacon_name mkWorkerOcc `thenM` \ datacon_wkr_name ->
139 mapM (lookupSysName class_name . mkSuperDictSelOcc)
140 [1..length context] `thenM` \ sc_sel_names ->
141 -- We number off the superclass selectors, 1, 2, 3 etc so that we
142 -- can construct names for the selectors. Thus
143 -- class (C a, C b) => D a b where ...
144 -- gives superclass selectors
146 -- (We used to call them D_C, but now we can have two different
147 -- superclasses both called C!)
148 lookupSysName class_name mkClassTyConOcc `thenM` \ tycon_name ->
150 (op_tys, op_items) = unzip sig_stuff
151 sc_tys = mkPredTys sc_theta
152 dict_component_tys = sc_tys ++ op_tys
153 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
155 dict_con = mkDataCon datacon_name
156 [NotMarkedStrict | _ <- dict_component_tys]
157 [{- No labelled fields -}]
160 [{-No existential tyvars-}] [{-Or context-}]
163 dict_con_id dict_wrap_id
165 dict_con_id = mkDataConId datacon_wkr_name dict_con
166 dict_wrap_id = mkDataConWrapId dict_con
168 returnM (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con tycon_name)
172 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
173 -> TcM (Maybe (NameEnv Bool))
174 -- The returned environment says
175 -- x not in env => no default method
176 -- x -> True => generic default method
177 -- x -> False => polymorphic default method
179 -- Check default bindings
180 -- a) must be for a class op for this class
181 -- b) must be all generic or all non-generic
182 -- and return a mapping from class-op to DefMeth info
184 -- But do all this only for source binds
186 checkDefaultBinds clas ops Nothing
189 checkDefaultBinds clas ops (Just mbs)
190 = go mbs `thenM` \ dm_env ->
191 returnM (Just dm_env)
193 go EmptyMonoBinds = returnM emptyNameEnv
195 go (AndMonoBinds b1 b2)
196 = go b1 `thenM` \ dm_info1 ->
197 go b2 `thenM` \ dm_info2 ->
198 returnM (dm_info1 `plusNameEnv` dm_info2)
200 go (FunMonoBind op _ matches loc)
203 -- Check that the op is from this class
204 checkTc (op `elem` ops) (badMethodErr clas op) `thenM_`
206 -- Check that all the defns ar generic, or none are
207 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenM_`
209 returnM (unitNameEnv op all_generic)
211 n_generic = count (isJust . maybeGenericMatch) matches
212 none_generic = n_generic == 0
213 all_generic = matches `lengthIs` n_generic
218 tcClassSig :: Class -- ...ditto...
219 -> [TyVar] -- The class type variable, used for error check only
220 -> Maybe (NameEnv Bool) -- Info about default methods;
221 -- Nothing => imported class defn with no method binds
223 -> TcM (Type, -- Type of the method
224 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
226 -- This warrants an explanation: we need to separate generic
227 -- default methods and default methods later on in the compiler
228 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
229 -- Class.DefMeth data structure.
231 tcClassSig clas clas_tyvars maybe_dm_env
232 (ClassOpSig op_name sig_dm op_ty src_loc)
233 = addSrcLoc src_loc $
235 -- Check the type signature. NB that the envt *already has*
236 -- bindings for the type variables; see comments in TcTyAndClassDcls.
237 tcHsType op_ty `thenM` \ local_ty ->
240 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
242 -- Build the selector id and default method id
243 sel_id = mkDictSelId op_name clas
244 DefMeth dm_name = sig_dm
246 dm_info = case maybe_dm_env of
248 Just dm_env -> mk_src_dm_info dm_env
250 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
252 Just True -> GenDefMeth
253 Just False -> DefMeth dm_name
255 returnM (local_ty, (sel_id, dm_info))
259 %************************************************************************
261 \subsection[Default methods]{Default methods}
263 %************************************************************************
265 The default methods for a class are each passed a dictionary for the
266 class, so that they get access to the other methods at the same type.
267 So, given the class decl
271 op2 :: Ord b => a -> b -> b -> b
274 op2 x y z = if (op1 x) && (y < z) then y else z
276 we get the default methods:
278 defm.Foo.op1 :: forall a. Foo a => a -> Bool
279 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
281 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
282 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
283 if (op1 a dfoo x) && (< b dord y z) then y else z
286 When we come across an instance decl, we may need to use the default
289 instance Foo Int where {}
293 const.Foo.Int.op1 :: Int -> Bool
294 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
296 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
297 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
299 dfun.Foo.Int :: Foo Int
300 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
302 Notice that, as with method selectors above, we assume that dictionary
303 application is curried, so there's no need to mention the Ord dictionary
304 in const.Foo.Int.op2 (or the type variable).
307 instance Foo a => Foo [a] where {}
309 dfun.Foo.List :: forall a. Foo a -> Foo [a]
311 = /\ a -> \ dfoo_a ->
313 op1 = defm.Foo.op1 [a] dfoo_list
314 op2 = defm.Foo.op2 [a] dfoo_list
315 dfoo_list = (op1, op2)
320 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
321 each local class decl.
324 tcClassDecls2 :: [RenamedTyClDecl] -> TcM (TcMonoBinds, [Id])
328 (returnM (EmptyMonoBinds, []))
329 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
330 -- The 'Just' picks out source ClassDecls
332 combine tc1 tc2 = tc1 `thenM` \ (binds1, ids1) ->
333 tc2 `thenM` \ (binds2, ids2) ->
334 returnM (binds1 `AndMonoBinds` binds2,
338 @tcClassDecl2@ generates bindings for polymorphic default methods
339 (generic default methods have by now turned into instance declarations)
342 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
343 -> TcM (TcMonoBinds, [Id])
345 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
346 tcdMeths = Just default_binds, tcdLoc = src_loc})
347 = -- The 'Just' picks out source ClassDecls
348 recoverM (returnM (EmptyMonoBinds, [])) $
350 tcLookupClass class_name `thenM` \ clas ->
352 -- We make a separate binding for each default method.
353 -- At one time I used a single AbsBinds for all of them, thus
354 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
355 -- But that desugars into
356 -- ds = \d -> (..., ..., ...)
357 -- dm1 = \d -> case ds d of (a,b,c) -> a
358 -- And since ds is big, it doesn't get inlined, so we don't get good
359 -- default methods. Better to make separate AbsBinds for each
361 (tyvars, _, _, op_items) = classBigSig clas
362 prags = filter isPragSig sigs
363 tc_dm = tcDefMeth clas tyvars default_binds prags
365 mapAndUnzipM tc_dm op_items `thenM` \ (defm_binds, dm_ids_s) ->
367 returnM (andMonoBindList defm_binds, concat dm_ids_s)
370 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnM (EmptyMonoBinds, [])
371 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnM (EmptyMonoBinds, [])
372 -- Generate code for polymorphic default methods only
373 -- (Generic default methods have turned into instance decls by now.)
374 -- This is incompatible with Hugs, which expects a polymorphic
375 -- default method for every class op, regardless of whether or not
376 -- the programmer supplied an explicit default decl for the class.
377 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
379 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
380 = tcInstTyVars ClsTv tyvars `thenM` \ (clas_tyvars, inst_tys, _) ->
382 dm_ty = idType sel_id -- Same as dict selector!
383 -- The default method's type should really come from the
384 -- iface file, since it could be usage-generalised, but this
385 -- requires altering the mess of knots in TcModule and I'm
386 -- too scared to do that. Instead, I have disabled generalisation
387 -- of types of default methods (and dict funs) by annotating them
388 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
390 theta = [mkClassPred clas inst_tys]
391 local_dm_id = mkDefaultMethodId dm_name dm_ty
392 xtve = tyvars `zip` clas_tyvars
394 newDicts origin theta `thenM` \ [this_dict] ->
396 mkMethodBind origin clas inst_tys binds_in op_item `thenM` \ (_, meth_info) ->
397 getLIE (tcMethodBind xtve clas_tyvars theta
398 [this_dict] prags meth_info) `thenM` \ (defm_bind, insts_needed) ->
400 addErrCtxt (defltMethCtxt clas) $
404 (ptext SLIT("class") <+> ppr clas)
407 insts_needed `thenM` \ dict_binds ->
409 -- Simplification can do unification
410 checkSigTyVars clas_tyvars `thenM` \ clas_tyvars' ->
413 (_,dm_inst_id,_) = meth_info
417 [(clas_tyvars', local_dm_id, dm_inst_id)]
418 emptyNameSet -- No inlines (yet)
419 (dict_binds `andMonoBinds` defm_bind)
421 returnM (full_bind, [local_dm_id])
423 origin = ClassDeclOrigin
428 %************************************************************************
430 \subsection{Typechecking a method}
432 %************************************************************************
434 @tcMethodBind@ is used to type-check both default-method and
435 instance-decl method declarations. We must type-check methods one at a
436 time, because their signatures may have different contexts and
440 type MethodSpec = (Id, -- Global selector Id
441 Id, -- Local Id (class tyvars instantiated)
442 RenamedMonoBinds) -- Binding for the method
445 :: [(TyVar,TcTyVar)] -- Bindings for type environment
446 -> [TcTyVar] -- Instantiated type variables for the
447 -- enclosing class/instance decl.
448 -- They'll be signature tyvars, and we
449 -- want to check that they don't get bound
450 -- Always equal the range of the type envt
451 -> TcThetaType -- Available theta; it's just used for the error message
452 -> [Inst] -- Available from context, used to simplify constraints
453 -- from the method body
454 -> [RenamedSig] -- Pragmas (e.g. inline pragmas)
455 -> MethodSpec -- Details of this method
458 tcMethodBind xtve inst_tyvars inst_theta avail_insts prags
459 (sel_id, meth_id, meth_bind)
460 = -- Check the bindings; first adding inst_tyvars to the envt
461 -- so that we don't quantify over them in nested places
462 mkTcSig meth_id `thenM` \ meth_sig ->
464 tcExtendTyVarEnv2 xtve (
465 addErrCtxt (methodCtxt sel_id) $
466 getLIE (tcMonoBinds meth_bind [meth_sig] NonRecursive)
467 ) `thenM` \ ((meth_bind, _, _), meth_lie) ->
469 -- Now do context reduction. We simplify wrt both the local tyvars
470 -- and the ones of the class/instance decl, so that there is
473 -- op :: Eq a => a -> b -> a
475 -- We do this for each method independently to localise error messages
478 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
480 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
481 newDicts SignatureOrigin meth_theta `thenM` \ meth_dicts ->
483 all_tyvars = meth_tvs ++ inst_tyvars
484 all_insts = avail_insts ++ meth_dicts
487 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
488 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
490 checkSigTyVars all_tyvars `thenM` \ all_tyvars' ->
493 -- Attach inline pragmas as appropriate
494 (final_meth_id, inlines)
495 | (InlineSig inl _ phase _ : _) <- filter is_inline prags
496 = (meth_id `setInlinePragma` phase,
497 if inl then unitNameSet (idName meth_id) else emptyNameSet)
499 = (meth_id, emptyNameSet)
501 is_inline (InlineSig _ name _ _) = name == idName sel_id
502 is_inline other = False
504 meth_tvs' = take (length meth_tvs) all_tyvars'
505 poly_meth_bind = AbsBinds meth_tvs'
506 (map instToId meth_dicts)
507 [(meth_tvs', final_meth_id, local_meth_id)]
509 (lie_binds `andMonoBinds` meth_bind)
511 returnM poly_meth_bind
514 mkMethodBind :: InstOrigin
515 -> Class -> [TcType] -- Class and instance types
516 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
518 -> TcM (Maybe Inst, -- Method inst
520 -- Find the binding for the specified method, or make
521 -- up a suitable default method if it isn't there
523 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
524 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
526 meth_name = idName meth_id
528 -- Figure out what method binding to use
529 -- If the user suppplied one, use it, else construct a default one
530 getSrcLocM `thenM` \ loc ->
531 (case find_bind (idName sel_id) meth_name meth_binds of
532 Just user_bind -> returnM user_bind
533 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
534 returnM (FunMonoBind meth_name False -- Not infix decl
535 [mkSimpleMatch [] rhs placeHolderType loc] loc)
536 ) `thenM` \ meth_bind ->
538 returnM (mb_inst, (sel_id, meth_id, meth_bind))
540 mkMethId :: InstOrigin -> Class
541 -> Id -> [TcType] -- Selector, and instance types
542 -> TcM (Maybe Inst, Id)
544 -- mkMethId instantiates the selector Id at the specified types
546 mkMethId origin clas sel_id inst_tys
548 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
549 rho_ty = ASSERT( length tyvars == length inst_tys )
550 substTyWith tyvars inst_tys rho
551 (preds,tau) = tcSplitPhiTy rho_ty
552 first_pred = head preds
554 -- The first predicate should be of form (C a b)
555 -- where C is the class in question
556 ASSERT( not (null preds) &&
557 case getClassPredTys_maybe first_pred of
558 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
560 if isSingleton preds then
561 -- If it's the only one, make a 'method'
562 getInstLoc origin `thenM` \ inst_loc ->
563 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
564 returnM (Just meth_inst, instToId meth_inst)
566 -- If it's not the only one we need to be careful
567 -- For example, given 'op' defined thus:
569 -- op :: (?x :: String) => a -> a
570 -- (mkMethId op T) should return an Inst with type
571 -- (?x :: String) => T -> T
572 -- That is, the class-op's context is still there.
573 -- BUT: it can't be a Method any more, because it breaks
574 -- INVARIANT 2 of methods. (See the data decl for Inst.)
575 newUnique `thenM` \ uniq ->
576 getSrcLocM `thenM` \ loc ->
578 real_tau = mkPhiTy (tail preds) tau
579 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau loc
581 returnM (Nothing, meth_id)
583 -- The user didn't supply a method binding,
584 -- so we have to make up a default binding
585 -- The RHS of a default method depends on the default-method info
586 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
587 = -- An polymorphic default method
588 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
589 returnM (HsVar dm_name)
591 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
592 = -- No default method
593 -- Warn only if -fwarn-missing-methods
594 doptM Opt_WarnMissingMethods `thenM` \ warn ->
595 warnTc (isInstDecl origin
597 && reportIfUnused (getOccName sel_id))
598 (omittedMethodWarn sel_id) `thenM_`
601 error_rhs = HsLam (mkSimpleMatch wild_pats simple_rhs placeHolderType loc)
602 simple_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
603 (HsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
604 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
606 -- When the type is of form t1 -> t2 -> t3
607 -- make a default method like (\ _ _ -> noMethBind "blah")
608 -- rather than simply (noMethBind "blah")
609 -- Reason: if t1 or t2 are higher-ranked types we get n
610 -- silly ambiguity messages.
611 -- Example: f :: (forall a. Eq a => a -> a) -> Int
613 -- Here, tcSub tries to force (error "urk") to have the right type,
614 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
615 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
617 -- NB: technically this changes the meaning of the default-default
618 -- method slightly, because `seq` can see the lambdas. Oh well.
619 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
620 (_,_,tau2) = tcSplitSigmaTy tau1
621 -- Need two splits because the selector can have a type like
622 -- forall a. Foo a => forall b. Eq b => ...
623 (arg_tys, _) = tcSplitFunTys tau2
624 wild_pats = [WildPat placeHolderType | ty <- arg_tys]
626 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
627 = -- A generic default method
628 -- If the method is defined generically, we can only do the job if the
629 -- instance declaration is for a single-parameter type class with
630 -- a type constructor applied to type arguments in the instance decl
631 -- (checkTc, so False provokes the error)
632 ASSERT( isInstDecl origin ) -- We never get here from a class decl
634 checkTc (isJust maybe_tycon)
635 (badGenericInstance sel_id (notSimple inst_tys)) `thenM_`
636 checkTc (isJust (tyConGenInfo tycon))
637 (badGenericInstance sel_id (notGeneric tycon)) `thenM_`
639 ioToTcRn (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenM_`
642 rhs = mkGenericRhs sel_id clas_tyvar tycon
644 stuff = vcat [ppr clas <+> ppr inst_tys,
645 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
647 -- The tycon is only used in the generic case, and in that
648 -- case we require that the instance decl is for a single-parameter
649 -- type class with type variable arguments:
650 -- instance (...) => C (T a b)
651 clas_tyvar = head (classTyVars clas)
652 Just tycon = maybe_tycon
653 maybe_tycon = case inst_tys of
654 [ty] -> case tcSplitTyConApp_maybe ty of
655 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
659 isInstDecl InstanceDeclOrigin = True
660 isInstDecl ClassDeclOrigin = False
665 -- The renamer just puts the selector ID as the binder in the method binding
666 -- but we must use the method name; so we substitute it here. Crude but simple.
667 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
668 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
669 find_bind sel_name meth_name (AndMonoBinds b1 b2)
670 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
671 find_bind sel_name meth_name other = Nothing -- Default case
673 -- Find the prags for this method, and replace the
674 -- selector name with the method name
675 find_prags sel_name meth_name [] = []
676 find_prags sel_name meth_name (SpecSig name ty loc : prags)
677 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
678 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
679 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
680 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
688 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
691 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
694 = hsep [ptext SLIT("Class"), quotes (ppr clas),
695 ptext SLIT("does not have a method"), quotes (ppr op)]
697 omittedMethodWarn sel_id
698 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
700 badGenericInstance sel_id because
701 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
705 = vcat [ptext SLIT("because the instance type(s)"),
706 nest 2 (ppr inst_tys),
707 ptext SLIT("is not a simple type of form (T a b c)")]
710 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
711 ptext SLIT("was not compiled with -fgenerics")]
714 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)