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, tcInstClassOp )
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
42 import Generics ( mkGenericRhs )
43 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
44 import Class ( classTyVars, classBigSig, classTyCon,
45 Class, ClassOpItem, DefMeth (..) )
46 import TyCon ( tyConGenInfo )
47 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
48 import DataCon ( mkDataCon )
49 import Id ( Id, idType, idName, setIdLocalExported, setInlinePragma )
50 import Name ( Name, NamedThing(..) )
51 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
52 import NameSet ( emptyNameSet, unitNameSet )
53 import OccName ( mkClassTyConOcc, mkClassDataConOcc, mkWorkerOcc,
54 mkSuperDictSelOcc, reportIfUnused )
58 import UnicodeUtil ( stringToUtf8 )
59 import ErrUtils ( dumpIfSet )
60 import Util ( count, lengthIs )
61 import Maybes ( seqMaybe )
62 import Maybe ( isJust )
70 Every class implicitly declares a new data type, corresponding to dictionaries
71 of that class. So, for example:
73 class (D a) => C a where
75 op2 :: forall b. Ord b => a -> b -> b
77 would implicitly declare
79 data CDict a = CDict (D a)
81 (forall b. Ord b => a -> b -> b)
83 (We could use a record decl, but that means changing more of the existing apparatus.
86 For classes with just one superclass+method, we use a newtype decl instead:
89 op :: forallb. a -> b -> b
93 newtype CDict a = CDict (forall b. a -> b -> b)
95 Now DictTy in Type is just a form of type synomym:
96 DictTy c t = TyConTy CDict `AppTy` t
98 Death to "ExpandingDicts".
101 %************************************************************************
103 \subsection{Type checking}
105 %************************************************************************
109 tcClassDecl1 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
110 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
111 tcdTyVars = tyvar_names, tcdFDs = fundeps,
112 tcdSigs = class_sigs, tcdMeths = def_methods,
114 = -- LOOK THINGS UP IN THE ENVIRONMENT
115 tcLookupClass class_name `thenM` \ clas ->
117 tyvars = classTyVars clas
118 op_sigs = filter isClassOpSig class_sigs
119 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
121 tcExtendTyVarEnv tyvars $
123 checkDefaultBinds clas op_names def_methods `thenM` \ mb_dm_env ->
126 -- The renamer has already checked that the context mentions
127 -- only the type variable of the class decl.
128 -- Context is already kind-checked
129 tcHsTheta context `thenM` \ sc_theta ->
131 -- CHECK THE CLASS SIGNATURES,
132 mappM (tcClassSig clas tyvars mb_dm_env) op_sigs `thenM` \ sig_stuff ->
134 -- MAKE THE CLASS DETAILS
135 lookupSysName class_name mkClassDataConOcc `thenM` \ datacon_name ->
136 lookupSysName datacon_name mkWorkerOcc `thenM` \ datacon_wkr_name ->
137 mapM (lookupSysName class_name . mkSuperDictSelOcc)
138 [1..length context] `thenM` \ sc_sel_names ->
139 -- We number off the superclass selectors, 1, 2, 3 etc so that we
140 -- can construct names for the selectors. Thus
141 -- class (C a, C b) => D a b where ...
142 -- gives superclass selectors
144 -- (We used to call them D_C, but now we can have two different
145 -- superclasses both called C!)
146 lookupSysName class_name mkClassTyConOcc `thenM` \ tycon_name ->
148 (op_tys, op_items) = unzip sig_stuff
149 sc_tys = mkPredTys sc_theta
150 dict_component_tys = sc_tys ++ op_tys
151 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
153 dict_con = mkDataCon datacon_name
154 [NotMarkedStrict | _ <- dict_component_tys]
155 [{- No labelled fields -}]
158 [{-No existential tyvars-}] [{-Or context-}]
161 dict_con_id dict_wrap_id
163 dict_con_id = mkDataConId datacon_wkr_name dict_con
164 dict_wrap_id = mkDataConWrapId dict_con
166 returnM (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con tycon_name)
170 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
171 -> TcM (Maybe (NameEnv Bool))
172 -- The returned environment says
173 -- x not in env => no default method
174 -- x -> True => generic default method
175 -- x -> False => polymorphic default method
177 -- Check default bindings
178 -- a) must be for a class op for this class
179 -- b) must be all generic or all non-generic
180 -- and return a mapping from class-op to DefMeth info
182 -- But do all this only for source binds
184 checkDefaultBinds clas ops Nothing
187 checkDefaultBinds clas ops (Just mbs)
188 = go mbs `thenM` \ dm_env ->
189 returnM (Just dm_env)
191 go EmptyMonoBinds = returnM emptyNameEnv
193 go (AndMonoBinds b1 b2)
194 = go b1 `thenM` \ dm_info1 ->
195 go b2 `thenM` \ dm_info2 ->
196 returnM (dm_info1 `plusNameEnv` dm_info2)
198 go (FunMonoBind op _ matches loc)
201 -- Check that the op is from this class
202 checkTc (op `elem` ops) (badMethodErr clas op) `thenM_`
204 -- Check that all the defns ar generic, or none are
205 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenM_`
207 returnM (unitNameEnv op all_generic)
209 n_generic = count (isJust . maybeGenericMatch) matches
210 none_generic = n_generic == 0
211 all_generic = matches `lengthIs` n_generic
216 tcClassSig :: Class -- ...ditto...
217 -> [TyVar] -- The class type variable, used for error check only
218 -> Maybe (NameEnv Bool) -- Info about default methods;
219 -- Nothing => imported class defn with no method binds
221 -> TcM (Type, -- Type of the method
222 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
224 -- This warrants an explanation: we need to separate generic
225 -- default methods and default methods later on in the compiler
226 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
227 -- Class.DefMeth data structure.
229 tcClassSig clas clas_tyvars maybe_dm_env
230 (ClassOpSig op_name sig_dm op_ty src_loc)
231 = addSrcLoc src_loc $
233 -- Check the type signature. NB that the envt *already has*
234 -- bindings for the type variables; see comments in TcTyAndClassDcls.
235 tcHsType op_ty `thenM` \ local_ty ->
238 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
240 -- Build the selector id and default method id
241 sel_id = mkDictSelId op_name clas
242 DefMeth dm_name = sig_dm
244 dm_info = case maybe_dm_env of
246 Just dm_env -> mk_src_dm_info dm_env
248 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
250 Just True -> GenDefMeth
251 Just False -> DefMeth dm_name
253 returnM (local_ty, (sel_id, dm_info))
257 %************************************************************************
259 \subsection[Default methods]{Default methods}
261 %************************************************************************
263 The default methods for a class are each passed a dictionary for the
264 class, so that they get access to the other methods at the same type.
265 So, given the class decl
269 op2 :: Ord b => a -> b -> b -> b
272 op2 x y z = if (op1 x) && (y < z) then y else z
274 we get the default methods:
276 defm.Foo.op1 :: forall a. Foo a => a -> Bool
277 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
279 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
280 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
281 if (op1 a dfoo x) && (< b dord y z) then y else z
284 When we come across an instance decl, we may need to use the default
287 instance Foo Int where {}
291 const.Foo.Int.op1 :: Int -> Bool
292 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
294 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
295 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
297 dfun.Foo.Int :: Foo Int
298 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
300 Notice that, as with method selectors above, we assume that dictionary
301 application is curried, so there's no need to mention the Ord dictionary
302 in const.Foo.Int.op2 (or the type variable).
305 instance Foo a => Foo [a] where {}
307 dfun.Foo.List :: forall a. Foo a -> Foo [a]
309 = /\ a -> \ dfoo_a ->
311 op1 = defm.Foo.op1 [a] dfoo_list
312 op2 = defm.Foo.op2 [a] dfoo_list
313 dfoo_list = (op1, op2)
318 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
319 each local class decl.
322 tcClassDecls2 :: [RenamedTyClDecl] -> TcM (TcMonoBinds, [Id])
326 (returnM (EmptyMonoBinds, []))
327 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
328 -- The 'Just' picks out source ClassDecls
330 combine tc1 tc2 = tc1 `thenM` \ (binds1, ids1) ->
331 tc2 `thenM` \ (binds2, ids2) ->
332 returnM (binds1 `AndMonoBinds` binds2,
336 @tcClassDecl2@ generates bindings for polymorphic default methods
337 (generic default methods have by now turned into instance declarations)
340 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
341 -> TcM (TcMonoBinds, [Id])
343 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
344 tcdMeths = Just default_binds, tcdLoc = src_loc})
345 = -- The 'Just' picks out source ClassDecls
346 recoverM (returnM (EmptyMonoBinds, [])) $
348 tcLookupClass class_name `thenM` \ clas ->
350 -- We make a separate binding for each default method.
351 -- At one time I used a single AbsBinds for all of them, thus
352 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
353 -- But that desugars into
354 -- ds = \d -> (..., ..., ...)
355 -- dm1 = \d -> case ds d of (a,b,c) -> a
356 -- And since ds is big, it doesn't get inlined, so we don't get good
357 -- default methods. Better to make separate AbsBinds for each
359 (tyvars, _, _, op_items) = classBigSig clas
360 prags = filter isPragSig sigs
361 tc_dm = tcDefMeth clas tyvars default_binds prags
363 mapAndUnzipM tc_dm op_items `thenM` \ (defm_binds, dm_ids_s) ->
365 returnM (andMonoBindList defm_binds, concat dm_ids_s)
368 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnM (EmptyMonoBinds, [])
369 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnM (EmptyMonoBinds, [])
370 -- Generate code for polymorphic default methods only
371 -- (Generic default methods have turned into instance decls by now.)
372 -- This is incompatible with Hugs, which expects a polymorphic
373 -- default method for every class op, regardless of whether or not
374 -- the programmer supplied an explicit default decl for the class.
375 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
377 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
378 = tcInstTyVars ClsTv tyvars `thenM` \ (clas_tyvars, inst_tys, _) ->
380 dm_ty = idType sel_id -- Same as dict selector!
381 -- The default method's type should really come from the
382 -- iface file, since it could be usage-generalised, but this
383 -- requires altering the mess of knots in TcModule and I'm
384 -- too scared to do that. Instead, I have disabled generalisation
385 -- of types of default methods (and dict funs) by annotating them
386 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
388 theta = [mkClassPred clas inst_tys]
389 local_dm_id = mkDefaultMethodId dm_name dm_ty
390 xtve = tyvars `zip` clas_tyvars
392 newDicts origin theta `thenM` \ [this_dict] ->
394 mkMethodBind origin clas inst_tys binds_in op_item `thenM` \ (dm_inst, meth_info) ->
395 getLIE (tcMethodBind xtve clas_tyvars theta
396 [this_dict] prags meth_info) `thenM` \ (defm_bind, insts_needed) ->
398 addErrCtxt (defltMethCtxt clas) $
402 (ptext SLIT("class") <+> ppr clas)
405 insts_needed `thenM` \ dict_binds ->
407 -- Simplification can do unification
408 checkSigTyVars clas_tyvars `thenM` \ clas_tyvars' ->
414 [(clas_tyvars', local_dm_id, instToId dm_inst)]
415 emptyNameSet -- No inlines (yet)
416 (dict_binds `andMonoBinds` defm_bind)
418 returnM (full_bind, [local_dm_id])
420 origin = ClassDeclOrigin
425 %************************************************************************
427 \subsection{Typechecking a method}
429 %************************************************************************
431 @tcMethodBind@ is used to type-check both default-method and
432 instance-decl method declarations. We must type-check methods one at a
433 time, because their signatures may have different contexts and
437 type MethodSpec = (Id, -- Global selector Id
438 TcSigInfo, -- Signature
439 RenamedMonoBinds) -- Binding for the method
442 :: [(TyVar,TcTyVar)] -- Bindings for type environment
443 -> [TcTyVar] -- Instantiated type variables for the
444 -- enclosing class/instance decl.
445 -- They'll be signature tyvars, and we
446 -- want to check that they don't get bound
447 -- Always equal the range of the type envt
448 -> TcThetaType -- Available theta; it's just used for the error message
449 -> [Inst] -- Available from context, used to simplify constraints
450 -- from the method body
451 -> [RenamedSig] -- Pragmas (e.g. inline pragmas)
452 -> MethodSpec -- Details of this method
455 tcMethodBind xtve inst_tyvars inst_theta avail_insts prags
456 (sel_id, meth_sig, meth_bind)
457 = -- Check the bindings; first adding inst_tyvars to the envt
458 -- so that we don't quantify over them in nested places
459 tcExtendTyVarEnv2 xtve (
460 addErrCtxt (methodCtxt sel_id) $
461 getLIE (tcMonoBinds meth_bind [meth_sig] NonRecursive)
462 ) `thenM` \ ((meth_bind, _, _), meth_lie) ->
464 -- Now do context reduction. We simplify wrt both the local tyvars
465 -- and the ones of the class/instance decl, so that there is
468 -- op :: Eq a => a -> b -> a
470 -- We do this for each method independently to localise error messages
473 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
475 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
476 newDicts SignatureOrigin meth_theta `thenM` \ meth_dicts ->
478 all_tyvars = meth_tvs ++ inst_tyvars
479 all_insts = avail_insts ++ meth_dicts
482 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
483 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
485 checkSigTyVars all_tyvars `thenM` \ all_tyvars' ->
488 -- Attach inline pragmas as appropriate
489 (final_meth_id, inlines)
490 | (InlineSig inl _ phase _ : _) <- filter is_inline prags
491 = (meth_id `setInlinePragma` phase,
492 if inl then unitNameSet (idName meth_id) else emptyNameSet)
494 = (meth_id, emptyNameSet)
496 is_inline (InlineSig _ name _ _) = name == idName sel_id
497 is_inline other = False
499 meth_tvs' = take (length meth_tvs) all_tyvars'
500 poly_meth_bind = AbsBinds meth_tvs'
501 (map instToId meth_dicts)
502 [(meth_tvs', final_meth_id, local_meth_id)]
504 (lie_binds `andMonoBinds` meth_bind)
506 returnM poly_meth_bind
509 mkMethodBind :: InstOrigin
510 -> Class -> [TcType] -- Class and instance types
511 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
513 -> TcM (Inst, -- Method inst
515 -- Find the binding for the specified method, or make
516 -- up a suitable default method if it isn't there
518 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
519 = getInstLoc origin `thenM` \ inst_loc ->
520 tcInstClassOp inst_loc sel_id inst_tys `thenM` \ meth_inst ->
521 -- Do not dump anything into the LIE
523 meth_id = instToId meth_inst
524 meth_name = idName meth_id
526 -- Figure out what method binding to use
527 -- If the user suppplied one, use it, else construct a default one
528 getSrcLocM `thenM` \ loc ->
529 (case find_bind (idName sel_id) meth_name meth_binds of
530 Just user_bind -> returnM user_bind
531 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
532 returnM (FunMonoBind meth_name False -- Not infix decl
533 [mkSimpleMatch [] rhs placeHolderType loc] loc)
534 ) `thenM` \ meth_bind ->
536 mkTcSig meth_id loc `thenM` \ meth_sig ->
538 returnM (meth_inst, (sel_id, meth_sig, meth_bind))
541 -- The user didn't supply a method binding,
542 -- so we have to make up a default binding
543 -- The RHS of a default method depends on the default-method info
544 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
545 = -- An polymorphic default method
546 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
547 returnM (HsVar dm_name)
549 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
550 = -- No default method
551 -- Warn only if -fwarn-missing-methods
552 doptM Opt_WarnMissingMethods `thenM` \ warn ->
553 warnTc (isInstDecl origin
555 && reportIfUnused (getOccName sel_id))
556 (omittedMethodWarn sel_id) `thenM_`
559 error_rhs = HsLam (mkSimpleMatch wild_pats simple_rhs placeHolderType loc)
560 simple_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
561 (HsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
562 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
564 -- When the type is of form t1 -> t2 -> t3
565 -- make a default method like (\ _ _ -> noMethBind "blah")
566 -- rather than simply (noMethBind "blah")
567 -- Reason: if t1 or t2 are higher-ranked types we get n
568 -- silly ambiguity messages.
569 -- Example: f :: (forall a. Eq a => a -> a) -> Int
571 -- Here, tcSub tries to force (error "urk") to have the right type,
572 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
573 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
575 -- NB: technically this changes the meaning of the default-default
576 -- method slightly, because `seq` can see the lambdas. Oh well.
577 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
578 (_,_,tau2) = tcSplitSigmaTy tau1
579 -- Need two splits because the selector can have a type like
580 -- forall a. Foo a => forall b. Eq b => ...
581 (arg_tys, _) = tcSplitFunTys tau2
582 wild_pats = [WildPat placeHolderType | ty <- arg_tys]
584 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
585 = -- A generic default method
586 -- If the method is defined generically, we can only do the job if the
587 -- instance declaration is for a single-parameter type class with
588 -- a type constructor applied to type arguments in the instance decl
589 -- (checkTc, so False provokes the error)
590 ASSERT( isInstDecl origin ) -- We never get here from a class decl
592 checkTc (isJust maybe_tycon)
593 (badGenericInstance sel_id (notSimple inst_tys)) `thenM_`
594 checkTc (isJust (tyConGenInfo tycon))
595 (badGenericInstance sel_id (notGeneric tycon)) `thenM_`
597 ioToTcRn (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenM_`
600 rhs = mkGenericRhs sel_id clas_tyvar tycon
602 stuff = vcat [ppr clas <+> ppr inst_tys,
603 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
605 -- The tycon is only used in the generic case, and in that
606 -- case we require that the instance decl is for a single-parameter
607 -- type class with type variable arguments:
608 -- instance (...) => C (T a b)
609 clas_tyvar = head (classTyVars clas)
610 Just tycon = maybe_tycon
611 maybe_tycon = case inst_tys of
612 [ty] -> case tcSplitTyConApp_maybe ty of
613 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
617 isInstDecl InstanceDeclOrigin = True
618 isInstDecl ClassDeclOrigin = False
623 -- The renamer just puts the selector ID as the binder in the method binding
624 -- but we must use the method name; so we substitute it here. Crude but simple.
625 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
626 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
627 find_bind sel_name meth_name (AndMonoBinds b1 b2)
628 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
629 find_bind sel_name meth_name other = Nothing -- Default case
631 -- Find the prags for this method, and replace the
632 -- selector name with the method name
633 find_prags sel_name meth_name [] = []
634 find_prags sel_name meth_name (SpecSig name ty loc : prags)
635 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
636 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
637 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
638 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
646 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
649 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
652 = hsep [ptext SLIT("Class"), quotes (ppr clas),
653 ptext SLIT("does not have a method"), quotes (ppr op)]
655 omittedMethodWarn sel_id
656 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
658 badGenericInstance sel_id because
659 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
663 = vcat [ptext SLIT("because the instance type(s)"),
664 nest 2 (ppr inst_tys),
665 ptext SLIT("is not a simple type of form (T a b c)")]
668 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
669 ptext SLIT("was not compiled with -fgenerics")]
672 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)