2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, tcClassDecls2, mkImplicitClassBinds,
8 tcMethodBind, badMethodErr
11 #include "HsVersions.h"
13 import HsSyn ( HsDecl(..), TyClDecl(..), Sig(..), MonoBinds(..),
14 HsExpr(..), HsLit(..), HsType(..), HsPred(..),
15 mkSimpleMatch, andMonoBinds, andMonoBindList,
16 isClassDecl, isClassOpSig, isPragSig,
17 fromClassDeclNameList, tyClDeclName
19 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
22 RenamedContext, RenamedHsDecl, RenamedSig,
25 import TcHsSyn ( TcMonoBinds, idsToMonoBinds )
27 import Inst ( InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
29 import TcEnv ( TcId, TcEnv, TyThingDetails(..), tcAddImportedIdInfo,
30 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
31 tcExtendLocalValEnv, tcExtendTyVarEnv, newDefaultMethodName
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcMonoType ( tcHsSigType, tcClassContext, checkSigTyVars, sigCtxt, mkTcSig )
35 import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
36 import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcSigTyVars )
38 import Generics ( mkGenericRhs, validGenericMethodType )
39 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
40 import Class ( classTyVars, classBigSig, classSelIds, classTyCon,
41 Class, ClassOpItem, DefMeth (..) )
42 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
43 import DataCon ( mkDataCon, notMarkedStrict )
44 import Id ( Id, idType, idName )
45 import Name ( Name, isLocallyDefined, NamedThing(..),
46 NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv,
47 plusNameEnv, nameEnvElts )
48 import NameSet ( emptyNameSet )
50 import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, mkSigmaTy, mkClassPred,
51 splitTyConApp_maybe, isTyVarTy
54 import VarSet ( mkVarSet, emptyVarSet )
56 import ErrUtils ( dumpIfSet )
58 import Maybes ( seqMaybe, maybeToBool, orElse )
65 Every class implicitly declares a new data type, corresponding to dictionaries
66 of that class. So, for example:
68 class (D a) => C a where
70 op2 :: forall b. Ord b => a -> b -> b
72 would implicitly declare
74 data CDict a = CDict (D a)
76 (forall b. Ord b => a -> b -> b)
78 (We could use a record decl, but that means changing more of the existing apparatus.
81 For classes with just one superclass+method, we use a newtype decl instead:
84 op :: forallb. a -> b -> b
88 newtype CDict a = CDict (forall b. a -> b -> b)
90 Now DictTy in Type is just a form of type synomym:
91 DictTy c t = TyConTy CDict `AppTy` t
93 Death to "ExpandingDicts".
96 %************************************************************************
98 \subsection{Type checking}
100 %************************************************************************
103 tcClassDecl1 :: TcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 (ClassDecl context class_name
106 tyvar_names fundeps class_sigs def_methods pragmas
108 = -- CHECK ARITY 1 FOR HASKELL 1.4
109 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
110 checkTc (glaExts || length tyvar_names == 1)
111 (classArityErr class_name) `thenTc_`
113 -- LOOK THINGS UP IN THE ENVIRONMENT
114 tcLookupClass class_name `thenTc` \ clas ->
116 tyvars = classTyVars clas
117 op_sigs = filter isClassOpSig class_sigs
118 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
119 (_, datacon_name, datacon_wkr_name, sc_sel_names) = fromClassDeclNameList sys_names
121 tcExtendTyVarEnv tyvars $
123 -- CHECK THAT THE DEFAULT BINDINGS ARE LEGAL
124 checkDefaultBinds clas op_names def_methods `thenTc` \ dm_info ->
125 checkGenericClassIsUnary clas dm_info `thenTc_`
128 tcSuperClasses clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
130 -- CHECK THE CLASS SIGNATURES,
131 mapTc (tcClassSig rec_env clas tyvars dm_info) op_sigs `thenTc` \ sig_stuff ->
133 -- MAKE THE CLASS DETAILS
135 (op_tys, op_items) = unzip sig_stuff
136 sc_tys = mkDictTys sc_theta
137 dict_component_tys = sc_tys ++ op_tys
139 dict_con = mkDataCon datacon_name
140 [notMarkedStrict | _ <- dict_component_tys]
141 [{- No labelled fields -}]
144 [{-No existential tyvars-}] [{-Or context-}]
147 dict_con_id dict_wrap_id
149 dict_con_id = mkDataConId datacon_wkr_name dict_con
150 dict_wrap_id = mkDataConWrapId dict_con
152 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
156 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds -> TcM (NameEnv (DefMeth Name))
157 -- Check default bindings
158 -- a) must be for a class op for this class
159 -- b) must be all generic or all non-generic
160 -- and return a mapping from class-op to DefMeth info
162 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
164 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
165 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
166 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
167 returnTc (dm_info1 `plusNameEnv` dm_info2)
169 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
172 -- Check that the op is from this class
173 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
175 -- Check that all the defns ar generic, or none are
176 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
178 -- Make up the right dm_info
180 returnTc (unitNameEnv op GenDefMeth)
182 -- An explicit non-generic default method
183 newDefaultMethodName op loc `thenNF_Tc` \ dm_name ->
184 returnTc (unitNameEnv op (DefMeth dm_name))
187 n_generic = count (maybeToBool . maybeGenericMatch) matches
188 none_generic = n_generic == 0
189 all_generic = n_generic == length matches
191 checkGenericClassIsUnary clas dm_info
192 = -- Check that if the class has generic methods, then the
193 -- class has only one parameter. We can't do generic
194 -- multi-parameter type classes!
195 checkTc (unary || no_generics) (genericMultiParamErr clas)
197 unary = length (classTyVars clas) == 1
198 no_generics = null [() | GenDefMeth <- nameEnvElts dm_info]
203 tcSuperClasses :: Class
204 -> RenamedContext -- class context
205 -> [Name] -- Names for superclass selectors
206 -> TcM (ClassContext, -- the superclass context
207 [Id]) -- superclass selector Ids
209 tcSuperClasses clas context sc_sel_names
210 = -- Check the context.
211 -- The renamer has already checked that the context mentions
212 -- only the type variable of the class decl.
214 -- For std Haskell check that the context constrains only tyvars
215 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
219 mapTc_ check_constraint context
222 -- Context is already kind-checked
223 tcClassContext context `thenTc` \ sc_theta ->
225 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
228 returnTc (sc_theta, sc_sel_ids)
231 check_constraint sc@(HsPClass c tys)
232 = checkTc (all is_tyvar tys) (superClassErr clas sc)
234 is_tyvar (HsTyVar _) = True
235 is_tyvar other = False
238 tcClassSig :: TcEnv -- Knot tying only!
239 -> Class -- ...ditto...
240 -> [TyVar] -- The class type variable, used for error check only
241 -> NameEnv (DefMeth Name) -- Info about default methods
243 -> TcM (Type, -- Type of the method
244 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
246 -- This warrants an explanation: we need to separate generic
247 -- default methods and default methods later on in the compiler
248 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
249 -- Class.DefMeth data structure.
251 tcClassSig rec_env clas clas_tyvars dm_info
252 (ClassOpSig op_name maybe_dm op_ty src_loc)
253 = tcAddSrcLoc src_loc $
255 -- Check the type signature. NB that the envt *already has*
256 -- bindings for the type variables; see comments in TcTyAndClassDcls.
258 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
259 -- and that it is not constrained by theta
260 tcHsSigType op_ty `thenTc` \ local_ty ->
262 global_ty = mkSigmaTy clas_tyvars
263 [mkClassPred clas (mkTyVarTys clas_tyvars)]
266 -- Build the selector id and default method id
267 sel_id = mkDictSelId op_name clas
269 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
271 dm_info_id = case dm_info_name of
272 NoDefMeth -> NoDefMeth
273 GenDefMeth -> GenDefMeth
274 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo rec_env dm_id)
276 dm_id = mkDefaultMethodId dm_name clas global_ty
278 -- Check that for a generic method, the type of
279 -- the method is sufficiently simple
280 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
281 (badGenericMethodType op_name op_ty) `thenTc_`
283 returnTc (local_ty, (sel_id, dm_info_id))
287 %************************************************************************
289 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
291 %************************************************************************
293 @mkImplicitClassBinds@ produces a binding for the selector function for each method
294 and superclass dictionary.
297 mkImplicitClassBinds :: [Class] -> NF_TcM ([Id], TcMonoBinds)
298 mkImplicitClassBinds classes
299 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
300 -- The selector binds are already in the selector Id's unfoldings
301 -- We don't return the data constructor etc from the class,
302 -- because that's done via the class's TyCon
304 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
306 mk_implicit clas = (sel_ids, binds)
308 sel_ids = classSelIds clas
309 binds | isLocallyDefined clas = idsToMonoBinds sel_ids
310 | otherwise = EmptyMonoBinds
315 %************************************************************************
317 \subsection[Default methods]{Default methods}
319 %************************************************************************
321 The default methods for a class are each passed a dictionary for the
322 class, so that they get access to the other methods at the same type.
323 So, given the class decl
327 op2 :: Ord b => a -> b -> b -> b
330 op2 x y z = if (op1 x) && (y < z) then y else z
332 we get the default methods:
334 defm.Foo.op1 :: forall a. Foo a => a -> Bool
335 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
337 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
338 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
339 if (op1 a dfoo x) && (< b dord y z) then y else z
342 When we come across an instance decl, we may need to use the default
345 instance Foo Int where {}
349 const.Foo.Int.op1 :: Int -> Bool
350 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
352 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
353 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
355 dfun.Foo.Int :: Foo Int
356 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
358 Notice that, as with method selectors above, we assume that dictionary
359 application is curried, so there's no need to mention the Ord dictionary
360 in const.Foo.Int.op2 (or the type variable).
363 instance Foo a => Foo [a] where {}
365 dfun.Foo.List :: forall a. Foo a -> Foo [a]
367 = /\ a -> \ dfoo_a ->
369 op1 = defm.Foo.op1 [a] dfoo_list
370 op2 = defm.Foo.op2 [a] dfoo_list
371 dfoo_list = (op1, op2)
376 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
377 each local class decl.
380 tcClassDecls2 :: [RenamedHsDecl] -> NF_TcM (LIE, TcMonoBinds)
384 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
385 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
386 isClassDecl cls_decl,
387 isLocallyDefined (tyClDeclName cls_decl)]
389 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
390 tc2 `thenNF_Tc` \ (lie2, binds2) ->
391 returnNF_Tc (lie1 `plusLIE` lie2,
392 binds1 `AndMonoBinds` binds2)
395 @tcClassDecl2@ generates bindings for polymorphic default methods
396 (generic default methods have by now turned into instance declarations)
399 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
400 -> NF_TcM (LIE, TcMonoBinds)
402 tcClassDecl2 (ClassDecl context class_name
403 tyvar_names _ sigs default_binds pragmas _ src_loc)
404 = -- A locally defined class
405 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
406 tcAddSrcLoc src_loc $
407 tcLookupClass class_name `thenNF_Tc` \ clas ->
409 -- We make a separate binding for each default method.
410 -- At one time I used a single AbsBinds for all of them, thus
411 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
412 -- But that desugars into
413 -- ds = \d -> (..., ..., ...)
414 -- dm1 = \d -> case ds d of (a,b,c) -> a
415 -- And since ds is big, it doesn't get inlined, so we don't get good
416 -- default methods. Better to make separate AbsBinds for each
418 (tyvars, _, _, op_items) = classBigSig clas
419 prags = filter isPragSig sigs
420 tc_dm = tcDefMeth clas tyvars default_binds prags
422 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
424 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
427 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
428 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
429 -- Generate code for polymorphic default methods only
430 -- (Generic default methods have turned into instance decls by now.)
431 -- This is incompatible with Hugs, which expects a polymorphic
432 -- default method for every class op, regardless of whether or not
433 -- the programmer supplied an explicit default decl for the class.
434 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
436 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
437 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
439 theta = [(mkClassPred clas inst_tys)]
441 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
443 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
444 tcMethodBind clas origin clas_tyvars inst_tys theta
445 binds_in prags False op_item
446 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
448 tcAddErrCtxt (defltMethCtxt clas) $
450 -- tcMethodBind has checked that the class_tyvars havn't
451 -- been unified with each other or another type, but we must
452 -- still zonk them before passing them to tcSimplifyAndCheck
453 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
457 (ptext SLIT("class") <+> ppr clas)
458 (mkVarSet clas_tyvars')
460 insts_needed `thenTc` \ (const_lie, dict_binds) ->
466 [(clas_tyvars', dm_id, local_dm_id)]
467 emptyNameSet -- No inlines (yet)
468 (dict_binds `andMonoBinds` defm_bind)
470 returnTc (full_bind, const_lie)
472 origin = ClassDeclOrigin
477 %************************************************************************
479 \subsection{Typechecking a method}
481 %************************************************************************
483 @tcMethodBind@ is used to type-check both default-method and
484 instance-decl method declarations. We must type-check methods one at a
485 time, because their signatures may have different contexts and
492 -> [TcTyVar] -- Instantiated type variables for the
493 -- enclosing class/instance decl.
494 -- They'll be signature tyvars, and we
495 -- want to check that they don't get bound
496 -> [TcType] -- Instance types
497 -> TcThetaType -- Available theta; this could be used to check
498 -- the method signature, but actually that's done by
499 -- the caller; here, it's just used for the error message
500 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
501 -> [RenamedSig] -- Pramgas (just for this one)
502 -> Bool -- True <=> This method is from an instance declaration
503 -> ClassOpItem -- The method selector and default-method Id
504 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
506 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
507 meth_binds prags is_inst_decl (sel_id, dm_info)
508 = tcGetSrcLoc `thenNF_Tc` \ loc ->
509 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
510 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
512 meth_name = idName meth_id
513 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
514 meth_prags = find_prags (idName sel_id) meth_name prags
516 -- Figure out what method binding to use
517 -- If the user suppplied one, use it, else construct a default one
518 (case find_bind (idName sel_id) meth_name meth_binds of
519 Just user_bind -> returnTc user_bind
520 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
521 returnTc (FunMonoBind meth_name False -- Not infix decl
522 [mkSimpleMatch [] rhs Nothing loc] loc)
523 ) `thenTc` \ meth_bind ->
524 -- Check the bindings; first add inst_tyvars to the envt
525 -- so that we don't quantify over them in nested places
526 -- The *caller* put the class/inst decl tyvars into the envt
527 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
528 (tcAddErrCtxt (methodCtxt sel_id) $
529 tcBindWithSigs NotTopLevel meth_bind
530 [sig_info] meth_prags NonRecursive
531 ) `thenTc` \ (binds, insts, _) ->
533 tcExtendLocalValEnv [(meth_name, meth_id)]
534 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
536 -- The prag_lie for a SPECIALISE pragma will mention the function
537 -- itself, so we have to simplify them away right now lest they float
539 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
541 -- Now check that the instance type variables
542 -- (or, in the case of a class decl, the class tyvars)
543 -- have not been unified with anything in the environment
545 -- We do this for each method independently to localise error messages
546 -- ...and this is why the call to tcExtendGlobalTyVars must be here
547 -- rather than in the caller
548 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
549 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
551 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
552 insts `plusLIE` prag_lie',
555 -- The user didn't supply a method binding,
556 -- so we have to make up a default binding
557 -- The RHS of a default method depends on the default-method info
558 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
559 = -- An polymorphic default method
560 returnTc (HsVar (idName dm_id))
562 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
563 = -- No default method
564 -- Warn only if -fwarn-missing-methods
565 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
566 warnTc (is_inst_decl && warn)
567 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
570 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
571 (HsLit (HsString (_PK_ error_msg)))
572 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
575 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
576 = -- A generic default method
577 -- If the method is defined generically, we can only do the job if the
578 -- instance declaration is for a single-parameter type class with
579 -- a type constructor applied to type arguments in the instance decl
580 -- (checkTc, so False provokes the error)
581 checkTc (not is_inst_decl || simple_inst)
582 (badGenericInstance sel_id clas) `thenTc_`
584 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
587 rhs = mkGenericRhs sel_id clas_tyvar tycon
589 stuff = vcat [ppr clas <+> ppr inst_tys,
590 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
592 -- The tycon is only used in the generic case, and in that
593 -- case we require that the instance decl is for a single-parameter
594 -- type class with type variable arguments:
595 -- instance (...) => C (T a b)
596 simple_inst = maybeToBool maybe_tycon
597 clas_tyvar = head (classTyVars clas)
598 Just tycon = maybe_tycon
599 maybe_tycon = case inst_tys of
600 [ty] -> case splitTyConApp_maybe ty of
601 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
608 -- The renamer just puts the selector ID as the binder in the method binding
609 -- but we must use the method name; so we substitute it here. Crude but simple.
610 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
611 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
612 find_bind sel_name meth_name (AndMonoBinds b1 b2)
613 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
614 find_bind sel_name meth_name other = Nothing -- Default case
616 -- Find the prags for this method, and replace the
617 -- selector name with the method name
618 find_prags sel_name meth_name [] = []
619 find_prags sel_name meth_name (SpecSig name ty loc : prags)
620 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
621 find_prags sel_name meth_name (InlineSig name phase loc : prags)
622 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
623 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
624 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
625 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
632 classArityErr class_name
633 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
635 superClassErr clas sc
636 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
637 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
640 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
643 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
646 = hsep [ptext SLIT("Class"), quotes (ppr clas),
647 ptext SLIT("does not have a method"), quotes (ppr op)]
649 omittedMethodWarn sel_id clas
650 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
651 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
653 badGenericMethodType op op_ty
654 = hang (ptext SLIT("Generic method type is too complex"))
655 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
656 ptext SLIT("You can only use type variables, arrows, and tuples")])
658 badGenericInstance sel_id clas
659 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
660 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
661 ptext SLIT("(where T is a derivable type constructor)"),
662 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
665 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
667 genericMultiParamErr clas
668 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
669 ptext SLIT("cannot have generic methods")