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 getClassDeclSysNames, 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, RecTcEnv, TyThingDetails(..), tcAddImportedIdInfo,
30 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
31 tcExtendLocalValEnv, tcExtendTyVarEnv, newDefaultMethodName
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcMonoType ( tcHsSigType, tcClassContext, checkSigTyVars, checkAmbiguity, 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, classTvsFds,
41 Class, ClassOpItem, DefMeth (..), FunDep )
42 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
43 import DataCon ( mkDataCon, notMarkedStrict )
44 import Id ( Id, idType, idName )
45 import Module ( Module )
46 import Name ( Name, NamedThing(..), isFrom )
47 import Name ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
48 import NameSet ( emptyNameSet )
50 import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, 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 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 (ClassDecl context class_name
106 tyvar_names fundeps class_sigs def_methods
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, fds) = classTvsFds 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) = getClassDeclSysNames 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 fds dm_info)
132 op_sigs `thenTc` \ sig_stuff ->
134 -- MAKE THE CLASS DETAILS
136 (op_tys, op_items) = unzip sig_stuff
137 sc_tys = mkDictTys sc_theta
138 dict_component_tys = sc_tys ++ op_tys
140 dict_con = mkDataCon datacon_name
141 [notMarkedStrict | _ <- dict_component_tys]
142 [{- No labelled fields -}]
145 [{-No existential tyvars-}] [{-Or context-}]
148 dict_con_id dict_wrap_id
150 dict_con_id = mkDataConId datacon_wkr_name dict_con
151 dict_wrap_id = mkDataConWrapId dict_con
153 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
157 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds -> TcM (NameEnv (DefMeth Name))
158 -- Check default bindings
159 -- a) must be for a class op for this class
160 -- b) must be all generic or all non-generic
161 -- and return a mapping from class-op to DefMeth info
163 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
165 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
166 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
167 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
168 returnTc (dm_info1 `plusNameEnv` dm_info2)
170 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
173 -- Check that the op is from this class
174 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
176 -- Check that all the defns ar generic, or none are
177 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
179 -- Make up the right dm_info
181 returnTc (unitNameEnv op GenDefMeth)
183 -- An explicit non-generic default method
184 newDefaultMethodName op loc `thenNF_Tc` \ dm_name ->
185 returnTc (unitNameEnv op (DefMeth dm_name))
188 n_generic = count (maybeToBool . maybeGenericMatch) matches
189 none_generic = n_generic == 0
190 all_generic = n_generic == length matches
192 checkGenericClassIsUnary clas dm_info
193 = -- Check that if the class has generic methods, then the
194 -- class has only one parameter. We can't do generic
195 -- multi-parameter type classes!
196 checkTc (unary || no_generics) (genericMultiParamErr clas)
198 unary = length (classTyVars clas) == 1
199 no_generics = null [() | GenDefMeth <- nameEnvElts dm_info]
204 tcSuperClasses :: Class
205 -> RenamedContext -- class context
206 -> [Name] -- Names for superclass selectors
207 -> TcM (ClassContext, -- the superclass context
208 [Id]) -- superclass selector Ids
210 tcSuperClasses clas context sc_sel_names
211 = -- Check the context.
212 -- The renamer has already checked that the context mentions
213 -- only the type variable of the class decl.
215 -- For std Haskell check that the context constrains only tyvars
216 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
220 mapTc_ check_constraint context
223 -- Context is already kind-checked
224 tcClassContext context `thenTc` \ sc_theta ->
226 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
229 returnTc (sc_theta, sc_sel_ids)
232 check_constraint sc@(HsPClass c tys)
233 = checkTc (all is_tyvar tys) (superClassErr clas sc)
235 is_tyvar (HsTyVar _) = True
236 is_tyvar other = False
239 tcClassSig :: RecTcEnv
240 -> Class -- ...ditto...
241 -> [TyVar] -- The class type variable, used for error check only
243 -> NameEnv (DefMeth Name) -- Info about default methods
245 -> TcM (Type, -- Type of the method
246 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
248 -- This warrants an explanation: we need to separate generic
249 -- default methods and default methods later on in the compiler
250 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
251 -- Class.DefMeth data structure.
253 tcClassSig unf_env clas clas_tyvars fds dm_info
254 (ClassOpSig op_name maybe_dm op_ty src_loc)
255 = tcAddSrcLoc src_loc $
257 -- Check the type signature. NB that the envt *already has*
258 -- bindings for the type variables; see comments in TcTyAndClassDcls.
260 tcHsSigType op_ty `thenTc` \ local_ty ->
262 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
264 -- Check for ambiguous class op types
265 checkAmbiguity True clas_tyvars theta local_ty `thenTc` \ global_ty ->
268 -- Build the selector id and default method id
269 sel_id = mkDictSelId op_name clas
271 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
273 dm_info_id = case dm_info_name of
274 NoDefMeth -> NoDefMeth
275 GenDefMeth -> GenDefMeth
276 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
278 dm_id = mkDefaultMethodId dm_name clas global_ty
280 -- Check that for a generic method, the type of
281 -- the method is sufficiently simple
282 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
283 (badGenericMethodType op_name op_ty) `thenTc_`
285 returnTc (local_ty, (sel_id, dm_info_id))
289 %************************************************************************
291 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
293 %************************************************************************
295 @mkImplicitClassBinds@ produces a binding for the selector function for each method
296 and superclass dictionary.
299 mkImplicitClassBinds :: Module -> [Class] -> NF_TcM ([Id], TcMonoBinds)
300 mkImplicitClassBinds this_mod classes
301 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
302 -- The selector binds are already in the selector Id's unfoldings
303 -- We don't return the data constructor etc from the class,
304 -- because that's done via the class's TyCon
306 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
308 mk_implicit clas = (sel_ids, binds)
310 sel_ids = classSelIds clas
311 binds | isFrom this_mod clas = idsToMonoBinds sel_ids
312 | otherwise = EmptyMonoBinds
317 %************************************************************************
319 \subsection[Default methods]{Default methods}
321 %************************************************************************
323 The default methods for a class are each passed a dictionary for the
324 class, so that they get access to the other methods at the same type.
325 So, given the class decl
329 op2 :: Ord b => a -> b -> b -> b
332 op2 x y z = if (op1 x) && (y < z) then y else z
334 we get the default methods:
336 defm.Foo.op1 :: forall a. Foo a => a -> Bool
337 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
339 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
340 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
341 if (op1 a dfoo x) && (< b dord y z) then y else z
344 When we come across an instance decl, we may need to use the default
347 instance Foo Int where {}
351 const.Foo.Int.op1 :: Int -> Bool
352 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
354 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
355 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
357 dfun.Foo.Int :: Foo Int
358 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
360 Notice that, as with method selectors above, we assume that dictionary
361 application is curried, so there's no need to mention the Ord dictionary
362 in const.Foo.Int.op2 (or the type variable).
365 instance Foo a => Foo [a] where {}
367 dfun.Foo.List :: forall a. Foo a -> Foo [a]
369 = /\ a -> \ dfoo_a ->
371 op1 = defm.Foo.op1 [a] dfoo_list
372 op2 = defm.Foo.op2 [a] dfoo_list
373 dfoo_list = (op1, op2)
378 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
379 each local class decl.
382 tcClassDecls2 :: Module -> [RenamedHsDecl] -> NF_TcM (LIE, TcMonoBinds)
384 tcClassDecls2 this_mod decls
386 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
387 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
388 isClassDecl cls_decl,
389 isFrom this_mod (tyClDeclName cls_decl)]
391 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
392 tc2 `thenNF_Tc` \ (lie2, binds2) ->
393 returnNF_Tc (lie1 `plusLIE` lie2,
394 binds1 `AndMonoBinds` binds2)
397 @tcClassDecl2@ generates bindings for polymorphic default methods
398 (generic default methods have by now turned into instance declarations)
401 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
402 -> NF_TcM (LIE, TcMonoBinds)
404 tcClassDecl2 (ClassDecl context class_name
405 tyvar_names _ sigs default_binds _ src_loc)
406 = -- A locally defined class
407 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
408 tcAddSrcLoc src_loc $
409 tcLookupClass class_name `thenNF_Tc` \ clas ->
411 -- We make a separate binding for each default method.
412 -- At one time I used a single AbsBinds for all of them, thus
413 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
414 -- But that desugars into
415 -- ds = \d -> (..., ..., ...)
416 -- dm1 = \d -> case ds d of (a,b,c) -> a
417 -- And since ds is big, it doesn't get inlined, so we don't get good
418 -- default methods. Better to make separate AbsBinds for each
420 (tyvars, _, _, op_items) = classBigSig clas
421 prags = filter isPragSig sigs
422 tc_dm = tcDefMeth clas tyvars default_binds prags
424 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
426 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
429 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
430 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
431 -- Generate code for polymorphic default methods only
432 -- (Generic default methods have turned into instance decls by now.)
433 -- This is incompatible with Hugs, which expects a polymorphic
434 -- default method for every class op, regardless of whether or not
435 -- the programmer supplied an explicit default decl for the class.
436 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
438 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
439 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
441 theta = [(mkClassPred clas inst_tys)]
443 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
445 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
446 tcMethodBind clas origin clas_tyvars inst_tys theta
447 binds_in prags False op_item
448 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
450 tcAddErrCtxt (defltMethCtxt clas) $
452 -- tcMethodBind has checked that the class_tyvars havn't
453 -- been unified with each other or another type, but we must
454 -- still zonk them before passing them to tcSimplifyAndCheck
455 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
459 (ptext SLIT("class") <+> ppr clas)
460 (mkVarSet clas_tyvars')
462 insts_needed `thenTc` \ (const_lie, dict_binds) ->
468 [(clas_tyvars', dm_id, local_dm_id)]
469 emptyNameSet -- No inlines (yet)
470 (dict_binds `andMonoBinds` defm_bind)
472 returnTc (full_bind, const_lie)
474 origin = ClassDeclOrigin
479 %************************************************************************
481 \subsection{Typechecking a method}
483 %************************************************************************
485 @tcMethodBind@ is used to type-check both default-method and
486 instance-decl method declarations. We must type-check methods one at a
487 time, because their signatures may have different contexts and
494 -> [TcTyVar] -- Instantiated type variables for the
495 -- enclosing class/instance decl.
496 -- They'll be signature tyvars, and we
497 -- want to check that they don't get bound
498 -> [TcType] -- Instance types
499 -> TcThetaType -- Available theta; this could be used to check
500 -- the method signature, but actually that's done by
501 -- the caller; here, it's just used for the error message
502 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
503 -> [RenamedSig] -- Pramgas (just for this one)
504 -> Bool -- True <=> This method is from an instance declaration
505 -> ClassOpItem -- The method selector and default-method Id
506 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
508 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
509 meth_binds prags is_inst_decl (sel_id, dm_info)
510 = tcGetSrcLoc `thenNF_Tc` \ loc ->
511 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
512 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
514 meth_name = idName meth_id
515 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
516 meth_prags = find_prags (idName sel_id) meth_name prags
518 -- Figure out what method binding to use
519 -- If the user suppplied one, use it, else construct a default one
520 (case find_bind (idName sel_id) meth_name meth_binds of
521 Just user_bind -> returnTc user_bind
522 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
523 returnTc (FunMonoBind meth_name False -- Not infix decl
524 [mkSimpleMatch [] rhs Nothing loc] loc)
525 ) `thenTc` \ meth_bind ->
526 -- Check the bindings; first add inst_tyvars to the envt
527 -- so that we don't quantify over them in nested places
528 -- The *caller* put the class/inst decl tyvars into the envt
529 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
530 (tcAddErrCtxt (methodCtxt sel_id) $
531 tcBindWithSigs NotTopLevel meth_bind
532 [sig_info] meth_prags NonRecursive
533 ) `thenTc` \ (binds, insts, _) ->
535 tcExtendLocalValEnv [(meth_name, meth_id)]
536 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
538 -- The prag_lie for a SPECIALISE pragma will mention the function
539 -- itself, so we have to simplify them away right now lest they float
541 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
543 -- Now check that the instance type variables
544 -- (or, in the case of a class decl, the class tyvars)
545 -- have not been unified with anything in the environment
547 -- We do this for each method independently to localise error messages
548 -- ...and this is why the call to tcExtendGlobalTyVars must be here
549 -- rather than in the caller
550 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
551 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
553 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
554 insts `plusLIE` prag_lie',
557 -- The user didn't supply a method binding,
558 -- so we have to make up a default binding
559 -- The RHS of a default method depends on the default-method info
560 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
561 = -- An polymorphic default method
562 returnTc (HsVar (idName dm_id))
564 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
565 = -- No default method
566 -- Warn only if -fwarn-missing-methods
567 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
568 warnTc (is_inst_decl && warn)
569 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
572 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
573 (HsLit (HsString (_PK_ error_msg)))
574 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
577 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
578 = -- A generic default method
579 -- If the method is defined generically, we can only do the job if the
580 -- instance declaration is for a single-parameter type class with
581 -- a type constructor applied to type arguments in the instance decl
582 -- (checkTc, so False provokes the error)
583 checkTc (not is_inst_decl || simple_inst)
584 (badGenericInstance sel_id clas) `thenTc_`
586 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
589 rhs = mkGenericRhs sel_id clas_tyvar tycon
591 stuff = vcat [ppr clas <+> ppr inst_tys,
592 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
594 -- The tycon is only used in the generic case, and in that
595 -- case we require that the instance decl is for a single-parameter
596 -- type class with type variable arguments:
597 -- instance (...) => C (T a b)
598 simple_inst = maybeToBool maybe_tycon
599 clas_tyvar = head (classTyVars clas)
600 Just tycon = maybe_tycon
601 maybe_tycon = case inst_tys of
602 [ty] -> case splitTyConApp_maybe ty of
603 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
610 -- The renamer just puts the selector ID as the binder in the method binding
611 -- but we must use the method name; so we substitute it here. Crude but simple.
612 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
613 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
614 find_bind sel_name meth_name (AndMonoBinds b1 b2)
615 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
616 find_bind sel_name meth_name other = Nothing -- Default case
618 -- Find the prags for this method, and replace the
619 -- selector name with the method name
620 find_prags sel_name meth_name [] = []
621 find_prags sel_name meth_name (SpecSig name ty loc : prags)
622 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
623 find_prags sel_name meth_name (InlineSig name phase loc : prags)
624 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
625 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
626 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
627 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
634 classArityErr class_name
635 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
637 superClassErr clas sc
638 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
639 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
642 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
645 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
648 = hsep [ptext SLIT("Class"), quotes (ppr clas),
649 ptext SLIT("does not have a method"), quotes (ppr op)]
651 omittedMethodWarn sel_id clas
652 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
653 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
655 badGenericMethodType op op_ty
656 = hang (ptext SLIT("Generic method type is too complex"))
657 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
658 ptext SLIT("You can only use type variables, arrows, and tuples")])
660 badGenericInstance sel_id clas
661 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
662 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
663 ptext SLIT("(where T is a derivable type constructor)"),
664 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
667 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
669 genericMultiParamErr clas
670 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
671 ptext SLIT("cannot have generic methods")