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 NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv,
48 plusNameEnv, nameEnvElts )
49 import NameSet ( emptyNameSet )
51 import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, mkClassPred,
52 splitTyConApp_maybe, isTyVarTy
55 import VarSet ( mkVarSet, emptyVarSet )
57 import ErrUtils ( dumpIfSet )
59 import Maybes ( seqMaybe, maybeToBool, orElse )
66 Every class implicitly declares a new data type, corresponding to dictionaries
67 of that class. So, for example:
69 class (D a) => C a where
71 op2 :: forall b. Ord b => a -> b -> b
73 would implicitly declare
75 data CDict a = CDict (D a)
77 (forall b. Ord b => a -> b -> b)
79 (We could use a record decl, but that means changing more of the existing apparatus.
82 For classes with just one superclass+method, we use a newtype decl instead:
85 op :: forallb. a -> b -> b
89 newtype CDict a = CDict (forall b. a -> b -> b)
91 Now DictTy in Type is just a form of type synomym:
92 DictTy c t = TyConTy CDict `AppTy` t
94 Death to "ExpandingDicts".
97 %************************************************************************
99 \subsection{Type checking}
101 %************************************************************************
104 tcClassDecl1 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
106 (ClassDecl context class_name
107 tyvar_names fundeps class_sigs def_methods
109 = -- CHECK ARITY 1 FOR HASKELL 1.4
110 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
111 checkTc (glaExts || length tyvar_names == 1)
112 (classArityErr class_name) `thenTc_`
114 -- LOOK THINGS UP IN THE ENVIRONMENT
115 tcLookupClass class_name `thenTc` \ clas ->
117 (tyvars, fds) = classTvsFds clas
118 op_sigs = filter isClassOpSig class_sigs
119 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
120 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
122 tcExtendTyVarEnv tyvars $
124 -- CHECK THAT THE DEFAULT BINDINGS ARE LEGAL
125 checkDefaultBinds clas op_names def_methods `thenTc` \ dm_info ->
126 checkGenericClassIsUnary clas dm_info `thenTc_`
129 tcSuperClasses clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
131 -- CHECK THE CLASS SIGNATURES,
132 mapTc (tcClassSig rec_env clas tyvars fds dm_info)
133 op_sigs `thenTc` \ sig_stuff ->
135 -- MAKE THE CLASS DETAILS
137 (op_tys, op_items) = unzip sig_stuff
138 sc_tys = mkDictTys sc_theta
139 dict_component_tys = sc_tys ++ op_tys
141 dict_con = mkDataCon datacon_name
142 [notMarkedStrict | _ <- dict_component_tys]
143 [{- No labelled fields -}]
146 [{-No existential tyvars-}] [{-Or context-}]
149 dict_con_id dict_wrap_id
151 dict_con_id = mkDataConId datacon_wkr_name dict_con
152 dict_wrap_id = mkDataConWrapId dict_con
154 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
158 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds -> TcM (NameEnv (DefMeth Name))
159 -- Check default bindings
160 -- a) must be for a class op for this class
161 -- b) must be all generic or all non-generic
162 -- and return a mapping from class-op to DefMeth info
164 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
166 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
167 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
168 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
169 returnTc (dm_info1 `plusNameEnv` dm_info2)
171 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
174 -- Check that the op is from this class
175 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
177 -- Check that all the defns ar generic, or none are
178 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
180 -- Make up the right dm_info
182 returnTc (unitNameEnv op GenDefMeth)
184 -- An explicit non-generic default method
185 newDefaultMethodName op loc `thenNF_Tc` \ dm_name ->
186 returnTc (unitNameEnv op (DefMeth dm_name))
189 n_generic = count (maybeToBool . maybeGenericMatch) matches
190 none_generic = n_generic == 0
191 all_generic = n_generic == length matches
193 checkGenericClassIsUnary clas dm_info
194 = -- Check that if the class has generic methods, then the
195 -- class has only one parameter. We can't do generic
196 -- multi-parameter type classes!
197 checkTc (unary || no_generics) (genericMultiParamErr clas)
199 unary = length (classTyVars clas) == 1
200 no_generics = null [() | GenDefMeth <- nameEnvElts dm_info]
205 tcSuperClasses :: Class
206 -> RenamedContext -- class context
207 -> [Name] -- Names for superclass selectors
208 -> TcM (ClassContext, -- the superclass context
209 [Id]) -- superclass selector Ids
211 tcSuperClasses clas context sc_sel_names
212 = -- Check the context.
213 -- The renamer has already checked that the context mentions
214 -- only the type variable of the class decl.
216 -- For std Haskell check that the context constrains only tyvars
217 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
221 mapTc_ check_constraint context
224 -- Context is already kind-checked
225 tcClassContext context `thenTc` \ sc_theta ->
227 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
230 returnTc (sc_theta, sc_sel_ids)
233 check_constraint sc@(HsPClass c tys)
234 = checkTc (all is_tyvar tys) (superClassErr clas sc)
236 is_tyvar (HsTyVar _) = True
237 is_tyvar other = False
240 tcClassSig :: RecTcEnv
241 -> Class -- ...ditto...
242 -> [TyVar] -- The class type variable, used for error check only
244 -> NameEnv (DefMeth Name) -- Info about default methods
246 -> TcM (Type, -- Type of the method
247 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
249 -- This warrants an explanation: we need to separate generic
250 -- default methods and default methods later on in the compiler
251 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
252 -- Class.DefMeth data structure.
254 tcClassSig unf_env clas clas_tyvars fds dm_info
255 (ClassOpSig op_name maybe_dm op_ty src_loc)
256 = tcAddSrcLoc src_loc $
258 -- Check the type signature. NB that the envt *already has*
259 -- bindings for the type variables; see comments in TcTyAndClassDcls.
261 tcHsSigType op_ty `thenTc` \ local_ty ->
263 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
265 -- Check for ambiguous class op types
266 checkAmbiguity True clas_tyvars theta local_ty `thenTc` \ global_ty ->
269 -- Build the selector id and default method id
270 sel_id = mkDictSelId op_name clas
272 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
274 dm_info_id = case dm_info_name of
275 NoDefMeth -> NoDefMeth
276 GenDefMeth -> GenDefMeth
277 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
279 dm_id = mkDefaultMethodId dm_name clas global_ty
281 -- Check that for a generic method, the type of
282 -- the method is sufficiently simple
283 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
284 (badGenericMethodType op_name op_ty) `thenTc_`
286 returnTc (local_ty, (sel_id, dm_info_id))
290 %************************************************************************
292 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
294 %************************************************************************
296 @mkImplicitClassBinds@ produces a binding for the selector function for each method
297 and superclass dictionary.
300 mkImplicitClassBinds :: Module -> [Class] -> NF_TcM ([Id], TcMonoBinds)
301 mkImplicitClassBinds this_mod classes
302 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
303 -- The selector binds are already in the selector Id's unfoldings
304 -- We don't return the data constructor etc from the class,
305 -- because that's done via the class's TyCon
307 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
309 mk_implicit clas = (sel_ids, binds)
311 sel_ids = classSelIds clas
312 binds | isFrom this_mod clas = idsToMonoBinds sel_ids
313 | otherwise = EmptyMonoBinds
318 %************************************************************************
320 \subsection[Default methods]{Default methods}
322 %************************************************************************
324 The default methods for a class are each passed a dictionary for the
325 class, so that they get access to the other methods at the same type.
326 So, given the class decl
330 op2 :: Ord b => a -> b -> b -> b
333 op2 x y z = if (op1 x) && (y < z) then y else z
335 we get the default methods:
337 defm.Foo.op1 :: forall a. Foo a => a -> Bool
338 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
340 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
341 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
342 if (op1 a dfoo x) && (< b dord y z) then y else z
345 When we come across an instance decl, we may need to use the default
348 instance Foo Int where {}
352 const.Foo.Int.op1 :: Int -> Bool
353 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
355 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
356 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
358 dfun.Foo.Int :: Foo Int
359 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
361 Notice that, as with method selectors above, we assume that dictionary
362 application is curried, so there's no need to mention the Ord dictionary
363 in const.Foo.Int.op2 (or the type variable).
366 instance Foo a => Foo [a] where {}
368 dfun.Foo.List :: forall a. Foo a -> Foo [a]
370 = /\ a -> \ dfoo_a ->
372 op1 = defm.Foo.op1 [a] dfoo_list
373 op2 = defm.Foo.op2 [a] dfoo_list
374 dfoo_list = (op1, op2)
379 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
380 each local class decl.
383 tcClassDecls2 :: Module -> [RenamedHsDecl] -> NF_TcM (LIE, TcMonoBinds)
385 tcClassDecls2 this_mod decls
387 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
388 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
389 isClassDecl cls_decl,
390 isFrom this_mod (tyClDeclName cls_decl)]
392 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
393 tc2 `thenNF_Tc` \ (lie2, binds2) ->
394 returnNF_Tc (lie1 `plusLIE` lie2,
395 binds1 `AndMonoBinds` binds2)
398 @tcClassDecl2@ generates bindings for polymorphic default methods
399 (generic default methods have by now turned into instance declarations)
402 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
403 -> NF_TcM (LIE, TcMonoBinds)
405 tcClassDecl2 (ClassDecl context class_name
406 tyvar_names _ sigs default_binds _ src_loc)
407 = -- A locally defined class
408 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
409 tcAddSrcLoc src_loc $
410 tcLookupClass class_name `thenNF_Tc` \ clas ->
412 -- We make a separate binding for each default method.
413 -- At one time I used a single AbsBinds for all of them, thus
414 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
415 -- But that desugars into
416 -- ds = \d -> (..., ..., ...)
417 -- dm1 = \d -> case ds d of (a,b,c) -> a
418 -- And since ds is big, it doesn't get inlined, so we don't get good
419 -- default methods. Better to make separate AbsBinds for each
421 (tyvars, _, _, op_items) = classBigSig clas
422 prags = filter isPragSig sigs
423 tc_dm = tcDefMeth clas tyvars default_binds prags
425 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
427 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
430 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
431 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
432 -- Generate code for polymorphic default methods only
433 -- (Generic default methods have turned into instance decls by now.)
434 -- This is incompatible with Hugs, which expects a polymorphic
435 -- default method for every class op, regardless of whether or not
436 -- the programmer supplied an explicit default decl for the class.
437 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
439 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
440 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
442 theta = [(mkClassPred clas inst_tys)]
444 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
446 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
447 tcMethodBind clas origin clas_tyvars inst_tys theta
448 binds_in prags False op_item
449 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
451 tcAddErrCtxt (defltMethCtxt clas) $
453 -- tcMethodBind has checked that the class_tyvars havn't
454 -- been unified with each other or another type, but we must
455 -- still zonk them before passing them to tcSimplifyAndCheck
456 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
460 (ptext SLIT("class") <+> ppr clas)
461 (mkVarSet clas_tyvars')
463 insts_needed `thenTc` \ (const_lie, dict_binds) ->
469 [(clas_tyvars', dm_id, local_dm_id)]
470 emptyNameSet -- No inlines (yet)
471 (dict_binds `andMonoBinds` defm_bind)
473 returnTc (full_bind, const_lie)
475 origin = ClassDeclOrigin
480 %************************************************************************
482 \subsection{Typechecking a method}
484 %************************************************************************
486 @tcMethodBind@ is used to type-check both default-method and
487 instance-decl method declarations. We must type-check methods one at a
488 time, because their signatures may have different contexts and
495 -> [TcTyVar] -- Instantiated type variables for the
496 -- enclosing class/instance decl.
497 -- They'll be signature tyvars, and we
498 -- want to check that they don't get bound
499 -> [TcType] -- Instance types
500 -> TcThetaType -- Available theta; this could be used to check
501 -- the method signature, but actually that's done by
502 -- the caller; here, it's just used for the error message
503 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
504 -> [RenamedSig] -- Pramgas (just for this one)
505 -> Bool -- True <=> This method is from an instance declaration
506 -> ClassOpItem -- The method selector and default-method Id
507 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
509 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
510 meth_binds prags is_inst_decl (sel_id, dm_info)
511 = tcGetSrcLoc `thenNF_Tc` \ loc ->
512 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
513 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
515 meth_name = idName meth_id
516 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
517 meth_prags = find_prags (idName sel_id) meth_name prags
519 -- Figure out what method binding to use
520 -- If the user suppplied one, use it, else construct a default one
521 (case find_bind (idName sel_id) meth_name meth_binds of
522 Just user_bind -> returnTc user_bind
523 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
524 returnTc (FunMonoBind meth_name False -- Not infix decl
525 [mkSimpleMatch [] rhs Nothing loc] loc)
526 ) `thenTc` \ meth_bind ->
527 -- Check the bindings; first add inst_tyvars to the envt
528 -- so that we don't quantify over them in nested places
529 -- The *caller* put the class/inst decl tyvars into the envt
530 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
531 (tcAddErrCtxt (methodCtxt sel_id) $
532 tcBindWithSigs NotTopLevel meth_bind
533 [sig_info] meth_prags NonRecursive
534 ) `thenTc` \ (binds, insts, _) ->
536 tcExtendLocalValEnv [(meth_name, meth_id)]
537 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
539 -- The prag_lie for a SPECIALISE pragma will mention the function
540 -- itself, so we have to simplify them away right now lest they float
542 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
544 -- Now check that the instance type variables
545 -- (or, in the case of a class decl, the class tyvars)
546 -- have not been unified with anything in the environment
548 -- We do this for each method independently to localise error messages
549 -- ...and this is why the call to tcExtendGlobalTyVars must be here
550 -- rather than in the caller
551 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
552 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
554 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
555 insts `plusLIE` prag_lie',
558 -- The user didn't supply a method binding,
559 -- so we have to make up a default binding
560 -- The RHS of a default method depends on the default-method info
561 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
562 = -- An polymorphic default method
563 returnTc (HsVar (idName dm_id))
565 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
566 = -- No default method
567 -- Warn only if -fwarn-missing-methods
568 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
569 warnTc (is_inst_decl && warn)
570 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
573 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
574 (HsLit (HsString (_PK_ error_msg)))
575 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
578 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
579 = -- A generic default method
580 -- If the method is defined generically, we can only do the job if the
581 -- instance declaration is for a single-parameter type class with
582 -- a type constructor applied to type arguments in the instance decl
583 -- (checkTc, so False provokes the error)
584 checkTc (not is_inst_decl || simple_inst)
585 (badGenericInstance sel_id clas) `thenTc_`
587 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
590 rhs = mkGenericRhs sel_id clas_tyvar tycon
592 stuff = vcat [ppr clas <+> ppr inst_tys,
593 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
595 -- The tycon is only used in the generic case, and in that
596 -- case we require that the instance decl is for a single-parameter
597 -- type class with type variable arguments:
598 -- instance (...) => C (T a b)
599 simple_inst = maybeToBool maybe_tycon
600 clas_tyvar = head (classTyVars clas)
601 Just tycon = maybe_tycon
602 maybe_tycon = case inst_tys of
603 [ty] -> case splitTyConApp_maybe ty of
604 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
611 -- The renamer just puts the selector ID as the binder in the method binding
612 -- but we must use the method name; so we substitute it here. Crude but simple.
613 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
614 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
615 find_bind sel_name meth_name (AndMonoBinds b1 b2)
616 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
617 find_bind sel_name meth_name other = Nothing -- Default case
619 -- Find the prags for this method, and replace the
620 -- selector name with the method name
621 find_prags sel_name meth_name [] = []
622 find_prags sel_name meth_name (SpecSig name ty loc : prags)
623 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
624 find_prags sel_name meth_name (InlineSig name phase loc : prags)
625 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
626 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
627 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
628 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
635 classArityErr class_name
636 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
638 superClassErr clas sc
639 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
640 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
643 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
646 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
649 = hsep [ptext SLIT("Class"), quotes (ppr clas),
650 ptext SLIT("does not have a method"), quotes (ppr op)]
652 omittedMethodWarn sel_id clas
653 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
654 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
656 badGenericMethodType op op_ty
657 = hang (ptext SLIT("Generic method type is too complex"))
658 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
659 ptext SLIT("You can only use type variables, arrows, and tuples")])
661 badGenericInstance sel_id clas
662 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
663 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
664 ptext SLIT("(where T is a derivable type constructor)"),
665 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
668 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
670 genericMultiParamErr clas
671 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
672 ptext SLIT("cannot have generic methods")