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, 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,
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
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 tyvar_names 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 :: TcEnv -- Knot tying only!
240 -> [HsTyVarBndr Name] -- From the declaration, for error messages
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 rec_env tyvar_names 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)]
264 global_ty = mkSigmaTy clas_tyvars theta local_ty
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 full_hs_ty = HsForAllTy (Just tyvar_names) op_ty
280 -- Check for ambiguous class op types
281 checkAmbiguity full_ty clas_tyvars theta local_ty `thenRn_`
283 -- Check that for a generic method, the type of
284 -- the method is sufficiently simple
285 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
286 (badGenericMethodType op_name op_ty) `thenTc_`
288 returnTc (local_ty, (sel_id, dm_info_id))
292 %************************************************************************
294 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
296 %************************************************************************
298 @mkImplicitClassBinds@ produces a binding for the selector function for each method
299 and superclass dictionary.
302 mkImplicitClassBinds :: [Class] -> NF_TcM ([Id], TcMonoBinds)
303 mkImplicitClassBinds classes
304 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
305 -- The selector binds are already in the selector Id's unfoldings
306 -- We don't return the data constructor etc from the class,
307 -- because that's done via the class's TyCon
309 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
311 mk_implicit clas = (sel_ids, binds)
313 sel_ids = classSelIds clas
314 binds | isLocallyDefined clas = idsToMonoBinds sel_ids
315 | otherwise = EmptyMonoBinds
320 %************************************************************************
322 \subsection[Default methods]{Default methods}
324 %************************************************************************
326 The default methods for a class are each passed a dictionary for the
327 class, so that they get access to the other methods at the same type.
328 So, given the class decl
332 op2 :: Ord b => a -> b -> b -> b
335 op2 x y z = if (op1 x) && (y < z) then y else z
337 we get the default methods:
339 defm.Foo.op1 :: forall a. Foo a => a -> Bool
340 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
342 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
343 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
344 if (op1 a dfoo x) && (< b dord y z) then y else z
347 When we come across an instance decl, we may need to use the default
350 instance Foo Int where {}
354 const.Foo.Int.op1 :: Int -> Bool
355 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
357 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
358 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
360 dfun.Foo.Int :: Foo Int
361 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
363 Notice that, as with method selectors above, we assume that dictionary
364 application is curried, so there's no need to mention the Ord dictionary
365 in const.Foo.Int.op2 (or the type variable).
368 instance Foo a => Foo [a] where {}
370 dfun.Foo.List :: forall a. Foo a -> Foo [a]
372 = /\ a -> \ dfoo_a ->
374 op1 = defm.Foo.op1 [a] dfoo_list
375 op2 = defm.Foo.op2 [a] dfoo_list
376 dfoo_list = (op1, op2)
381 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
382 each local class decl.
385 tcClassDecls2 :: [RenamedHsDecl] -> NF_TcM (LIE, TcMonoBinds)
389 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
390 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
391 isClassDecl cls_decl,
392 isLocallyDefined (tyClDeclName cls_decl)]
394 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
395 tc2 `thenNF_Tc` \ (lie2, binds2) ->
396 returnNF_Tc (lie1 `plusLIE` lie2,
397 binds1 `AndMonoBinds` binds2)
400 @tcClassDecl2@ generates bindings for polymorphic default methods
401 (generic default methods have by now turned into instance declarations)
404 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
405 -> NF_TcM (LIE, TcMonoBinds)
407 tcClassDecl2 (ClassDecl context class_name
408 tyvar_names _ sigs default_binds _ src_loc)
409 = -- A locally defined class
410 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
411 tcAddSrcLoc src_loc $
412 tcLookupClass class_name `thenNF_Tc` \ clas ->
414 -- We make a separate binding for each default method.
415 -- At one time I used a single AbsBinds for all of them, thus
416 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
417 -- But that desugars into
418 -- ds = \d -> (..., ..., ...)
419 -- dm1 = \d -> case ds d of (a,b,c) -> a
420 -- And since ds is big, it doesn't get inlined, so we don't get good
421 -- default methods. Better to make separate AbsBinds for each
423 (tyvars, _, _, op_items) = classBigSig clas
424 prags = filter isPragSig sigs
425 tc_dm = tcDefMeth clas tyvars default_binds prags
427 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
429 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
432 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
433 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
434 -- Generate code for polymorphic default methods only
435 -- (Generic default methods have turned into instance decls by now.)
436 -- This is incompatible with Hugs, which expects a polymorphic
437 -- default method for every class op, regardless of whether or not
438 -- the programmer supplied an explicit default decl for the class.
439 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
441 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
442 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
444 theta = [(mkClassPred clas inst_tys)]
446 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
448 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
449 tcMethodBind clas origin clas_tyvars inst_tys theta
450 binds_in prags False op_item
451 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
453 tcAddErrCtxt (defltMethCtxt clas) $
455 -- tcMethodBind has checked that the class_tyvars havn't
456 -- been unified with each other or another type, but we must
457 -- still zonk them before passing them to tcSimplifyAndCheck
458 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
462 (ptext SLIT("class") <+> ppr clas)
463 (mkVarSet clas_tyvars')
465 insts_needed `thenTc` \ (const_lie, dict_binds) ->
471 [(clas_tyvars', dm_id, local_dm_id)]
472 emptyNameSet -- No inlines (yet)
473 (dict_binds `andMonoBinds` defm_bind)
475 returnTc (full_bind, const_lie)
477 origin = ClassDeclOrigin
482 %************************************************************************
484 \subsection{Typechecking a method}
486 %************************************************************************
488 @tcMethodBind@ is used to type-check both default-method and
489 instance-decl method declarations. We must type-check methods one at a
490 time, because their signatures may have different contexts and
497 -> [TcTyVar] -- Instantiated type variables for the
498 -- enclosing class/instance decl.
499 -- They'll be signature tyvars, and we
500 -- want to check that they don't get bound
501 -> [TcType] -- Instance types
502 -> TcThetaType -- Available theta; this could be used to check
503 -- the method signature, but actually that's done by
504 -- the caller; here, it's just used for the error message
505 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
506 -> [RenamedSig] -- Pramgas (just for this one)
507 -> Bool -- True <=> This method is from an instance declaration
508 -> ClassOpItem -- The method selector and default-method Id
509 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
511 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
512 meth_binds prags is_inst_decl (sel_id, dm_info)
513 = tcGetSrcLoc `thenNF_Tc` \ loc ->
514 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
515 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
517 meth_name = idName meth_id
518 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
519 meth_prags = find_prags (idName sel_id) meth_name prags
521 -- Figure out what method binding to use
522 -- If the user suppplied one, use it, else construct a default one
523 (case find_bind (idName sel_id) meth_name meth_binds of
524 Just user_bind -> returnTc user_bind
525 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
526 returnTc (FunMonoBind meth_name False -- Not infix decl
527 [mkSimpleMatch [] rhs Nothing loc] loc)
528 ) `thenTc` \ meth_bind ->
529 -- Check the bindings; first add inst_tyvars to the envt
530 -- so that we don't quantify over them in nested places
531 -- The *caller* put the class/inst decl tyvars into the envt
532 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
533 (tcAddErrCtxt (methodCtxt sel_id) $
534 tcBindWithSigs NotTopLevel meth_bind
535 [sig_info] meth_prags NonRecursive
536 ) `thenTc` \ (binds, insts, _) ->
538 tcExtendLocalValEnv [(meth_name, meth_id)]
539 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
541 -- The prag_lie for a SPECIALISE pragma will mention the function
542 -- itself, so we have to simplify them away right now lest they float
544 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
546 -- Now check that the instance type variables
547 -- (or, in the case of a class decl, the class tyvars)
548 -- have not been unified with anything in the environment
550 -- We do this for each method independently to localise error messages
551 -- ...and this is why the call to tcExtendGlobalTyVars must be here
552 -- rather than in the caller
553 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
554 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
556 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
557 insts `plusLIE` prag_lie',
560 -- The user didn't supply a method binding,
561 -- so we have to make up a default binding
562 -- The RHS of a default method depends on the default-method info
563 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
564 = -- An polymorphic default method
565 returnTc (HsVar (idName dm_id))
567 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
568 = -- No default method
569 -- Warn only if -fwarn-missing-methods
570 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
571 warnTc (is_inst_decl && warn)
572 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
575 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
576 (HsLit (HsString (_PK_ error_msg)))
577 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
580 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
581 = -- A generic default method
582 -- If the method is defined generically, we can only do the job if the
583 -- instance declaration is for a single-parameter type class with
584 -- a type constructor applied to type arguments in the instance decl
585 -- (checkTc, so False provokes the error)
586 checkTc (not is_inst_decl || simple_inst)
587 (badGenericInstance sel_id clas) `thenTc_`
589 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
592 rhs = mkGenericRhs sel_id clas_tyvar tycon
594 stuff = vcat [ppr clas <+> ppr inst_tys,
595 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
597 -- The tycon is only used in the generic case, and in that
598 -- case we require that the instance decl is for a single-parameter
599 -- type class with type variable arguments:
600 -- instance (...) => C (T a b)
601 simple_inst = maybeToBool maybe_tycon
602 clas_tyvar = head (classTyVars clas)
603 Just tycon = maybe_tycon
604 maybe_tycon = case inst_tys of
605 [ty] -> case splitTyConApp_maybe ty of
606 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
613 -- The renamer just puts the selector ID as the binder in the method binding
614 -- but we must use the method name; so we substitute it here. Crude but simple.
615 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
616 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
617 find_bind sel_name meth_name (AndMonoBinds b1 b2)
618 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
619 find_bind sel_name meth_name other = Nothing -- Default case
621 -- Find the prags for this method, and replace the
622 -- selector name with the method name
623 find_prags sel_name meth_name [] = []
624 find_prags sel_name meth_name (SpecSig name ty loc : prags)
625 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
626 find_prags sel_name meth_name (InlineSig name phase loc : prags)
627 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
628 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
629 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
630 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
637 classArityErr class_name
638 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
640 superClassErr clas sc
641 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
642 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
645 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
648 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
651 = hsep [ptext SLIT("Class"), quotes (ppr clas),
652 ptext SLIT("does not have a method"), quotes (ppr op)]
654 omittedMethodWarn sel_id clas
655 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
656 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
658 badGenericMethodType op op_ty
659 = hang (ptext SLIT("Generic method type is too complex"))
660 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
661 ptext SLIT("You can only use type variables, arrows, and tuples")])
663 badGenericInstance sel_id clas
664 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
665 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
666 ptext SLIT("(where T is a derivable type constructor)"),
667 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
670 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
672 genericMultiParamErr clas
673 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
674 ptext SLIT("cannot have generic methods")