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 ( NewOrData(..), TopLevelFlag(..), RecFlag(..), EP(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
22 RenamedContext, RenamedHsDecl, RenamedSig,
23 RenamedHsExpr, maybeGenericMatch
25 import TcHsSyn ( TcMonoBinds, idsToMonoBinds )
27 import Inst ( InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs, newDicts, newMethod )
28 import TcEnv ( TcId, TcEnv, TyThing(..), TyThingDetails(..), tcAddImportedIdInfo,
29 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
30 tcExtendLocalValEnv, tcExtendTyVarEnv, newDefaultMethodName
32 import TcBinds ( tcBindWithSigs, tcSpecSigs )
33 import TcMonoType ( tcHsSigType, tcClassContext, checkSigTyVars, sigCtxt, mkTcSig )
34 import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns )
35 import TcType ( TcType, TcTyVar, tcInstTyVars, zonkTcSigTyVars )
37 import Generics ( mkGenericRhs, validGenericMethodType )
38 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
39 import Class ( classTyVars, classBigSig, classSelIds, classTyCon, Class, ClassOpItem,
41 import Bag ( bagToList )
42 import CmdLineOpts ( dopt_GlasgowExts, opt_WarnMissingMethods, opt_PprStyle_Debug )
43 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
44 import DataCon ( mkDataCon, notMarkedStrict )
45 import Id ( Id, idType, idName )
46 import Name ( Name, nameOccName, isLocallyDefined, NamedThing(..), mkSysLocalName,
47 NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
48 import NameSet ( NameSet, mkNameSet, elemNameSet, emptyNameSet )
50 import Type ( Type, ClassContext, mkTyVarTys, mkDictTys, mkSigmaTy, mkClassPred,
51 splitTyConApp_maybe, isTyVarTy
54 import VarSet ( mkVarSet, emptyVarSet )
55 import ErrUtils ( dumpIfSet )
57 import Maybes ( seqMaybe, maybeToBool, orElse )
64 Every class implicitly declares a new data type, corresponding to dictionaries
65 of that class. So, for example:
67 class (D a) => C a where
69 op2 :: forall b. Ord b => a -> b -> b
71 would implicitly declare
73 data CDict a = CDict (D a)
75 (forall b. Ord b => a -> b -> b)
77 (We could use a record decl, but that means changing more of the existing apparatus.
80 For classes with just one superclass+method, we use a newtype decl instead:
83 op :: forallb. a -> b -> b
87 newtype CDict a = CDict (forall b. a -> b -> b)
89 Now DictTy in Type is just a form of type synomym:
90 DictTy c t = TyConTy CDict `AppTy` t
92 Death to "ExpandingDicts".
95 %************************************************************************
97 \subsection{Type checking}
99 %************************************************************************
102 tcClassDecl1 :: TcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
104 (ClassDecl context class_name
105 tyvar_names fundeps class_sigs def_methods pragmas
107 = -- CHECK ARITY 1 FOR HASKELL 1.4
108 doptsTc dopt_GlasgowExts `thenTc` \ glaExts ->
109 checkTc (glaExts || length tyvar_names == 1)
110 (classArityErr class_name) `thenTc_`
112 -- LOOK THINGS UP IN THE ENVIRONMENT
113 tcLookupClass class_name `thenTc` \ clas ->
115 tyvars = classTyVars clas
116 op_sigs = filter isClassOpSig class_sigs
117 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
118 (_, datacon_name, datacon_wkr_name, sc_sel_names) = fromClassDeclNameList sys_names
120 tcExtendTyVarEnv tyvars $
122 -- CHECK THAT THE DEFAULT BINDINGS ARE LEGAL
123 checkDefaultBinds clas op_names def_methods `thenTc` \ dm_info ->
124 checkGenericClassIsUnary clas dm_info `thenTc_`
127 tcSuperClasses clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
129 -- CHECK THE CLASS SIGNATURES,
130 mapTc (tcClassSig rec_env clas tyvars dm_info) op_sigs `thenTc` \ sig_stuff ->
132 -- MAKE THE CLASS DETAILS
134 (op_tys, op_items) = unzip sig_stuff
135 sc_tys = mkDictTys sc_theta
136 dict_component_tys = sc_tys ++ op_tys
138 dict_con = mkDataCon datacon_name
139 [notMarkedStrict | _ <- dict_component_tys]
140 [{- No labelled fields -}]
143 [{-No existential tyvars-}] [{-Or context-}]
146 dict_con_id dict_wrap_id
148 dict_con_id = mkDataConId datacon_wkr_name dict_con
149 dict_wrap_id = mkDataConWrapId dict_con
151 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
155 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds -> TcM (NameEnv (DefMeth Name))
156 -- Check default bindings
157 -- a) must be for a class op for this class
158 -- b) must be all generic or all non-generic
159 -- and return a mapping from class-op to DefMeth info
161 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
163 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
164 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
165 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
166 returnTc (dm_info1 `plusNameEnv` dm_info2)
168 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
171 -- Check that the op is from this class
172 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
174 -- Check that all the defns ar generic, or none are
175 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
177 -- Make up the right dm_info
179 returnTc (unitNameEnv op GenDefMeth)
181 -- An explicit non-generic default method
182 newDefaultMethodName op loc `thenNF_Tc` \ dm_name ->
183 returnTc (unitNameEnv op (DefMeth dm_name))
186 n_generic = count (maybeToBool . maybeGenericMatch) matches
187 none_generic = n_generic == 0
188 all_generic = n_generic == length matches
190 checkGenericClassIsUnary clas dm_info
191 = -- Check that if the class has generic methods, then the
192 -- class has only one parameter. We can't do generic
193 -- multi-parameter type classes!
194 checkTc (unary || no_generics) (genericMultiParamErr clas)
196 unary = length (classTyVars clas) == 1
197 no_generics = null [() | GenDefMeth <- nameEnvElts dm_info]
202 tcSuperClasses :: Class
203 -> RenamedContext -- class context
204 -> [Name] -- Names for superclass selectors
205 -> TcM (ClassContext, -- the superclass context
206 [Id]) -- superclass selector Ids
208 tcSuperClasses clas context sc_sel_names
209 = -- Check the context.
210 -- The renamer has already checked that the context mentions
211 -- only the type variable of the class decl.
213 -- For std Haskell check that the context constrains only tyvars
214 doptsTc dopt_GlasgowExts `thenTc` \ glaExts ->
218 mapTc_ check_constraint context
221 -- Context is already kind-checked
222 tcClassContext context `thenTc` \ sc_theta ->
224 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
227 returnTc (sc_theta, sc_sel_ids)
230 check_constraint sc@(HsPClass c tys)
231 = checkTc (all is_tyvar tys) (superClassErr clas sc)
233 is_tyvar (HsTyVar _) = True
234 is_tyvar other = False
237 tcClassSig :: TcEnv -- Knot tying only!
238 -> Class -- ...ditto...
239 -> [TyVar] -- The class type variable, used for error check only
240 -> NameEnv (DefMeth Name) -- Info about default methods
242 -> TcM (Type, -- Type of the method
243 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
245 -- This warrants an explanation: we need to separate generic
246 -- default methods and default methods later on in the compiler
247 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
248 -- Class.DefMeth data structure.
250 tcClassSig rec_env clas clas_tyvars dm_info
251 (ClassOpSig op_name maybe_dm op_ty src_loc)
252 = tcAddSrcLoc src_loc $
254 -- Check the type signature. NB that the envt *already has*
255 -- bindings for the type variables; see comments in TcTyAndClassDcls.
257 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
258 -- and that it is not constrained by theta
259 tcHsSigType op_ty `thenTc` \ local_ty ->
261 global_ty = mkSigmaTy clas_tyvars
262 [mkClassPred clas (mkTyVarTys clas_tyvars)]
265 -- Build the selector id and default method id
266 sel_id = mkDictSelId op_name clas
268 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
270 dm_info_id = case dm_info_name of
271 NoDefMeth -> NoDefMeth
272 GenDefMeth -> GenDefMeth
273 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo rec_env dm_id)
275 dm_id = mkDefaultMethodId dm_name clas global_ty
277 -- Check that for a generic method, the type of
278 -- the method is sufficiently simple
279 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
280 (badGenericMethodType op_name op_ty) `thenTc_`
282 returnTc (local_ty, (sel_id, dm_info_id))
286 %************************************************************************
288 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
290 %************************************************************************
292 @mkImplicitClassBinds@ produces a binding for the selector function for each method
293 and superclass dictionary.
296 mkImplicitClassBinds :: [Class] -> NF_TcM ([Id], TcMonoBinds)
297 mkImplicitClassBinds classes
298 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
299 -- The selector binds are already in the selector Id's unfoldings
300 -- We don't return the data constructor etc from the class,
301 -- because that's done via the class's TyCon
303 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
305 mk_implicit clas = (sel_ids, binds)
307 sel_ids = classSelIds clas
308 binds | isLocallyDefined clas = idsToMonoBinds sel_ids
309 | otherwise = EmptyMonoBinds
314 %************************************************************************
316 \subsection[Default methods]{Default methods}
318 %************************************************************************
320 The default methods for a class are each passed a dictionary for the
321 class, so that they get access to the other methods at the same type.
322 So, given the class decl
326 op2 :: Ord b => a -> b -> b -> b
329 op2 x y z = if (op1 x) && (y < z) then y else z
331 we get the default methods:
333 defm.Foo.op1 :: forall a. Foo a => a -> Bool
334 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
336 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
337 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
338 if (op1 a dfoo x) && (< b dord y z) then y else z
341 When we come across an instance decl, we may need to use the default
344 instance Foo Int where {}
348 const.Foo.Int.op1 :: Int -> Bool
349 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
351 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
352 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
354 dfun.Foo.Int :: Foo Int
355 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
357 Notice that, as with method selectors above, we assume that dictionary
358 application is curried, so there's no need to mention the Ord dictionary
359 in const.Foo.Int.op2 (or the type variable).
362 instance Foo a => Foo [a] where {}
364 dfun.Foo.List :: forall a. Foo a -> Foo [a]
366 = /\ a -> \ dfoo_a ->
368 op1 = defm.Foo.op1 [a] dfoo_list
369 op2 = defm.Foo.op2 [a] dfoo_list
370 dfoo_list = (op1, op2)
375 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
376 each local class decl.
379 tcClassDecls2 :: [RenamedHsDecl] -> NF_TcM (LIE, TcMonoBinds)
383 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
384 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
385 isClassDecl cls_decl,
386 isLocallyDefined (tyClDeclName cls_decl)]
388 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
389 tc2 `thenNF_Tc` \ (lie2, binds2) ->
390 returnNF_Tc (lie1 `plusLIE` lie2,
391 binds1 `AndMonoBinds` binds2)
394 @tcClassDecl2@ generates bindings for polymorphic default methods
395 (generic default methods have by now turned into instance declarations)
398 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
399 -> NF_TcM (LIE, TcMonoBinds)
401 tcClassDecl2 (ClassDecl context class_name
402 tyvar_names _ sigs default_binds pragmas _ src_loc)
403 = -- A locally defined class
404 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
405 tcAddSrcLoc src_loc $
406 tcLookupClass class_name `thenNF_Tc` \ clas ->
408 -- We make a separate binding for each default method.
409 -- At one time I used a single AbsBinds for all of them, thus
410 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
411 -- But that desugars into
412 -- ds = \d -> (..., ..., ...)
413 -- dm1 = \d -> case ds d of (a,b,c) -> a
414 -- And since ds is big, it doesn't get inlined, so we don't get good
415 -- default methods. Better to make separate AbsBinds for each
417 (tyvars, _, _, op_items) = classBigSig clas
418 prags = filter isPragSig sigs
419 tc_dm = tcDefMeth clas tyvars default_binds prags
421 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
423 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
426 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
427 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
428 -- Generate code for polymorphic default methods only
429 -- (Generic default methods have turned into instance decls by now.)
430 -- This is incompatible with Hugs, which expects a polymorphic
431 -- default method for every class op, regardless of whether or not
432 -- the programmer supplied an explicit default decl for the class.
433 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
435 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
436 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
438 theta = [(mkClassPred clas inst_tys)]
440 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
442 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
443 tcMethodBind clas origin clas_tyvars inst_tys theta
444 binds_in prags False op_item
445 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
447 tcAddErrCtxt (defltMethCtxt clas) $
449 -- tcMethodBind has checked that the class_tyvars havn't
450 -- been unified with each other or another type, but we must
451 -- still zonk them before passing them to tcSimplifyAndCheck
452 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
456 (ptext SLIT("class") <+> ppr clas)
457 (mkVarSet clas_tyvars')
459 insts_needed `thenTc` \ (const_lie, dict_binds) ->
465 [(clas_tyvars', dm_id, local_dm_id)]
466 emptyNameSet -- No inlines (yet)
467 (dict_binds `andMonoBinds` defm_bind)
469 returnTc (full_bind, const_lie)
471 origin = ClassDeclOrigin
476 %************************************************************************
478 \subsection{Typechecking a method}
480 %************************************************************************
482 @tcMethodBind@ is used to type-check both default-method and
483 instance-decl method declarations. We must type-check methods one at a
484 time, because their signatures may have different contexts and
491 -> [TcTyVar] -- Instantiated type variables for the
492 -- enclosing class/instance decl.
493 -- They'll be signature tyvars, and we
494 -- want to check that they don't get bound
495 -> [TcType] -- Instance types
496 -> TcThetaType -- Available theta; this could be used to check
497 -- the method signature, but actually that's done by
498 -- the caller; here, it's just used for the error message
499 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
500 -> [RenamedSig] -- Pramgas (just for this one)
501 -> Bool -- True <=> This method is from an instance declaration
502 -> ClassOpItem -- The method selector and default-method Id
503 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
505 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
506 meth_binds prags is_inst_decl (sel_id, dm_info)
507 = tcGetSrcLoc `thenNF_Tc` \ loc ->
508 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
509 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
511 meth_name = idName meth_id
512 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
513 meth_prags = find_prags (idName sel_id) meth_name prags
515 -- Figure out what method binding to use
516 -- If the user suppplied one, use it, else construct a default one
517 (case find_bind (idName sel_id) meth_name meth_binds of
518 Just user_bind -> returnTc user_bind
519 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
520 returnTc (FunMonoBind meth_name False -- Not infix decl
521 [mkSimpleMatch [] rhs Nothing loc] loc)
522 ) `thenTc` \ meth_bind ->
523 -- Check the bindings; first add inst_tyvars to the envt
524 -- so that we don't quantify over them in nested places
525 -- The *caller* put the class/inst decl tyvars into the envt
526 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
527 (tcAddErrCtxt (methodCtxt sel_id) $
528 tcBindWithSigs NotTopLevel meth_bind
529 [sig_info] meth_prags NonRecursive
530 ) `thenTc` \ (binds, insts, _) ->
532 tcExtendLocalValEnv [(meth_name, meth_id)]
533 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
535 -- The prag_lie for a SPECIALISE pragma will mention the function
536 -- itself, so we have to simplify them away right now lest they float
538 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
540 -- Now check that the instance type variables
541 -- (or, in the case of a class decl, the class tyvars)
542 -- have not been unified with anything in the environment
544 -- We do this for each method independently to localise error messages
545 -- ...and this is why the call to tcExtendGlobalTyVars must be here
546 -- rather than in the caller
547 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
548 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
550 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
551 insts `plusLIE` prag_lie',
554 -- The user didn't supply a method binding,
555 -- so we have to make up a default binding
556 -- The RHS of a default method depends on the default-method info
557 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
558 = -- An polymorphic default method
559 returnTc (HsVar (idName dm_id))
561 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
562 = -- No default method
563 -- Warn only if -fwarn-missing-methods
564 warnTc (is_inst_decl && opt_WarnMissingMethods)
565 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
568 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
569 (HsLit (HsString (_PK_ error_msg)))
570 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
573 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
574 = -- A generic default method
575 -- If the method is defined generically, we can only do the job if the
576 -- instance declaration is for a single-parameter type class with
577 -- a type constructor applied to type arguments in the instance decl
578 -- (checkTc, so False provokes the error)
579 checkTc (not is_inst_decl || simple_inst)
580 (badGenericInstance sel_id clas) `thenTc_`
582 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
585 rhs = mkGenericRhs sel_id clas_tyvar tycon
587 stuff = vcat [ppr clas <+> ppr inst_tys,
588 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
590 -- The tycon is only used in the generic case, and in that
591 -- case we require that the instance decl is for a single-parameter
592 -- type class with type variable arguments:
593 -- instance (...) => C (T a b)
594 simple_inst = maybeToBool maybe_tycon
595 clas_tyvar = head (classTyVars clas)
596 Just tycon = maybe_tycon
597 maybe_tycon = case inst_tys of
598 [ty] -> case splitTyConApp_maybe ty of
599 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
606 -- The renamer just puts the selector ID as the binder in the method binding
607 -- but we must use the method name; so we substitute it here. Crude but simple.
608 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
609 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
610 find_bind sel_name meth_name (AndMonoBinds b1 b2)
611 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
612 find_bind sel_name meth_name other = Nothing -- Default case
614 -- Find the prags for this method, and replace the
615 -- selector name with the method name
616 find_prags sel_name meth_name [] = []
617 find_prags sel_name meth_name (SpecSig name ty loc : prags)
618 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
619 find_prags sel_name meth_name (InlineSig name phase loc : prags)
620 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
621 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
622 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
623 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
630 classArityErr class_name
631 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
633 superClassErr clas sc
634 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
635 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
638 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
641 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
644 = hsep [ptext SLIT("Class"), quotes (ppr clas),
645 ptext SLIT("does not have a method"), quotes (ppr op)]
647 omittedMethodWarn sel_id clas
648 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
649 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
651 badGenericMethodType op op_ty
652 = hang (ptext SLIT("Generic method type is too complex"))
653 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
654 ptext SLIT("You can only use type variables, arrows, and tuples")])
656 badGenericInstance sel_id clas
657 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
658 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
659 ptext SLIT("(where T is a derivable type constructor)"),
660 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
663 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
665 genericMultiParamErr clas
666 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
667 ptext SLIT("cannot have generic methods")