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, ValueEnv, TyThing(..), TyThingDetails(..), tcAddImportedIdInfo,
29 tcLookupTy, 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 ( opt_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 :: ValueEnv -> RenamedTyClDecl -> TcM s (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 checkTc (opt_GlasgowExts || length tyvar_names == 1)
109 (classArityErr class_name) `thenTc_`
111 -- LOOK THINGS UP IN THE ENVIRONMENT
112 tcLookupTy class_name `thenTc` \ (AClass clas) ->
114 tyvars = classTyVars clas
115 op_sigs = filter isClassOpSig class_sigs
116 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
117 (_, datacon_name, datacon_wkr_name, sc_sel_names) = fromClassDeclNameList sys_names
119 tcExtendTyVarEnv tyvars $
121 -- CHECK THAT THE DEFAULT BINDINGS ARE LEGAL
122 checkDefaultBinds clas op_names def_methods `thenTc` \ dm_info ->
123 checkGenericClassIsUnary clas dm_info `thenTc_`
126 tcSuperClasses clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
128 -- CHECK THE CLASS SIGNATURES,
129 mapTc (tcClassSig rec_env clas tyvars dm_info) op_sigs `thenTc` \ sig_stuff ->
131 -- MAKE THE CLASS DETAILS
133 (op_tys, op_items) = unzip sig_stuff
134 sc_tys = mkDictTys sc_theta
135 dict_component_tys = sc_tys ++ op_tys
137 dict_con = mkDataCon datacon_name
138 [notMarkedStrict | _ <- dict_component_tys]
139 [{- No labelled fields -}]
142 [{-No existential tyvars-}] [{-Or context-}]
145 dict_con_id dict_wrap_id
147 dict_con_id = mkDataConId datacon_wkr_name dict_con
148 dict_wrap_id = mkDataConWrapId dict_con
150 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
154 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds -> TcM s (NameEnv (DefMeth Name))
155 -- Check default bindings
156 -- a) must be for a class op for this class
157 -- b) must be all generic or all non-generic
158 -- and return a mapping from class-op to DefMeth info
160 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
162 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
163 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
164 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
165 returnTc (dm_info1 `plusNameEnv` dm_info2)
167 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
170 -- Check that the op is from this class
171 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
173 -- Check that all the defns ar generic, or none are
174 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
176 -- Make up the right dm_info
178 returnTc (unitNameEnv op GenDefMeth)
180 -- An explicit non-generic default method
181 newDefaultMethodName op loc `thenNF_Tc` \ dm_name ->
182 returnTc (unitNameEnv op (DefMeth dm_name))
185 n_generic = count (maybeToBool . maybeGenericMatch) matches
186 none_generic = n_generic == 0
187 all_generic = n_generic == length matches
189 checkGenericClassIsUnary clas dm_info
190 = -- Check that if the class has generic methods, then the
191 -- class has only one parameter. We can't do generic
192 -- multi-parameter type classes!
193 checkTc (unary || no_generics) (genericMultiParamErr clas)
195 unary = length (classTyVars clas) == 1
196 no_generics = null [() | GenDefMeth <- nameEnvElts dm_info]
201 tcSuperClasses :: Class
202 -> RenamedContext -- class context
203 -> [Name] -- Names for superclass selectors
204 -> TcM s (ClassContext, -- the superclass context
205 [Id]) -- superclass selector Ids
207 tcSuperClasses clas context sc_sel_names
208 = -- Check the context.
209 -- The renamer has already checked that the context mentions
210 -- only the type variable of the class decl.
212 -- For std Haskell check that the context constrains only tyvars
213 (if opt_GlasgowExts then
216 mapTc_ check_constraint context
219 -- Context is already kind-checked
220 tcClassContext context `thenTc` \ sc_theta ->
222 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
225 returnTc (sc_theta, sc_sel_ids)
228 check_constraint sc@(HsPClass c tys)
229 = checkTc (all is_tyvar tys) (superClassErr clas sc)
231 is_tyvar (HsTyVar _) = True
232 is_tyvar other = False
235 tcClassSig :: ValueEnv -- Knot tying only!
236 -> Class -- ...ditto...
237 -> [TyVar] -- The class type variable, used for error check only
238 -> NameEnv (DefMeth Name) -- Info about default methods
240 -> TcM s (Type, -- Type of the method
241 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
243 -- This warrants an explanation: we need to separate generic
244 -- default methods and default methods later on in the compiler
245 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
246 -- Class.DefMeth data structure.
248 tcClassSig rec_env clas clas_tyvars dm_info
249 (ClassOpSig op_name maybe_dm op_ty src_loc)
250 = tcAddSrcLoc src_loc $
252 -- Check the type signature. NB that the envt *already has*
253 -- bindings for the type variables; see comments in TcTyAndClassDcls.
255 -- NB: Renamer checks that the class type variable is mentioned in local_ty,
256 -- and that it is not constrained by theta
257 tcHsSigType op_ty `thenTc` \ local_ty ->
259 global_ty = mkSigmaTy clas_tyvars
260 [mkClassPred clas (mkTyVarTys clas_tyvars)]
263 -- Build the selector id and default method id
264 sel_id = mkDictSelId op_name clas
266 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
268 dm_info_id = case dm_info_name of
269 NoDefMeth -> NoDefMeth
270 GenDefMeth -> GenDefMeth
271 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo rec_env dm_id)
273 dm_id = mkDefaultMethodId dm_name clas global_ty
275 -- Check that for a generic method, the type of
276 -- the method is sufficiently simple
277 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
278 (badGenericMethodType op_name op_ty) `thenTc_`
280 returnTc (local_ty, (sel_id, dm_info_id))
284 %************************************************************************
286 \subsection[ClassDcl-pass2]{Class decls pass 2: default methods}
288 %************************************************************************
290 @mkImplicitClassBinds@ produces a binding for the selector function for each method
291 and superclass dictionary.
294 mkImplicitClassBinds :: [Class] -> NF_TcM s ([Id], TcMonoBinds)
295 mkImplicitClassBinds classes
296 = returnNF_Tc (concat cls_ids_s, andMonoBindList binds_s)
297 -- The selector binds are already in the selector Id's unfoldings
298 -- We don't return the data constructor etc from the class,
299 -- because that's done via the class's TyCon
301 (cls_ids_s, binds_s) = unzip (map mk_implicit classes)
303 mk_implicit clas = (sel_ids, binds)
305 sel_ids = classSelIds clas
306 binds | isLocallyDefined clas = idsToMonoBinds sel_ids
307 | otherwise = EmptyMonoBinds
312 %************************************************************************
314 \subsection[Default methods]{Default methods}
316 %************************************************************************
318 The default methods for a class are each passed a dictionary for the
319 class, so that they get access to the other methods at the same type.
320 So, given the class decl
324 op2 :: Ord b => a -> b -> b -> b
327 op2 x y z = if (op1 x) && (y < z) then y else z
329 we get the default methods:
331 defm.Foo.op1 :: forall a. Foo a => a -> Bool
332 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
334 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
335 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
336 if (op1 a dfoo x) && (< b dord y z) then y else z
339 When we come across an instance decl, we may need to use the default
342 instance Foo Int where {}
346 const.Foo.Int.op1 :: Int -> Bool
347 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
349 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
350 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
352 dfun.Foo.Int :: Foo Int
353 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
355 Notice that, as with method selectors above, we assume that dictionary
356 application is curried, so there's no need to mention the Ord dictionary
357 in const.Foo.Int.op2 (or the type variable).
360 instance Foo a => Foo [a] where {}
362 dfun.Foo.List :: forall a. Foo a -> Foo [a]
364 = /\ a -> \ dfoo_a ->
366 op1 = defm.Foo.op1 [a] dfoo_list
367 op2 = defm.Foo.op2 [a] dfoo_list
368 dfoo_list = (op1, op2)
373 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
374 each local class decl.
377 tcClassDecls2 :: [RenamedHsDecl] -> NF_TcM s (LIE, TcMonoBinds)
381 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
382 [tcClassDecl2 cls_decl | TyClD cls_decl <- decls,
383 isClassDecl cls_decl,
384 isLocallyDefined (tyClDeclName cls_decl)]
386 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
387 tc2 `thenNF_Tc` \ (lie2, binds2) ->
388 returnNF_Tc (lie1 `plusLIE` lie2,
389 binds1 `AndMonoBinds` binds2)
392 @tcClassDecl2@ generates bindings for polymorphic default methods
393 (generic default methods have by now turned into instance declarations)
396 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
397 -> NF_TcM s (LIE, TcMonoBinds)
399 tcClassDecl2 (ClassDecl context class_name
400 tyvar_names _ sigs default_binds pragmas _ src_loc)
401 = -- A locally defined class
402 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
403 tcAddSrcLoc src_loc $
404 tcLookupTy class_name `thenNF_Tc` \ (AClass clas) ->
406 -- We make a separate binding for each default method.
407 -- At one time I used a single AbsBinds for all of them, thus
408 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
409 -- But that desugars into
410 -- ds = \d -> (..., ..., ...)
411 -- dm1 = \d -> case ds d of (a,b,c) -> a
412 -- And since ds is big, it doesn't get inlined, so we don't get good
413 -- default methods. Better to make separate AbsBinds for each
415 (tyvars, _, _, op_items) = classBigSig clas
416 prags = filter isPragSig sigs
417 tc_dm = tcDefMeth clas tyvars default_binds prags
419 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
421 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
424 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
425 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
426 -- Generate code for polymorphic default methods only
427 -- (Generic default methods have turned into instance decls by now.)
428 -- This is incompatible with Hugs, which expects a polymorphic
429 -- default method for every class op, regardless of whether or not
430 -- the programmer supplied an explicit default decl for the class.
431 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
433 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
434 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
436 theta = [(mkClassPred clas inst_tys)]
438 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
440 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
441 tcMethodBind clas origin clas_tyvars inst_tys theta
442 binds_in prags False op_item
443 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
445 tcAddErrCtxt (defltMethCtxt clas) $
447 -- tcMethodBind has checked that the class_tyvars havn't
448 -- been unified with each other or another type, but we must
449 -- still zonk them before passing them to tcSimplifyAndCheck
450 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
454 (ptext SLIT("class") <+> ppr clas)
455 (mkVarSet clas_tyvars')
457 insts_needed `thenTc` \ (const_lie, dict_binds) ->
463 [(clas_tyvars', dm_id, local_dm_id)]
464 emptyNameSet -- No inlines (yet)
465 (dict_binds `andMonoBinds` defm_bind)
467 returnTc (full_bind, const_lie)
469 origin = ClassDeclOrigin
474 %************************************************************************
476 \subsection{Typechecking a method}
478 %************************************************************************
480 @tcMethodBind@ is used to type-check both default-method and
481 instance-decl method declarations. We must type-check methods one at a
482 time, because their signatures may have different contexts and
489 -> [TcTyVar] -- Instantiated type variables for the
490 -- enclosing class/instance decl.
491 -- They'll be signature tyvars, and we
492 -- want to check that they don't get bound
493 -> [TcType] -- Instance types
494 -> TcThetaType -- Available theta; this could be used to check
495 -- the method signature, but actually that's done by
496 -- the caller; here, it's just used for the error message
497 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
498 -> [RenamedSig] -- Pramgas (just for this one)
499 -> Bool -- True <=> This method is from an instance declaration
500 -> ClassOpItem -- The method selector and default-method Id
501 -> TcM s (TcMonoBinds, LIE, (LIE, TcId))
503 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
504 meth_binds prags is_inst_decl (sel_id, dm_info)
505 = tcGetSrcLoc `thenNF_Tc` \ loc ->
506 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
507 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
509 meth_name = idName meth_id
510 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
511 meth_prags = find_prags (idName sel_id) meth_name prags
513 -- Figure out what method binding to use
514 -- If the user suppplied one, use it, else construct a default one
515 (case find_bind (idName sel_id) meth_name meth_binds of
516 Just user_bind -> returnTc user_bind
517 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
518 returnTc (FunMonoBind meth_name False -- Not infix decl
519 [mkSimpleMatch [] rhs Nothing loc] loc)
520 ) `thenTc` \ meth_bind ->
521 -- Check the bindings; first add inst_tyvars to the envt
522 -- so that we don't quantify over them in nested places
523 -- The *caller* put the class/inst decl tyvars into the envt
524 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
525 (tcAddErrCtxt (methodCtxt sel_id) $
526 tcBindWithSigs NotTopLevel meth_bind
527 [sig_info] meth_prags NonRecursive
528 ) `thenTc` \ (binds, insts, _) ->
530 tcExtendLocalValEnv [(meth_name, meth_id)]
531 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
533 -- The prag_lie for a SPECIALISE pragma will mention the function
534 -- itself, so we have to simplify them away right now lest they float
536 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
538 -- Now check that the instance type variables
539 -- (or, in the case of a class decl, the class tyvars)
540 -- have not been unified with anything in the environment
542 -- We do this for each method independently to localise error messages
543 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
544 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
546 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
547 insts `plusLIE` prag_lie',
550 -- The user didn't supply a method binding,
551 -- so we have to make up a default binding
552 -- The RHS of a default method depends on the default-method info
553 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
554 = -- An polymorphic default method
555 returnTc (HsVar (idName dm_id))
557 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
558 = -- No default method
559 -- Warn only if -fwarn-missing-methods
560 warnTc (is_inst_decl && opt_WarnMissingMethods)
561 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
564 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
565 (HsLit (HsString (_PK_ error_msg)))
566 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
569 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
570 = -- A generic default method
571 -- If the method is defined generically, we can only do the job if the
572 -- instance declaration is for a single-parameter type class with
573 -- a type constructor applied to type arguments in the instance decl
574 -- (checkTc, so False provokes the error)
575 checkTc (not is_inst_decl || simple_inst)
576 (badGenericInstance sel_id clas) `thenTc_`
578 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
581 rhs = mkGenericRhs sel_id clas_tyvar tycon
583 stuff = vcat [ppr clas <+> ppr inst_tys,
584 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
586 -- The tycon is only used in the generic case, and in that
587 -- case we require that the instance decl is for a single-parameter
588 -- type class with type variable arguments:
589 -- instance (...) => C (T a b)
590 simple_inst = maybeToBool maybe_tycon
591 clas_tyvar = head (classTyVars clas)
592 Just tycon = maybe_tycon
593 maybe_tycon = case inst_tys of
594 [ty] -> case splitTyConApp_maybe ty of
595 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
602 -- The renamer just puts the selector ID as the binder in the method binding
603 -- but we must use the method name; so we substitute it here. Crude but simple.
604 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
605 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
606 find_bind sel_name meth_name (AndMonoBinds b1 b2)
607 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
608 find_bind sel_name meth_name other = Nothing -- Default case
610 -- Find the prags for this method, and replace the
611 -- selector name with the method name
612 find_prags sel_name meth_name [] = []
613 find_prags sel_name meth_name (SpecSig name ty loc : prags)
614 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
615 find_prags sel_name meth_name (InlineSig name phase loc : prags)
616 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
617 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
618 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
619 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
626 classArityErr class_name
627 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
629 superClassErr clas sc
630 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
631 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
634 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
637 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
640 = hsep [ptext SLIT("Class"), quotes (ppr clas),
641 ptext SLIT("does not have a method"), quotes (ppr op)]
643 omittedMethodWarn sel_id clas
644 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
645 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
647 badGenericMethodType op op_ty
648 = hang (ptext SLIT("Generic method type is too complex"))
649 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
650 ptext SLIT("You can only use type variables, arrows, and tuples")])
652 badGenericInstance sel_id clas
653 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
654 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
655 ptext SLIT("(where T is a derivable type constructor)"),
656 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
659 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
661 genericMultiParamErr clas
662 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
663 ptext SLIT("cannot have generic methods")