2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, tcClassDecls2,
8 tcMethodBind, badMethodErr
11 #include "HsVersions.h"
13 import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..),
14 HsExpr(..), HsLit(..), HsType(..), HsPred(..),
15 mkSimpleMatch, andMonoBinds, andMonoBindList,
16 isClassOpSig, isPragSig,
19 import BasicTypes ( TopLevelFlag(..), RecFlag(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
22 RenamedContext, RenamedSig,
25 import TcHsSyn ( TcMonoBinds )
27 import Inst ( InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
29 import TcEnv ( TcId, TcEnv, RecTcEnv, TyThingDetails(..), tcAddImportedIdInfo,
30 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
31 tcExtendLocalValEnv, tcExtendTyVarEnv
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcMonoType ( tcHsRecType, tcRecClassContext, 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, 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 Module ( Module )
46 import Name ( Name, NamedThing(..) )
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 )
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 %************************************************************************
104 tcClassDecl1 :: RecFlag -> RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 tcClassDecl1 is_rec rec_env
106 (ClassDecl {tcdCtxt = context, tcdName = class_name,
107 tcdTyVars = tyvar_names, tcdFDs = fundeps,
108 tcdSigs = class_sigs, tcdMeths = def_methods,
109 tcdSysNames = sys_names, tcdLoc = src_loc})
110 = -- CHECK ARITY 1 FOR HASKELL 1.4
111 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
112 checkTc (glaExts || length tyvar_names == 1)
113 (classArityErr class_name) `thenTc_`
115 -- LOOK THINGS UP IN THE ENVIRONMENT
116 tcLookupClass class_name `thenTc` \ clas ->
118 tyvars = classTyVars clas
119 op_sigs = filter isClassOpSig class_sigs
120 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
121 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
123 tcExtendTyVarEnv tyvars $
125 -- SOURCE-CODE CONSISTENCY CHECKS
127 Nothing -> returnTc Nothing -- Not source
128 Just dms -> checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
129 checkGenericClassIsUnary clas dm_env `thenTc_`
130 returnTc (Just dm_env)
131 ) `thenTc` \ mb_dm_env ->
134 tcSuperClasses is_rec clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
136 -- CHECK THE CLASS SIGNATURES,
137 mapTc (tcClassSig is_rec rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
139 -- MAKE THE CLASS DETAILS
141 (op_tys, op_items) = unzip sig_stuff
142 sc_tys = mkDictTys sc_theta
143 dict_component_tys = sc_tys ++ op_tys
145 dict_con = mkDataCon datacon_name
146 [notMarkedStrict | _ <- dict_component_tys]
147 [{- No labelled fields -}]
150 [{-No existential tyvars-}] [{-Or context-}]
153 dict_con_id dict_wrap_id
155 dict_con_id = mkDataConId datacon_wkr_name dict_con
156 dict_wrap_id = mkDataConWrapId dict_con
158 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
162 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds
163 -> TcM (NameEnv Bool)
164 -- The returned environment says
165 -- x not in env => no default method
166 -- x -> True => generic default method
167 -- x -> False => polymorphic default method
169 -- Check default bindings
170 -- a) must be for a class op for this class
171 -- b) must be all generic or all non-generic
172 -- and return a mapping from class-op to DefMeth info
174 -- But do all this only for source binds
176 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
178 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
179 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
180 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
181 returnTc (dm_info1 `plusNameEnv` dm_info2)
183 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
186 -- Check that the op is from this class
187 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
189 -- Check that all the defns ar generic, or none are
190 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
192 returnTc (unitNameEnv op all_generic)
194 n_generic = count (maybeToBool . maybeGenericMatch) matches
195 none_generic = n_generic == 0
196 all_generic = n_generic == length matches
198 checkGenericClassIsUnary clas dm_env
199 = -- Check that if the class has generic methods, then the
200 -- class has only one parameter. We can't do generic
201 -- multi-parameter type classes!
202 checkTc (unary || no_generics) (genericMultiParamErr clas)
204 unary = length (classTyVars clas) == 1
205 no_generics = not (or (nameEnvElts dm_env))
210 tcSuperClasses :: RecFlag -> Class
211 -> RenamedContext -- class context
212 -> [Name] -- Names for superclass selectors
213 -> TcM (ClassContext, -- the superclass context
214 [Id]) -- superclass selector Ids
216 tcSuperClasses is_rec clas context sc_sel_names
217 = -- Check the context.
218 -- The renamer has already checked that the context mentions
219 -- only the type variable of the class decl.
221 -- For std Haskell check that the context constrains only tyvars
222 doptsTc Opt_GlasgowExts `thenTc` \ glaExts ->
226 mapTc_ check_constraint context
229 -- Context is already kind-checked
230 tcRecClassContext is_rec context `thenTc` \ sc_theta ->
232 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
235 returnTc (sc_theta, sc_sel_ids)
238 check_constraint sc@(HsPClass c tys)
239 = checkTc (all is_tyvar tys) (superClassErr clas sc)
241 is_tyvar (HsTyVar _) = True
242 is_tyvar other = False
245 tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
246 -> Class -- ...ditto...
247 -> [TyVar] -- The class type variable, used for error check only
248 -> Maybe (NameEnv Bool) -- Info about default methods
250 -> TcM (Type, -- Type of the method
251 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
253 -- This warrants an explanation: we need to separate generic
254 -- default methods and default methods later on in the compiler
255 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
256 -- Class.DefMeth data structure.
258 tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
259 (ClassOpSig op_name sig_dm op_ty src_loc)
260 = tcAddSrcLoc src_loc $
262 -- Check the type signature. NB that the envt *already has*
263 -- bindings for the type variables; see comments in TcTyAndClassDcls.
265 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
267 -- Check for ambiguous class op types
269 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
271 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
272 -- The default method's type should really come from the
273 -- iface file, since it could be usage-generalised, but this
274 -- requires altering the mess of knots in TcModule and I'm
275 -- too scared to do that. Instead, I have disabled generalisation
276 -- of types of default methods (and dict funs) by annotating them
277 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
280 -- Build the selector id and default method id
281 sel_id = mkDictSelId op_name clas
282 dm_id = mkDefaultMethodId dm_name clas global_ty
283 DefMeth dm_name = sig_dm
285 dm_info = case maybe_dm_env of
286 Nothing -> iface_dm_info
287 Just dm_env -> mk_src_dm_info dm_env
289 iface_dm_info = case sig_dm of
290 NoDefMeth -> NoDefMeth
291 GenDefMeth -> GenDefMeth
292 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
294 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
296 Just True -> GenDefMeth
297 Just False -> DefMeth dm_id
299 -- Check that for a generic method, the type of
300 -- the method is sufficiently simple
301 checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
302 (badGenericMethodType op_name op_ty) `thenTc_`
304 returnTc (local_ty, (sel_id, dm_info))
308 %************************************************************************
310 \subsection[Default methods]{Default methods}
312 %************************************************************************
314 The default methods for a class are each passed a dictionary for the
315 class, so that they get access to the other methods at the same type.
316 So, given the class decl
320 op2 :: Ord b => a -> b -> b -> b
323 op2 x y z = if (op1 x) && (y < z) then y else z
325 we get the default methods:
327 defm.Foo.op1 :: forall a. Foo a => a -> Bool
328 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
330 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
331 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
332 if (op1 a dfoo x) && (< b dord y z) then y else z
335 When we come across an instance decl, we may need to use the default
338 instance Foo Int where {}
342 const.Foo.Int.op1 :: Int -> Bool
343 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
345 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
346 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
348 dfun.Foo.Int :: Foo Int
349 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
351 Notice that, as with method selectors above, we assume that dictionary
352 application is curried, so there's no need to mention the Ord dictionary
353 in const.Foo.Int.op2 (or the type variable).
356 instance Foo a => Foo [a] where {}
358 dfun.Foo.List :: forall a. Foo a -> Foo [a]
360 = /\ a -> \ dfoo_a ->
362 op1 = defm.Foo.op1 [a] dfoo_list
363 op2 = defm.Foo.op2 [a] dfoo_list
364 dfoo_list = (op1, op2)
369 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
370 each local class decl.
373 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
375 tcClassDecls2 this_mod decls
377 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
378 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
379 -- The 'Just' picks out source ClassDecls
381 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
382 tc2 `thenNF_Tc` \ (lie2, binds2) ->
383 returnNF_Tc (lie1 `plusLIE` lie2,
384 binds1 `AndMonoBinds` binds2)
387 @tcClassDecl2@ generates bindings for polymorphic default methods
388 (generic default methods have by now turned into instance declarations)
391 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
392 -> NF_TcM (LIE, TcMonoBinds)
394 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
395 tcdMeths = Just default_binds, tcdLoc = src_loc})
396 = -- The 'Just' picks out source ClassDecls
397 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
398 tcAddSrcLoc src_loc $
399 tcLookupClass class_name `thenNF_Tc` \ clas ->
401 -- We make a separate binding for each default method.
402 -- At one time I used a single AbsBinds for all of them, thus
403 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
404 -- But that desugars into
405 -- ds = \d -> (..., ..., ...)
406 -- dm1 = \d -> case ds d of (a,b,c) -> a
407 -- And since ds is big, it doesn't get inlined, so we don't get good
408 -- default methods. Better to make separate AbsBinds for each
410 (tyvars, _, _, op_items) = classBigSig clas
411 prags = filter isPragSig sigs
412 tc_dm = tcDefMeth clas tyvars default_binds prags
414 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
416 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
419 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
420 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
421 -- Generate code for polymorphic default methods only
422 -- (Generic default methods have turned into instance decls by now.)
423 -- This is incompatible with Hugs, which expects a polymorphic
424 -- default method for every class op, regardless of whether or not
425 -- the programmer supplied an explicit default decl for the class.
426 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
428 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
429 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
431 theta = [(mkClassPred clas inst_tys)]
433 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
435 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
436 tcMethodBind clas origin clas_tyvars inst_tys theta
437 binds_in prags False op_item
438 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
440 tcAddErrCtxt (defltMethCtxt clas) $
442 -- tcMethodBind has checked that the class_tyvars havn't
443 -- been unified with each other or another type, but we must
444 -- still zonk them before passing them to tcSimplifyAndCheck
445 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
449 (ptext SLIT("class") <+> ppr clas)
450 (mkVarSet clas_tyvars')
452 insts_needed `thenTc` \ (const_lie, dict_binds) ->
458 [(clas_tyvars', dm_id, local_dm_id)]
459 emptyNameSet -- No inlines (yet)
460 (dict_binds `andMonoBinds` defm_bind)
462 returnTc (full_bind, const_lie)
464 origin = ClassDeclOrigin
469 %************************************************************************
471 \subsection{Typechecking a method}
473 %************************************************************************
475 @tcMethodBind@ is used to type-check both default-method and
476 instance-decl method declarations. We must type-check methods one at a
477 time, because their signatures may have different contexts and
484 -> [TcTyVar] -- Instantiated type variables for the
485 -- enclosing class/instance decl.
486 -- They'll be signature tyvars, and we
487 -- want to check that they don't get bound
488 -> [TcType] -- Instance types
489 -> TcThetaType -- Available theta; this could be used to check
490 -- the method signature, but actually that's done by
491 -- the caller; here, it's just used for the error message
492 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
493 -> [RenamedSig] -- Pramgas (just for this one)
494 -> Bool -- True <=> This method is from an instance declaration
495 -> ClassOpItem -- The method selector and default-method Id
496 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
498 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
499 meth_binds prags is_inst_decl (sel_id, dm_info)
500 = tcGetSrcLoc `thenNF_Tc` \ loc ->
501 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
502 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
504 meth_name = idName meth_id
505 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
506 meth_prags = find_prags (idName sel_id) meth_name prags
508 -- Figure out what method binding to use
509 -- If the user suppplied one, use it, else construct a default one
510 (case find_bind (idName sel_id) meth_name meth_binds of
511 Just user_bind -> returnTc user_bind
512 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
513 returnTc (FunMonoBind meth_name False -- Not infix decl
514 [mkSimpleMatch [] rhs Nothing loc] loc)
515 ) `thenTc` \ meth_bind ->
516 -- Check the bindings; first add inst_tyvars to the envt
517 -- so that we don't quantify over them in nested places
518 -- The *caller* put the class/inst decl tyvars into the envt
519 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
520 (tcAddErrCtxt (methodCtxt sel_id) $
521 tcBindWithSigs NotTopLevel meth_bind
522 [sig_info] meth_prags NonRecursive
523 ) `thenTc` \ (binds, insts, _) ->
525 tcExtendLocalValEnv [(meth_name, meth_id)]
526 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
528 -- The prag_lie for a SPECIALISE pragma will mention the function
529 -- itself, so we have to simplify them away right now lest they float
531 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
533 -- Now check that the instance type variables
534 -- (or, in the case of a class decl, the class tyvars)
535 -- have not been unified with anything in the environment
537 -- We do this for each method independently to localise error messages
538 -- ...and this is why the call to tcExtendGlobalTyVars must be here
539 -- rather than in the caller
540 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
541 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
543 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
544 insts `plusLIE` prag_lie',
547 -- The user didn't supply a method binding,
548 -- so we have to make up a default binding
549 -- The RHS of a default method depends on the default-method info
550 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
551 = -- An polymorphic default method
552 returnTc (HsVar (idName dm_id))
554 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
555 = -- No default method
556 -- Warn only if -fwarn-missing-methods
557 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
558 warnTc (is_inst_decl && warn)
559 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
562 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
563 (HsLit (HsString (_PK_ error_msg)))
564 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
567 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
568 = -- A generic default method
569 -- If the method is defined generically, we can only do the job if the
570 -- instance declaration is for a single-parameter type class with
571 -- a type constructor applied to type arguments in the instance decl
572 -- (checkTc, so False provokes the error)
573 checkTc (not is_inst_decl || simple_inst)
574 (badGenericInstance sel_id clas) `thenTc_`
576 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
579 rhs = mkGenericRhs sel_id clas_tyvar tycon
581 stuff = vcat [ppr clas <+> ppr inst_tys,
582 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
584 -- The tycon is only used in the generic case, and in that
585 -- case we require that the instance decl is for a single-parameter
586 -- type class with type variable arguments:
587 -- instance (...) => C (T a b)
588 simple_inst = maybeToBool maybe_tycon
589 clas_tyvar = head (classTyVars clas)
590 Just tycon = maybe_tycon
591 maybe_tycon = case inst_tys of
592 [ty] -> case splitTyConApp_maybe ty of
593 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
600 -- The renamer just puts the selector ID as the binder in the method binding
601 -- but we must use the method name; so we substitute it here. Crude but simple.
602 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
603 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
604 find_bind sel_name meth_name (AndMonoBinds b1 b2)
605 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
606 find_bind sel_name meth_name other = Nothing -- Default case
608 -- Find the prags for this method, and replace the
609 -- selector name with the method name
610 find_prags sel_name meth_name [] = []
611 find_prags sel_name meth_name (SpecSig name ty loc : prags)
612 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
613 find_prags sel_name meth_name (InlineSig name phase loc : prags)
614 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
615 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
616 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
617 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
624 classArityErr class_name
625 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
627 superClassErr clas sc
628 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
629 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
632 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
635 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
638 = hsep [ptext SLIT("Class"), quotes (ppr clas),
639 ptext SLIT("does not have a method"), quotes (ppr op)]
641 omittedMethodWarn sel_id clas
642 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
643 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
645 badGenericMethodType op op_ty
646 = hang (ptext SLIT("Generic method type is too complex"))
647 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
648 ptext SLIT("You can only use type variables, arrows, and tuples")])
650 badGenericInstance sel_id clas
651 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
652 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
653 ptext SLIT("(where T is a derivable type constructor)"),
654 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
657 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
659 genericMultiParamErr clas
660 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
661 ptext SLIT("cannot have generic methods")