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 isClassDecl, isClassOpSig, isPragSig,
17 getClassDeclSysNames, tyClDeclName
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, newDefaultMethodName
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(..), isFrom )
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, 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 %************************************************************************
104 tcClassDecl1 :: RecFlag -> RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 tcClassDecl1 is_rec rec_env
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 = classTyVars 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 is_rec clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
131 -- CHECK THE CLASS SIGNATURES,
132 mapTc (tcClassSig is_rec rec_env clas tyvars dm_info) 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 :: RecFlag -> Class
205 -> RenamedContext -- class context
206 -> [Name] -- Names for superclass selectors
207 -> TcM (ClassContext, -- the superclass context
208 [Id]) -- superclass selector Ids
210 tcSuperClasses is_rec 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 tcRecClassContext is_rec 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 :: RecFlag -> RecTcEnv -- Knot tying only!
240 -> Class -- ...ditto...
241 -> [TyVar] -- The class type variable, used for error check only
242 -> NameEnv (DefMeth Name) -- Info about default methods
244 -> TcM (Type, -- Type of the method
245 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
247 -- This warrants an explanation: we need to separate generic
248 -- default methods and default methods later on in the compiler
249 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
250 -- Class.DefMeth data structure.
252 tcClassSig is_rec unf_env clas clas_tyvars dm_info
253 (ClassOpSig op_name maybe_dm op_ty src_loc)
254 = tcAddSrcLoc src_loc $
256 -- Check the type signature. NB that the envt *already has*
257 -- bindings for the type variables; see comments in TcTyAndClassDcls.
259 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
261 -- Check for ambiguous class op types
263 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
265 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
266 -- The default method's type should really come from the
267 -- iface file, since it could be usage-generalised, but this
268 -- requires altering the mess of knots in TcModule and I'm
269 -- too scared to do that. Instead, I have disabled generalisation
270 -- of types of default methods (and dict funs) by annotating them
271 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
274 -- Build the selector id and default method id
275 sel_id = mkDictSelId op_name clas
277 dm_info_name = maybe_dm `orElse` lookupNameEnv dm_info op_name `orElse` NoDefMeth
279 dm_info_id = case dm_info_name of
280 NoDefMeth -> NoDefMeth
281 GenDefMeth -> GenDefMeth
282 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
284 dm_id = mkDefaultMethodId dm_name clas global_ty
286 -- Check that for a generic method, the type of
287 -- the method is sufficiently simple
288 checkTc (dm_info_name /= GenDefMeth || validGenericMethodType local_ty)
289 (badGenericMethodType op_name op_ty) `thenTc_`
291 returnTc (local_ty, (sel_id, dm_info_id))
295 %************************************************************************
297 \subsection[Default methods]{Default methods}
299 %************************************************************************
301 The default methods for a class are each passed a dictionary for the
302 class, so that they get access to the other methods at the same type.
303 So, given the class decl
307 op2 :: Ord b => a -> b -> b -> b
310 op2 x y z = if (op1 x) && (y < z) then y else z
312 we get the default methods:
314 defm.Foo.op1 :: forall a. Foo a => a -> Bool
315 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
317 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
318 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
319 if (op1 a dfoo x) && (< b dord y z) then y else z
322 When we come across an instance decl, we may need to use the default
325 instance Foo Int where {}
329 const.Foo.Int.op1 :: Int -> Bool
330 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
332 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
333 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
335 dfun.Foo.Int :: Foo Int
336 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
338 Notice that, as with method selectors above, we assume that dictionary
339 application is curried, so there's no need to mention the Ord dictionary
340 in const.Foo.Int.op2 (or the type variable).
343 instance Foo a => Foo [a] where {}
345 dfun.Foo.List :: forall a. Foo a -> Foo [a]
347 = /\ a -> \ dfoo_a ->
349 op1 = defm.Foo.op1 [a] dfoo_list
350 op2 = defm.Foo.op2 [a] dfoo_list
351 dfoo_list = (op1, op2)
356 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
357 each local class decl.
360 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
362 tcClassDecls2 this_mod decls
364 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
365 [tcClassDecl2 cls_decl | cls_decl <- decls,
366 isClassDecl cls_decl,
367 isFrom this_mod (tyClDeclName cls_decl)]
369 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
370 tc2 `thenNF_Tc` \ (lie2, binds2) ->
371 returnNF_Tc (lie1 `plusLIE` lie2,
372 binds1 `AndMonoBinds` binds2)
375 @tcClassDecl2@ generates bindings for polymorphic default methods
376 (generic default methods have by now turned into instance declarations)
379 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
380 -> NF_TcM (LIE, TcMonoBinds)
382 tcClassDecl2 (ClassDecl context class_name
383 tyvar_names _ sigs default_binds _ src_loc)
384 = -- A locally defined class
385 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
386 tcAddSrcLoc src_loc $
387 tcLookupClass class_name `thenNF_Tc` \ clas ->
389 -- We make a separate binding for each default method.
390 -- At one time I used a single AbsBinds for all of them, thus
391 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
392 -- But that desugars into
393 -- ds = \d -> (..., ..., ...)
394 -- dm1 = \d -> case ds d of (a,b,c) -> a
395 -- And since ds is big, it doesn't get inlined, so we don't get good
396 -- default methods. Better to make separate AbsBinds for each
398 (tyvars, _, _, op_items) = classBigSig clas
399 prags = filter isPragSig sigs
400 tc_dm = tcDefMeth clas tyvars default_binds prags
402 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
404 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
407 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
408 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
409 -- Generate code for polymorphic default methods only
410 -- (Generic default methods have turned into instance decls by now.)
411 -- This is incompatible with Hugs, which expects a polymorphic
412 -- default method for every class op, regardless of whether or not
413 -- the programmer supplied an explicit default decl for the class.
414 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
416 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
417 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
419 theta = [(mkClassPred clas inst_tys)]
421 newDicts origin theta `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
423 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
424 tcMethodBind clas origin clas_tyvars inst_tys theta
425 binds_in prags False op_item
426 ) `thenTc` \ (defm_bind, insts_needed, (_, local_dm_id)) ->
428 tcAddErrCtxt (defltMethCtxt clas) $
430 -- tcMethodBind has checked that the class_tyvars havn't
431 -- been unified with each other or another type, but we must
432 -- still zonk them before passing them to tcSimplifyAndCheck
433 zonkTcSigTyVars clas_tyvars `thenNF_Tc` \ clas_tyvars' ->
437 (ptext SLIT("class") <+> ppr clas)
438 (mkVarSet clas_tyvars')
440 insts_needed `thenTc` \ (const_lie, dict_binds) ->
446 [(clas_tyvars', dm_id, local_dm_id)]
447 emptyNameSet -- No inlines (yet)
448 (dict_binds `andMonoBinds` defm_bind)
450 returnTc (full_bind, const_lie)
452 origin = ClassDeclOrigin
457 %************************************************************************
459 \subsection{Typechecking a method}
461 %************************************************************************
463 @tcMethodBind@ is used to type-check both default-method and
464 instance-decl method declarations. We must type-check methods one at a
465 time, because their signatures may have different contexts and
472 -> [TcTyVar] -- Instantiated type variables for the
473 -- enclosing class/instance decl.
474 -- They'll be signature tyvars, and we
475 -- want to check that they don't get bound
476 -> [TcType] -- Instance types
477 -> TcThetaType -- Available theta; this could be used to check
478 -- the method signature, but actually that's done by
479 -- the caller; here, it's just used for the error message
480 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
481 -> [RenamedSig] -- Pramgas (just for this one)
482 -> Bool -- True <=> This method is from an instance declaration
483 -> ClassOpItem -- The method selector and default-method Id
484 -> TcM (TcMonoBinds, LIE, (LIE, TcId))
486 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
487 meth_binds prags is_inst_decl (sel_id, dm_info)
488 = tcGetSrcLoc `thenNF_Tc` \ loc ->
489 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth@(_, meth_id) ->
490 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
492 meth_name = idName meth_id
493 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
494 meth_prags = find_prags (idName sel_id) meth_name prags
496 -- Figure out what method binding to use
497 -- If the user suppplied one, use it, else construct a default one
498 (case find_bind (idName sel_id) meth_name meth_binds of
499 Just user_bind -> returnTc user_bind
500 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
501 returnTc (FunMonoBind meth_name False -- Not infix decl
502 [mkSimpleMatch [] rhs Nothing loc] loc)
503 ) `thenTc` \ meth_bind ->
504 -- Check the bindings; first add inst_tyvars to the envt
505 -- so that we don't quantify over them in nested places
506 -- The *caller* put the class/inst decl tyvars into the envt
507 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
508 (tcAddErrCtxt (methodCtxt sel_id) $
509 tcBindWithSigs NotTopLevel meth_bind
510 [sig_info] meth_prags NonRecursive
511 ) `thenTc` \ (binds, insts, _) ->
513 tcExtendLocalValEnv [(meth_name, meth_id)]
514 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
516 -- The prag_lie for a SPECIALISE pragma will mention the function
517 -- itself, so we have to simplify them away right now lest they float
519 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
521 -- Now check that the instance type variables
522 -- (or, in the case of a class decl, the class tyvars)
523 -- have not been unified with anything in the environment
525 -- We do this for each method independently to localise error messages
526 -- ...and this is why the call to tcExtendGlobalTyVars must be here
527 -- rather than in the caller
528 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
529 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
531 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
532 insts `plusLIE` prag_lie',
535 -- The user didn't supply a method binding,
536 -- so we have to make up a default binding
537 -- The RHS of a default method depends on the default-method info
538 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
539 = -- An polymorphic default method
540 returnTc (HsVar (idName dm_id))
542 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
543 = -- No default method
544 -- Warn only if -fwarn-missing-methods
545 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
546 warnTc (is_inst_decl && warn)
547 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
550 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
551 (HsLit (HsString (_PK_ error_msg)))
552 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
555 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
556 = -- A generic default method
557 -- If the method is defined generically, we can only do the job if the
558 -- instance declaration is for a single-parameter type class with
559 -- a type constructor applied to type arguments in the instance decl
560 -- (checkTc, so False provokes the error)
561 checkTc (not is_inst_decl || simple_inst)
562 (badGenericInstance sel_id clas) `thenTc_`
564 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
567 rhs = mkGenericRhs sel_id clas_tyvar tycon
569 stuff = vcat [ppr clas <+> ppr inst_tys,
570 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
572 -- The tycon is only used in the generic case, and in that
573 -- case we require that the instance decl is for a single-parameter
574 -- type class with type variable arguments:
575 -- instance (...) => C (T a b)
576 simple_inst = maybeToBool maybe_tycon
577 clas_tyvar = head (classTyVars clas)
578 Just tycon = maybe_tycon
579 maybe_tycon = case inst_tys of
580 [ty] -> case splitTyConApp_maybe ty of
581 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
588 -- The renamer just puts the selector ID as the binder in the method binding
589 -- but we must use the method name; so we substitute it here. Crude but simple.
590 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
591 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
592 find_bind sel_name meth_name (AndMonoBinds b1 b2)
593 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
594 find_bind sel_name meth_name other = Nothing -- Default case
596 -- Find the prags for this method, and replace the
597 -- selector name with the method name
598 find_prags sel_name meth_name [] = []
599 find_prags sel_name meth_name (SpecSig name ty loc : prags)
600 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
601 find_prags sel_name meth_name (InlineSig name phase loc : prags)
602 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
603 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
604 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
605 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
612 classArityErr class_name
613 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
615 superClassErr clas sc
616 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
617 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
620 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
623 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
626 = hsep [ptext SLIT("Class"), quotes (ppr clas),
627 ptext SLIT("does not have a method"), quotes (ppr op)]
629 omittedMethodWarn sel_id clas
630 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
631 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
633 badGenericMethodType op op_ty
634 = hang (ptext SLIT("Generic method type is too complex"))
635 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
636 ptext SLIT("You can only use type variables, arrows, and tuples")])
638 badGenericInstance sel_id clas
639 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
640 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
641 ptext SLIT("(where T is a derivable type constructor)"),
642 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
645 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
647 genericMultiParamErr clas
648 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
649 ptext SLIT("cannot have generic methods")