2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, checkValidClass, tcClassDecls2,
8 tcMethodBind, mkMethodBind, badMethodErr
11 #include "HsVersions.h"
13 import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..),
14 HsExpr(..), HsLit(..),
15 mkSimpleMatch, andMonoBinds, andMonoBindList,
16 isClassOpSig, isPragSig,
17 getClassDeclSysNames, placeHolderType
19 import BasicTypes ( RecFlag(..), StrictnessMark(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
24 import TcHsSyn ( TcMonoBinds )
26 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
27 instToId, newDicts, newMethod )
28 import TcEnv ( TyThingDetails(..),
29 tcLookupClass, tcExtendTyVarEnv2,
32 import TcBinds ( tcMonoBinds )
33 import TcMonoType ( TcSigInfo(..), tcHsType, tcHsTheta, mkTcSig )
34 import TcSimplify ( tcSimplifyCheck )
35 import TcUnify ( checkSigTyVars, sigCtxt )
36 import TcMType ( tcInstTyVars, checkValidTheta, checkValidType, SourceTyCtxt(..), UserTypeCtxt(..) )
37 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
38 mkTyVarTys, mkPredTys, mkClassPred,
39 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitSigmaTy
42 import Generics ( mkGenericRhs, validGenericMethodType )
43 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
44 import Class ( classTyVars, classBigSig, classTyCon, className,
45 Class, ClassOpItem, DefMeth (..) )
46 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
47 import DataCon ( mkDataCon )
48 import Id ( Id, idType, idName, setIdLocalExported )
49 import Module ( Module )
50 import Name ( Name, NamedThing(..) )
51 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
52 import NameSet ( emptyNameSet )
56 import ErrUtils ( dumpIfSet )
57 import Util ( count, isSingleton, lengthIs, equalLength )
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 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
106 tcdTyVars = tyvar_names, tcdFDs = fundeps,
107 tcdSigs = class_sigs, tcdMeths = def_methods,
108 tcdSysNames = sys_names, tcdLoc = src_loc})
109 = -- LOOK THINGS UP IN THE ENVIRONMENT
110 tcLookupClass class_name `thenTc` \ clas ->
112 tyvars = classTyVars clas
113 op_sigs = filter isClassOpSig class_sigs
114 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
115 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
117 tcExtendTyVarEnv tyvars $
119 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
122 -- The renamer has already checked that the context mentions
123 -- only the type variable of the class decl.
124 -- Context is already kind-checked
125 ASSERT( equalLength context sc_sel_names )
126 tcHsTheta context `thenTc` \ sc_theta ->
128 -- CHECK THE CLASS SIGNATURES,
129 mapTc (tcClassSig clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
131 -- MAKE THE CLASS DETAILS
133 (op_tys, op_items) = unzip sig_stuff
134 sc_tys = mkPredTys sc_theta
135 dict_component_tys = sc_tys ++ op_tys
136 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
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] -> Maybe RenamedMonoBinds
156 -> TcM (Maybe (NameEnv Bool))
157 -- The returned environment says
158 -- x not in env => no default method
159 -- x -> True => generic default method
160 -- x -> False => polymorphic default method
162 -- Check default bindings
163 -- a) must be for a class op for this class
164 -- b) must be all generic or all non-generic
165 -- and return a mapping from class-op to DefMeth info
167 -- But do all this only for source binds
169 checkDefaultBinds clas ops Nothing
172 checkDefaultBinds clas ops (Just mbs)
173 = go mbs `thenTc` \ dm_env ->
174 returnTc (Just dm_env)
176 go EmptyMonoBinds = returnTc emptyNameEnv
178 go (AndMonoBinds b1 b2)
179 = go b1 `thenTc` \ dm_info1 ->
180 go b2 `thenTc` \ dm_info2 ->
181 returnTc (dm_info1 `plusNameEnv` dm_info2)
183 go (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 = matches `lengthIs` n_generic
201 tcClassSig :: Class -- ...ditto...
202 -> [TyVar] -- The class type variable, used for error check only
203 -> Maybe (NameEnv Bool) -- Info about default methods;
204 -- Nothing => imported class defn with no method binds
206 -> TcM (Type, -- Type of the method
207 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
209 -- This warrants an explanation: we need to separate generic
210 -- default methods and default methods later on in the compiler
211 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
212 -- Class.DefMeth data structure.
214 tcClassSig clas clas_tyvars maybe_dm_env
215 (ClassOpSig op_name sig_dm op_ty src_loc)
216 = tcAddSrcLoc src_loc $
218 -- Check the type signature. NB that the envt *already has*
219 -- bindings for the type variables; see comments in TcTyAndClassDcls.
220 tcHsType op_ty `thenTc` \ local_ty ->
223 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
225 -- Build the selector id and default method id
226 sel_id = mkDictSelId op_name clas
227 DefMeth dm_name = sig_dm
229 dm_info = case maybe_dm_env of
231 Just dm_env -> mk_src_dm_info dm_env
233 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
235 Just True -> GenDefMeth
236 Just False -> DefMeth dm_name
238 returnTc (local_ty, (sel_id, dm_info))
241 checkValidClass is called once the mutually-recursive knot has been
242 tied, so we can look at things freely.
245 checkValidClass :: Class -> TcM ()
247 = -- CHECK ARITY 1 FOR HASKELL 1.4
248 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
250 -- Check that the class is unary, unless GlaExs
251 checkTc (not (null tyvars)) (nullaryClassErr cls) `thenTc_`
252 checkTc (gla_exts || unary) (classArityErr cls) `thenTc_`
254 -- Check the super-classes
255 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
257 -- Check the class operations
258 mapTc_ check_op op_stuff `thenTc_`
260 -- Check that if the class has generic methods, then the
261 -- class has only one parameter. We can't do generic
262 -- multi-parameter type classes!
263 checkTc (unary || no_generics) (genericMultiParamErr cls)
266 (tyvars, theta, _, op_stuff) = classBigSig cls
267 unary = isSingleton tyvars
268 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
270 check_op (sel_id, dm)
271 = checkValidTheta SigmaCtxt (tail theta) `thenTc_`
272 -- The 'tail' removes the initial (C a) from the
273 -- class itself, leaving just the method type
275 checkValidType (FunSigCtxt op_name) tau `thenTc_`
277 -- Check that for a generic method, the type of
278 -- the method is sufficiently simple
279 checkTc (dm /= GenDefMeth || validGenericMethodType op_ty)
280 (badGenericMethodType op_name op_ty)
282 op_name = idName sel_id
283 op_ty = idType sel_id
284 (_,theta,tau) = tcSplitSigmaTy op_ty
288 %************************************************************************
290 \subsection[Default methods]{Default methods}
292 %************************************************************************
294 The default methods for a class are each passed a dictionary for the
295 class, so that they get access to the other methods at the same type.
296 So, given the class decl
300 op2 :: Ord b => a -> b -> b -> b
303 op2 x y z = if (op1 x) && (y < z) then y else z
305 we get the default methods:
307 defm.Foo.op1 :: forall a. Foo a => a -> Bool
308 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
310 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
311 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
312 if (op1 a dfoo x) && (< b dord y z) then y else z
315 When we come across an instance decl, we may need to use the default
318 instance Foo Int where {}
322 const.Foo.Int.op1 :: Int -> Bool
323 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
325 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
326 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
328 dfun.Foo.Int :: Foo Int
329 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
331 Notice that, as with method selectors above, we assume that dictionary
332 application is curried, so there's no need to mention the Ord dictionary
333 in const.Foo.Int.op2 (or the type variable).
336 instance Foo a => Foo [a] where {}
338 dfun.Foo.List :: forall a. Foo a -> Foo [a]
340 = /\ a -> \ dfoo_a ->
342 op1 = defm.Foo.op1 [a] dfoo_list
343 op2 = defm.Foo.op2 [a] dfoo_list
344 dfoo_list = (op1, op2)
349 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
350 each local class decl.
353 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
355 tcClassDecls2 this_mod decls
357 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
358 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
359 -- The 'Just' picks out source ClassDecls
361 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
362 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
363 returnNF_Tc (lie1 `plusLIE` lie2,
364 binds1 `AndMonoBinds` binds2,
368 @tcClassDecl2@ generates bindings for polymorphic default methods
369 (generic default methods have by now turned into instance declarations)
372 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
373 -> NF_TcM (LIE, TcMonoBinds, [Id])
375 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
376 tcdMeths = Just default_binds, tcdLoc = src_loc})
377 = -- The 'Just' picks out source ClassDecls
378 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
379 tcAddSrcLoc src_loc $
380 tcLookupClass class_name `thenNF_Tc` \ clas ->
382 -- We make a separate binding for each default method.
383 -- At one time I used a single AbsBinds for all of them, thus
384 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
385 -- But that desugars into
386 -- ds = \d -> (..., ..., ...)
387 -- dm1 = \d -> case ds d of (a,b,c) -> a
388 -- And since ds is big, it doesn't get inlined, so we don't get good
389 -- default methods. Better to make separate AbsBinds for each
391 (tyvars, _, _, op_items) = classBigSig clas
392 prags = filter isPragSig sigs
393 tc_dm = tcDefMeth clas tyvars default_binds prags
395 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
397 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
400 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
401 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
402 -- Generate code for polymorphic default methods only
403 -- (Generic default methods have turned into instance decls by now.)
404 -- This is incompatible with Hugs, which expects a polymorphic
405 -- default method for every class op, regardless of whether or not
406 -- the programmer supplied an explicit default decl for the class.
407 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
409 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
410 = tcInstTyVars ClsTv tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
412 dm_ty = idType sel_id -- Same as dict selector!
413 -- The default method's type should really come from the
414 -- iface file, since it could be usage-generalised, but this
415 -- requires altering the mess of knots in TcModule and I'm
416 -- too scared to do that. Instead, I have disabled generalisation
417 -- of types of default methods (and dict funs) by annotating them
418 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
420 theta = [mkClassPred clas inst_tys]
421 dm_id = mkDefaultMethodId dm_name dm_ty
422 local_dm_id = setIdLocalExported dm_id
423 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
424 xtve = tyvars `zip` clas_tyvars
426 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
428 mkMethodBind origin clas inst_tys binds_in op_item `thenTc` \ (dm_inst, meth_info) ->
429 tcMethodBind xtve clas_tyvars theta
430 [this_dict] meth_info `thenTc` \ (defm_bind, insts_needed) ->
432 tcAddErrCtxt (defltMethCtxt clas) $
436 (ptext SLIT("class") <+> ppr clas)
439 insts_needed `thenTc` \ (const_lie, dict_binds) ->
441 -- Simplification can do unification
442 checkSigTyVars clas_tyvars `thenTc` \ clas_tyvars' ->
448 [(clas_tyvars', local_dm_id, instToId dm_inst)]
449 emptyNameSet -- No inlines (yet)
450 (dict_binds `andMonoBinds` defm_bind)
452 returnTc (full_bind, const_lie, [dm_id])
454 origin = ClassDeclOrigin
459 %************************************************************************
461 \subsection{Typechecking a method}
463 %************************************************************************
465 @tcMethodBind@ is used to type-check both default-method and
466 instance-decl method declarations. We must type-check methods one at a
467 time, because their signatures may have different contexts and
472 :: [(TyVar,TcTyVar)] -- Bindings for type environment
473 -> [TcTyVar] -- Instantiated type variables for the
474 -- enclosing class/instance decl.
475 -- They'll be signature tyvars, and we
476 -- want to check that they don't get bound
477 -- Always equal the range of the type envt
478 -> TcThetaType -- Available theta; it's just used for the error message
479 -> [Inst] -- Available from context, used to simplify constraints
480 -- from the method body
481 -> (Id, TcSigInfo, RenamedMonoBinds) -- Details of this method
482 -> TcM (TcMonoBinds, LIE)
484 tcMethodBind xtve inst_tyvars inst_theta avail_insts
485 (sel_id, meth_sig, meth_bind)
487 -- Check the bindings; first adding inst_tyvars to the envt
488 -- so that we don't quantify over them in nested places
489 tcExtendTyVarEnv2 xtve (
490 tcAddErrCtxt (methodCtxt sel_id) $
491 tcMonoBinds meth_bind [meth_sig] NonRecursive
492 ) `thenTc` \ (meth_bind, meth_lie, _, _) ->
494 -- Now do context reduction. We simplify wrt both the local tyvars
495 -- and the ones of the class/instance decl, so that there is
498 -- op :: Eq a => a -> b -> a
500 -- We do this for each method independently to localise error messages
503 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
505 tcAddErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
506 newDicts SignatureOrigin meth_theta `thenNF_Tc` \ meth_dicts ->
508 all_tyvars = meth_tvs ++ inst_tyvars
509 all_insts = avail_insts ++ meth_dicts
512 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
513 all_tyvars all_insts meth_lie `thenTc` \ (lie, lie_binds) ->
515 checkSigTyVars all_tyvars `thenTc` \ all_tyvars' ->
518 meth_tvs' = take (length meth_tvs) all_tyvars'
519 poly_meth_bind = AbsBinds meth_tvs'
520 (map instToId meth_dicts)
521 [(meth_tvs', meth_id, local_meth_id)]
522 emptyNameSet -- Inlines?
523 (lie_binds `andMonoBinds` meth_bind)
525 returnTc (poly_meth_bind, lie)
528 mkMethodBind :: InstOrigin
529 -> Class -> [TcType] -- Class and instance types
530 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
532 -> TcM (Inst, -- Method inst
533 (Id, -- Global selector Id
534 TcSigInfo, -- Signature
535 RenamedMonoBinds)) -- Binding for the method
537 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
538 = tcGetSrcLoc `thenNF_Tc` \ loc ->
539 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth_inst ->
541 meth_id = instToId meth_inst
542 meth_name = idName meth_id
544 -- Figure out what method binding to use
545 -- If the user suppplied one, use it, else construct a default one
546 (case find_bind (idName sel_id) meth_name meth_binds of
547 Just user_bind -> returnTc user_bind
548 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
549 returnTc (FunMonoBind meth_name False -- Not infix decl
550 [mkSimpleMatch [] rhs placeHolderType loc] loc)
551 ) `thenTc` \ meth_bind ->
553 mkTcSig meth_id loc `thenNF_Tc` \ meth_sig ->
555 returnTc (meth_inst, (sel_id, meth_sig, meth_bind))
558 -- The user didn't supply a method binding,
559 -- so we have to make up a default binding
560 -- The RHS of a default method depends on the default-method info
561 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
562 = -- An polymorphic default method
563 returnTc (HsVar dm_name)
565 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
566 = -- No default method
567 -- Warn only if -fwarn-missing-methods
568 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
569 warnTc (isInstDecl origin && warn)
570 (omittedMethodWarn sel_id) `thenNF_Tc_`
573 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
574 (HsLit (HsString (_PK_ error_msg)))
575 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
578 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
579 = -- A generic default method
580 -- If the method is defined generically, we can only do the job if the
581 -- instance declaration is for a single-parameter type class with
582 -- a type constructor applied to type arguments in the instance decl
583 -- (checkTc, so False provokes the error)
584 checkTc (not (isInstDecl origin) || simple_inst)
585 (badGenericInstance sel_id) `thenTc_`
587 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
590 rhs = mkGenericRhs sel_id clas_tyvar tycon
592 stuff = vcat [ppr clas <+> ppr inst_tys,
593 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
595 -- The tycon is only used in the generic case, and in that
596 -- case we require that the instance decl is for a single-parameter
597 -- type class with type variable arguments:
598 -- instance (...) => C (T a b)
599 simple_inst = maybeToBool maybe_tycon
600 clas_tyvar = head (classTyVars clas)
601 Just tycon = maybe_tycon
602 maybe_tycon = case inst_tys of
603 [ty] -> case tcSplitTyConApp_maybe ty of
604 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
608 isInstDecl InstanceDeclOrigin = True
609 isInstDecl ClassDeclOrigin = False
614 -- The renamer just puts the selector ID as the binder in the method binding
615 -- but we must use the method name; so we substitute it here. Crude but simple.
616 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
617 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
618 find_bind sel_name meth_name (AndMonoBinds b1 b2)
619 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
620 find_bind sel_name meth_name other = Nothing -- Default case
622 -- Find the prags for this method, and replace the
623 -- selector name with the method name
624 find_prags sel_name meth_name [] = []
625 find_prags sel_name meth_name (SpecSig name ty loc : prags)
626 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
627 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
628 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
629 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
637 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
640 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
641 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
644 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
647 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
650 = hsep [ptext SLIT("Class"), quotes (ppr clas),
651 ptext SLIT("does not have a method"), quotes (ppr op)]
653 omittedMethodWarn sel_id
654 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
656 badGenericMethodType op op_ty
657 = hang (ptext SLIT("Generic method type is too complex"))
658 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
659 ptext SLIT("You can only use type variables, arrows, and tuples")])
661 badGenericInstance sel_id
662 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
663 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
664 ptext SLIT("(where T is a derivable type constructor)")]
667 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
669 genericMultiParamErr clas
670 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
671 ptext SLIT("cannot have generic methods")