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 ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
28 instToId, newDicts, newMethod )
29 import TcEnv ( RecTcEnv, TyThingDetails(..), tcAddImportedIdInfo,
30 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
31 tcExtendLocalValEnv, tcExtendTyVarEnv
33 import TcBinds ( tcBindWithSigs, tcSpecSigs )
34 import TcMonoType ( tcHsRecType, tcRecTheta, checkSigTyVars, checkAmbiguity, sigCtxt, mkTcSig )
35 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
36 import TcType ( TcType, TcTyVar, tcInstTyVars )
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 NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
48 import NameSet ( emptyNameSet )
50 import Type ( Type, ThetaType, mkTyVarTys, mkPredTys, 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` \ gla_ext_opt ->
113 gla_exts = gla_ext_opt || not (maybeToBool def_methods)
114 -- Accept extensions if gla_exts is on,
115 -- or if we're looking at an interface file decl
116 in -- (in which case def_methods = Nothing
118 -- LOOK THINGS UP IN THE ENVIRONMENT
119 tcLookupClass class_name `thenTc` \ clas ->
121 tyvars = classTyVars clas
122 op_sigs = filter isClassOpSig class_sigs
123 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
124 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
126 tcExtendTyVarEnv tyvars $
128 -- SOURCE-CODE CONSISTENCY CHECKS
130 Nothing -> -- Not source
133 Just dms -> -- Source so do error checks
134 checkTc (gla_exts || length tyvar_names == 1)
135 (classArityErr class_name) `thenTc_`
137 checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
138 checkGenericClassIsUnary clas dm_env `thenTc_`
139 returnTc (Just dm_env)
140 ) `thenTc` \ mb_dm_env ->
143 tcSuperClasses is_rec gla_exts clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
145 -- CHECK THE CLASS SIGNATURES,
146 mapTc (tcClassSig is_rec rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
148 -- MAKE THE CLASS DETAILS
150 (op_tys, op_items) = unzip sig_stuff
151 sc_tys = mkPredTys sc_theta
152 dict_component_tys = sc_tys ++ op_tys
154 dict_con = mkDataCon datacon_name
155 [notMarkedStrict | _ <- dict_component_tys]
156 [{- No labelled fields -}]
159 [{-No existential tyvars-}] [{-Or context-}]
162 dict_con_id dict_wrap_id
164 dict_con_id = mkDataConId datacon_wkr_name dict_con
165 dict_wrap_id = mkDataConWrapId dict_con
167 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
171 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds
172 -> TcM (NameEnv Bool)
173 -- The returned environment says
174 -- x not in env => no default method
175 -- x -> True => generic default method
176 -- x -> False => polymorphic default method
178 -- Check default bindings
179 -- a) must be for a class op for this class
180 -- b) must be all generic or all non-generic
181 -- and return a mapping from class-op to DefMeth info
183 -- But do all this only for source binds
185 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
187 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
188 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
189 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
190 returnTc (dm_info1 `plusNameEnv` dm_info2)
192 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
195 -- Check that the op is from this class
196 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
198 -- Check that all the defns ar generic, or none are
199 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
201 returnTc (unitNameEnv op all_generic)
203 n_generic = count (maybeToBool . maybeGenericMatch) matches
204 none_generic = n_generic == 0
205 all_generic = n_generic == length matches
207 checkGenericClassIsUnary clas dm_env
208 = -- Check that if the class has generic methods, then the
209 -- class has only one parameter. We can't do generic
210 -- multi-parameter type classes!
211 checkTc (unary || no_generics) (genericMultiParamErr clas)
213 unary = length (classTyVars clas) == 1
214 no_generics = not (or (nameEnvElts dm_env))
219 tcSuperClasses :: RecFlag -> Bool -> Class
220 -> RenamedContext -- class context
221 -> [Name] -- Names for superclass selectors
222 -> TcM (ThetaType, -- the superclass context
223 [Id]) -- superclass selector Ids
225 tcSuperClasses is_rec gla_exts clas context sc_sel_names
226 = ASSERT( length context == length sc_sel_names )
227 -- Check the context.
228 -- The renamer has already checked that the context mentions
229 -- only the type variable of the class decl.
231 -- For std Haskell check that the context constrains only tyvars
232 mapTc_ check_constraint context `thenTc_`
234 -- Context is already kind-checked
235 tcRecTheta is_rec context `thenTc` \ sc_theta ->
237 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
240 returnTc (sc_theta, sc_sel_ids)
243 check_constraint sc = checkTc (ok sc) (superClassErr clas sc)
244 ok (HsClassP c tys) | gla_exts = True
245 | otherwise = all is_tyvar tys
246 ok (HsIParam _ _) = False -- Never legal
248 is_tyvar (HsTyVar _) = True
249 is_tyvar other = False
252 tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
253 -> Class -- ...ditto...
254 -> [TyVar] -- The class type variable, used for error check only
255 -> Maybe (NameEnv Bool) -- Info about default methods
257 -> TcM (Type, -- Type of the method
258 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
260 -- This warrants an explanation: we need to separate generic
261 -- default methods and default methods later on in the compiler
262 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
263 -- Class.DefMeth data structure.
265 tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
266 (ClassOpSig op_name sig_dm op_ty src_loc)
267 = tcAddSrcLoc src_loc $
269 -- Check the type signature. NB that the envt *already has*
270 -- bindings for the type variables; see comments in TcTyAndClassDcls.
272 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
274 -- Check for ambiguous class op types
276 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
278 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
279 -- The default method's type should really come from the
280 -- iface file, since it could be usage-generalised, but this
281 -- requires altering the mess of knots in TcModule and I'm
282 -- too scared to do that. Instead, I have disabled generalisation
283 -- of types of default methods (and dict funs) by annotating them
284 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
287 -- Build the selector id and default method id
288 sel_id = mkDictSelId op_name clas
289 dm_id = mkDefaultMethodId dm_name global_ty
290 DefMeth dm_name = sig_dm
292 dm_info = case maybe_dm_env of
293 Nothing -> iface_dm_info
294 Just dm_env -> mk_src_dm_info dm_env
296 iface_dm_info = case sig_dm of
297 NoDefMeth -> NoDefMeth
298 GenDefMeth -> GenDefMeth
299 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
301 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
303 Just True -> GenDefMeth
304 Just False -> DefMeth dm_id
306 -- Check that for a generic method, the type of
307 -- the method is sufficiently simple
308 checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
309 (badGenericMethodType op_name op_ty) `thenTc_`
311 returnTc (local_ty, (sel_id, dm_info))
315 %************************************************************************
317 \subsection[Default methods]{Default methods}
319 %************************************************************************
321 The default methods for a class are each passed a dictionary for the
322 class, so that they get access to the other methods at the same type.
323 So, given the class decl
327 op2 :: Ord b => a -> b -> b -> b
330 op2 x y z = if (op1 x) && (y < z) then y else z
332 we get the default methods:
334 defm.Foo.op1 :: forall a. Foo a => a -> Bool
335 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
337 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
338 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
339 if (op1 a dfoo x) && (< b dord y z) then y else z
342 When we come across an instance decl, we may need to use the default
345 instance Foo Int where {}
349 const.Foo.Int.op1 :: Int -> Bool
350 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
352 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
353 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
355 dfun.Foo.Int :: Foo Int
356 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
358 Notice that, as with method selectors above, we assume that dictionary
359 application is curried, so there's no need to mention the Ord dictionary
360 in const.Foo.Int.op2 (or the type variable).
363 instance Foo a => Foo [a] where {}
365 dfun.Foo.List :: forall a. Foo a -> Foo [a]
367 = /\ a -> \ dfoo_a ->
369 op1 = defm.Foo.op1 [a] dfoo_list
370 op2 = defm.Foo.op2 [a] dfoo_list
371 dfoo_list = (op1, op2)
376 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
377 each local class decl.
380 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
382 tcClassDecls2 this_mod decls
384 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
385 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
386 -- The 'Just' picks out source ClassDecls
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 {tcdName = class_name, tcdSigs = sigs,
402 tcdMeths = Just default_binds, tcdLoc = src_loc})
403 = -- The 'Just' picks out source ClassDecls
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] ->
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_inst) ->
447 tcAddErrCtxt (defltMethCtxt clas) $
451 (ptext SLIT("class") <+> ppr clas)
454 insts_needed `thenTc` \ (const_lie, dict_binds) ->
456 -- Simplification can do unification
457 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
463 [(clas_tyvars', dm_id, instToId local_dm_inst)]
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 (TcMonoBinds, LIE, Inst)
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 ->
508 meth_id = instToId meth
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 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
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 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
565 warnTc (is_inst_decl && warn)
566 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
569 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
570 (HsLit (HsString (_PK_ error_msg)))
571 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
574 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
575 = -- A generic default method
576 -- If the method is defined generically, we can only do the job if the
577 -- instance declaration is for a single-parameter type class with
578 -- a type constructor applied to type arguments in the instance decl
579 -- (checkTc, so False provokes the error)
580 checkTc (not is_inst_decl || simple_inst)
581 (badGenericInstance sel_id clas) `thenTc_`
583 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
586 rhs = mkGenericRhs sel_id clas_tyvar tycon
588 stuff = vcat [ppr clas <+> ppr inst_tys,
589 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
591 -- The tycon is only used in the generic case, and in that
592 -- case we require that the instance decl is for a single-parameter
593 -- type class with type variable arguments:
594 -- instance (...) => C (T a b)
595 simple_inst = maybeToBool maybe_tycon
596 clas_tyvar = head (classTyVars clas)
597 Just tycon = maybe_tycon
598 maybe_tycon = case inst_tys of
599 [ty] -> case splitTyConApp_maybe ty of
600 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
607 -- The renamer just puts the selector ID as the binder in the method binding
608 -- but we must use the method name; so we substitute it here. Crude but simple.
609 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
610 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
611 find_bind sel_name meth_name (AndMonoBinds b1 b2)
612 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
613 find_bind sel_name meth_name other = Nothing -- Default case
615 -- Find the prags for this method, and replace the
616 -- selector name with the method name
617 find_prags sel_name meth_name [] = []
618 find_prags sel_name meth_name (SpecSig name ty loc : prags)
619 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
620 find_prags sel_name meth_name (InlineSig name phase loc : prags)
621 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
622 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
623 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
624 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
631 classArityErr class_name
632 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
634 superClassErr clas sc
635 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
636 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
639 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
642 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
645 = hsep [ptext SLIT("Class"), quotes (ppr clas),
646 ptext SLIT("does not have a method"), quotes (ppr op)]
648 omittedMethodWarn sel_id clas
649 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
650 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
652 badGenericMethodType op op_ty
653 = hang (ptext SLIT("Generic method type is too complex"))
654 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
655 ptext SLIT("You can only use type variables, arrows, and tuples")])
657 badGenericInstance sel_id clas
658 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
659 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
660 ptext SLIT("(where T is a derivable type constructor)"),
661 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
664 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
666 genericMultiParamErr clas
667 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
668 ptext SLIT("cannot have generic methods")