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, tcRecClassContext, 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, 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` \ 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 = mkDictTys 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 (ClassContext, -- the superclass context
223 [Id]) -- superclass selector Ids
225 tcSuperClasses is_rec gla_exts clas context sc_sel_names
226 = -- Check the context.
227 -- The renamer has already checked that the context mentions
228 -- only the type variable of the class decl.
230 -- For std Haskell check that the context constrains only tyvars
234 mapTc_ check_constraint context
237 -- Context is already kind-checked
238 tcRecClassContext is_rec context `thenTc` \ sc_theta ->
240 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
243 returnTc (sc_theta, sc_sel_ids)
246 check_constraint sc@(HsPClass c tys)
247 = checkTc (all is_tyvar tys) (superClassErr clas sc)
249 is_tyvar (HsTyVar _) = True
250 is_tyvar other = False
253 tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
254 -> Class -- ...ditto...
255 -> [TyVar] -- The class type variable, used for error check only
256 -> Maybe (NameEnv Bool) -- Info about default methods
258 -> TcM (Type, -- Type of the method
259 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
261 -- This warrants an explanation: we need to separate generic
262 -- default methods and default methods later on in the compiler
263 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
264 -- Class.DefMeth data structure.
266 tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
267 (ClassOpSig op_name sig_dm op_ty src_loc)
268 = tcAddSrcLoc src_loc $
270 -- Check the type signature. NB that the envt *already has*
271 -- bindings for the type variables; see comments in TcTyAndClassDcls.
273 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
275 -- Check for ambiguous class op types
277 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
279 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
280 -- The default method's type should really come from the
281 -- iface file, since it could be usage-generalised, but this
282 -- requires altering the mess of knots in TcModule and I'm
283 -- too scared to do that. Instead, I have disabled generalisation
284 -- of types of default methods (and dict funs) by annotating them
285 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
288 -- Build the selector id and default method id
289 sel_id = mkDictSelId op_name clas
290 dm_id = mkDefaultMethodId dm_name global_ty
291 DefMeth dm_name = sig_dm
293 dm_info = case maybe_dm_env of
294 Nothing -> iface_dm_info
295 Just dm_env -> mk_src_dm_info dm_env
297 iface_dm_info = case sig_dm of
298 NoDefMeth -> NoDefMeth
299 GenDefMeth -> GenDefMeth
300 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
302 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
304 Just True -> GenDefMeth
305 Just False -> DefMeth dm_id
307 -- Check that for a generic method, the type of
308 -- the method is sufficiently simple
309 checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
310 (badGenericMethodType op_name op_ty) `thenTc_`
312 returnTc (local_ty, (sel_id, dm_info))
316 %************************************************************************
318 \subsection[Default methods]{Default methods}
320 %************************************************************************
322 The default methods for a class are each passed a dictionary for the
323 class, so that they get access to the other methods at the same type.
324 So, given the class decl
328 op2 :: Ord b => a -> b -> b -> b
331 op2 x y z = if (op1 x) && (y < z) then y else z
333 we get the default methods:
335 defm.Foo.op1 :: forall a. Foo a => a -> Bool
336 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
338 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
339 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
340 if (op1 a dfoo x) && (< b dord y z) then y else z
343 When we come across an instance decl, we may need to use the default
346 instance Foo Int where {}
350 const.Foo.Int.op1 :: Int -> Bool
351 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
353 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
354 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
356 dfun.Foo.Int :: Foo Int
357 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
359 Notice that, as with method selectors above, we assume that dictionary
360 application is curried, so there's no need to mention the Ord dictionary
361 in const.Foo.Int.op2 (or the type variable).
364 instance Foo a => Foo [a] where {}
366 dfun.Foo.List :: forall a. Foo a -> Foo [a]
368 = /\ a -> \ dfoo_a ->
370 op1 = defm.Foo.op1 [a] dfoo_list
371 op2 = defm.Foo.op2 [a] dfoo_list
372 dfoo_list = (op1, op2)
377 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
378 each local class decl.
381 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
383 tcClassDecls2 this_mod decls
385 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
386 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
387 -- The 'Just' picks out source ClassDecls
389 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
390 tc2 `thenNF_Tc` \ (lie2, binds2) ->
391 returnNF_Tc (lie1 `plusLIE` lie2,
392 binds1 `AndMonoBinds` binds2)
395 @tcClassDecl2@ generates bindings for polymorphic default methods
396 (generic default methods have by now turned into instance declarations)
399 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
400 -> NF_TcM (LIE, TcMonoBinds)
402 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
403 tcdMeths = Just default_binds, tcdLoc = src_loc})
404 = -- The 'Just' picks out source ClassDecls
405 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
406 tcAddSrcLoc src_loc $
407 tcLookupClass class_name `thenNF_Tc` \ clas ->
409 -- We make a separate binding for each default method.
410 -- At one time I used a single AbsBinds for all of them, thus
411 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
412 -- But that desugars into
413 -- ds = \d -> (..., ..., ...)
414 -- dm1 = \d -> case ds d of (a,b,c) -> a
415 -- And since ds is big, it doesn't get inlined, so we don't get good
416 -- default methods. Better to make separate AbsBinds for each
418 (tyvars, _, _, op_items) = classBigSig clas
419 prags = filter isPragSig sigs
420 tc_dm = tcDefMeth clas tyvars default_binds prags
422 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
424 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
427 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
428 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
429 -- Generate code for polymorphic default methods only
430 -- (Generic default methods have turned into instance decls by now.)
431 -- This is incompatible with Hugs, which expects a polymorphic
432 -- default method for every class op, regardless of whether or not
433 -- the programmer supplied an explicit default decl for the class.
434 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
436 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
437 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
439 theta = [(mkClassPred clas inst_tys)]
441 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
443 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
444 tcMethodBind clas origin clas_tyvars inst_tys theta
445 binds_in prags False op_item
446 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
448 tcAddErrCtxt (defltMethCtxt clas) $
452 (ptext SLIT("class") <+> ppr clas)
455 insts_needed `thenTc` \ (const_lie, dict_binds) ->
457 -- Simplification can do unification
458 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
464 [(clas_tyvars', dm_id, instToId local_dm_inst)]
465 emptyNameSet -- No inlines (yet)
466 (dict_binds `andMonoBinds` defm_bind)
468 returnTc (full_bind, const_lie)
470 origin = ClassDeclOrigin
475 %************************************************************************
477 \subsection{Typechecking a method}
479 %************************************************************************
481 @tcMethodBind@ is used to type-check both default-method and
482 instance-decl method declarations. We must type-check methods one at a
483 time, because their signatures may have different contexts and
490 -> [TcTyVar] -- Instantiated type variables for the
491 -- enclosing class/instance decl.
492 -- They'll be signature tyvars, and we
493 -- want to check that they don't get bound
494 -> [TcType] -- Instance types
495 -> TcThetaType -- Available theta; this could be used to check
496 -- the method signature, but actually that's done by
497 -- the caller; here, it's just used for the error message
498 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
499 -> [RenamedSig] -- Pramgas (just for this one)
500 -> Bool -- True <=> This method is from an instance declaration
501 -> ClassOpItem -- The method selector and default-method Id
502 -> TcM (TcMonoBinds, LIE, Inst)
504 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
505 meth_binds prags is_inst_decl (sel_id, dm_info)
506 = tcGetSrcLoc `thenNF_Tc` \ loc ->
507 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
509 meth_id = instToId meth
510 meth_name = idName meth_id
511 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
512 meth_prags = find_prags (idName sel_id) meth_name prags
514 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
516 -- Figure out what method binding to use
517 -- If the user suppplied one, use it, else construct a default one
518 (case find_bind (idName sel_id) meth_name meth_binds of
519 Just user_bind -> returnTc user_bind
520 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
521 returnTc (FunMonoBind meth_name False -- Not infix decl
522 [mkSimpleMatch [] rhs Nothing loc] loc)
523 ) `thenTc` \ meth_bind ->
524 -- Check the bindings; first add inst_tyvars to the envt
525 -- so that we don't quantify over them in nested places
526 -- The *caller* put the class/inst decl tyvars into the envt
527 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
528 (tcAddErrCtxt (methodCtxt sel_id) $
529 tcBindWithSigs NotTopLevel meth_bind
530 [sig_info] meth_prags NonRecursive
531 ) `thenTc` \ (binds, insts, _) ->
533 tcExtendLocalValEnv [(meth_name, meth_id)]
534 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
536 -- The prag_lie for a SPECIALISE pragma will mention the function
537 -- itself, so we have to simplify them away right now lest they float
539 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
541 -- Now check that the instance type variables
542 -- (or, in the case of a class decl, the class tyvars)
543 -- have not been unified with anything in the environment
545 -- We do this for each method independently to localise error messages
546 -- ...and this is why the call to tcExtendGlobalTyVars must be here
547 -- rather than in the caller
548 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
549 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
551 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
552 insts `plusLIE` prag_lie',
555 -- The user didn't supply a method binding,
556 -- so we have to make up a default binding
557 -- The RHS of a default method depends on the default-method info
558 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
559 = -- An polymorphic default method
560 returnTc (HsVar (idName dm_id))
562 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
563 = -- No default method
564 -- Warn only if -fwarn-missing-methods
565 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
566 warnTc (is_inst_decl && warn)
567 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
570 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
571 (HsLit (HsString (_PK_ error_msg)))
572 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
575 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
576 = -- A generic default method
577 -- If the method is defined generically, we can only do the job if the
578 -- instance declaration is for a single-parameter type class with
579 -- a type constructor applied to type arguments in the instance decl
580 -- (checkTc, so False provokes the error)
581 checkTc (not is_inst_decl || simple_inst)
582 (badGenericInstance sel_id clas) `thenTc_`
584 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
587 rhs = mkGenericRhs sel_id clas_tyvar tycon
589 stuff = vcat [ppr clas <+> ppr inst_tys,
590 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
592 -- The tycon is only used in the generic case, and in that
593 -- case we require that the instance decl is for a single-parameter
594 -- type class with type variable arguments:
595 -- instance (...) => C (T a b)
596 simple_inst = maybeToBool maybe_tycon
597 clas_tyvar = head (classTyVars clas)
598 Just tycon = maybe_tycon
599 maybe_tycon = case inst_tys of
600 [ty] -> case splitTyConApp_maybe ty of
601 Just (tycon, arg_tys) | all isTyVarTy arg_tys -> Just tycon
608 -- The renamer just puts the selector ID as the binder in the method binding
609 -- but we must use the method name; so we substitute it here. Crude but simple.
610 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
611 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
612 find_bind sel_name meth_name (AndMonoBinds b1 b2)
613 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
614 find_bind sel_name meth_name other = Nothing -- Default case
616 -- Find the prags for this method, and replace the
617 -- selector name with the method name
618 find_prags sel_name meth_name [] = []
619 find_prags sel_name meth_name (SpecSig name ty loc : prags)
620 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
621 find_prags sel_name meth_name (InlineSig name phase loc : prags)
622 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
623 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
624 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
625 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
632 classArityErr class_name
633 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
635 superClassErr clas sc
636 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
637 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
640 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
643 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
646 = hsep [ptext SLIT("Class"), quotes (ppr clas),
647 ptext SLIT("does not have a method"), quotes (ppr op)]
649 omittedMethodWarn sel_id clas
650 = sep [ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id),
651 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
653 badGenericMethodType op op_ty
654 = hang (ptext SLIT("Generic method type is too complex"))
655 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
656 ptext SLIT("You can only use type variables, arrows, and tuples")])
658 badGenericInstance sel_id clas
659 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
660 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
661 ptext SLIT("(where T is a derivable type constructor)"),
662 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
665 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
667 genericMultiParamErr clas
668 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
669 ptext SLIT("cannot have generic methods")