2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, checkValidClass, tcClassDecls2,
8 tcMethodBind, 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 ( TopLevelFlag(..), RecFlag(..), StrictnessMark(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
22 RenamedSig, maybeGenericMatch
24 import TcHsSyn ( TcMonoBinds )
26 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
27 instToId, newDicts, newMethod )
28 import TcEnv ( RecTcEnv, TyThingDetails(..), tcAddImportedIdInfo,
29 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
30 tcExtendLocalValEnv, tcExtendTyVarEnv
32 import TcBinds ( tcBindWithSigs, tcSpecSigs )
33 import TcMonoType ( tcHsType, tcHsTheta, checkSigTyVars, sigCtxt, mkTcSig )
34 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
35 import TcMType ( tcInstTyVars, checkValidTheta, checkValidType, SourceTyCtxt(..), UserTypeCtxt(..) )
36 import TcType ( Type, mkSigmaTy, mkTyVarTys, mkPredTys, mkClassPred,
37 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitSigmaTy
40 import Generics ( mkGenericRhs, validGenericMethodType )
41 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
42 import Class ( classTyVars, classBigSig, classTyCon, className,
43 Class, ClassOpItem, DefMeth (..) )
44 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
45 import DataCon ( mkDataCon )
46 import Id ( idType, idName, setIdLocalExported )
47 import Module ( Module )
48 import Name ( Name, NamedThing(..) )
49 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
50 import NameSet ( emptyNameSet )
53 import VarSet ( mkVarSet, emptyVarSet )
55 import ErrUtils ( dumpIfSet )
57 import Maybes ( seqMaybe, maybeToBool )
64 Every class implicitly declares a new data type, corresponding to dictionaries
65 of that class. So, for example:
67 class (D a) => C a where
69 op2 :: forall b. Ord b => a -> b -> b
71 would implicitly declare
73 data CDict a = CDict (D a)
75 (forall b. Ord b => a -> b -> b)
77 (We could use a record decl, but that means changing more of the existing apparatus.
80 For classes with just one superclass+method, we use a newtype decl instead:
83 op :: forallb. a -> b -> b
87 newtype CDict a = CDict (forall b. a -> b -> b)
89 Now DictTy in Type is just a form of type synomym:
90 DictTy c t = TyConTy CDict `AppTy` t
92 Death to "ExpandingDicts".
95 %************************************************************************
97 \subsection{Type checking}
99 %************************************************************************
103 tcClassDecl1 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
105 (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( length context == length sc_sel_names )
126 tcHsTheta context `thenTc` \ sc_theta ->
128 -- CHECK THE CLASS SIGNATURES,
129 mapTc (tcClassSig rec_env 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 = n_generic == length matches
201 tcClassSig :: RecTcEnv -- Knot tying only!
202 -> Class -- ...ditto...
203 -> [TyVar] -- The class type variable, used for error check only
204 -> Maybe (NameEnv Bool) -- Info about default methods;
205 -- Nothing => imported class defn with no method binds
207 -> TcM (Type, -- Type of the method
208 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
210 -- This warrants an explanation: we need to separate generic
211 -- default methods and default methods later on in the compiler
212 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
213 -- Class.DefMeth data structure.
215 tcClassSig unf_env clas clas_tyvars maybe_dm_env
216 (ClassOpSig op_name sig_dm op_ty src_loc)
217 = tcAddSrcLoc src_loc $
219 -- Check the type signature. NB that the envt *already has*
220 -- bindings for the type variables; see comments in TcTyAndClassDcls.
221 tcHsType op_ty `thenTc` \ local_ty ->
224 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
225 global_ty = mkSigmaTy clas_tyvars theta local_ty
226 -- The default method's type should really come from the
227 -- iface file, since it could be usage-generalised, but this
228 -- requires altering the mess of knots in TcModule and I'm
229 -- too scared to do that. Instead, I have disabled generalisation
230 -- of types of default methods (and dict funs) by annotating them
231 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
233 -- Build the selector id and default method id
234 sel_id = mkDictSelId op_name clas
235 dm_id = mkDefaultMethodId dm_name global_ty
236 DefMeth dm_name = sig_dm
238 dm_info = case maybe_dm_env of
239 Nothing -> iface_dm_info
240 Just dm_env -> mk_src_dm_info dm_env
242 iface_dm_info = case sig_dm of
243 NoDefMeth -> NoDefMeth
244 GenDefMeth -> GenDefMeth
245 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
247 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
249 Just True -> GenDefMeth
250 Just False -> DefMeth dm_id
252 returnTc (local_ty, (sel_id, dm_info))
255 checkValidClass is called once the mutually-recursive knot has been
256 tied, so we can look at things freely.
259 checkValidClass :: Class -> TcM ()
261 = -- CHECK ARITY 1 FOR HASKELL 1.4
262 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
264 -- Check that the class is unary, unless GlaExs
265 checkTc (arity > 0) (nullaryClassErr cls) `thenTc_`
266 checkTc (gla_exts || unary) (classArityErr cls) `thenTc_`
268 -- Check the super-classes
269 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
271 -- Check the class operations
272 mapTc_ check_op op_stuff `thenTc_`
274 -- Check that if the class has generic methods, then the
275 -- class has only one parameter. We can't do generic
276 -- multi-parameter type classes!
277 checkTc (unary || no_generics) (genericMultiParamErr cls)
280 (tyvars, theta, sel_ids, op_stuff) = classBigSig cls
281 arity = length tyvars
283 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
285 check_op (sel_id, dm)
286 = checkValidTheta SigmaCtxt (tail theta) `thenTc_`
287 -- The 'tail' removes the initial (C a) from the
288 -- class itself, leaving just the method type
290 checkValidType (FunSigCtxt op_name) tau `thenTc_`
292 -- Check that for a generic method, the type of
293 -- the method is sufficiently simple
294 checkTc (dm /= GenDefMeth || validGenericMethodType op_ty)
295 (badGenericMethodType op_name op_ty)
297 op_name = idName sel_id
298 op_ty = idType sel_id
299 (_,theta,tau) = tcSplitSigmaTy op_ty
303 %************************************************************************
305 \subsection[Default methods]{Default methods}
307 %************************************************************************
309 The default methods for a class are each passed a dictionary for the
310 class, so that they get access to the other methods at the same type.
311 So, given the class decl
315 op2 :: Ord b => a -> b -> b -> b
318 op2 x y z = if (op1 x) && (y < z) then y else z
320 we get the default methods:
322 defm.Foo.op1 :: forall a. Foo a => a -> Bool
323 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
325 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
326 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
327 if (op1 a dfoo x) && (< b dord y z) then y else z
330 When we come across an instance decl, we may need to use the default
333 instance Foo Int where {}
337 const.Foo.Int.op1 :: Int -> Bool
338 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
340 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
341 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
343 dfun.Foo.Int :: Foo Int
344 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
346 Notice that, as with method selectors above, we assume that dictionary
347 application is curried, so there's no need to mention the Ord dictionary
348 in const.Foo.Int.op2 (or the type variable).
351 instance Foo a => Foo [a] where {}
353 dfun.Foo.List :: forall a. Foo a -> Foo [a]
355 = /\ a -> \ dfoo_a ->
357 op1 = defm.Foo.op1 [a] dfoo_list
358 op2 = defm.Foo.op2 [a] dfoo_list
359 dfoo_list = (op1, op2)
364 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
365 each local class decl.
368 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
370 tcClassDecls2 this_mod decls
372 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
373 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
374 -- The 'Just' picks out source ClassDecls
376 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
377 tc2 `thenNF_Tc` \ (lie2, binds2) ->
378 returnNF_Tc (lie1 `plusLIE` lie2,
379 binds1 `AndMonoBinds` binds2)
382 @tcClassDecl2@ generates bindings for polymorphic default methods
383 (generic default methods have by now turned into instance declarations)
386 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
387 -> NF_TcM (LIE, TcMonoBinds)
389 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
390 tcdMeths = Just default_binds, tcdLoc = src_loc})
391 = -- The 'Just' picks out source ClassDecls
392 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
393 tcAddSrcLoc src_loc $
394 tcLookupClass class_name `thenNF_Tc` \ clas ->
396 -- We make a separate binding for each default method.
397 -- At one time I used a single AbsBinds for all of them, thus
398 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
399 -- But that desugars into
400 -- ds = \d -> (..., ..., ...)
401 -- dm1 = \d -> case ds d of (a,b,c) -> a
402 -- And since ds is big, it doesn't get inlined, so we don't get good
403 -- default methods. Better to make separate AbsBinds for each
405 (tyvars, _, _, op_items) = classBigSig clas
406 prags = filter isPragSig sigs
407 tc_dm = tcDefMeth clas tyvars default_binds prags
409 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
411 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
414 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
415 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
416 -- Generate code for polymorphic default methods only
417 -- (Generic default methods have turned into instance decls by now.)
418 -- This is incompatible with Hugs, which expects a polymorphic
419 -- default method for every class op, regardless of whether or not
420 -- the programmer supplied an explicit default decl for the class.
421 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
423 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
424 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
426 theta = [(mkClassPred clas inst_tys)]
427 local_dm_id = setIdLocalExported dm_id
428 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
430 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
432 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
433 tcMethodBind clas origin clas_tyvars inst_tys theta
434 binds_in prags False op_item
435 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
437 tcAddErrCtxt (defltMethCtxt clas) $
441 (ptext SLIT("class") <+> ppr clas)
444 insts_needed `thenTc` \ (const_lie, dict_binds) ->
446 -- Simplification can do unification
447 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
453 [(clas_tyvars', local_dm_id, instToId local_dm_inst)]
454 emptyNameSet -- No inlines (yet)
455 (dict_binds `andMonoBinds` defm_bind)
457 returnTc (full_bind, const_lie)
459 origin = ClassDeclOrigin
464 %************************************************************************
466 \subsection{Typechecking a method}
468 %************************************************************************
470 @tcMethodBind@ is used to type-check both default-method and
471 instance-decl method declarations. We must type-check methods one at a
472 time, because their signatures may have different contexts and
479 -> [TcTyVar] -- Instantiated type variables for the
480 -- enclosing class/instance decl.
481 -- They'll be signature tyvars, and we
482 -- want to check that they don't get bound
483 -> [TcType] -- Instance types
484 -> TcThetaType -- Available theta; this could be used to check
485 -- the method signature, but actually that's done by
486 -- the caller; here, it's just used for the error message
487 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
488 -> [RenamedSig] -- Pramgas (just for this one)
489 -> Bool -- True <=> This method is from an instance declaration
490 -> ClassOpItem -- The method selector and default-method Id
491 -> TcM (TcMonoBinds, LIE, Inst)
493 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
494 meth_binds prags is_inst_decl (sel_id, dm_info)
495 = tcGetSrcLoc `thenNF_Tc` \ loc ->
496 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
498 meth_id = instToId meth
499 meth_name = idName meth_id
500 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
501 meth_prags = find_prags (idName sel_id) meth_name prags
503 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
505 -- Figure out what method binding to use
506 -- If the user suppplied one, use it, else construct a default one
507 (case find_bind (idName sel_id) meth_name meth_binds of
508 Just user_bind -> returnTc user_bind
509 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
510 returnTc (FunMonoBind meth_name False -- Not infix decl
511 [mkSimpleMatch [] rhs placeHolderType loc] loc)
512 ) `thenTc` \ meth_bind ->
513 -- Check the bindings; first add inst_tyvars to the envt
514 -- so that we don't quantify over them in nested places
515 -- The *caller* put the class/inst decl tyvars into the envt
516 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
517 (tcAddErrCtxt (methodCtxt sel_id) $
518 tcBindWithSigs NotTopLevel meth_bind
519 [sig_info] meth_prags NonRecursive
520 ) `thenTc` \ (binds, insts, _) ->
522 tcExtendLocalValEnv [(meth_name, meth_id)]
523 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
525 -- The prag_lie for a SPECIALISE pragma will mention the function
526 -- itself, so we have to simplify them away right now lest they float
528 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
530 -- Now check that the instance type variables
531 -- (or, in the case of a class decl, the class tyvars)
532 -- have not been unified with anything in the environment
534 -- We do this for each method independently to localise error messages
535 -- ...and this is why the call to tcExtendGlobalTyVars must be here
536 -- rather than in the caller
537 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
538 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
540 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
541 insts `plusLIE` prag_lie',
544 -- The user didn't supply a method binding,
545 -- so we have to make up a default binding
546 -- The RHS of a default method depends on the default-method info
547 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
548 = -- An polymorphic default method
549 returnTc (HsVar (idName dm_id))
551 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
552 = -- No default method
553 -- Warn only if -fwarn-missing-methods
554 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
555 warnTc (is_inst_decl && warn)
556 (omittedMethodWarn sel_id) `thenNF_Tc_`
559 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
560 (HsLit (HsString (_PK_ error_msg)))
561 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
564 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
565 = -- A generic default method
566 -- If the method is defined generically, we can only do the job if the
567 -- instance declaration is for a single-parameter type class with
568 -- a type constructor applied to type arguments in the instance decl
569 -- (checkTc, so False provokes the error)
570 checkTc (not is_inst_decl || simple_inst)
571 (badGenericInstance sel_id) `thenTc_`
573 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
576 rhs = mkGenericRhs sel_id clas_tyvar tycon
578 stuff = vcat [ppr clas <+> ppr inst_tys,
579 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
581 -- The tycon is only used in the generic case, and in that
582 -- case we require that the instance decl is for a single-parameter
583 -- type class with type variable arguments:
584 -- instance (...) => C (T a b)
585 simple_inst = maybeToBool maybe_tycon
586 clas_tyvar = head (classTyVars clas)
587 Just tycon = maybe_tycon
588 maybe_tycon = case inst_tys of
589 [ty] -> case tcSplitTyConApp_maybe ty of
590 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
597 -- The renamer just puts the selector ID as the binder in the method binding
598 -- but we must use the method name; so we substitute it here. Crude but simple.
599 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
600 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
601 find_bind sel_name meth_name (AndMonoBinds b1 b2)
602 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
603 find_bind sel_name meth_name other = Nothing -- Default case
605 -- Find the prags for this method, and replace the
606 -- selector name with the method name
607 find_prags sel_name meth_name [] = []
608 find_prags sel_name meth_name (SpecSig name ty loc : prags)
609 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
610 find_prags sel_name meth_name (InlineSig name phase loc : prags)
611 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
612 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
613 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
614 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
622 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
625 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
626 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
629 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
632 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
635 = hsep [ptext SLIT("Class"), quotes (ppr clas),
636 ptext SLIT("does not have a method"), quotes (ppr op)]
638 omittedMethodWarn sel_id
639 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
641 badGenericMethodType op op_ty
642 = hang (ptext SLIT("Generic method type is too complex"))
643 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
644 ptext SLIT("You can only use type variables, arrows, and tuples")])
646 badGenericInstance sel_id
647 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
648 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
649 ptext SLIT("(where T is a derivable type constructor)")]
652 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
654 genericMultiParamErr clas
655 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
656 ptext SLIT("cannot have generic methods")