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(..),
29 tcLookupClass, tcExtendTyVarEnvForMeths, tcExtendGlobalTyVars,
30 tcExtendLocalValEnv, tcExtendTyVarEnv
32 import TcBinds ( tcBindWithSigs, tcSpecSigs )
33 import TcMonoType ( tcHsType, tcHsTheta, mkTcSig )
34 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
35 import TcUnify ( checkSigTyVars, sigCtxt )
36 import TcMType ( tcInstSigTyVars, 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 )
55 import VarSet ( mkVarSet, emptyVarSet )
57 import ErrUtils ( dumpIfSet )
58 import Util ( count, isSingleton, lengthIs, equalLength )
59 import Maybes ( seqMaybe, maybeToBool )
66 Every class implicitly declares a new data type, corresponding to dictionaries
67 of that class. So, for example:
69 class (D a) => C a where
71 op2 :: forall b. Ord b => a -> b -> b
73 would implicitly declare
75 data CDict a = CDict (D a)
77 (forall b. Ord b => a -> b -> b)
79 (We could use a record decl, but that means changing more of the existing apparatus.
82 For classes with just one superclass+method, we use a newtype decl instead:
85 op :: forallb. a -> b -> b
89 newtype CDict a = CDict (forall b. a -> b -> b)
91 Now DictTy in Type is just a form of type synomym:
92 DictTy c t = TyConTy CDict `AppTy` t
94 Death to "ExpandingDicts".
97 %************************************************************************
99 \subsection{Type checking}
101 %************************************************************************
105 tcClassDecl1 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
107 (ClassDecl {tcdCtxt = context, tcdName = class_name,
108 tcdTyVars = tyvar_names, tcdFDs = fundeps,
109 tcdSigs = class_sigs, tcdMeths = def_methods,
110 tcdSysNames = sys_names, tcdLoc = src_loc})
111 = -- LOOK THINGS UP IN THE ENVIRONMENT
112 tcLookupClass class_name `thenTc` \ clas ->
114 tyvars = classTyVars clas
115 op_sigs = filter isClassOpSig class_sigs
116 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
117 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
119 tcExtendTyVarEnv tyvars $
121 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
124 -- The renamer has already checked that the context mentions
125 -- only the type variable of the class decl.
126 -- Context is already kind-checked
127 ASSERT( equalLength context sc_sel_names )
128 tcHsTheta context `thenTc` \ sc_theta ->
130 -- CHECK THE CLASS SIGNATURES,
131 mapTc (tcClassSig rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
133 -- MAKE THE CLASS DETAILS
135 (op_tys, op_items) = unzip sig_stuff
136 sc_tys = mkPredTys sc_theta
137 dict_component_tys = sc_tys ++ op_tys
138 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
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] -> Maybe RenamedMonoBinds
158 -> TcM (Maybe (NameEnv Bool))
159 -- The returned environment says
160 -- x not in env => no default method
161 -- x -> True => generic default method
162 -- x -> False => polymorphic default method
164 -- Check default bindings
165 -- a) must be for a class op for this class
166 -- b) must be all generic or all non-generic
167 -- and return a mapping from class-op to DefMeth info
169 -- But do all this only for source binds
171 checkDefaultBinds clas ops Nothing
174 checkDefaultBinds clas ops (Just mbs)
175 = go mbs `thenTc` \ dm_env ->
176 returnTc (Just dm_env)
178 go EmptyMonoBinds = returnTc emptyNameEnv
180 go (AndMonoBinds b1 b2)
181 = go b1 `thenTc` \ dm_info1 ->
182 go b2 `thenTc` \ dm_info2 ->
183 returnTc (dm_info1 `plusNameEnv` dm_info2)
185 go (FunMonoBind op _ matches loc)
188 -- Check that the op is from this class
189 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
191 -- Check that all the defns ar generic, or none are
192 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
194 returnTc (unitNameEnv op all_generic)
196 n_generic = count (maybeToBool . maybeGenericMatch) matches
197 none_generic = n_generic == 0
198 all_generic = matches `lengthIs` n_generic
203 tcClassSig :: RecTcEnv -- Knot tying only!
204 -> Class -- ...ditto...
205 -> [TyVar] -- The class type variable, used for error check only
206 -> Maybe (NameEnv Bool) -- Info about default methods;
207 -- Nothing => imported class defn with no method binds
209 -> TcM (Type, -- Type of the method
210 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
212 -- This warrants an explanation: we need to separate generic
213 -- default methods and default methods later on in the compiler
214 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
215 -- Class.DefMeth data structure.
217 tcClassSig unf_env clas clas_tyvars maybe_dm_env
218 (ClassOpSig op_name sig_dm op_ty src_loc)
219 = tcAddSrcLoc src_loc $
221 -- Check the type signature. NB that the envt *already has*
222 -- bindings for the type variables; see comments in TcTyAndClassDcls.
223 tcHsType op_ty `thenTc` \ local_ty ->
226 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
228 -- Build the selector id and default method id
229 sel_id = mkDictSelId op_name clas
230 DefMeth dm_name = sig_dm
232 dm_info = case maybe_dm_env of
234 Just dm_env -> mk_src_dm_info dm_env
236 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
238 Just True -> GenDefMeth
239 Just False -> DefMeth dm_name
241 returnTc (local_ty, (sel_id, dm_info))
244 checkValidClass is called once the mutually-recursive knot has been
245 tied, so we can look at things freely.
248 checkValidClass :: Class -> TcM ()
250 = -- CHECK ARITY 1 FOR HASKELL 1.4
251 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
253 -- Check that the class is unary, unless GlaExs
254 checkTc (not (null tyvars)) (nullaryClassErr cls) `thenTc_`
255 checkTc (gla_exts || unary) (classArityErr cls) `thenTc_`
257 -- Check the super-classes
258 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
260 -- Check the class operations
261 mapTc_ check_op op_stuff `thenTc_`
263 -- Check that if the class has generic methods, then the
264 -- class has only one parameter. We can't do generic
265 -- multi-parameter type classes!
266 checkTc (unary || no_generics) (genericMultiParamErr cls)
269 (tyvars, theta, _, op_stuff) = classBigSig cls
270 unary = isSingleton tyvars
271 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
273 check_op (sel_id, dm)
274 = checkValidTheta SigmaCtxt (tail theta) `thenTc_`
275 -- The 'tail' removes the initial (C a) from the
276 -- class itself, leaving just the method type
278 checkValidType (FunSigCtxt op_name) tau `thenTc_`
280 -- Check that for a generic method, the type of
281 -- the method is sufficiently simple
282 checkTc (dm /= GenDefMeth || validGenericMethodType op_ty)
283 (badGenericMethodType op_name op_ty)
285 op_name = idName sel_id
286 op_ty = idType sel_id
287 (_,theta,tau) = tcSplitSigmaTy op_ty
291 %************************************************************************
293 \subsection[Default methods]{Default methods}
295 %************************************************************************
297 The default methods for a class are each passed a dictionary for the
298 class, so that they get access to the other methods at the same type.
299 So, given the class decl
303 op2 :: Ord b => a -> b -> b -> b
306 op2 x y z = if (op1 x) && (y < z) then y else z
308 we get the default methods:
310 defm.Foo.op1 :: forall a. Foo a => a -> Bool
311 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
313 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
314 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
315 if (op1 a dfoo x) && (< b dord y z) then y else z
318 When we come across an instance decl, we may need to use the default
321 instance Foo Int where {}
325 const.Foo.Int.op1 :: Int -> Bool
326 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
328 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
329 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
331 dfun.Foo.Int :: Foo Int
332 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
334 Notice that, as with method selectors above, we assume that dictionary
335 application is curried, so there's no need to mention the Ord dictionary
336 in const.Foo.Int.op2 (or the type variable).
339 instance Foo a => Foo [a] where {}
341 dfun.Foo.List :: forall a. Foo a -> Foo [a]
343 = /\ a -> \ dfoo_a ->
345 op1 = defm.Foo.op1 [a] dfoo_list
346 op2 = defm.Foo.op2 [a] dfoo_list
347 dfoo_list = (op1, op2)
352 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
353 each local class decl.
356 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
358 tcClassDecls2 this_mod decls
360 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
361 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
362 -- The 'Just' picks out source ClassDecls
364 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
365 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
366 returnNF_Tc (lie1 `plusLIE` lie2,
367 binds1 `AndMonoBinds` binds2,
371 @tcClassDecl2@ generates bindings for polymorphic default methods
372 (generic default methods have by now turned into instance declarations)
375 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
376 -> NF_TcM (LIE, TcMonoBinds, [Id])
378 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
379 tcdMeths = Just default_binds, tcdLoc = src_loc})
380 = -- The 'Just' picks out source ClassDecls
381 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
382 tcAddSrcLoc src_loc $
383 tcLookupClass class_name `thenNF_Tc` \ clas ->
385 -- We make a separate binding for each default method.
386 -- At one time I used a single AbsBinds for all of them, thus
387 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
388 -- But that desugars into
389 -- ds = \d -> (..., ..., ...)
390 -- dm1 = \d -> case ds d of (a,b,c) -> a
391 -- And since ds is big, it doesn't get inlined, so we don't get good
392 -- default methods. Better to make separate AbsBinds for each
394 (tyvars, _, _, op_items) = classBigSig clas
395 prags = filter isPragSig sigs
396 tc_dm = tcDefMeth clas tyvars default_binds prags
398 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
400 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
403 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
404 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
405 -- Generate code for polymorphic default methods only
406 -- (Generic default methods have turned into instance decls by now.)
407 -- This is incompatible with Hugs, which expects a polymorphic
408 -- default method for every class op, regardless of whether or not
409 -- the programmer supplied an explicit default decl for the class.
410 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
412 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
413 = tcInstSigTyVars ClsTv tyvars `thenNF_Tc` \ clas_tyvars ->
415 dm_ty = idType sel_id -- Same as dict selector!
416 -- The default method's type should really come from the
417 -- iface file, since it could be usage-generalised, but this
418 -- requires altering the mess of knots in TcModule and I'm
419 -- too scared to do that. Instead, I have disabled generalisation
420 -- of types of default methods (and dict funs) by annotating them
421 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
423 inst_tys = mkTyVarTys clas_tyvars
424 theta = [mkClassPred clas inst_tys]
425 dm_id = mkDefaultMethodId dm_name dm_ty
426 local_dm_id = setIdLocalExported dm_id
427 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
429 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
431 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
432 tcMethodBind clas origin clas_tyvars inst_tys theta
433 binds_in prags False op_item
434 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
436 tcAddErrCtxt (defltMethCtxt clas) $
440 (ptext SLIT("class") <+> ppr clas)
443 insts_needed `thenTc` \ (const_lie, dict_binds) ->
445 -- Simplification can do unification
446 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
452 [(clas_tyvars', local_dm_id, instToId local_dm_inst)]
453 emptyNameSet -- No inlines (yet)
454 (dict_binds `andMonoBinds` defm_bind)
456 returnTc (full_bind, const_lie, [dm_id])
458 origin = ClassDeclOrigin
463 %************************************************************************
465 \subsection{Typechecking a method}
467 %************************************************************************
469 @tcMethodBind@ is used to type-check both default-method and
470 instance-decl method declarations. We must type-check methods one at a
471 time, because their signatures may have different contexts and
478 -> [TcTyVar] -- Instantiated type variables for the
479 -- enclosing class/instance decl.
480 -- They'll be signature tyvars, and we
481 -- want to check that they don't get bound
482 -> [TcType] -- Instance types
483 -> TcThetaType -- Available theta; this could be used to check
484 -- the method signature, but actually that's done by
485 -- the caller; here, it's just used for the error message
486 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
487 -> [RenamedSig] -- Pramgas (just for this one)
488 -> Bool -- True <=> This method is from an instance declaration
489 -> ClassOpItem -- The method selector and default-method Id
490 -> TcM (TcMonoBinds, LIE, Inst)
492 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
493 meth_binds prags is_inst_decl (sel_id, dm_info)
494 = tcGetSrcLoc `thenNF_Tc` \ loc ->
495 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
497 meth_id = instToId meth
498 meth_name = idName meth_id
499 meth_prags = find_prags (idName sel_id) meth_name prags
501 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
503 -- Figure out what method binding to use
504 -- If the user suppplied one, use it, else construct a default one
505 (case find_bind (idName sel_id) meth_name meth_binds of
506 Just user_bind -> returnTc user_bind
507 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
508 returnTc (FunMonoBind meth_name False -- Not infix decl
509 [mkSimpleMatch [] rhs placeHolderType loc] loc)
510 ) `thenTc` \ meth_bind ->
511 -- Check the bindings; first add inst_tyvars to the envt
512 -- so that we don't quantify over them in nested places
513 -- The *caller* put the class/inst decl tyvars into the envt
514 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
515 (tcAddErrCtxt (methodCtxt sel_id) $
516 tcBindWithSigs NotTopLevel meth_bind
517 [sig_info] meth_prags NonRecursive
518 ) `thenTc` \ (binds, insts, _) ->
520 tcExtendLocalValEnv [(meth_name, meth_id)]
521 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
523 -- The prag_lie for a SPECIALISE pragma will mention the function
524 -- itself, so we have to simplify them away right now lest they float
526 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
528 -- Now check that the instance type variables
529 -- (or, in the case of a class decl, the class tyvars)
530 -- have not been unified with anything in the environment
532 -- We do this for each method independently to localise error messages
533 -- ...and this is why the call to tcExtendGlobalTyVars must be here
534 -- rather than in the caller
535 tcAddErrCtxt (ptext SLIT("When checking the type of class method")
536 <+> quotes (ppr sel_id)) $
537 tcAddErrCtxtM (sigCtxt 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_name)
548 = -- An polymorphic default method
549 returnTc (HsVar dm_name)
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 sense name phase loc : prags)
611 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
612 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
620 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
623 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
624 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
627 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
630 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
633 = hsep [ptext SLIT("Class"), quotes (ppr clas),
634 ptext SLIT("does not have a method"), quotes (ppr op)]
636 omittedMethodWarn sel_id
637 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
639 badGenericMethodType op op_ty
640 = hang (ptext SLIT("Generic method type is too complex"))
641 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
642 ptext SLIT("You can only use type variables, arrows, and tuples")])
644 badGenericInstance sel_id
645 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
646 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
647 ptext SLIT("(where T is a derivable type constructor)")]
650 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
652 genericMultiParamErr clas
653 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
654 ptext SLIT("cannot have generic methods")