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 ( 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 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
106 tcClassDecl1 (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 = -- LOOK THINGS UP IN THE ENVIRONMENT
111 tcLookupClass class_name `thenTc` \ clas ->
113 tyvars = classTyVars clas
114 op_sigs = filter isClassOpSig class_sigs
115 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
116 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
118 tcExtendTyVarEnv tyvars $
120 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
123 -- The renamer has already checked that the context mentions
124 -- only the type variable of the class decl.
125 -- Context is already kind-checked
126 ASSERT( equalLength context sc_sel_names )
127 tcHsTheta context `thenTc` \ sc_theta ->
129 -- CHECK THE CLASS SIGNATURES,
130 mapTc (tcClassSig clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
132 -- MAKE THE CLASS DETAILS
134 (op_tys, op_items) = unzip sig_stuff
135 sc_tys = mkPredTys sc_theta
136 dict_component_tys = sc_tys ++ op_tys
137 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
139 dict_con = mkDataCon datacon_name
140 [NotMarkedStrict | _ <- dict_component_tys]
141 [{- No labelled fields -}]
144 [{-No existential tyvars-}] [{-Or context-}]
147 dict_con_id dict_wrap_id
149 dict_con_id = mkDataConId datacon_wkr_name dict_con
150 dict_wrap_id = mkDataConWrapId dict_con
152 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
156 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
157 -> TcM (Maybe (NameEnv Bool))
158 -- The returned environment says
159 -- x not in env => no default method
160 -- x -> True => generic default method
161 -- x -> False => polymorphic default method
163 -- Check default bindings
164 -- a) must be for a class op for this class
165 -- b) must be all generic or all non-generic
166 -- and return a mapping from class-op to DefMeth info
168 -- But do all this only for source binds
170 checkDefaultBinds clas ops Nothing
173 checkDefaultBinds clas ops (Just mbs)
174 = go mbs `thenTc` \ dm_env ->
175 returnTc (Just dm_env)
177 go EmptyMonoBinds = returnTc emptyNameEnv
179 go (AndMonoBinds b1 b2)
180 = go b1 `thenTc` \ dm_info1 ->
181 go b2 `thenTc` \ dm_info2 ->
182 returnTc (dm_info1 `plusNameEnv` dm_info2)
184 go (FunMonoBind op _ matches loc)
187 -- Check that the op is from this class
188 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
190 -- Check that all the defns ar generic, or none are
191 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
193 returnTc (unitNameEnv op all_generic)
195 n_generic = count (maybeToBool . maybeGenericMatch) matches
196 none_generic = n_generic == 0
197 all_generic = matches `lengthIs` n_generic
202 tcClassSig :: 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 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)]
226 -- Build the selector id and default method id
227 sel_id = mkDictSelId op_name clas
228 DefMeth dm_name = sig_dm
230 dm_info = case maybe_dm_env of
232 Just dm_env -> mk_src_dm_info dm_env
234 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
236 Just True -> GenDefMeth
237 Just False -> DefMeth dm_name
239 returnTc (local_ty, (sel_id, dm_info))
242 checkValidClass is called once the mutually-recursive knot has been
243 tied, so we can look at things freely.
246 checkValidClass :: Class -> TcM ()
248 = -- CHECK ARITY 1 FOR HASKELL 1.4
249 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
251 -- Check that the class is unary, unless GlaExs
252 checkTc (not (null tyvars)) (nullaryClassErr cls) `thenTc_`
253 checkTc (gla_exts || unary) (classArityErr cls) `thenTc_`
255 -- Check the super-classes
256 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
258 -- Check the class operations
259 mapTc_ check_op op_stuff `thenTc_`
261 -- Check that if the class has generic methods, then the
262 -- class has only one parameter. We can't do generic
263 -- multi-parameter type classes!
264 checkTc (unary || no_generics) (genericMultiParamErr cls)
267 (tyvars, theta, _, op_stuff) = classBigSig cls
268 unary = isSingleton tyvars
269 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
271 check_op (sel_id, dm)
272 = checkValidTheta SigmaCtxt (tail theta) `thenTc_`
273 -- The 'tail' removes the initial (C a) from the
274 -- class itself, leaving just the method type
276 checkValidType (FunSigCtxt op_name) tau `thenTc_`
278 -- Check that for a generic method, the type of
279 -- the method is sufficiently simple
280 checkTc (dm /= GenDefMeth || validGenericMethodType op_ty)
281 (badGenericMethodType op_name op_ty)
283 op_name = idName sel_id
284 op_ty = idType sel_id
285 (_,theta,tau) = tcSplitSigmaTy op_ty
289 %************************************************************************
291 \subsection[Default methods]{Default methods}
293 %************************************************************************
295 The default methods for a class are each passed a dictionary for the
296 class, so that they get access to the other methods at the same type.
297 So, given the class decl
301 op2 :: Ord b => a -> b -> b -> b
304 op2 x y z = if (op1 x) && (y < z) then y else z
306 we get the default methods:
308 defm.Foo.op1 :: forall a. Foo a => a -> Bool
309 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
311 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
312 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
313 if (op1 a dfoo x) && (< b dord y z) then y else z
316 When we come across an instance decl, we may need to use the default
319 instance Foo Int where {}
323 const.Foo.Int.op1 :: Int -> Bool
324 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
326 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
327 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
329 dfun.Foo.Int :: Foo Int
330 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
332 Notice that, as with method selectors above, we assume that dictionary
333 application is curried, so there's no need to mention the Ord dictionary
334 in const.Foo.Int.op2 (or the type variable).
337 instance Foo a => Foo [a] where {}
339 dfun.Foo.List :: forall a. Foo a -> Foo [a]
341 = /\ a -> \ dfoo_a ->
343 op1 = defm.Foo.op1 [a] dfoo_list
344 op2 = defm.Foo.op2 [a] dfoo_list
345 dfoo_list = (op1, op2)
350 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
351 each local class decl.
354 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
356 tcClassDecls2 this_mod decls
358 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
359 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
360 -- The 'Just' picks out source ClassDecls
362 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
363 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
364 returnNF_Tc (lie1 `plusLIE` lie2,
365 binds1 `AndMonoBinds` binds2,
369 @tcClassDecl2@ generates bindings for polymorphic default methods
370 (generic default methods have by now turned into instance declarations)
373 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
374 -> NF_TcM (LIE, TcMonoBinds, [Id])
376 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
377 tcdMeths = Just default_binds, tcdLoc = src_loc})
378 = -- The 'Just' picks out source ClassDecls
379 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
380 tcAddSrcLoc src_loc $
381 tcLookupClass class_name `thenNF_Tc` \ clas ->
383 -- We make a separate binding for each default method.
384 -- At one time I used a single AbsBinds for all of them, thus
385 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
386 -- But that desugars into
387 -- ds = \d -> (..., ..., ...)
388 -- dm1 = \d -> case ds d of (a,b,c) -> a
389 -- And since ds is big, it doesn't get inlined, so we don't get good
390 -- default methods. Better to make separate AbsBinds for each
392 (tyvars, _, _, op_items) = classBigSig clas
393 prags = filter isPragSig sigs
394 tc_dm = tcDefMeth clas tyvars default_binds prags
396 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
398 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
401 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
402 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
403 -- Generate code for polymorphic default methods only
404 -- (Generic default methods have turned into instance decls by now.)
405 -- This is incompatible with Hugs, which expects a polymorphic
406 -- default method for every class op, regardless of whether or not
407 -- the programmer supplied an explicit default decl for the class.
408 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
410 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
411 = tcInstSigTyVars ClsTv tyvars `thenNF_Tc` \ clas_tyvars ->
413 dm_ty = idType sel_id -- Same as dict selector!
414 -- The default method's type should really come from the
415 -- iface file, since it could be usage-generalised, but this
416 -- requires altering the mess of knots in TcModule and I'm
417 -- too scared to do that. Instead, I have disabled generalisation
418 -- of types of default methods (and dict funs) by annotating them
419 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
421 inst_tys = mkTyVarTys clas_tyvars
422 theta = [mkClassPred clas inst_tys]
423 dm_id = mkDefaultMethodId dm_name dm_ty
424 local_dm_id = setIdLocalExported dm_id
425 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
427 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
429 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
430 tcMethodBind clas origin clas_tyvars inst_tys theta
431 binds_in prags False op_item
432 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
434 tcAddErrCtxt (defltMethCtxt clas) $
438 (ptext SLIT("class") <+> ppr clas)
441 insts_needed `thenTc` \ (const_lie, dict_binds) ->
443 -- Simplification can do unification
444 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
450 [(clas_tyvars', local_dm_id, instToId local_dm_inst)]
451 emptyNameSet -- No inlines (yet)
452 (dict_binds `andMonoBinds` defm_bind)
454 returnTc (full_bind, const_lie, [dm_id])
456 origin = ClassDeclOrigin
461 %************************************************************************
463 \subsection{Typechecking a method}
465 %************************************************************************
467 @tcMethodBind@ is used to type-check both default-method and
468 instance-decl method declarations. We must type-check methods one at a
469 time, because their signatures may have different contexts and
476 -> [TcTyVar] -- Instantiated type variables for the
477 -- enclosing class/instance decl.
478 -- They'll be signature tyvars, and we
479 -- want to check that they don't get bound
480 -> [TcType] -- Instance types
481 -> TcThetaType -- Available theta; this could be used to check
482 -- the method signature, but actually that's done by
483 -- the caller; here, it's just used for the error message
484 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
485 -> [RenamedSig] -- Pramgas (just for this one)
486 -> Bool -- True <=> This method is from an instance declaration
487 -> ClassOpItem -- The method selector and default-method Id
488 -> TcM (TcMonoBinds, LIE, Inst)
490 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
491 meth_binds prags is_inst_decl (sel_id, dm_info)
492 = tcGetSrcLoc `thenNF_Tc` \ loc ->
493 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
495 meth_id = instToId meth
496 meth_name = idName meth_id
497 meth_prags = find_prags (idName sel_id) meth_name prags
499 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
501 -- Figure out what method binding to use
502 -- If the user suppplied one, use it, else construct a default one
503 (case find_bind (idName sel_id) meth_name meth_binds of
504 Just user_bind -> returnTc user_bind
505 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
506 returnTc (FunMonoBind meth_name False -- Not infix decl
507 [mkSimpleMatch [] rhs placeHolderType loc] loc)
508 ) `thenTc` \ meth_bind ->
509 -- Check the bindings; first add inst_tyvars to the envt
510 -- so that we don't quantify over them in nested places
511 -- The *caller* put the class/inst decl tyvars into the envt
512 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
513 (tcAddErrCtxt (methodCtxt sel_id) $
514 tcBindWithSigs NotTopLevel meth_bind
515 [sig_info] meth_prags NonRecursive
516 ) `thenTc` \ (binds, insts, _) ->
518 tcExtendLocalValEnv [(meth_name, meth_id)]
519 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
521 -- The prag_lie for a SPECIALISE pragma will mention the function
522 -- itself, so we have to simplify them away right now lest they float
524 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
526 -- Now check that the instance type variables
527 -- (or, in the case of a class decl, the class tyvars)
528 -- have not been unified with anything in the environment
530 -- We do this for each method independently to localise error messages
531 -- ...and this is why the call to tcExtendGlobalTyVars must be here
532 -- rather than in the caller
533 tcAddErrCtxt (ptext SLIT("When checking the type of class method")
534 <+> quotes (ppr sel_id)) $
535 tcAddErrCtxtM (sigCtxt inst_tyvars inst_theta (idType meth_id)) $
536 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
538 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
539 insts `plusLIE` prag_lie',
542 -- The user didn't supply a method binding,
543 -- so we have to make up a default binding
544 -- The RHS of a default method depends on the default-method info
545 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_name)
546 = -- An polymorphic default method
547 returnTc (HsVar dm_name)
549 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
550 = -- No default method
551 -- Warn only if -fwarn-missing-methods
552 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
553 warnTc (is_inst_decl && warn)
554 (omittedMethodWarn sel_id) `thenNF_Tc_`
557 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
558 (HsLit (HsString (_PK_ error_msg)))
559 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
562 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
563 = -- A generic default method
564 -- If the method is defined generically, we can only do the job if the
565 -- instance declaration is for a single-parameter type class with
566 -- a type constructor applied to type arguments in the instance decl
567 -- (checkTc, so False provokes the error)
568 checkTc (not is_inst_decl || simple_inst)
569 (badGenericInstance sel_id) `thenTc_`
571 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
574 rhs = mkGenericRhs sel_id clas_tyvar tycon
576 stuff = vcat [ppr clas <+> ppr inst_tys,
577 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
579 -- The tycon is only used in the generic case, and in that
580 -- case we require that the instance decl is for a single-parameter
581 -- type class with type variable arguments:
582 -- instance (...) => C (T a b)
583 simple_inst = maybeToBool maybe_tycon
584 clas_tyvar = head (classTyVars clas)
585 Just tycon = maybe_tycon
586 maybe_tycon = case inst_tys of
587 [ty] -> case tcSplitTyConApp_maybe ty of
588 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
595 -- The renamer just puts the selector ID as the binder in the method binding
596 -- but we must use the method name; so we substitute it here. Crude but simple.
597 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
598 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
599 find_bind sel_name meth_name (AndMonoBinds b1 b2)
600 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
601 find_bind sel_name meth_name other = Nothing -- Default case
603 -- Find the prags for this method, and replace the
604 -- selector name with the method name
605 find_prags sel_name meth_name [] = []
606 find_prags sel_name meth_name (SpecSig name ty loc : prags)
607 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
608 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
609 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
610 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
618 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
621 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
622 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
625 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
628 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
631 = hsep [ptext SLIT("Class"), quotes (ppr clas),
632 ptext SLIT("does not have a method"), quotes (ppr op)]
634 omittedMethodWarn sel_id
635 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
637 badGenericMethodType op op_ty
638 = hang (ptext SLIT("Generic method type is too complex"))
639 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
640 ptext SLIT("You can only use type variables, arrows, and tuples")])
642 badGenericInstance sel_id
643 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
644 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
645 ptext SLIT("(where T is a derivable type constructor)")]
648 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
650 genericMultiParamErr clas
651 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
652 ptext SLIT("cannot have generic methods")