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 ( tcInstSigTyVars, checkValidTheta, checkValidType, SourceTyCtxt(..), UserTypeCtxt(..) )
36 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
37 mkSigmaTy, mkTyVarTys, mkPredTys, mkClassPred,
38 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitSigmaTy
41 import Generics ( mkGenericRhs, validGenericMethodType )
42 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
43 import Class ( classTyVars, classBigSig, classTyCon, className,
44 Class, ClassOpItem, DefMeth (..) )
45 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
46 import DataCon ( mkDataCon )
47 import Id ( idType, idName, setIdLocalExported )
48 import Module ( Module )
49 import Name ( Name, NamedThing(..) )
50 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
51 import NameSet ( emptyNameSet )
54 import VarSet ( mkVarSet, emptyVarSet )
56 import ErrUtils ( dumpIfSet )
57 import Util ( count, isSingleton, lengthIs, equalLength )
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 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
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 = -- 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 rec_env 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 :: RecTcEnv -- Knot tying only!
203 -> Class -- ...ditto...
204 -> [TyVar] -- The class type variable, used for error check only
205 -> Maybe (NameEnv Bool) -- Info about default methods;
206 -- Nothing => imported class defn with no method binds
208 -> TcM (Type, -- Type of the method
209 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
211 -- This warrants an explanation: we need to separate generic
212 -- default methods and default methods later on in the compiler
213 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
214 -- Class.DefMeth data structure.
216 tcClassSig unf_env clas clas_tyvars maybe_dm_env
217 (ClassOpSig op_name sig_dm op_ty src_loc)
218 = tcAddSrcLoc src_loc $
220 -- Check the type signature. NB that the envt *already has*
221 -- bindings for the type variables; see comments in TcTyAndClassDcls.
222 tcHsType op_ty `thenTc` \ local_ty ->
225 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
226 global_ty = mkSigmaTy clas_tyvars theta local_ty
227 -- The default method's type should really come from the
228 -- iface file, since it could be usage-generalised, but this
229 -- requires altering the mess of knots in TcModule and I'm
230 -- too scared to do that. Instead, I have disabled generalisation
231 -- of types of default methods (and dict funs) by annotating them
232 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
234 -- Build the selector id and default method id
235 sel_id = mkDictSelId op_name clas
236 dm_id = mkDefaultMethodId dm_name global_ty
237 DefMeth dm_name = sig_dm
239 dm_info = case maybe_dm_env of
240 Nothing -> iface_dm_info
241 Just dm_env -> mk_src_dm_info dm_env
243 iface_dm_info = case sig_dm of
244 NoDefMeth -> NoDefMeth
245 GenDefMeth -> GenDefMeth
246 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
248 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
250 Just True -> GenDefMeth
251 Just False -> DefMeth dm_id
253 returnTc (local_ty, (sel_id, dm_info))
256 checkValidClass is called once the mutually-recursive knot has been
257 tied, so we can look at things freely.
260 checkValidClass :: Class -> TcM ()
262 = -- CHECK ARITY 1 FOR HASKELL 1.4
263 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
265 -- Check that the class is unary, unless GlaExs
266 checkTc (not (null tyvars)) (nullaryClassErr cls) `thenTc_`
267 checkTc (gla_exts || unary) (classArityErr cls) `thenTc_`
269 -- Check the super-classes
270 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
272 -- Check the class operations
273 mapTc_ check_op op_stuff `thenTc_`
275 -- Check that if the class has generic methods, then the
276 -- class has only one parameter. We can't do generic
277 -- multi-parameter type classes!
278 checkTc (unary || no_generics) (genericMultiParamErr cls)
281 (tyvars, theta, _, op_stuff) = classBigSig cls
282 unary = isSingleton 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 = tcInstSigTyVars ClsTv tyvars `thenNF_Tc` \ clas_tyvars ->
426 inst_tys = mkTyVarTys clas_tyvars
427 theta = [mkClassPred clas inst_tys]
428 local_dm_id = setIdLocalExported dm_id
429 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
431 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
433 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
434 tcMethodBind clas origin clas_tyvars inst_tys theta
435 binds_in prags False op_item
436 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
438 tcAddErrCtxt (defltMethCtxt clas) $
442 (ptext SLIT("class") <+> ppr clas)
445 insts_needed `thenTc` \ (const_lie, dict_binds) ->
447 -- Simplification can do unification
448 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
454 [(clas_tyvars', local_dm_id, instToId local_dm_inst)]
455 emptyNameSet -- No inlines (yet)
456 (dict_binds `andMonoBinds` defm_bind)
458 returnTc (full_bind, const_lie)
460 origin = ClassDeclOrigin
465 %************************************************************************
467 \subsection{Typechecking a method}
469 %************************************************************************
471 @tcMethodBind@ is used to type-check both default-method and
472 instance-decl method declarations. We must type-check methods one at a
473 time, because their signatures may have different contexts and
480 -> [TcTyVar] -- Instantiated type variables for the
481 -- enclosing class/instance decl.
482 -- They'll be signature tyvars, and we
483 -- want to check that they don't get bound
484 -> [TcType] -- Instance types
485 -> TcThetaType -- Available theta; this could be used to check
486 -- the method signature, but actually that's done by
487 -- the caller; here, it's just used for the error message
488 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
489 -> [RenamedSig] -- Pramgas (just for this one)
490 -> Bool -- True <=> This method is from an instance declaration
491 -> ClassOpItem -- The method selector and default-method Id
492 -> TcM (TcMonoBinds, LIE, Inst)
494 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
495 meth_binds prags is_inst_decl (sel_id, dm_info)
496 = tcGetSrcLoc `thenNF_Tc` \ loc ->
497 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
499 meth_id = instToId meth
500 meth_name = idName meth_id
501 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
502 meth_prags = find_prags (idName sel_id) meth_name prags
504 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
506 -- Figure out what method binding to use
507 -- If the user suppplied one, use it, else construct a default one
508 (case find_bind (idName sel_id) meth_name meth_binds of
509 Just user_bind -> returnTc user_bind
510 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
511 returnTc (FunMonoBind meth_name False -- Not infix decl
512 [mkSimpleMatch [] rhs placeHolderType loc] loc)
513 ) `thenTc` \ meth_bind ->
514 -- Check the bindings; first add inst_tyvars to the envt
515 -- so that we don't quantify over them in nested places
516 -- The *caller* put the class/inst decl tyvars into the envt
517 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
518 (tcAddErrCtxt (methodCtxt sel_id) $
519 tcBindWithSigs NotTopLevel meth_bind
520 [sig_info] meth_prags NonRecursive
521 ) `thenTc` \ (binds, insts, _) ->
523 tcExtendLocalValEnv [(meth_name, meth_id)]
524 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
526 -- The prag_lie for a SPECIALISE pragma will mention the function
527 -- itself, so we have to simplify them away right now lest they float
529 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
531 -- Now check that the instance type variables
532 -- (or, in the case of a class decl, the class tyvars)
533 -- have not been unified with anything in the environment
535 -- We do this for each method independently to localise error messages
536 -- ...and this is why the call to tcExtendGlobalTyVars must be here
537 -- rather than in the caller
538 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
539 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
541 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
542 insts `plusLIE` prag_lie',
545 -- The user didn't supply a method binding,
546 -- so we have to make up a default binding
547 -- The RHS of a default method depends on the default-method info
548 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
549 = -- An polymorphic default method
550 returnTc (HsVar (idName dm_id))
552 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
553 = -- No default method
554 -- Warn only if -fwarn-missing-methods
555 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
556 warnTc (is_inst_decl && warn)
557 (omittedMethodWarn sel_id) `thenNF_Tc_`
560 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
561 (HsLit (HsString (_PK_ error_msg)))
562 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
565 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
566 = -- A generic default method
567 -- If the method is defined generically, we can only do the job if the
568 -- instance declaration is for a single-parameter type class with
569 -- a type constructor applied to type arguments in the instance decl
570 -- (checkTc, so False provokes the error)
571 checkTc (not is_inst_decl || simple_inst)
572 (badGenericInstance sel_id) `thenTc_`
574 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
577 rhs = mkGenericRhs sel_id clas_tyvar tycon
579 stuff = vcat [ppr clas <+> ppr inst_tys,
580 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
582 -- The tycon is only used in the generic case, and in that
583 -- case we require that the instance decl is for a single-parameter
584 -- type class with type variable arguments:
585 -- instance (...) => C (T a b)
586 simple_inst = maybeToBool maybe_tycon
587 clas_tyvar = head (classTyVars clas)
588 Just tycon = maybe_tycon
589 maybe_tycon = case inst_tys of
590 [ty] -> case tcSplitTyConApp_maybe ty of
591 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
598 -- The renamer just puts the selector ID as the binder in the method binding
599 -- but we must use the method name; so we substitute it here. Crude but simple.
600 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
601 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
602 find_bind sel_name meth_name (AndMonoBinds b1 b2)
603 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
604 find_bind sel_name meth_name other = Nothing -- Default case
606 -- Find the prags for this method, and replace the
607 -- selector name with the method name
608 find_prags sel_name meth_name [] = []
609 find_prags sel_name meth_name (SpecSig name ty loc : prags)
610 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
611 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
612 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
613 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
621 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
624 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
625 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
628 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
631 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
634 = hsep [ptext SLIT("Class"), quotes (ppr clas),
635 ptext SLIT("does not have a method"), quotes (ppr op)]
637 omittedMethodWarn sel_id
638 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
640 badGenericMethodType op op_ty
641 = hang (ptext SLIT("Generic method type is too complex"))
642 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
643 ptext SLIT("You can only use type variables, arrows, and tuples")])
645 badGenericInstance sel_id
646 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
647 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
648 ptext SLIT("(where T is a derivable type constructor)")]
651 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
653 genericMultiParamErr clas
654 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
655 ptext SLIT("cannot have generic methods")