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,
17 getClassDeclSysNames, placeHolderType
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, tcRecTheta, checkSigTyVars, checkAmbiguity, sigCtxt, mkTcSig )
35 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
36 import TcMType ( tcInstTyVars )
37 import TcType ( Type, ThetaType, mkTyVarTys, mkPredTys, mkClassPred, tcIsTyVarTy, tcSplitTyConApp_maybe )
39 import Generics ( mkGenericRhs, validGenericMethodType )
40 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
41 import Class ( classTyVars, classBigSig, classTyCon,
42 Class, ClassOpItem, DefMeth (..) )
43 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
44 import DataCon ( mkDataCon )
45 import Demand ( StrictnessMark(..) )
46 import Id ( Id, idType, idName )
47 import Module ( Module )
48 import Name ( Name, NamedThing(..) )
49 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
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 :: RecFlag -> RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
104 tcClassDecl1 is_rec rec_env
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 = -- CHECK ARITY 1 FOR HASKELL 1.4
110 doptsTc Opt_GlasgowExts `thenTc` \ gla_ext_opt ->
112 gla_exts = gla_ext_opt || not (maybeToBool def_methods)
113 -- Accept extensions if gla_exts is on,
114 -- or if we're looking at an interface file decl
115 in -- (in which case def_methods = Nothing
117 -- LOOK THINGS UP IN THE ENVIRONMENT
118 tcLookupClass class_name `thenTc` \ clas ->
120 tyvars = classTyVars clas
121 op_sigs = filter isClassOpSig class_sigs
122 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
123 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
125 tcExtendTyVarEnv tyvars $
127 -- SOURCE-CODE CONSISTENCY CHECKS
129 Nothing -> -- Not source
132 Just dms -> -- Source so do error checks
133 checkTc (gla_exts || length tyvar_names == 1)
134 (classArityErr class_name) `thenTc_`
136 checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
137 checkGenericClassIsUnary clas dm_env `thenTc_`
138 returnTc (Just dm_env)
139 ) `thenTc` \ mb_dm_env ->
142 tcSuperClasses is_rec gla_exts clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
144 -- CHECK THE CLASS SIGNATURES,
145 mapTc (tcClassSig is_rec rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
147 -- MAKE THE CLASS DETAILS
149 (op_tys, op_items) = unzip sig_stuff
150 sc_tys = mkPredTys sc_theta
151 dict_component_tys = sc_tys ++ op_tys
153 dict_con = mkDataCon datacon_name
154 [NotMarkedStrict | _ <- dict_component_tys]
155 [{- No labelled fields -}]
158 [{-No existential tyvars-}] [{-Or context-}]
161 dict_con_id dict_wrap_id
163 dict_con_id = mkDataConId datacon_wkr_name dict_con
164 dict_wrap_id = mkDataConWrapId dict_con
166 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
170 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds
171 -> TcM (NameEnv Bool)
172 -- The returned environment says
173 -- x not in env => no default method
174 -- x -> True => generic default method
175 -- x -> False => polymorphic default method
177 -- Check default bindings
178 -- a) must be for a class op for this class
179 -- b) must be all generic or all non-generic
180 -- and return a mapping from class-op to DefMeth info
182 -- But do all this only for source binds
184 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
186 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
187 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
188 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
189 returnTc (dm_info1 `plusNameEnv` dm_info2)
191 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
194 -- Check that the op is from this class
195 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
197 -- Check that all the defns ar generic, or none are
198 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
200 returnTc (unitNameEnv op all_generic)
202 n_generic = count (maybeToBool . maybeGenericMatch) matches
203 none_generic = n_generic == 0
204 all_generic = n_generic == length matches
206 checkGenericClassIsUnary clas dm_env
207 = -- Check that if the class has generic methods, then the
208 -- class has only one parameter. We can't do generic
209 -- multi-parameter type classes!
210 checkTc (unary || no_generics) (genericMultiParamErr clas)
212 unary = length (classTyVars clas) == 1
213 no_generics = not (or (nameEnvElts dm_env))
218 tcSuperClasses :: RecFlag -> Bool -> Class
219 -> RenamedContext -- class context
220 -> [Name] -- Names for superclass selectors
221 -> TcM (ThetaType, -- the superclass context
222 [Id]) -- superclass selector Ids
224 tcSuperClasses is_rec gla_exts clas context sc_sel_names
225 = ASSERT( length context == length 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
231 mapTc_ check_constraint context `thenTc_`
233 -- Context is already kind-checked
234 tcRecTheta is_rec context `thenTc` \ sc_theta ->
236 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
239 returnTc (sc_theta, sc_sel_ids)
242 check_constraint sc = checkTc (ok sc) (superClassErr clas sc)
243 ok (HsClassP c tys) | gla_exts = True
244 | otherwise = all is_tyvar tys
245 ok (HsIParam _ _) = False -- Never legal
247 is_tyvar (HsTyVar _) = True
248 is_tyvar other = False
251 tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
252 -> Class -- ...ditto...
253 -> [TyVar] -- The class type variable, used for error check only
254 -> Maybe (NameEnv Bool) -- Info about default methods
256 -> TcM (Type, -- Type of the method
257 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
259 -- This warrants an explanation: we need to separate generic
260 -- default methods and default methods later on in the compiler
261 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
262 -- Class.DefMeth data structure.
264 tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
265 (ClassOpSig op_name sig_dm op_ty src_loc)
266 = tcAddSrcLoc src_loc $
268 -- Check the type signature. NB that the envt *already has*
269 -- bindings for the type variables; see comments in TcTyAndClassDcls.
271 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
273 -- Check for ambiguous class op types
275 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
277 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
278 -- The default method's type should really come from the
279 -- iface file, since it could be usage-generalised, but this
280 -- requires altering the mess of knots in TcModule and I'm
281 -- too scared to do that. Instead, I have disabled generalisation
282 -- of types of default methods (and dict funs) by annotating them
283 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
286 -- Build the selector id and default method id
287 sel_id = mkDictSelId op_name clas
288 dm_id = mkDefaultMethodId dm_name global_ty
289 DefMeth dm_name = sig_dm
291 dm_info = case maybe_dm_env of
292 Nothing -> iface_dm_info
293 Just dm_env -> mk_src_dm_info dm_env
295 iface_dm_info = case sig_dm of
296 NoDefMeth -> NoDefMeth
297 GenDefMeth -> GenDefMeth
298 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
300 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
302 Just True -> GenDefMeth
303 Just False -> DefMeth dm_id
305 -- Check that for a generic method, the type of
306 -- the method is sufficiently simple
307 checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
308 (badGenericMethodType op_name op_ty) `thenTc_`
310 returnTc (local_ty, (sel_id, dm_info))
314 %************************************************************************
316 \subsection[Default methods]{Default methods}
318 %************************************************************************
320 The default methods for a class are each passed a dictionary for the
321 class, so that they get access to the other methods at the same type.
322 So, given the class decl
326 op2 :: Ord b => a -> b -> b -> b
329 op2 x y z = if (op1 x) && (y < z) then y else z
331 we get the default methods:
333 defm.Foo.op1 :: forall a. Foo a => a -> Bool
334 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
336 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
337 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
338 if (op1 a dfoo x) && (< b dord y z) then y else z
341 When we come across an instance decl, we may need to use the default
344 instance Foo Int where {}
348 const.Foo.Int.op1 :: Int -> Bool
349 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
351 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
352 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
354 dfun.Foo.Int :: Foo Int
355 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
357 Notice that, as with method selectors above, we assume that dictionary
358 application is curried, so there's no need to mention the Ord dictionary
359 in const.Foo.Int.op2 (or the type variable).
362 instance Foo a => Foo [a] where {}
364 dfun.Foo.List :: forall a. Foo a -> Foo [a]
366 = /\ a -> \ dfoo_a ->
368 op1 = defm.Foo.op1 [a] dfoo_list
369 op2 = defm.Foo.op2 [a] dfoo_list
370 dfoo_list = (op1, op2)
375 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
376 each local class decl.
379 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
381 tcClassDecls2 this_mod decls
383 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
384 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
385 -- The 'Just' picks out source ClassDecls
387 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
388 tc2 `thenNF_Tc` \ (lie2, binds2) ->
389 returnNF_Tc (lie1 `plusLIE` lie2,
390 binds1 `AndMonoBinds` binds2)
393 @tcClassDecl2@ generates bindings for polymorphic default methods
394 (generic default methods have by now turned into instance declarations)
397 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
398 -> NF_TcM (LIE, TcMonoBinds)
400 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
401 tcdMeths = Just default_binds, tcdLoc = src_loc})
402 = -- The 'Just' picks out source ClassDecls
403 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
404 tcAddSrcLoc src_loc $
405 tcLookupClass class_name `thenNF_Tc` \ clas ->
407 -- We make a separate binding for each default method.
408 -- At one time I used a single AbsBinds for all of them, thus
409 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
410 -- But that desugars into
411 -- ds = \d -> (..., ..., ...)
412 -- dm1 = \d -> case ds d of (a,b,c) -> a
413 -- And since ds is big, it doesn't get inlined, so we don't get good
414 -- default methods. Better to make separate AbsBinds for each
416 (tyvars, _, _, op_items) = classBigSig clas
417 prags = filter isPragSig sigs
418 tc_dm = tcDefMeth clas tyvars default_binds prags
420 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
422 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
425 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
426 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
427 -- Generate code for polymorphic default methods only
428 -- (Generic default methods have turned into instance decls by now.)
429 -- This is incompatible with Hugs, which expects a polymorphic
430 -- default method for every class op, regardless of whether or not
431 -- the programmer supplied an explicit default decl for the class.
432 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
434 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
435 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
437 theta = [(mkClassPred clas inst_tys)]
439 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
441 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
442 tcMethodBind clas origin clas_tyvars inst_tys theta
443 binds_in prags False op_item
444 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
446 tcAddErrCtxt (defltMethCtxt clas) $
450 (ptext SLIT("class") <+> ppr clas)
453 insts_needed `thenTc` \ (const_lie, dict_binds) ->
455 -- Simplification can do unification
456 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
462 [(clas_tyvars', dm_id, instToId local_dm_inst)]
463 emptyNameSet -- No inlines (yet)
464 (dict_binds `andMonoBinds` defm_bind)
466 returnTc (full_bind, const_lie)
468 origin = ClassDeclOrigin
473 %************************************************************************
475 \subsection{Typechecking a method}
477 %************************************************************************
479 @tcMethodBind@ is used to type-check both default-method and
480 instance-decl method declarations. We must type-check methods one at a
481 time, because their signatures may have different contexts and
488 -> [TcTyVar] -- Instantiated type variables for the
489 -- enclosing class/instance decl.
490 -- They'll be signature tyvars, and we
491 -- want to check that they don't get bound
492 -> [TcType] -- Instance types
493 -> TcThetaType -- Available theta; this could be used to check
494 -- the method signature, but actually that's done by
495 -- the caller; here, it's just used for the error message
496 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
497 -> [RenamedSig] -- Pramgas (just for this one)
498 -> Bool -- True <=> This method is from an instance declaration
499 -> ClassOpItem -- The method selector and default-method Id
500 -> TcM (TcMonoBinds, LIE, Inst)
502 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
503 meth_binds prags is_inst_decl (sel_id, dm_info)
504 = tcGetSrcLoc `thenNF_Tc` \ loc ->
505 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
507 meth_id = instToId meth
508 meth_name = idName meth_id
509 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
510 meth_prags = find_prags (idName sel_id) meth_name prags
512 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
514 -- Figure out what method binding to use
515 -- If the user suppplied one, use it, else construct a default one
516 (case find_bind (idName sel_id) meth_name meth_binds of
517 Just user_bind -> returnTc user_bind
518 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
519 returnTc (FunMonoBind meth_name False -- Not infix decl
520 [mkSimpleMatch [] rhs placeHolderType loc] loc)
521 ) `thenTc` \ meth_bind ->
522 -- Check the bindings; first add inst_tyvars to the envt
523 -- so that we don't quantify over them in nested places
524 -- The *caller* put the class/inst decl tyvars into the envt
525 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
526 (tcAddErrCtxt (methodCtxt sel_id) $
527 tcBindWithSigs NotTopLevel meth_bind
528 [sig_info] meth_prags NonRecursive
529 ) `thenTc` \ (binds, insts, _) ->
531 tcExtendLocalValEnv [(meth_name, meth_id)]
532 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
534 -- The prag_lie for a SPECIALISE pragma will mention the function
535 -- itself, so we have to simplify them away right now lest they float
537 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
539 -- Now check that the instance type variables
540 -- (or, in the case of a class decl, the class tyvars)
541 -- have not been unified with anything in the environment
543 -- We do this for each method independently to localise error messages
544 -- ...and this is why the call to tcExtendGlobalTyVars must be here
545 -- rather than in the caller
546 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
547 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
549 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
550 insts `plusLIE` prag_lie',
553 -- The user didn't supply a method binding,
554 -- so we have to make up a default binding
555 -- The RHS of a default method depends on the default-method info
556 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
557 = -- An polymorphic default method
558 returnTc (HsVar (idName dm_id))
560 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
561 = -- No default method
562 -- Warn only if -fwarn-missing-methods
563 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
564 warnTc (is_inst_decl && warn)
565 (omittedMethodWarn sel_id) `thenNF_Tc_`
568 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
569 (HsLit (HsString (_PK_ error_msg)))
570 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
573 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
574 = -- A generic default method
575 -- If the method is defined generically, we can only do the job if the
576 -- instance declaration is for a single-parameter type class with
577 -- a type constructor applied to type arguments in the instance decl
578 -- (checkTc, so False provokes the error)
579 checkTc (not is_inst_decl || simple_inst)
580 (badGenericInstance sel_id) `thenTc_`
582 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
585 rhs = mkGenericRhs sel_id clas_tyvar tycon
587 stuff = vcat [ppr clas <+> ppr inst_tys,
588 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
590 -- The tycon is only used in the generic case, and in that
591 -- case we require that the instance decl is for a single-parameter
592 -- type class with type variable arguments:
593 -- instance (...) => C (T a b)
594 simple_inst = maybeToBool maybe_tycon
595 clas_tyvar = head (classTyVars clas)
596 Just tycon = maybe_tycon
597 maybe_tycon = case inst_tys of
598 [ty] -> case tcSplitTyConApp_maybe ty of
599 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
606 -- The renamer just puts the selector ID as the binder in the method binding
607 -- but we must use the method name; so we substitute it here. Crude but simple.
608 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
609 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
610 find_bind sel_name meth_name (AndMonoBinds b1 b2)
611 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
612 find_bind sel_name meth_name other = Nothing -- Default case
614 -- Find the prags for this method, and replace the
615 -- selector name with the method name
616 find_prags sel_name meth_name [] = []
617 find_prags sel_name meth_name (SpecSig name ty loc : prags)
618 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
619 find_prags sel_name meth_name (InlineSig name phase loc : prags)
620 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
621 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
622 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
623 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
630 classArityErr class_name
631 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
633 superClassErr clas sc
634 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
635 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
638 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
641 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
644 = hsep [ptext SLIT("Class"), quotes (ppr clas),
645 ptext SLIT("does not have a method"), quotes (ppr op)]
647 omittedMethodWarn sel_id
648 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
650 badGenericMethodType op op_ty
651 = hang (ptext SLIT("Generic method type is too complex"))
652 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
653 ptext SLIT("You can only use type variables, arrows, and tuples")])
655 badGenericInstance sel_id
656 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
657 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
658 ptext SLIT("(where T is a derivable type constructor)")]
661 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
663 genericMultiParamErr clas
664 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
665 ptext SLIT("cannot have generic methods")