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(..), StrictnessMark(..) )
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 Id ( Id, idType, idName )
46 import Module ( Module )
47 import Name ( Name, NamedThing(..) )
48 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv, nameEnvElts )
49 import NameSet ( emptyNameSet )
52 import VarSet ( mkVarSet, emptyVarSet )
54 import ErrUtils ( dumpIfSet )
56 import Maybes ( seqMaybe, maybeToBool )
63 Every class implicitly declares a new data type, corresponding to dictionaries
64 of that class. So, for example:
66 class (D a) => C a where
68 op2 :: forall b. Ord b => a -> b -> b
70 would implicitly declare
72 data CDict a = CDict (D a)
74 (forall b. Ord b => a -> b -> b)
76 (We could use a record decl, but that means changing more of the existing apparatus.
79 For classes with just one superclass+method, we use a newtype decl instead:
82 op :: forallb. a -> b -> b
86 newtype CDict a = CDict (forall b. a -> b -> b)
88 Now DictTy in Type is just a form of type synomym:
89 DictTy c t = TyConTy CDict `AppTy` t
91 Death to "ExpandingDicts".
94 %************************************************************************
96 \subsection{Type checking}
98 %************************************************************************
102 tcClassDecl1 :: RecFlag -> RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
103 tcClassDecl1 is_rec rec_env
104 (ClassDecl {tcdCtxt = context, tcdName = class_name,
105 tcdTyVars = tyvar_names, tcdFDs = fundeps,
106 tcdSigs = class_sigs, tcdMeths = def_methods,
107 tcdSysNames = sys_names, tcdLoc = src_loc})
108 = -- CHECK ARITY 1 FOR HASKELL 1.4
109 doptsTc Opt_GlasgowExts `thenTc` \ gla_ext_opt ->
111 gla_exts = gla_ext_opt || not (maybeToBool def_methods)
112 -- Accept extensions if gla_exts is on,
113 -- or if we're looking at an interface file decl
114 in -- (in which case def_methods = Nothing
116 -- LOOK THINGS UP IN THE ENVIRONMENT
117 tcLookupClass class_name `thenTc` \ clas ->
119 tyvars = classTyVars clas
120 op_sigs = filter isClassOpSig class_sigs
121 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
122 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
124 tcExtendTyVarEnv tyvars $
126 -- SOURCE-CODE CONSISTENCY CHECKS
128 Nothing -> -- Not source
131 Just dms -> -- Source so do error checks
132 checkTc (gla_exts || length tyvar_names == 1)
133 (classArityErr class_name) `thenTc_`
135 checkDefaultBinds clas op_names dms `thenTc` \ dm_env ->
136 checkGenericClassIsUnary clas dm_env `thenTc_`
137 returnTc (Just dm_env)
138 ) `thenTc` \ mb_dm_env ->
141 tcSuperClasses is_rec gla_exts clas context sc_sel_names `thenTc` \ (sc_theta, sc_sel_ids) ->
143 -- CHECK THE CLASS SIGNATURES,
144 mapTc (tcClassSig is_rec rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
146 -- MAKE THE CLASS DETAILS
148 (op_tys, op_items) = unzip sig_stuff
149 sc_tys = mkPredTys sc_theta
150 dict_component_tys = sc_tys ++ op_tys
152 dict_con = mkDataCon datacon_name
153 [NotMarkedStrict | _ <- dict_component_tys]
154 [{- No labelled fields -}]
157 [{-No existential tyvars-}] [{-Or context-}]
160 dict_con_id dict_wrap_id
162 dict_con_id = mkDataConId datacon_wkr_name dict_con
163 dict_wrap_id = mkDataConWrapId dict_con
165 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
169 checkDefaultBinds :: Class -> [Name] -> RenamedMonoBinds
170 -> TcM (NameEnv Bool)
171 -- The returned environment says
172 -- x not in env => no default method
173 -- x -> True => generic default method
174 -- x -> False => polymorphic default method
176 -- Check default bindings
177 -- a) must be for a class op for this class
178 -- b) must be all generic or all non-generic
179 -- and return a mapping from class-op to DefMeth info
181 -- But do all this only for source binds
183 checkDefaultBinds clas ops EmptyMonoBinds = returnTc emptyNameEnv
185 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
186 = checkDefaultBinds clas ops b1 `thenTc` \ dm_info1 ->
187 checkDefaultBinds clas ops b2 `thenTc` \ dm_info2 ->
188 returnTc (dm_info1 `plusNameEnv` dm_info2)
190 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
193 -- Check that the op is from this class
194 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
196 -- Check that all the defns ar generic, or none are
197 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
199 returnTc (unitNameEnv op all_generic)
201 n_generic = count (maybeToBool . maybeGenericMatch) matches
202 none_generic = n_generic == 0
203 all_generic = n_generic == length matches
205 checkGenericClassIsUnary clas dm_env
206 = -- Check that if the class has generic methods, then the
207 -- class has only one parameter. We can't do generic
208 -- multi-parameter type classes!
209 checkTc (unary || no_generics) (genericMultiParamErr clas)
211 unary = length (classTyVars clas) == 1
212 no_generics = not (or (nameEnvElts dm_env))
217 tcSuperClasses :: RecFlag -> Bool -> Class
218 -> RenamedContext -- class context
219 -> [Name] -- Names for superclass selectors
220 -> TcM (ThetaType, -- the superclass context
221 [Id]) -- superclass selector Ids
223 tcSuperClasses is_rec gla_exts clas context sc_sel_names
224 = ASSERT( length context == length sc_sel_names )
225 -- Check the context.
226 -- The renamer has already checked that the context mentions
227 -- only the type variable of the class decl.
229 -- For std Haskell check that the context constrains only tyvars
230 mapTc_ check_constraint context `thenTc_`
232 -- Context is already kind-checked
233 tcRecTheta is_rec context `thenTc` \ sc_theta ->
235 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
238 returnTc (sc_theta, sc_sel_ids)
241 check_constraint sc = checkTc (ok sc) (superClassErr clas sc)
242 ok (HsClassP c tys) | gla_exts = True
243 | otherwise = all is_tyvar tys
244 ok (HsIParam _ _) = False -- Never legal
246 is_tyvar (HsTyVar _) = True
247 is_tyvar other = False
250 tcClassSig :: RecFlag -> RecTcEnv -- Knot tying only!
251 -> Class -- ...ditto...
252 -> [TyVar] -- The class type variable, used for error check only
253 -> Maybe (NameEnv Bool) -- Info about default methods
255 -> TcM (Type, -- Type of the method
256 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
258 -- This warrants an explanation: we need to separate generic
259 -- default methods and default methods later on in the compiler
260 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
261 -- Class.DefMeth data structure.
263 tcClassSig is_rec unf_env clas clas_tyvars maybe_dm_env
264 (ClassOpSig op_name sig_dm op_ty src_loc)
265 = tcAddSrcLoc src_loc $
267 -- Check the type signature. NB that the envt *already has*
268 -- bindings for the type variables; see comments in TcTyAndClassDcls.
270 tcHsRecType is_rec op_ty `thenTc` \ local_ty ->
272 -- Check for ambiguous class op types
274 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
276 checkAmbiguity is_rec True clas_tyvars theta local_ty `thenTc` \ global_ty ->
277 -- The default method's type should really come from the
278 -- iface file, since it could be usage-generalised, but this
279 -- requires altering the mess of knots in TcModule and I'm
280 -- too scared to do that. Instead, I have disabled generalisation
281 -- of types of default methods (and dict funs) by annotating them
282 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
285 -- Build the selector id and default method id
286 sel_id = mkDictSelId op_name clas
287 dm_id = mkDefaultMethodId dm_name global_ty
288 DefMeth dm_name = sig_dm
290 dm_info = case maybe_dm_env of
291 Nothing -> iface_dm_info
292 Just dm_env -> mk_src_dm_info dm_env
294 iface_dm_info = case sig_dm of
295 NoDefMeth -> NoDefMeth
296 GenDefMeth -> GenDefMeth
297 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
299 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
301 Just True -> GenDefMeth
302 Just False -> DefMeth dm_id
304 -- Check that for a generic method, the type of
305 -- the method is sufficiently simple
306 checkTc (dm_info /= GenDefMeth || validGenericMethodType local_ty)
307 (badGenericMethodType op_name op_ty) `thenTc_`
309 returnTc (local_ty, (sel_id, dm_info))
313 %************************************************************************
315 \subsection[Default methods]{Default methods}
317 %************************************************************************
319 The default methods for a class are each passed a dictionary for the
320 class, so that they get access to the other methods at the same type.
321 So, given the class decl
325 op2 :: Ord b => a -> b -> b -> b
328 op2 x y z = if (op1 x) && (y < z) then y else z
330 we get the default methods:
332 defm.Foo.op1 :: forall a. Foo a => a -> Bool
333 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
335 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
336 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
337 if (op1 a dfoo x) && (< b dord y z) then y else z
340 When we come across an instance decl, we may need to use the default
343 instance Foo Int where {}
347 const.Foo.Int.op1 :: Int -> Bool
348 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
350 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
351 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
353 dfun.Foo.Int :: Foo Int
354 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
356 Notice that, as with method selectors above, we assume that dictionary
357 application is curried, so there's no need to mention the Ord dictionary
358 in const.Foo.Int.op2 (or the type variable).
361 instance Foo a => Foo [a] where {}
363 dfun.Foo.List :: forall a. Foo a -> Foo [a]
365 = /\ a -> \ dfoo_a ->
367 op1 = defm.Foo.op1 [a] dfoo_list
368 op2 = defm.Foo.op2 [a] dfoo_list
369 dfoo_list = (op1, op2)
374 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
375 each local class decl.
378 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
380 tcClassDecls2 this_mod decls
382 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
383 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
384 -- The 'Just' picks out source ClassDecls
386 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
387 tc2 `thenNF_Tc` \ (lie2, binds2) ->
388 returnNF_Tc (lie1 `plusLIE` lie2,
389 binds1 `AndMonoBinds` binds2)
392 @tcClassDecl2@ generates bindings for polymorphic default methods
393 (generic default methods have by now turned into instance declarations)
396 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
397 -> NF_TcM (LIE, TcMonoBinds)
399 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
400 tcdMeths = Just default_binds, tcdLoc = src_loc})
401 = -- The 'Just' picks out source ClassDecls
402 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
403 tcAddSrcLoc src_loc $
404 tcLookupClass class_name `thenNF_Tc` \ clas ->
406 -- We make a separate binding for each default method.
407 -- At one time I used a single AbsBinds for all of them, thus
408 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
409 -- But that desugars into
410 -- ds = \d -> (..., ..., ...)
411 -- dm1 = \d -> case ds d of (a,b,c) -> a
412 -- And since ds is big, it doesn't get inlined, so we don't get good
413 -- default methods. Better to make separate AbsBinds for each
415 (tyvars, _, _, op_items) = classBigSig clas
416 prags = filter isPragSig sigs
417 tc_dm = tcDefMeth clas tyvars default_binds prags
419 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
421 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
424 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
425 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
426 -- Generate code for polymorphic default methods only
427 -- (Generic default methods have turned into instance decls by now.)
428 -- This is incompatible with Hugs, which expects a polymorphic
429 -- default method for every class op, regardless of whether or not
430 -- the programmer supplied an explicit default decl for the class.
431 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
433 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
434 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
436 theta = [(mkClassPred clas inst_tys)]
438 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
440 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
441 tcMethodBind clas origin clas_tyvars inst_tys theta
442 binds_in prags False op_item
443 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
445 tcAddErrCtxt (defltMethCtxt clas) $
449 (ptext SLIT("class") <+> ppr clas)
452 insts_needed `thenTc` \ (const_lie, dict_binds) ->
454 -- Simplification can do unification
455 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
461 [(clas_tyvars', dm_id, instToId local_dm_inst)]
462 emptyNameSet -- No inlines (yet)
463 (dict_binds `andMonoBinds` defm_bind)
465 returnTc (full_bind, const_lie)
467 origin = ClassDeclOrigin
472 %************************************************************************
474 \subsection{Typechecking a method}
476 %************************************************************************
478 @tcMethodBind@ is used to type-check both default-method and
479 instance-decl method declarations. We must type-check methods one at a
480 time, because their signatures may have different contexts and
487 -> [TcTyVar] -- Instantiated type variables for the
488 -- enclosing class/instance decl.
489 -- They'll be signature tyvars, and we
490 -- want to check that they don't get bound
491 -> [TcType] -- Instance types
492 -> TcThetaType -- Available theta; this could be used to check
493 -- the method signature, but actually that's done by
494 -- the caller; here, it's just used for the error message
495 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
496 -> [RenamedSig] -- Pramgas (just for this one)
497 -> Bool -- True <=> This method is from an instance declaration
498 -> ClassOpItem -- The method selector and default-method Id
499 -> TcM (TcMonoBinds, LIE, Inst)
501 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
502 meth_binds prags is_inst_decl (sel_id, dm_info)
503 = tcGetSrcLoc `thenNF_Tc` \ loc ->
504 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
506 meth_id = instToId meth
507 meth_name = idName meth_id
508 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_id
509 meth_prags = find_prags (idName sel_id) meth_name prags
511 mkTcSig meth_id loc `thenNF_Tc` \ sig_info ->
513 -- Figure out what method binding to use
514 -- If the user suppplied one, use it, else construct a default one
515 (case find_bind (idName sel_id) meth_name meth_binds of
516 Just user_bind -> returnTc user_bind
517 Nothing -> mkDefMethRhs is_inst_decl clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
518 returnTc (FunMonoBind meth_name False -- Not infix decl
519 [mkSimpleMatch [] rhs placeHolderType loc] loc)
520 ) `thenTc` \ meth_bind ->
521 -- Check the bindings; first add inst_tyvars to the envt
522 -- so that we don't quantify over them in nested places
523 -- The *caller* put the class/inst decl tyvars into the envt
524 tcExtendGlobalTyVars (mkVarSet inst_tyvars)
525 (tcAddErrCtxt (methodCtxt sel_id) $
526 tcBindWithSigs NotTopLevel meth_bind
527 [sig_info] meth_prags NonRecursive
528 ) `thenTc` \ (binds, insts, _) ->
530 tcExtendLocalValEnv [(meth_name, meth_id)]
531 (tcSpecSigs meth_prags) `thenTc` \ (prag_binds1, prag_lie) ->
533 -- The prag_lie for a SPECIALISE pragma will mention the function
534 -- itself, so we have to simplify them away right now lest they float
536 bindInstsOfLocalFuns prag_lie [meth_id] `thenTc` \ (prag_lie', prag_binds2) ->
538 -- Now check that the instance type variables
539 -- (or, in the case of a class decl, the class tyvars)
540 -- have not been unified with anything in the environment
542 -- We do this for each method independently to localise error messages
543 -- ...and this is why the call to tcExtendGlobalTyVars must be here
544 -- rather than in the caller
545 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
546 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
548 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
549 insts `plusLIE` prag_lie',
552 -- The user didn't supply a method binding,
553 -- so we have to make up a default binding
554 -- The RHS of a default method depends on the default-method info
555 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
556 = -- An polymorphic default method
557 returnTc (HsVar (idName dm_id))
559 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
560 = -- No default method
561 -- Warn only if -fwarn-missing-methods
562 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
563 warnTc (is_inst_decl && warn)
564 (omittedMethodWarn sel_id) `thenNF_Tc_`
567 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
568 (HsLit (HsString (_PK_ error_msg)))
569 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
572 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
573 = -- A generic default method
574 -- If the method is defined generically, we can only do the job if the
575 -- instance declaration is for a single-parameter type class with
576 -- a type constructor applied to type arguments in the instance decl
577 -- (checkTc, so False provokes the error)
578 checkTc (not is_inst_decl || simple_inst)
579 (badGenericInstance sel_id) `thenTc_`
581 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
584 rhs = mkGenericRhs sel_id clas_tyvar tycon
586 stuff = vcat [ppr clas <+> ppr inst_tys,
587 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
589 -- The tycon is only used in the generic case, and in that
590 -- case we require that the instance decl is for a single-parameter
591 -- type class with type variable arguments:
592 -- instance (...) => C (T a b)
593 simple_inst = maybeToBool maybe_tycon
594 clas_tyvar = head (classTyVars clas)
595 Just tycon = maybe_tycon
596 maybe_tycon = case inst_tys of
597 [ty] -> case tcSplitTyConApp_maybe ty of
598 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
605 -- The renamer just puts the selector ID as the binder in the method binding
606 -- but we must use the method name; so we substitute it here. Crude but simple.
607 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
608 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
609 find_bind sel_name meth_name (AndMonoBinds b1 b2)
610 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
611 find_bind sel_name meth_name other = Nothing -- Default case
613 -- Find the prags for this method, and replace the
614 -- selector name with the method name
615 find_prags sel_name meth_name [] = []
616 find_prags sel_name meth_name (SpecSig name ty loc : prags)
617 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
618 find_prags sel_name meth_name (InlineSig name phase loc : prags)
619 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
620 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
621 | name == sel_name = NoInlineSig meth_name phase loc : find_prags sel_name meth_name prags
622 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
629 classArityErr class_name
630 = ptext SLIT("Too many parameters for class") <+> quotes (ppr class_name)
632 superClassErr clas sc
633 = ptext SLIT("Illegal superclass constraint") <+> quotes (ppr sc)
634 <+> ptext SLIT("in declaration for class") <+> quotes (ppr clas)
637 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
640 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
643 = hsep [ptext SLIT("Class"), quotes (ppr clas),
644 ptext SLIT("does not have a method"), quotes (ppr op)]
646 omittedMethodWarn sel_id
647 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
649 badGenericMethodType op op_ty
650 = hang (ptext SLIT("Generic method type is too complex"))
651 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
652 ptext SLIT("You can only use type variables, arrows, and tuples")])
654 badGenericInstance sel_id
655 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
656 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
657 ptext SLIT("(where T is a derivable type constructor)")]
660 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
662 genericMultiParamErr clas
663 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
664 ptext SLIT("cannot have generic methods")