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 ( tcInstTyVars, checkValidTheta, checkValidType, SourceTyCtxt(..), UserTypeCtxt(..) )
36 import TcType ( Type, mkSigmaTy, mkTyVarTys, mkPredTys, mkClassPred,
37 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitSigmaTy
40 import Generics ( mkGenericRhs, validGenericMethodType )
41 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
42 import Class ( classTyVars, classBigSig, classTyCon, className,
43 Class, ClassOpItem, DefMeth (..) )
44 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
45 import DataCon ( mkDataCon )
46 import Id ( idType, idName )
47 import Module ( Module )
48 import Name ( Name, NamedThing(..) )
49 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
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 :: RecTcEnv -> RenamedTyClDecl -> TcM (Name, TyThingDetails)
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 = -- LOOK THINGS UP IN THE ENVIRONMENT
110 tcLookupClass class_name `thenTc` \ clas ->
112 tyvars = classTyVars clas
113 op_sigs = filter isClassOpSig class_sigs
114 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
115 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
117 tcExtendTyVarEnv tyvars $
119 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
122 -- The renamer has already checked that the context mentions
123 -- only the type variable of the class decl.
124 -- Context is already kind-checked
125 ASSERT( length context == length sc_sel_names )
126 tcHsTheta context `thenTc` \ sc_theta ->
128 -- CHECK THE CLASS SIGNATURES,
129 mapTc (tcClassSig rec_env clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
131 -- MAKE THE CLASS DETAILS
133 (op_tys, op_items) = unzip sig_stuff
134 sc_tys = mkPredTys sc_theta
135 dict_component_tys = sc_tys ++ op_tys
136 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
138 dict_con = mkDataCon datacon_name
139 [NotMarkedStrict | _ <- dict_component_tys]
140 [{- No labelled fields -}]
143 [{-No existential tyvars-}] [{-Or context-}]
146 dict_con_id dict_wrap_id
148 dict_con_id = mkDataConId datacon_wkr_name dict_con
149 dict_wrap_id = mkDataConWrapId dict_con
151 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
155 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
156 -> TcM (Maybe (NameEnv Bool))
157 -- The returned environment says
158 -- x not in env => no default method
159 -- x -> True => generic default method
160 -- x -> False => polymorphic default method
162 -- Check default bindings
163 -- a) must be for a class op for this class
164 -- b) must be all generic or all non-generic
165 -- and return a mapping from class-op to DefMeth info
167 -- But do all this only for source binds
169 checkDefaultBinds clas ops Nothing
172 checkDefaultBinds clas ops (Just mbs)
173 = go mbs `thenTc` \ dm_env ->
174 returnTc (Just dm_env)
176 go EmptyMonoBinds = returnTc emptyNameEnv
178 go (AndMonoBinds b1 b2)
179 = go b1 `thenTc` \ dm_info1 ->
180 go b2 `thenTc` \ dm_info2 ->
181 returnTc (dm_info1 `plusNameEnv` dm_info2)
183 go (FunMonoBind op _ matches loc)
186 -- Check that the op is from this class
187 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
189 -- Check that all the defns ar generic, or none are
190 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
192 returnTc (unitNameEnv op all_generic)
194 n_generic = count (maybeToBool . maybeGenericMatch) matches
195 none_generic = n_generic == 0
196 all_generic = n_generic == length matches
201 tcClassSig :: RecTcEnv -- Knot tying only!
202 -> Class -- ...ditto...
203 -> [TyVar] -- The class type variable, used for error check only
204 -> Maybe (NameEnv Bool) -- Info about default methods
206 -> TcM (Type, -- Type of the method
207 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
209 -- This warrants an explanation: we need to separate generic
210 -- default methods and default methods later on in the compiler
211 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
212 -- Class.DefMeth data structure.
214 tcClassSig unf_env clas clas_tyvars maybe_dm_env
215 (ClassOpSig op_name sig_dm op_ty src_loc)
216 = tcAddSrcLoc src_loc $
218 -- Check the type signature. NB that the envt *already has*
219 -- bindings for the type variables; see comments in TcTyAndClassDcls.
220 tcHsType op_ty `thenTc` \ local_ty ->
223 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
224 global_ty = mkSigmaTy clas_tyvars theta local_ty
225 -- The default method's type should really come from the
226 -- iface file, since it could be usage-generalised, but this
227 -- requires altering the mess of knots in TcModule and I'm
228 -- too scared to do that. Instead, I have disabled generalisation
229 -- of types of default methods (and dict funs) by annotating them
230 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
232 -- Build the selector id and default method id
233 sel_id = mkDictSelId op_name clas
234 dm_id = mkDefaultMethodId dm_name global_ty
235 DefMeth dm_name = sig_dm
237 dm_info = case maybe_dm_env of
238 Nothing -> iface_dm_info
239 Just dm_env -> mk_src_dm_info dm_env
241 iface_dm_info = case sig_dm of
242 NoDefMeth -> NoDefMeth
243 GenDefMeth -> GenDefMeth
244 DefMeth dm_name -> DefMeth (tcAddImportedIdInfo unf_env dm_id)
246 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
248 Just True -> GenDefMeth
249 Just False -> DefMeth dm_id
251 returnTc (local_ty, (sel_id, dm_info))
254 checkValidClass is called once the mutually-recursive knot has been
255 tied, so we can look at things freely.
258 checkValidClass :: Class -> TcM ()
260 = -- CHECK ARITY 1 FOR HASKELL 1.4
261 doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
263 -- Check that the class is unary, unless GlaExs
264 checkTc (gla_exts || unary)
265 (classArityErr cls) `thenTc_`
267 -- Check the super-classes
268 checkValidTheta (ClassSCCtxt (className cls)) theta `thenTc_`
270 -- Check the class operations
271 mapTc_ check_op op_stuff `thenTc_`
273 -- Check that if the class has generic methods, then the
274 -- class has only one parameter. We can't do generic
275 -- multi-parameter type classes!
276 checkTc (unary || no_generics) (genericMultiParamErr cls)
279 (tyvars, theta, sel_ids, op_stuff) = classBigSig cls
280 unary = length tyvars == 1
281 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
283 check_op (sel_id, dm)
284 = checkValidTheta SigmaCtxt (tail theta) `thenTc_`
285 -- The 'tail' removes the initial (C a) from the
286 -- class itself, leaving just the method type
288 checkValidType (FunSigCtxt op_name) tau `thenTc_`
290 -- Check that for a generic method, the type of
291 -- the method is sufficiently simple
292 checkTc (dm /= GenDefMeth || validGenericMethodType op_ty)
293 (badGenericMethodType op_name op_ty)
295 op_name = idName sel_id
296 op_ty = idType sel_id
297 (_,theta,tau) = tcSplitSigmaTy op_ty
301 %************************************************************************
303 \subsection[Default methods]{Default methods}
305 %************************************************************************
307 The default methods for a class are each passed a dictionary for the
308 class, so that they get access to the other methods at the same type.
309 So, given the class decl
313 op2 :: Ord b => a -> b -> b -> b
316 op2 x y z = if (op1 x) && (y < z) then y else z
318 we get the default methods:
320 defm.Foo.op1 :: forall a. Foo a => a -> Bool
321 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
323 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
324 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
325 if (op1 a dfoo x) && (< b dord y z) then y else z
328 When we come across an instance decl, we may need to use the default
331 instance Foo Int where {}
335 const.Foo.Int.op1 :: Int -> Bool
336 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
338 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
339 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
341 dfun.Foo.Int :: Foo Int
342 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
344 Notice that, as with method selectors above, we assume that dictionary
345 application is curried, so there's no need to mention the Ord dictionary
346 in const.Foo.Int.op2 (or the type variable).
349 instance Foo a => Foo [a] where {}
351 dfun.Foo.List :: forall a. Foo a -> Foo [a]
353 = /\ a -> \ dfoo_a ->
355 op1 = defm.Foo.op1 [a] dfoo_list
356 op2 = defm.Foo.op2 [a] dfoo_list
357 dfoo_list = (op1, op2)
362 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
363 each local class decl.
366 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds)
368 tcClassDecls2 this_mod decls
370 (returnNF_Tc (emptyLIE, EmptyMonoBinds))
371 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
372 -- The 'Just' picks out source ClassDecls
374 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
375 tc2 `thenNF_Tc` \ (lie2, binds2) ->
376 returnNF_Tc (lie1 `plusLIE` lie2,
377 binds1 `AndMonoBinds` binds2)
380 @tcClassDecl2@ generates bindings for polymorphic default methods
381 (generic default methods have by now turned into instance declarations)
384 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
385 -> NF_TcM (LIE, TcMonoBinds)
387 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
388 tcdMeths = Just default_binds, tcdLoc = src_loc})
389 = -- The 'Just' picks out source ClassDecls
390 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
391 tcAddSrcLoc src_loc $
392 tcLookupClass class_name `thenNF_Tc` \ clas ->
394 -- We make a separate binding for each default method.
395 -- At one time I used a single AbsBinds for all of them, thus
396 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
397 -- But that desugars into
398 -- ds = \d -> (..., ..., ...)
399 -- dm1 = \d -> case ds d of (a,b,c) -> a
400 -- And since ds is big, it doesn't get inlined, so we don't get good
401 -- default methods. Better to make separate AbsBinds for each
403 (tyvars, _, _, op_items) = classBigSig clas
404 prags = filter isPragSig sigs
405 tc_dm = tcDefMeth clas tyvars default_binds prags
407 mapAndUnzipTc tc_dm op_items `thenTc` \ (defm_binds, const_lies) ->
409 returnTc (plusLIEs const_lies, andMonoBindList defm_binds)
412 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
413 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE)
414 -- Generate code for polymorphic default methods only
415 -- (Generic default methods have turned into instance decls by now.)
416 -- This is incompatible with Hugs, which expects a polymorphic
417 -- default method for every class op, regardless of whether or not
418 -- the programmer supplied an explicit default decl for the class.
419 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
421 tcDefMeth clas tyvars binds_in prags op_item@(_, DefMeth dm_id)
422 = tcInstTyVars tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
424 theta = [(mkClassPred clas inst_tys)]
426 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
428 tcExtendTyVarEnvForMeths tyvars clas_tyvars (
429 tcMethodBind clas origin clas_tyvars inst_tys theta
430 binds_in prags False op_item
431 ) `thenTc` \ (defm_bind, insts_needed, local_dm_inst) ->
433 tcAddErrCtxt (defltMethCtxt clas) $
437 (ptext SLIT("class") <+> ppr clas)
440 insts_needed `thenTc` \ (const_lie, dict_binds) ->
442 -- Simplification can do unification
443 checkSigTyVars clas_tyvars emptyVarSet `thenTc` \ clas_tyvars' ->
449 [(clas_tyvars', dm_id, instToId local_dm_inst)]
450 emptyNameSet -- No inlines (yet)
451 (dict_binds `andMonoBinds` defm_bind)
453 returnTc (full_bind, const_lie)
455 origin = ClassDeclOrigin
460 %************************************************************************
462 \subsection{Typechecking a method}
464 %************************************************************************
466 @tcMethodBind@ is used to type-check both default-method and
467 instance-decl method declarations. We must type-check methods one at a
468 time, because their signatures may have different contexts and
475 -> [TcTyVar] -- Instantiated type variables for the
476 -- enclosing class/instance decl.
477 -- They'll be signature tyvars, and we
478 -- want to check that they don't get bound
479 -> [TcType] -- Instance types
480 -> TcThetaType -- Available theta; this could be used to check
481 -- the method signature, but actually that's done by
482 -- the caller; here, it's just used for the error message
483 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
484 -> [RenamedSig] -- Pramgas (just for this one)
485 -> Bool -- True <=> This method is from an instance declaration
486 -> ClassOpItem -- The method selector and default-method Id
487 -> TcM (TcMonoBinds, LIE, Inst)
489 tcMethodBind clas origin inst_tyvars inst_tys inst_theta
490 meth_binds prags is_inst_decl (sel_id, dm_info)
491 = tcGetSrcLoc `thenNF_Tc` \ loc ->
492 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth ->
494 meth_id = instToId meth
495 meth_name = idName meth_id
496 sig_msg = ptext SLIT("When checking the expected type for class method") <+> ppr sel_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 tcAddErrCtxtM (sigCtxt sig_msg inst_tyvars inst_theta (idType meth_id)) $
534 checkSigTyVars inst_tyvars emptyVarSet `thenTc_`
536 returnTc (binds `AndMonoBinds` prag_binds1 `AndMonoBinds` prag_binds2,
537 insts `plusLIE` prag_lie',
540 -- The user didn't supply a method binding,
541 -- so we have to make up a default binding
542 -- The RHS of a default method depends on the default-method info
543 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc (DefMeth dm_id)
544 = -- An polymorphic default method
545 returnTc (HsVar (idName dm_id))
547 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc NoDefMeth
548 = -- No default method
549 -- Warn only if -fwarn-missing-methods
550 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
551 warnTc (is_inst_decl && warn)
552 (omittedMethodWarn sel_id) `thenNF_Tc_`
555 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
556 (HsLit (HsString (_PK_ error_msg)))
557 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
560 mkDefMethRhs is_inst_decl clas inst_tys sel_id loc GenDefMeth
561 = -- A generic default method
562 -- If the method is defined generically, we can only do the job if the
563 -- instance declaration is for a single-parameter type class with
564 -- a type constructor applied to type arguments in the instance decl
565 -- (checkTc, so False provokes the error)
566 checkTc (not is_inst_decl || simple_inst)
567 (badGenericInstance sel_id) `thenTc_`
569 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
572 rhs = mkGenericRhs sel_id clas_tyvar tycon
574 stuff = vcat [ppr clas <+> ppr inst_tys,
575 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
577 -- The tycon is only used in the generic case, and in that
578 -- case we require that the instance decl is for a single-parameter
579 -- type class with type variable arguments:
580 -- instance (...) => C (T a b)
581 simple_inst = maybeToBool maybe_tycon
582 clas_tyvar = head (classTyVars clas)
583 Just tycon = maybe_tycon
584 maybe_tycon = case inst_tys of
585 [ty] -> case tcSplitTyConApp_maybe ty of
586 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
593 -- The renamer just puts the selector ID as the binder in the method binding
594 -- but we must use the method name; so we substitute it here. Crude but simple.
595 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
596 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
597 find_bind sel_name meth_name (AndMonoBinds b1 b2)
598 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
599 find_bind sel_name meth_name other = Nothing -- Default case
601 -- Find the prags for this method, and replace the
602 -- selector name with the method name
603 find_prags sel_name meth_name [] = []
604 find_prags sel_name meth_name (SpecSig name ty loc : prags)
605 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
606 find_prags sel_name meth_name (InlineSig name phase loc : prags)
607 | name == sel_name = InlineSig meth_name phase loc : find_prags sel_name meth_name prags
608 find_prags sel_name meth_name (NoInlineSig name phase loc : prags)
609 | name == sel_name = NoInlineSig 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("Too many parameters for class") <+> quotes (ppr cls)
621 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
624 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
627 = hsep [ptext SLIT("Class"), quotes (ppr clas),
628 ptext SLIT("does not have a method"), quotes (ppr op)]
630 omittedMethodWarn sel_id
631 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
633 badGenericMethodType op op_ty
634 = hang (ptext SLIT("Generic method type is too complex"))
635 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
636 ptext SLIT("You can only use type variables, arrows, and tuples")])
638 badGenericInstance sel_id
639 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
640 ptext SLIT("because the instance declaration is not for a simple type (T a b c)"),
641 ptext SLIT("(where T is a derivable type constructor)")]
644 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
646 genericMultiParamErr clas
647 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
648 ptext SLIT("cannot have generic methods")