2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassSigs, tcClassDecl2,
9 MethodSpec, tcMethodBind, mkMethodBind,
10 tcAddDeclCtxt, badMethodErr
13 #include "HsVersions.h"
15 import HsSyn ( TyClDecl(..), Sig(..), MonoBinds(..), HsType(..),
16 HsExpr(..), HsLit(..), Pat(WildPat), HsTyVarBndr(..),
18 mkSimpleMatch, andMonoBinds, andMonoBindList,
19 isPragSig, placeHolderType, mkExplicitHsForAllTy
21 import BasicTypes ( RecFlag(..), NewOrData(..) )
22 import RnHsSyn ( RenamedTyClDecl, RenamedSig,
23 RenamedClassOpSig, RenamedMonoBinds,
24 maybeGenericMatch, extractHsTyVars
26 import RnExpr ( rnExpr )
27 import RnEnv ( lookupTopBndrRn, lookupImportedName )
28 import TcHsSyn ( TcMonoBinds )
30 import Inst ( Inst, InstOrigin(..), instToId, newDicts, newMethod )
31 import TcEnv ( tcLookupClass, tcExtendLocalValEnv2, tcExtendTyVarEnv2,
32 InstInfo(..), pprInstInfo, simpleInstInfoTyCon, simpleInstInfoTy,
33 InstBindings(..), newDFunName
35 import TcBinds ( tcMonoBinds, tcSpecSigs )
36 import TcHsType ( TcSigInfo(..), mkTcSig, tcHsKindedType, tcHsSigType )
37 import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns )
38 import TcUnify ( checkSigTyVars, sigCtxt )
39 import TcMType ( tcInstTyVars, UserTypeCtxt( GenPatCtxt ) )
40 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
41 mkClassPred, tcSplitSigmaTy, tcSplitFunTys,
42 tcIsTyVarTy, tcSplitTyConApp_maybe, tcSplitForAllTys, tcSplitPhiTy,
43 getClassPredTys_maybe, mkPhiTy, mkTyVarTy
46 import Generics ( mkGenericRhs, validGenericInstanceType )
47 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
48 import Class ( classTyVars, classBigSig,
49 Class, ClassOpItem, DefMeth (..) )
50 import TyCon ( TyCon, tyConName, tyConHasGenerics )
51 import Subst ( substTyWith )
52 import MkId ( mkDefaultMethodId, mkDictFunId )
53 import Id ( Id, idType, idName, mkUserLocal, setInlinePragma )
54 import Name ( Name, NamedThing(..) )
55 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
56 import NameSet ( emptyNameSet, unitNameSet, nameSetToList )
57 import OccName ( reportIfUnused, mkDefaultMethodOcc )
58 import RdrName ( RdrName, mkDerivedRdrName )
61 import PrelNames ( genericTyConNames )
63 import UnicodeUtil ( stringToUtf8 )
64 import ErrUtils ( dumpIfSet, dumpIfSet_dyn )
65 import Util ( count, lengthIs, isSingleton, lengthExceeds )
66 import Unique ( Uniquable(..) )
67 import ListSetOps ( equivClassesByUniq, minusList )
68 import SrcLoc ( SrcLoc )
69 import Maybes ( seqMaybe, isJust, mapCatMaybes )
70 import List ( partition )
78 Every class implicitly declares a new data type, corresponding to dictionaries
79 of that class. So, for example:
81 class (D a) => C a where
83 op2 :: forall b. Ord b => a -> b -> b
85 would implicitly declare
87 data CDict a = CDict (D a)
89 (forall b. Ord b => a -> b -> b)
91 (We could use a record decl, but that means changing more of the existing apparatus.
94 For classes with just one superclass+method, we use a newtype decl instead:
97 op :: forallb. a -> b -> b
101 newtype CDict a = CDict (forall b. a -> b -> b)
103 Now DictTy in Type is just a form of type synomym:
104 DictTy c t = TyConTy CDict `AppTy` t
106 Death to "ExpandingDicts".
109 %************************************************************************
111 Type-checking the class op signatures
113 %************************************************************************
116 tcClassSigs :: Name -- Name of the class
117 -> [RenamedClassOpSig]
121 type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
122 -- between tcClassSigs and buildClass
123 tcClassSigs clas sigs def_methods
124 = do { dm_env <- checkDefaultBinds clas op_names def_methods
125 ; mappM (tcClassSig dm_env) op_sigs }
127 op_sigs = [sig | sig@(Sig n _ _) <- sigs]
128 op_names = [n | sig@(Sig n _ _) <- op_sigs]
131 checkDefaultBinds :: Name -> [Name] -> RenamedMonoBinds
132 -> TcM (NameEnv Bool)
133 -- Check default bindings
134 -- a) must be for a class op for this class
135 -- b) must be all generic or all non-generic
136 -- and return a mapping from class-op to Bool
137 -- where True <=> it's a generic default method
139 checkDefaultBinds clas ops EmptyMonoBinds
140 = returnM emptyNameEnv
142 checkDefaultBinds clas ops (AndMonoBinds b1 b2)
143 = do { dm_info1 <- checkDefaultBinds clas ops b1
144 ; dm_info2 <- checkDefaultBinds clas ops b2
145 ; returnM (dm_info1 `plusNameEnv` dm_info2) }
147 checkDefaultBinds clas ops (FunMonoBind op _ matches loc)
149 { -- Check that the op is from this class
150 checkTc (op `elem` ops) (badMethodErr clas op)
152 -- Check that all the defns ar generic, or none are
153 ; checkTc (all_generic || none_generic) (mixedGenericErr op)
155 ; returnM (unitNameEnv op all_generic)
158 n_generic = count (isJust . maybeGenericMatch) matches
159 none_generic = n_generic == 0
160 all_generic = matches `lengthIs` n_generic
163 tcClassSig :: NameEnv Bool -- Info about default methods;
167 tcClassSig dm_env (Sig op_name op_hs_ty src_loc)
168 = addSrcLoc src_loc $ do
169 { op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
170 ; let dm = case lookupNameEnv dm_env op_name of
172 Just False -> DefMeth
173 Just True -> GenDefMeth
174 ; returnM (op_name, dm, op_ty) }
178 %************************************************************************
180 \subsection[Default methods]{Default methods}
182 %************************************************************************
184 The default methods for a class are each passed a dictionary for the
185 class, so that they get access to the other methods at the same type.
186 So, given the class decl
190 op2 :: Ord b => a -> b -> b -> b
193 op2 x y z = if (op1 x) && (y < z) then y else z
195 we get the default methods:
197 defm.Foo.op1 :: forall a. Foo a => a -> Bool
198 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
200 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
201 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
202 if (op1 a dfoo x) && (< b dord y z) then y else z
205 When we come across an instance decl, we may need to use the default
208 instance Foo Int where {}
212 const.Foo.Int.op1 :: Int -> Bool
213 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
215 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
216 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
218 dfun.Foo.Int :: Foo Int
219 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
221 Notice that, as with method selectors above, we assume that dictionary
222 application is curried, so there's no need to mention the Ord dictionary
223 in const.Foo.Int.op2 (or the type variable).
226 instance Foo a => Foo [a] where {}
228 dfun.Foo.List :: forall a. Foo a -> Foo [a]
230 = /\ a -> \ dfoo_a ->
232 op1 = defm.Foo.op1 [a] dfoo_list
233 op2 = defm.Foo.op2 [a] dfoo_list
234 dfoo_list = (op1, op2)
239 @tcClassDecls2@ generates bindings for polymorphic default methods
240 (generic default methods have by now turned into instance declarations)
243 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
244 -> TcM (TcMonoBinds, [Id])
246 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
247 tcdMeths = default_binds, tcdLoc = src_loc})
248 = recoverM (returnM (EmptyMonoBinds, [])) $
250 tcLookupClass class_name `thenM` \ clas ->
252 -- We make a separate binding for each default method.
253 -- At one time I used a single AbsBinds for all of them, thus
254 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
255 -- But that desugars into
256 -- ds = \d -> (..., ..., ...)
257 -- dm1 = \d -> case ds d of (a,b,c) -> a
258 -- And since ds is big, it doesn't get inlined, so we don't get good
259 -- default methods. Better to make separate AbsBinds for each
261 (tyvars, _, _, op_items) = classBigSig clas
262 prags = filter isPragSig sigs
263 tc_dm = tcDefMeth clas tyvars default_binds prags
265 dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
266 -- Generate code for polymorphic default methods only
267 -- (Generic default methods have turned into instance decls by now.)
268 -- This is incompatible with Hugs, which expects a polymorphic
269 -- default method for every class op, regardless of whether or not
270 -- the programmer supplied an explicit default decl for the class.
271 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
273 mapAndUnzipM tc_dm dm_sel_ids `thenM` \ (defm_binds, dm_ids_s) ->
274 returnM (andMonoBindList defm_binds, concat dm_ids_s)
276 tcDefMeth clas tyvars binds_in prags sel_id
277 = lookupTopBndrRn (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
278 tcInstTyVars ClsTv tyvars `thenM` \ (clas_tyvars, inst_tys, _) ->
280 dm_ty = idType sel_id -- Same as dict selector!
281 theta = [mkClassPred clas inst_tys]
282 local_dm_id = mkDefaultMethodId dm_name dm_ty
283 xtve = tyvars `zip` clas_tyvars
284 origin = ClassDeclOrigin
286 mkMethodBind origin clas inst_tys
287 binds_in (sel_id, DefMeth) `thenM` \ (_, meth_info) ->
288 newDicts origin theta `thenM` \ [this_dict] ->
289 getLIE (tcMethodBind xtve clas_tyvars theta
290 [this_dict] prags meth_info) `thenM` \ (defm_bind, insts_needed) ->
292 addErrCtxt (defltMethCtxt clas) $
296 (ptext SLIT("class") <+> ppr clas)
299 insts_needed `thenM` \ dict_binds ->
301 -- Simplification can do unification
302 checkSigTyVars clas_tyvars `thenM` \ clas_tyvars' ->
305 (_,dm_inst_id,_) = meth_info
309 [(clas_tyvars', local_dm_id, dm_inst_id)]
310 emptyNameSet -- No inlines (yet)
311 (dict_binds `andMonoBinds` defm_bind)
313 returnM (full_bind, [local_dm_id])
315 mkDefMethRdrName :: Id -> RdrName
316 mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
320 %************************************************************************
322 \subsection{Typechecking a method}
324 %************************************************************************
326 @tcMethodBind@ is used to type-check both default-method and
327 instance-decl method declarations. We must type-check methods one at a
328 time, because their signatures may have different contexts and
332 type MethodSpec = (Id, -- Global selector Id
333 Id, -- Local Id (class tyvars instantiated)
334 RenamedMonoBinds) -- Binding for the method
337 :: [(TyVar,TcTyVar)] -- Bindings for type environment
338 -> [TcTyVar] -- Instantiated type variables for the
339 -- enclosing class/instance decl.
340 -- They'll be signature tyvars, and we
341 -- want to check that they don't get bound
342 -- Always equal the range of the type envt
343 -> TcThetaType -- Available theta; it's just used for the error message
344 -> [Inst] -- Available from context, used to simplify constraints
345 -- from the method body
346 -> [RenamedSig] -- Pragmas (e.g. inline pragmas)
347 -> MethodSpec -- Details of this method
350 tcMethodBind xtve inst_tyvars inst_theta avail_insts prags
351 (sel_id, meth_id, meth_bind)
352 = -- Check the bindings; first adding inst_tyvars to the envt
353 -- so that we don't quantify over them in nested places
354 mkTcSig meth_id `thenM` \ meth_sig ->
356 tcExtendTyVarEnv2 xtve (
357 addErrCtxt (methodCtxt sel_id) $
359 tcMonoBinds meth_bind [meth_sig] NonRecursive
360 ) `thenM` \ ((meth_bind,_), meth_lie) ->
362 -- Now do context reduction. We simplify wrt both the local tyvars
363 -- and the ones of the class/instance decl, so that there is
366 -- op :: Eq a => a -> b -> a
368 -- We do this for each method independently to localise error messages
371 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
373 addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
374 newDicts SignatureOrigin meth_theta `thenM` \ meth_dicts ->
376 all_tyvars = meth_tvs ++ inst_tyvars
377 all_insts = avail_insts ++ meth_dicts
380 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
381 all_tyvars all_insts meth_lie `thenM` \ lie_binds ->
383 checkSigTyVars all_tyvars `thenM` \ all_tyvars' ->
386 sel_name = idName sel_id
387 inline_prags = [ (is_inl, phase)
388 | InlineSig is_inl name phase _ <- prags,
391 | prag@(SpecSig name _ _) <- prags,
394 -- Attach inline pragmas as appropriate
395 (final_meth_id, inlines)
396 | ((is_inline, phase) : _) <- inline_prags
397 = (meth_id `setInlinePragma` phase,
398 if is_inline then unitNameSet (idName meth_id) else emptyNameSet)
400 = (meth_id, emptyNameSet)
402 meth_tvs' = take (length meth_tvs) all_tyvars'
403 poly_meth_bind = AbsBinds meth_tvs'
404 (map instToId meth_dicts)
405 [(meth_tvs', final_meth_id, local_meth_id)]
407 (lie_binds `andMonoBinds` meth_bind)
410 -- Deal with specialisation pragmas
411 -- The sel_name is what appears in the pragma
412 tcExtendLocalValEnv2 [(sel_name, final_meth_id)] (
413 getLIE (tcSpecSigs spec_prags) `thenM` \ (spec_binds1, prag_lie) ->
415 -- The prag_lie for a SPECIALISE pragma will mention the function itself,
416 -- so we have to simplify them away right now lest they float outwards!
417 bindInstsOfLocalFuns prag_lie [final_meth_id] `thenM` \ spec_binds2 ->
418 returnM (spec_binds1 `andMonoBinds` spec_binds2)
419 ) `thenM` \ spec_binds ->
421 returnM (poly_meth_bind `andMonoBinds` spec_binds)
424 mkMethodBind :: InstOrigin
425 -> Class -> [TcType] -- Class and instance types
426 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
428 -> TcM (Maybe Inst, -- Method inst
430 -- Find the binding for the specified method, or make
431 -- up a suitable default method if it isn't there
433 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
434 = mkMethId origin clas sel_id inst_tys `thenM` \ (mb_inst, meth_id) ->
436 meth_name = idName meth_id
438 -- Figure out what method binding to use
439 -- If the user suppplied one, use it, else construct a default one
440 getSrcLocM `thenM` \ loc ->
441 (case find_bind (idName sel_id) meth_name meth_binds of
442 Just user_bind -> returnM user_bind
443 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenM` \ rhs ->
444 returnM (FunMonoBind meth_name False -- Not infix decl
445 [mkSimpleMatch [] rhs placeHolderType loc] loc)
446 ) `thenM` \ meth_bind ->
448 returnM (mb_inst, (sel_id, meth_id, meth_bind))
450 mkMethId :: InstOrigin -> Class
451 -> Id -> [TcType] -- Selector, and instance types
452 -> TcM (Maybe Inst, Id)
454 -- mkMethId instantiates the selector Id at the specified types
455 mkMethId origin clas sel_id inst_tys
457 (tyvars,rho) = tcSplitForAllTys (idType sel_id)
458 rho_ty = ASSERT( length tyvars == length inst_tys )
459 substTyWith tyvars inst_tys rho
460 (preds,tau) = tcSplitPhiTy rho_ty
461 first_pred = head preds
463 -- The first predicate should be of form (C a b)
464 -- where C is the class in question
465 ASSERT( not (null preds) &&
466 case getClassPredTys_maybe first_pred of
467 { Just (clas1,tys) -> clas == clas1 ; Nothing -> False }
469 if isSingleton preds then
470 -- If it's the only one, make a 'method'
471 getInstLoc origin `thenM` \ inst_loc ->
472 newMethod inst_loc sel_id inst_tys preds tau `thenM` \ meth_inst ->
473 returnM (Just meth_inst, instToId meth_inst)
475 -- If it's not the only one we need to be careful
476 -- For example, given 'op' defined thus:
478 -- op :: (?x :: String) => a -> a
479 -- (mkMethId op T) should return an Inst with type
480 -- (?x :: String) => T -> T
481 -- That is, the class-op's context is still there.
482 -- BUT: it can't be a Method any more, because it breaks
483 -- INVARIANT 2 of methods. (See the data decl for Inst.)
484 newUnique `thenM` \ uniq ->
485 getSrcLocM `thenM` \ loc ->
487 real_tau = mkPhiTy (tail preds) tau
488 meth_id = mkUserLocal (getOccName sel_id) uniq real_tau loc
490 returnM (Nothing, meth_id)
492 -- The user didn't supply a method binding,
493 -- so we have to make up a default binding
494 -- The RHS of a default method depends on the default-method info
495 mkDefMethRhs origin clas inst_tys sel_id loc DefMeth
496 = -- An polymorphic default method
497 lookupImportedName (mkDefMethRdrName sel_id) `thenM` \ dm_name ->
498 -- Might not be imported, but will be an OrigName
499 traceRn (text "mkDefMeth" <+> ppr dm_name) `thenM_`
500 returnM (HsVar dm_name)
502 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
503 = -- No default method
504 -- Warn only if -fwarn-missing-methods
505 doptM Opt_WarnMissingMethods `thenM` \ warn ->
506 warnTc (isInstDecl origin
508 && reportIfUnused (getOccName sel_id))
509 (omittedMethodWarn sel_id) `thenM_`
512 error_rhs = HsLam (mkSimpleMatch wild_pats simple_rhs placeHolderType loc)
513 simple_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
514 (HsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
515 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
517 -- When the type is of form t1 -> t2 -> t3
518 -- make a default method like (\ _ _ -> noMethBind "blah")
519 -- rather than simply (noMethBind "blah")
520 -- Reason: if t1 or t2 are higher-ranked types we get n
521 -- silly ambiguity messages.
522 -- Example: f :: (forall a. Eq a => a -> a) -> Int
524 -- Here, tcSub tries to force (error "urk") to have the right type,
525 -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
526 -- where 't' is fresh ty var. This leads directly to "ambiguous t".
528 -- NB: technically this changes the meaning of the default-default
529 -- method slightly, because `seq` can see the lambdas. Oh well.
530 (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
531 (_,_,tau2) = tcSplitSigmaTy tau1
532 -- Need two splits because the selector can have a type like
533 -- forall a. Foo a => forall b. Eq b => ...
534 (arg_tys, _) = tcSplitFunTys tau2
535 wild_pats = [WildPat placeHolderType | ty <- arg_tys]
537 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
538 = -- A generic default method
539 -- If the method is defined generically, we can only do the job if the
540 -- instance declaration is for a single-parameter type class with
541 -- a type constructor applied to type arguments in the instance decl
542 -- (checkTc, so False provokes the error)
543 ASSERT( isInstDecl origin ) -- We never get here from a class decl
545 checkTc (isJust maybe_tycon)
546 (badGenericInstance sel_id (notSimple inst_tys)) `thenM_`
547 checkTc (tyConHasGenerics tycon)
548 (badGenericInstance sel_id (notGeneric tycon)) `thenM_`
550 ioToTcRn (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenM_`
552 -- Rename it before returning it
553 rnExpr rhs `thenM` \ (rn_rhs, _) ->
556 rhs = mkGenericRhs sel_id clas_tyvar tycon
558 stuff = vcat [ppr clas <+> ppr inst_tys,
559 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
561 -- The tycon is only used in the generic case, and in that
562 -- case we require that the instance decl is for a single-parameter
563 -- type class with type variable arguments:
564 -- instance (...) => C (T a b)
565 clas_tyvar = head (classTyVars clas)
566 Just tycon = maybe_tycon
567 maybe_tycon = case inst_tys of
568 [ty] -> case tcSplitTyConApp_maybe ty of
569 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
573 isInstDecl InstanceDeclOrigin = True
574 isInstDecl ClassDeclOrigin = False
579 -- The renamer just puts the selector ID as the binder in the method binding
580 -- but we must use the method name; so we substitute it here. Crude but simple.
581 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
582 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
583 find_bind sel_name meth_name (AndMonoBinds b1 b2)
584 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
585 find_bind sel_name meth_name other = Nothing -- Default case
589 %************************************************************************
591 \subsection{Extracting generic instance declaration from class declarations}
593 %************************************************************************
595 @getGenericInstances@ extracts the generic instance declarations from a class
596 declaration. For exmaple
601 op{ x+y } (Inl v) = ...
602 op{ x+y } (Inr v) = ...
603 op{ x*y } (v :*: w) = ...
606 gives rise to the instance declarations
608 instance C (x+y) where
612 instance C (x*y) where
620 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
621 getGenericInstances class_decls
622 = do { gen_inst_infos <- mappM get_generics class_decls
623 ; let { gen_inst_info = concat gen_inst_infos }
625 -- Return right away if there is no generic stuff
626 ; if null gen_inst_info then returnM []
629 -- Otherwise print it out
631 ; ioToTcRn (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
632 (vcat (map pprInstInfo gen_inst_info)))
633 ; returnM gen_inst_info }}
635 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = def_methods, tcdLoc = loc})
637 = returnM [] -- The comon case: no generic default methods
639 | otherwise -- A source class decl with generic default methods
640 = recoverM (returnM []) $
642 tcLookupClass class_name `thenM` \ clas ->
644 -- Group by type, and
645 -- make an InstInfo out of each group
647 groups = groupWith andMonoBindList generic_binds
649 mappM (mkGenericInstance clas loc) groups `thenM` \ inst_infos ->
651 -- Check that there is only one InstInfo for each type constructor
652 -- The main way this can fail is if you write
653 -- f {| a+b |} ... = ...
654 -- f {| x+y |} ... = ...
655 -- Then at this point we'll have an InstInfo for each
657 tc_inst_infos :: [(TyCon, InstInfo)]
658 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
660 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
661 group `lengthExceeds` 1]
662 get_uniq (tc,_) = getUnique tc
664 mappM (addErrTc . dupGenericInsts) bad_groups `thenM_`
666 -- Check that there is an InstInfo for each generic type constructor
668 missing = genericTyConNames `minusList` [tyConName tc | (tc,_) <- tc_inst_infos]
670 checkTc (null missing) (missingGenericInstances missing) `thenM_`
675 generic_binds :: [(HsType Name, RenamedMonoBinds)]
676 generic_binds = getGenericBinds def_methods
679 ---------------------------------
680 getGenericBinds :: RenamedMonoBinds -> [(HsType Name, RenamedMonoBinds)]
681 -- Takes a group of method bindings, finds the generic ones, and returns
682 -- them in finite map indexed by the type parameter in the definition.
684 getGenericBinds EmptyMonoBinds = []
685 getGenericBinds (AndMonoBinds m1 m2) = getGenericBinds m1 ++ getGenericBinds m2
687 getGenericBinds (FunMonoBind id infixop matches loc)
688 = groupWith wrap (mapCatMaybes maybeGenericMatch matches)
690 wrap ms = FunMonoBind id infixop ms loc
692 groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
694 groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
697 (this,rest) = partition same_t prs
698 same_t (t',v) = t `eqPatType` t'
700 eqPatType :: HsType Name -> HsType Name -> Bool
701 -- A very simple equality function, only for
702 -- type patterns in generic function definitions.
703 eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
704 eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatType` s2 && t2 `eqPatType` t2
705 eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatType` s2 && t2 `eqPatType` t2 && op1 == op2
706 eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
707 eqPatType (HsParTy t1) t2 = t1 `eqPatType` t2
708 eqPatType t1 (HsParTy t2) = t1 `eqPatType` t2
709 eqPatType _ _ = False
711 ---------------------------------
712 mkGenericInstance :: Class -> SrcLoc
713 -> (HsType Name, RenamedMonoBinds)
716 mkGenericInstance clas loc (hs_ty, binds)
717 -- Make a generic instance declaration
718 -- For example: instance (C a, C b) => C (a+b) where { binds }
720 = -- Extract the universally quantified type variables
721 -- and wrap them as forall'd tyvars, so that kind inference
722 -- works in the standard way
724 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
725 hs_forall_ty = mkExplicitHsForAllTy sig_tvs [] hs_ty
727 -- Type-check the instance type, and check its form
728 tcHsSigType GenPatCtxt hs_forall_ty `thenM` \ forall_inst_ty ->
730 (tyvars, inst_ty) = tcSplitForAllTys forall_inst_ty
732 checkTc (validGenericInstanceType inst_ty)
733 (badGenericInstanceType binds) `thenM_`
735 -- Make the dictionary function.
736 newDFunName clas [inst_ty] loc `thenM` \ dfun_name ->
738 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
739 dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
742 returnM (InstInfo { iDFunId = dfun_id, iBinds = VanillaInst binds [] })
746 %************************************************************************
750 %************************************************************************
753 tcAddDeclCtxt decl thing_inside
754 = addSrcLoc (tcdLoc decl) $
759 ClassDecl {} -> "class"
760 TySynonym {} -> "type synonym"
761 TyData {tcdND = NewType} -> "newtype"
762 TyData {tcdND = DataType} -> "data type"
764 ctxt = hsep [ptext SLIT("In the"), text thing,
765 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
768 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
771 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
774 = hsep [ptext SLIT("Class"), quotes (ppr clas),
775 ptext SLIT("does not have a method"), quotes (ppr op)]
777 omittedMethodWarn sel_id
778 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
780 badGenericInstance sel_id because
781 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
785 = vcat [ptext SLIT("because the instance type(s)"),
786 nest 2 (ppr inst_tys),
787 ptext SLIT("is not a simple type of form (T a b c)")]
790 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
791 ptext SLIT("was not compiled with -fgenerics")]
793 badGenericInstanceType binds
794 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
797 missingGenericInstances missing
798 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
800 dupGenericInsts tc_inst_infos
801 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
802 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
803 ptext SLIT("All the type patterns for a generic type constructor must be identical")
806 ppr_inst_ty (tc,inst) = ppr tc <+> ppr (simpleInstInfoTy inst)
809 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)