2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcClassDcl]{Typechecking class declarations}
7 module TcClassDcl ( tcClassDecl1, tcClassDecls2,
8 tcMethodBind, mkMethodBind, 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 ( RecFlag(..), StrictnessMark(..) )
20 import RnHsSyn ( RenamedTyClDecl,
21 RenamedClassOpSig, RenamedMonoBinds,
24 import TcHsSyn ( TcMonoBinds )
26 import Inst ( Inst, InstOrigin(..), LIE, emptyLIE, plusLIE, plusLIEs,
27 instToId, newDicts, newMethod )
28 import TcEnv ( TyThingDetails(..),
29 tcLookupClass, tcExtendTyVarEnv2,
32 import TcBinds ( tcMonoBinds )
33 import TcMonoType ( TcSigInfo(..), tcHsType, tcHsTheta, mkTcSig )
34 import TcSimplify ( tcSimplifyCheck )
35 import TcUnify ( checkSigTyVars, sigCtxt )
36 import TcMType ( tcInstTyVars )
37 import TcType ( Type, TyVarDetails(..), TcType, TcThetaType, TcTyVar,
38 mkTyVarTys, mkPredTys, mkClassPred,
39 tcIsTyVarTy, tcSplitTyConApp_maybe
42 import Generics ( mkGenericRhs )
43 import PrelInfo ( nO_METHOD_BINDING_ERROR_ID )
44 import Class ( classTyVars, classBigSig, classTyCon,
45 Class, ClassOpItem, DefMeth (..) )
46 import TyCon ( tyConGenInfo )
47 import MkId ( mkDictSelId, mkDataConId, mkDataConWrapId, mkDefaultMethodId )
48 import DataCon ( mkDataCon )
49 import Id ( Id, idType, idName, setIdLocalExported )
50 import Module ( Module )
51 import Name ( Name, NamedThing(..) )
52 import NameEnv ( NameEnv, lookupNameEnv, emptyNameEnv, unitNameEnv, plusNameEnv )
53 import NameSet ( emptyNameSet )
57 import UnicodeUtil ( stringToUtf8 )
58 import ErrUtils ( dumpIfSet )
59 import Util ( count, lengthIs, equalLength )
60 import Maybes ( seqMaybe )
61 import Maybe ( isJust )
68 Every class implicitly declares a new data type, corresponding to dictionaries
69 of that class. So, for example:
71 class (D a) => C a where
73 op2 :: forall b. Ord b => a -> b -> b
75 would implicitly declare
77 data CDict a = CDict (D a)
79 (forall b. Ord b => a -> b -> b)
81 (We could use a record decl, but that means changing more of the existing apparatus.
84 For classes with just one superclass+method, we use a newtype decl instead:
87 op :: forallb. a -> b -> b
91 newtype CDict a = CDict (forall b. a -> b -> b)
93 Now DictTy in Type is just a form of type synomym:
94 DictTy c t = TyConTy CDict `AppTy` t
96 Death to "ExpandingDicts".
99 %************************************************************************
101 \subsection{Type checking}
103 %************************************************************************
107 tcClassDecl1 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
108 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
109 tcdTyVars = tyvar_names, tcdFDs = fundeps,
110 tcdSigs = class_sigs, tcdMeths = def_methods,
111 tcdSysNames = sys_names, tcdLoc = src_loc})
112 = -- LOOK THINGS UP IN THE ENVIRONMENT
113 tcLookupClass class_name `thenTc` \ clas ->
115 tyvars = classTyVars clas
116 op_sigs = filter isClassOpSig class_sigs
117 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
118 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
120 tcExtendTyVarEnv tyvars $
122 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
125 -- The renamer has already checked that the context mentions
126 -- only the type variable of the class decl.
127 -- Context is already kind-checked
128 ASSERT( equalLength context sc_sel_names )
129 tcHsTheta context `thenTc` \ sc_theta ->
131 -- CHECK THE CLASS SIGNATURES,
132 mapTc (tcClassSig clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
134 -- MAKE THE CLASS DETAILS
136 (op_tys, op_items) = unzip sig_stuff
137 sc_tys = mkPredTys sc_theta
138 dict_component_tys = sc_tys ++ op_tys
139 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
141 dict_con = mkDataCon datacon_name
142 [NotMarkedStrict | _ <- dict_component_tys]
143 [{- No labelled fields -}]
146 [{-No existential tyvars-}] [{-Or context-}]
149 dict_con_id dict_wrap_id
151 dict_con_id = mkDataConId datacon_wkr_name dict_con
152 dict_wrap_id = mkDataConWrapId dict_con
154 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
158 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
159 -> TcM (Maybe (NameEnv Bool))
160 -- The returned environment says
161 -- x not in env => no default method
162 -- x -> True => generic default method
163 -- x -> False => polymorphic default method
165 -- Check default bindings
166 -- a) must be for a class op for this class
167 -- b) must be all generic or all non-generic
168 -- and return a mapping from class-op to DefMeth info
170 -- But do all this only for source binds
172 checkDefaultBinds clas ops Nothing
175 checkDefaultBinds clas ops (Just mbs)
176 = go mbs `thenTc` \ dm_env ->
177 returnTc (Just dm_env)
179 go EmptyMonoBinds = returnTc emptyNameEnv
181 go (AndMonoBinds b1 b2)
182 = go b1 `thenTc` \ dm_info1 ->
183 go b2 `thenTc` \ dm_info2 ->
184 returnTc (dm_info1 `plusNameEnv` dm_info2)
186 go (FunMonoBind op _ matches loc)
189 -- Check that the op is from this class
190 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
192 -- Check that all the defns ar generic, or none are
193 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
195 returnTc (unitNameEnv op all_generic)
197 n_generic = count (isJust . maybeGenericMatch) matches
198 none_generic = n_generic == 0
199 all_generic = matches `lengthIs` n_generic
204 tcClassSig :: Class -- ...ditto...
205 -> [TyVar] -- The class type variable, used for error check only
206 -> Maybe (NameEnv Bool) -- Info about default methods;
207 -- Nothing => imported class defn with no method binds
209 -> TcM (Type, -- Type of the method
210 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
212 -- This warrants an explanation: we need to separate generic
213 -- default methods and default methods later on in the compiler
214 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
215 -- Class.DefMeth data structure.
217 tcClassSig clas clas_tyvars maybe_dm_env
218 (ClassOpSig op_name sig_dm op_ty src_loc)
219 = tcAddSrcLoc src_loc $
221 -- Check the type signature. NB that the envt *already has*
222 -- bindings for the type variables; see comments in TcTyAndClassDcls.
223 tcHsType op_ty `thenTc` \ local_ty ->
226 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
228 -- Build the selector id and default method id
229 sel_id = mkDictSelId op_name clas
230 DefMeth dm_name = sig_dm
232 dm_info = case maybe_dm_env of
234 Just dm_env -> mk_src_dm_info dm_env
236 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
238 Just True -> GenDefMeth
239 Just False -> DefMeth dm_name
241 returnTc (local_ty, (sel_id, dm_info))
245 %************************************************************************
247 \subsection[Default methods]{Default methods}
249 %************************************************************************
251 The default methods for a class are each passed a dictionary for the
252 class, so that they get access to the other methods at the same type.
253 So, given the class decl
257 op2 :: Ord b => a -> b -> b -> b
260 op2 x y z = if (op1 x) && (y < z) then y else z
262 we get the default methods:
264 defm.Foo.op1 :: forall a. Foo a => a -> Bool
265 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
267 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
268 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
269 if (op1 a dfoo x) && (< b dord y z) then y else z
272 When we come across an instance decl, we may need to use the default
275 instance Foo Int where {}
279 const.Foo.Int.op1 :: Int -> Bool
280 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
282 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
283 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
285 dfun.Foo.Int :: Foo Int
286 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
288 Notice that, as with method selectors above, we assume that dictionary
289 application is curried, so there's no need to mention the Ord dictionary
290 in const.Foo.Int.op2 (or the type variable).
293 instance Foo a => Foo [a] where {}
295 dfun.Foo.List :: forall a. Foo a -> Foo [a]
297 = /\ a -> \ dfoo_a ->
299 op1 = defm.Foo.op1 [a] dfoo_list
300 op2 = defm.Foo.op2 [a] dfoo_list
301 dfoo_list = (op1, op2)
306 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
307 each local class decl.
310 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
312 tcClassDecls2 this_mod decls
314 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
315 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
316 -- The 'Just' picks out source ClassDecls
318 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
319 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
320 returnNF_Tc (lie1 `plusLIE` lie2,
321 binds1 `AndMonoBinds` binds2,
325 @tcClassDecl2@ generates bindings for polymorphic default methods
326 (generic default methods have by now turned into instance declarations)
329 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
330 -> NF_TcM (LIE, TcMonoBinds, [Id])
332 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
333 tcdMeths = Just default_binds, tcdLoc = src_loc})
334 = -- The 'Just' picks out source ClassDecls
335 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
336 tcAddSrcLoc src_loc $
337 tcLookupClass class_name `thenNF_Tc` \ clas ->
339 -- We make a separate binding for each default method.
340 -- At one time I used a single AbsBinds for all of them, thus
341 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
342 -- But that desugars into
343 -- ds = \d -> (..., ..., ...)
344 -- dm1 = \d -> case ds d of (a,b,c) -> a
345 -- And since ds is big, it doesn't get inlined, so we don't get good
346 -- default methods. Better to make separate AbsBinds for each
348 (tyvars, _, _, op_items) = classBigSig clas
349 prags = filter isPragSig sigs
350 tc_dm = tcDefMeth clas tyvars default_binds prags
352 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
354 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
357 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
358 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
359 -- Generate code for polymorphic default methods only
360 -- (Generic default methods have turned into instance decls by now.)
361 -- This is incompatible with Hugs, which expects a polymorphic
362 -- default method for every class op, regardless of whether or not
363 -- the programmer supplied an explicit default decl for the class.
364 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
366 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
367 = tcInstTyVars ClsTv tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
369 dm_ty = idType sel_id -- Same as dict selector!
370 -- The default method's type should really come from the
371 -- iface file, since it could be usage-generalised, but this
372 -- requires altering the mess of knots in TcModule and I'm
373 -- too scared to do that. Instead, I have disabled generalisation
374 -- of types of default methods (and dict funs) by annotating them
375 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
377 theta = [mkClassPred clas inst_tys]
378 dm_id = mkDefaultMethodId dm_name dm_ty
379 local_dm_id = setIdLocalExported dm_id
380 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
381 xtve = tyvars `zip` clas_tyvars
383 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
385 mkMethodBind origin clas inst_tys binds_in op_item `thenTc` \ (dm_inst, meth_info) ->
386 tcMethodBind xtve clas_tyvars theta
387 [this_dict] meth_info `thenTc` \ (defm_bind, insts_needed) ->
389 tcAddErrCtxt (defltMethCtxt clas) $
393 (ptext SLIT("class") <+> ppr clas)
396 insts_needed `thenTc` \ (const_lie, dict_binds) ->
398 -- Simplification can do unification
399 checkSigTyVars clas_tyvars `thenTc` \ clas_tyvars' ->
405 [(clas_tyvars', local_dm_id, instToId dm_inst)]
406 emptyNameSet -- No inlines (yet)
407 (dict_binds `andMonoBinds` defm_bind)
409 returnTc (full_bind, const_lie, [dm_id])
411 origin = ClassDeclOrigin
416 %************************************************************************
418 \subsection{Typechecking a method}
420 %************************************************************************
422 @tcMethodBind@ is used to type-check both default-method and
423 instance-decl method declarations. We must type-check methods one at a
424 time, because their signatures may have different contexts and
429 :: [(TyVar,TcTyVar)] -- Bindings for type environment
430 -> [TcTyVar] -- Instantiated type variables for the
431 -- enclosing class/instance decl.
432 -- They'll be signature tyvars, and we
433 -- want to check that they don't get bound
434 -- Always equal the range of the type envt
435 -> TcThetaType -- Available theta; it's just used for the error message
436 -> [Inst] -- Available from context, used to simplify constraints
437 -- from the method body
438 -> (Id, TcSigInfo, RenamedMonoBinds) -- Details of this method
439 -> TcM (TcMonoBinds, LIE)
441 tcMethodBind xtve inst_tyvars inst_theta avail_insts
442 (sel_id, meth_sig, meth_bind)
444 -- Check the bindings; first adding inst_tyvars to the envt
445 -- so that we don't quantify over them in nested places
446 tcExtendTyVarEnv2 xtve (
447 tcAddErrCtxt (methodCtxt sel_id) $
448 tcMonoBinds meth_bind [meth_sig] NonRecursive
449 ) `thenTc` \ (meth_bind, meth_lie, _, _) ->
451 -- Now do context reduction. We simplify wrt both the local tyvars
452 -- and the ones of the class/instance decl, so that there is
455 -- op :: Eq a => a -> b -> a
457 -- We do this for each method independently to localise error messages
460 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
462 tcAddErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
463 newDicts SignatureOrigin meth_theta `thenNF_Tc` \ meth_dicts ->
465 all_tyvars = meth_tvs ++ inst_tyvars
466 all_insts = avail_insts ++ meth_dicts
469 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
470 all_tyvars all_insts meth_lie `thenTc` \ (lie, lie_binds) ->
472 checkSigTyVars all_tyvars `thenTc` \ all_tyvars' ->
475 meth_tvs' = take (length meth_tvs) all_tyvars'
476 poly_meth_bind = AbsBinds meth_tvs'
477 (map instToId meth_dicts)
478 [(meth_tvs', meth_id, local_meth_id)]
479 emptyNameSet -- Inlines?
480 (lie_binds `andMonoBinds` meth_bind)
482 returnTc (poly_meth_bind, lie)
485 mkMethodBind :: InstOrigin
486 -> Class -> [TcType] -- Class and instance types
487 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
489 -> TcM (Inst, -- Method inst
490 (Id, -- Global selector Id
491 TcSigInfo, -- Signature
492 RenamedMonoBinds)) -- Binding for the method
494 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
495 = tcGetSrcLoc `thenNF_Tc` \ loc ->
496 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth_inst ->
498 meth_id = instToId meth_inst
499 meth_name = idName meth_id
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 origin 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 ->
510 mkTcSig meth_id loc `thenNF_Tc` \ meth_sig ->
512 returnTc (meth_inst, (sel_id, meth_sig, meth_bind))
515 -- The user didn't supply a method binding,
516 -- so we have to make up a default binding
517 -- The RHS of a default method depends on the default-method info
518 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
519 = -- An polymorphic default method
520 returnTc (HsVar dm_name)
522 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
523 = -- No default method
524 -- Warn only if -fwarn-missing-methods
525 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
526 warnTc (isInstDecl origin && warn)
527 (omittedMethodWarn sel_id) `thenNF_Tc_`
530 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
531 (HsLit (HsStringPrim (_PK_ (stringToUtf8 error_msg))))
532 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
535 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
536 = -- A generic default method
537 -- If the method is defined generically, we can only do the job if the
538 -- instance declaration is for a single-parameter type class with
539 -- a type constructor applied to type arguments in the instance decl
540 -- (checkTc, so False provokes the error)
541 ASSERT( isInstDecl origin ) -- We never get here from a class decl
543 checkTc (isJust maybe_tycon)
544 (badGenericInstance sel_id (notSimple inst_tys)) `thenTc_`
545 checkTc (isJust (tyConGenInfo tycon))
546 (badGenericInstance sel_id (notGeneric tycon)) `thenTc_`
548 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
551 rhs = mkGenericRhs sel_id clas_tyvar tycon
553 stuff = vcat [ppr clas <+> ppr inst_tys,
554 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
556 -- The tycon is only used in the generic case, and in that
557 -- case we require that the instance decl is for a single-parameter
558 -- type class with type variable arguments:
559 -- instance (...) => C (T a b)
560 clas_tyvar = head (classTyVars clas)
561 Just tycon = maybe_tycon
562 maybe_tycon = case inst_tys of
563 [ty] -> case tcSplitTyConApp_maybe ty of
564 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
568 isInstDecl InstanceDeclOrigin = True
569 isInstDecl ClassDeclOrigin = False
574 -- The renamer just puts the selector ID as the binder in the method binding
575 -- but we must use the method name; so we substitute it here. Crude but simple.
576 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
577 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
578 find_bind sel_name meth_name (AndMonoBinds b1 b2)
579 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
580 find_bind sel_name meth_name other = Nothing -- Default case
582 -- Find the prags for this method, and replace the
583 -- selector name with the method name
584 find_prags sel_name meth_name [] = []
585 find_prags sel_name meth_name (SpecSig name ty loc : prags)
586 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
587 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
588 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
589 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
597 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
600 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
603 = hsep [ptext SLIT("Class"), quotes (ppr clas),
604 ptext SLIT("does not have a method"), quotes (ppr op)]
606 omittedMethodWarn sel_id
607 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
609 badGenericInstance sel_id because
610 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
614 = vcat [ptext SLIT("because the instance type(s)"),
615 nest 2 (ppr inst_tys),
616 ptext SLIT("is not a simple type of form (T a b c)")]
619 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
620 ptext SLIT("was not compiled with -fgenerics")]
623 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)