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 )
69 Every class implicitly declares a new data type, corresponding to dictionaries
70 of that class. So, for example:
72 class (D a) => C a where
74 op2 :: forall b. Ord b => a -> b -> b
76 would implicitly declare
78 data CDict a = CDict (D a)
80 (forall b. Ord b => a -> b -> b)
82 (We could use a record decl, but that means changing more of the existing apparatus.
85 For classes with just one superclass+method, we use a newtype decl instead:
88 op :: forallb. a -> b -> b
92 newtype CDict a = CDict (forall b. a -> b -> b)
94 Now DictTy in Type is just a form of type synomym:
95 DictTy c t = TyConTy CDict `AppTy` t
97 Death to "ExpandingDicts".
100 %************************************************************************
102 \subsection{Type checking}
104 %************************************************************************
108 tcClassDecl1 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
109 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
110 tcdTyVars = tyvar_names, tcdFDs = fundeps,
111 tcdSigs = class_sigs, tcdMeths = def_methods,
112 tcdSysNames = sys_names, tcdLoc = src_loc})
113 = -- LOOK THINGS UP IN THE ENVIRONMENT
114 tcLookupClass class_name `thenTc` \ clas ->
116 tyvars = classTyVars clas
117 op_sigs = filter isClassOpSig class_sigs
118 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
119 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
121 tcExtendTyVarEnv tyvars $
123 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
126 -- The renamer has already checked that the context mentions
127 -- only the type variable of the class decl.
128 -- Context is already kind-checked
129 ASSERT( equalLength context sc_sel_names )
130 tcHsTheta context `thenTc` \ sc_theta ->
132 -- CHECK THE CLASS SIGNATURES,
133 mapTc (tcClassSig clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
135 -- MAKE THE CLASS DETAILS
137 (op_tys, op_items) = unzip sig_stuff
138 sc_tys = mkPredTys sc_theta
139 dict_component_tys = sc_tys ++ op_tys
140 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
142 dict_con = mkDataCon datacon_name
143 [NotMarkedStrict | _ <- dict_component_tys]
144 [{- No labelled fields -}]
147 [{-No existential tyvars-}] [{-Or context-}]
150 dict_con_id dict_wrap_id
152 dict_con_id = mkDataConId datacon_wkr_name dict_con
153 dict_wrap_id = mkDataConWrapId dict_con
155 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
159 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
160 -> TcM (Maybe (NameEnv Bool))
161 -- The returned environment says
162 -- x not in env => no default method
163 -- x -> True => generic default method
164 -- x -> False => polymorphic default method
166 -- Check default bindings
167 -- a) must be for a class op for this class
168 -- b) must be all generic or all non-generic
169 -- and return a mapping from class-op to DefMeth info
171 -- But do all this only for source binds
173 checkDefaultBinds clas ops Nothing
176 checkDefaultBinds clas ops (Just mbs)
177 = go mbs `thenTc` \ dm_env ->
178 returnTc (Just dm_env)
180 go EmptyMonoBinds = returnTc emptyNameEnv
182 go (AndMonoBinds b1 b2)
183 = go b1 `thenTc` \ dm_info1 ->
184 go b2 `thenTc` \ dm_info2 ->
185 returnTc (dm_info1 `plusNameEnv` dm_info2)
187 go (FunMonoBind op _ matches loc)
190 -- Check that the op is from this class
191 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
193 -- Check that all the defns ar generic, or none are
194 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
196 returnTc (unitNameEnv op all_generic)
198 n_generic = count (isJust . maybeGenericMatch) matches
199 none_generic = n_generic == 0
200 all_generic = matches `lengthIs` n_generic
205 tcClassSig :: Class -- ...ditto...
206 -> [TyVar] -- The class type variable, used for error check only
207 -> Maybe (NameEnv Bool) -- Info about default methods;
208 -- Nothing => imported class defn with no method binds
210 -> TcM (Type, -- Type of the method
211 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
213 -- This warrants an explanation: we need to separate generic
214 -- default methods and default methods later on in the compiler
215 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
216 -- Class.DefMeth data structure.
218 tcClassSig clas clas_tyvars maybe_dm_env
219 (ClassOpSig op_name sig_dm op_ty src_loc)
220 = tcAddSrcLoc src_loc $
222 -- Check the type signature. NB that the envt *already has*
223 -- bindings for the type variables; see comments in TcTyAndClassDcls.
224 tcHsType op_ty `thenTc` \ local_ty ->
227 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
229 -- Build the selector id and default method id
230 sel_id = mkDictSelId op_name clas
231 DefMeth dm_name = sig_dm
233 dm_info = case maybe_dm_env of
235 Just dm_env -> mk_src_dm_info dm_env
237 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
239 Just True -> GenDefMeth
240 Just False -> DefMeth dm_name
242 returnTc (local_ty, (sel_id, dm_info))
246 %************************************************************************
248 \subsection[Default methods]{Default methods}
250 %************************************************************************
252 The default methods for a class are each passed a dictionary for the
253 class, so that they get access to the other methods at the same type.
254 So, given the class decl
258 op2 :: Ord b => a -> b -> b -> b
261 op2 x y z = if (op1 x) && (y < z) then y else z
263 we get the default methods:
265 defm.Foo.op1 :: forall a. Foo a => a -> Bool
266 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
268 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
269 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
270 if (op1 a dfoo x) && (< b dord y z) then y else z
273 When we come across an instance decl, we may need to use the default
276 instance Foo Int where {}
280 const.Foo.Int.op1 :: Int -> Bool
281 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
283 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
284 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
286 dfun.Foo.Int :: Foo Int
287 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
289 Notice that, as with method selectors above, we assume that dictionary
290 application is curried, so there's no need to mention the Ord dictionary
291 in const.Foo.Int.op2 (or the type variable).
294 instance Foo a => Foo [a] where {}
296 dfun.Foo.List :: forall a. Foo a -> Foo [a]
298 = /\ a -> \ dfoo_a ->
300 op1 = defm.Foo.op1 [a] dfoo_list
301 op2 = defm.Foo.op2 [a] dfoo_list
302 dfoo_list = (op1, op2)
307 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
308 each local class decl.
311 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
313 tcClassDecls2 this_mod decls
315 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
316 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
317 -- The 'Just' picks out source ClassDecls
319 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
320 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
321 returnNF_Tc (lie1 `plusLIE` lie2,
322 binds1 `AndMonoBinds` binds2,
326 @tcClassDecl2@ generates bindings for polymorphic default methods
327 (generic default methods have by now turned into instance declarations)
330 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
331 -> NF_TcM (LIE, TcMonoBinds, [Id])
333 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
334 tcdMeths = Just default_binds, tcdLoc = src_loc})
335 = -- The 'Just' picks out source ClassDecls
336 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
337 tcAddSrcLoc src_loc $
338 tcLookupClass class_name `thenNF_Tc` \ clas ->
340 -- We make a separate binding for each default method.
341 -- At one time I used a single AbsBinds for all of them, thus
342 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
343 -- But that desugars into
344 -- ds = \d -> (..., ..., ...)
345 -- dm1 = \d -> case ds d of (a,b,c) -> a
346 -- And since ds is big, it doesn't get inlined, so we don't get good
347 -- default methods. Better to make separate AbsBinds for each
349 (tyvars, _, _, op_items) = classBigSig clas
350 prags = filter isPragSig sigs
351 tc_dm = tcDefMeth clas tyvars default_binds prags
353 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
355 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
358 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
359 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
360 -- Generate code for polymorphic default methods only
361 -- (Generic default methods have turned into instance decls by now.)
362 -- This is incompatible with Hugs, which expects a polymorphic
363 -- default method for every class op, regardless of whether or not
364 -- the programmer supplied an explicit default decl for the class.
365 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
367 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
368 = tcInstTyVars ClsTv tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
370 dm_ty = idType sel_id -- Same as dict selector!
371 -- The default method's type should really come from the
372 -- iface file, since it could be usage-generalised, but this
373 -- requires altering the mess of knots in TcModule and I'm
374 -- too scared to do that. Instead, I have disabled generalisation
375 -- of types of default methods (and dict funs) by annotating them
376 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
378 theta = [mkClassPred clas inst_tys]
379 dm_id = mkDefaultMethodId dm_name dm_ty
380 local_dm_id = setIdLocalExported dm_id
381 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
382 xtve = tyvars `zip` clas_tyvars
384 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
386 mkMethodBind origin clas inst_tys binds_in op_item `thenTc` \ (dm_inst, meth_info) ->
387 tcMethodBind xtve clas_tyvars theta
388 [this_dict] meth_info `thenTc` \ (defm_bind, insts_needed) ->
390 tcAddErrCtxt (defltMethCtxt clas) $
394 (ptext SLIT("class") <+> ppr clas)
397 insts_needed `thenTc` \ (const_lie, dict_binds) ->
399 -- Simplification can do unification
400 checkSigTyVars clas_tyvars `thenTc` \ clas_tyvars' ->
406 [(clas_tyvars', local_dm_id, instToId dm_inst)]
407 emptyNameSet -- No inlines (yet)
408 (dict_binds `andMonoBinds` defm_bind)
410 returnTc (full_bind, const_lie, [dm_id])
412 origin = ClassDeclOrigin
417 %************************************************************************
419 \subsection{Typechecking a method}
421 %************************************************************************
423 @tcMethodBind@ is used to type-check both default-method and
424 instance-decl method declarations. We must type-check methods one at a
425 time, because their signatures may have different contexts and
430 :: [(TyVar,TcTyVar)] -- Bindings for type environment
431 -> [TcTyVar] -- Instantiated type variables for the
432 -- enclosing class/instance decl.
433 -- They'll be signature tyvars, and we
434 -- want to check that they don't get bound
435 -- Always equal the range of the type envt
436 -> TcThetaType -- Available theta; it's just used for the error message
437 -> [Inst] -- Available from context, used to simplify constraints
438 -- from the method body
439 -> (Id, TcSigInfo, RenamedMonoBinds) -- Details of this method
440 -> TcM (TcMonoBinds, LIE)
442 tcMethodBind xtve inst_tyvars inst_theta avail_insts
443 (sel_id, meth_sig, meth_bind)
445 -- Check the bindings; first adding inst_tyvars to the envt
446 -- so that we don't quantify over them in nested places
447 tcExtendTyVarEnv2 xtve (
448 tcAddErrCtxt (methodCtxt sel_id) $
449 tcMonoBinds meth_bind [meth_sig] NonRecursive
450 ) `thenTc` \ (meth_bind, meth_lie, _, _) ->
452 -- Now do context reduction. We simplify wrt both the local tyvars
453 -- and the ones of the class/instance decl, so that there is
456 -- op :: Eq a => a -> b -> a
458 -- We do this for each method independently to localise error messages
461 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
463 tcAddErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
464 newDicts SignatureOrigin meth_theta `thenNF_Tc` \ meth_dicts ->
466 all_tyvars = meth_tvs ++ inst_tyvars
467 all_insts = avail_insts ++ meth_dicts
470 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
471 all_tyvars all_insts meth_lie `thenTc` \ (lie, lie_binds) ->
473 checkSigTyVars all_tyvars `thenTc` \ all_tyvars' ->
476 meth_tvs' = take (length meth_tvs) all_tyvars'
477 poly_meth_bind = AbsBinds meth_tvs'
478 (map instToId meth_dicts)
479 [(meth_tvs', meth_id, local_meth_id)]
480 emptyNameSet -- Inlines?
481 (lie_binds `andMonoBinds` meth_bind)
483 returnTc (poly_meth_bind, lie)
486 mkMethodBind :: InstOrigin
487 -> Class -> [TcType] -- Class and instance types
488 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
490 -> TcM (Inst, -- Method inst
491 (Id, -- Global selector Id
492 TcSigInfo, -- Signature
493 RenamedMonoBinds)) -- Binding for the method
495 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
496 = tcGetSrcLoc `thenNF_Tc` \ loc ->
497 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth_inst ->
499 meth_id = instToId meth_inst
500 meth_name = idName meth_id
502 -- Figure out what method binding to use
503 -- If the user suppplied one, use it, else construct a default one
504 (case find_bind (idName sel_id) meth_name meth_binds of
505 Just user_bind -> returnTc user_bind
506 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
507 returnTc (FunMonoBind meth_name False -- Not infix decl
508 [mkSimpleMatch [] rhs placeHolderType loc] loc)
509 ) `thenTc` \ meth_bind ->
511 mkTcSig meth_id loc `thenNF_Tc` \ meth_sig ->
513 returnTc (meth_inst, (sel_id, meth_sig, meth_bind))
516 -- The user didn't supply a method binding,
517 -- so we have to make up a default binding
518 -- The RHS of a default method depends on the default-method info
519 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
520 = -- An polymorphic default method
521 returnTc (HsVar dm_name)
523 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
524 = -- No default method
525 -- Warn only if -fwarn-missing-methods
526 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
527 warnTc (isInstDecl origin && warn)
528 (omittedMethodWarn sel_id) `thenNF_Tc_`
531 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
532 (HsLit (HsStringPrim (mkFastString (stringToUtf8 error_msg))))
533 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
536 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
537 = -- A generic default method
538 -- If the method is defined generically, we can only do the job if the
539 -- instance declaration is for a single-parameter type class with
540 -- a type constructor applied to type arguments in the instance decl
541 -- (checkTc, so False provokes the error)
542 ASSERT( isInstDecl origin ) -- We never get here from a class decl
544 checkTc (isJust maybe_tycon)
545 (badGenericInstance sel_id (notSimple inst_tys)) `thenTc_`
546 checkTc (isJust (tyConGenInfo tycon))
547 (badGenericInstance sel_id (notGeneric tycon)) `thenTc_`
549 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
552 rhs = mkGenericRhs sel_id clas_tyvar tycon
554 stuff = vcat [ppr clas <+> ppr inst_tys,
555 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
557 -- The tycon is only used in the generic case, and in that
558 -- case we require that the instance decl is for a single-parameter
559 -- type class with type variable arguments:
560 -- instance (...) => C (T a b)
561 clas_tyvar = head (classTyVars clas)
562 Just tycon = maybe_tycon
563 maybe_tycon = case inst_tys of
564 [ty] -> case tcSplitTyConApp_maybe ty of
565 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
569 isInstDecl InstanceDeclOrigin = True
570 isInstDecl ClassDeclOrigin = False
575 -- The renamer just puts the selector ID as the binder in the method binding
576 -- but we must use the method name; so we substitute it here. Crude but simple.
577 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
578 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
579 find_bind sel_name meth_name (AndMonoBinds b1 b2)
580 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
581 find_bind sel_name meth_name other = Nothing -- Default case
583 -- Find the prags for this method, and replace the
584 -- selector name with the method name
585 find_prags sel_name meth_name [] = []
586 find_prags sel_name meth_name (SpecSig name ty loc : prags)
587 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
588 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
589 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
590 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
598 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
601 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
604 = hsep [ptext SLIT("Class"), quotes (ppr clas),
605 ptext SLIT("does not have a method"), quotes (ppr op)]
607 omittedMethodWarn sel_id
608 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
610 badGenericInstance sel_id because
611 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
615 = vcat [ptext SLIT("because the instance type(s)"),
616 nest 2 (ppr inst_tys),
617 ptext SLIT("is not a simple type of form (T a b c)")]
620 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
621 ptext SLIT("was not compiled with -fgenerics")]
624 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)