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 ErrUtils ( dumpIfSet )
58 import Util ( count, lengthIs, equalLength )
59 import Maybes ( seqMaybe )
60 import Maybe ( isJust )
67 Every class implicitly declares a new data type, corresponding to dictionaries
68 of that class. So, for example:
70 class (D a) => C a where
72 op2 :: forall b. Ord b => a -> b -> b
74 would implicitly declare
76 data CDict a = CDict (D a)
78 (forall b. Ord b => a -> b -> b)
80 (We could use a record decl, but that means changing more of the existing apparatus.
83 For classes with just one superclass+method, we use a newtype decl instead:
86 op :: forallb. a -> b -> b
90 newtype CDict a = CDict (forall b. a -> b -> b)
92 Now DictTy in Type is just a form of type synomym:
93 DictTy c t = TyConTy CDict `AppTy` t
95 Death to "ExpandingDicts".
98 %************************************************************************
100 \subsection{Type checking}
102 %************************************************************************
106 tcClassDecl1 :: RenamedTyClDecl -> TcM (Name, TyThingDetails)
107 tcClassDecl1 (ClassDecl {tcdCtxt = context, tcdName = class_name,
108 tcdTyVars = tyvar_names, tcdFDs = fundeps,
109 tcdSigs = class_sigs, tcdMeths = def_methods,
110 tcdSysNames = sys_names, tcdLoc = src_loc})
111 = -- LOOK THINGS UP IN THE ENVIRONMENT
112 tcLookupClass class_name `thenTc` \ clas ->
114 tyvars = classTyVars clas
115 op_sigs = filter isClassOpSig class_sigs
116 op_names = [n | ClassOpSig n _ _ _ <- op_sigs]
117 (_, datacon_name, datacon_wkr_name, sc_sel_names) = getClassDeclSysNames sys_names
119 tcExtendTyVarEnv tyvars $
121 checkDefaultBinds clas op_names def_methods `thenTc` \ mb_dm_env ->
124 -- The renamer has already checked that the context mentions
125 -- only the type variable of the class decl.
126 -- Context is already kind-checked
127 ASSERT( equalLength context sc_sel_names )
128 tcHsTheta context `thenTc` \ sc_theta ->
130 -- CHECK THE CLASS SIGNATURES,
131 mapTc (tcClassSig clas tyvars mb_dm_env) op_sigs `thenTc` \ sig_stuff ->
133 -- MAKE THE CLASS DETAILS
135 (op_tys, op_items) = unzip sig_stuff
136 sc_tys = mkPredTys sc_theta
137 dict_component_tys = sc_tys ++ op_tys
138 sc_sel_ids = [mkDictSelId sc_name clas | sc_name <- sc_sel_names]
140 dict_con = mkDataCon datacon_name
141 [NotMarkedStrict | _ <- dict_component_tys]
142 [{- No labelled fields -}]
145 [{-No existential tyvars-}] [{-Or context-}]
148 dict_con_id dict_wrap_id
150 dict_con_id = mkDataConId datacon_wkr_name dict_con
151 dict_wrap_id = mkDataConWrapId dict_con
153 returnTc (class_name, ClassDetails sc_theta sc_sel_ids op_items dict_con)
157 checkDefaultBinds :: Class -> [Name] -> Maybe RenamedMonoBinds
158 -> TcM (Maybe (NameEnv Bool))
159 -- The returned environment says
160 -- x not in env => no default method
161 -- x -> True => generic default method
162 -- x -> False => polymorphic default method
164 -- Check default bindings
165 -- a) must be for a class op for this class
166 -- b) must be all generic or all non-generic
167 -- and return a mapping from class-op to DefMeth info
169 -- But do all this only for source binds
171 checkDefaultBinds clas ops Nothing
174 checkDefaultBinds clas ops (Just mbs)
175 = go mbs `thenTc` \ dm_env ->
176 returnTc (Just dm_env)
178 go EmptyMonoBinds = returnTc emptyNameEnv
180 go (AndMonoBinds b1 b2)
181 = go b1 `thenTc` \ dm_info1 ->
182 go b2 `thenTc` \ dm_info2 ->
183 returnTc (dm_info1 `plusNameEnv` dm_info2)
185 go (FunMonoBind op _ matches loc)
188 -- Check that the op is from this class
189 checkTc (op `elem` ops) (badMethodErr clas op) `thenTc_`
191 -- Check that all the defns ar generic, or none are
192 checkTc (all_generic || none_generic) (mixedGenericErr op) `thenTc_`
194 returnTc (unitNameEnv op all_generic)
196 n_generic = count (isJust . maybeGenericMatch) matches
197 none_generic = n_generic == 0
198 all_generic = matches `lengthIs` n_generic
203 tcClassSig :: Class -- ...ditto...
204 -> [TyVar] -- The class type variable, used for error check only
205 -> Maybe (NameEnv Bool) -- Info about default methods;
206 -- Nothing => imported class defn with no method binds
208 -> TcM (Type, -- Type of the method
209 ClassOpItem) -- Selector Id, default-method Id, True if explicit default binding
211 -- This warrants an explanation: we need to separate generic
212 -- default methods and default methods later on in the compiler
213 -- so we distinguish them in checkDefaultBinds, and pass this knowledge in the
214 -- Class.DefMeth data structure.
216 tcClassSig clas clas_tyvars maybe_dm_env
217 (ClassOpSig op_name sig_dm op_ty src_loc)
218 = tcAddSrcLoc src_loc $
220 -- Check the type signature. NB that the envt *already has*
221 -- bindings for the type variables; see comments in TcTyAndClassDcls.
222 tcHsType op_ty `thenTc` \ local_ty ->
225 theta = [mkClassPred clas (mkTyVarTys clas_tyvars)]
227 -- Build the selector id and default method id
228 sel_id = mkDictSelId op_name clas
229 DefMeth dm_name = sig_dm
231 dm_info = case maybe_dm_env of
233 Just dm_env -> mk_src_dm_info dm_env
235 mk_src_dm_info dm_env = case lookupNameEnv dm_env op_name of
237 Just True -> GenDefMeth
238 Just False -> DefMeth dm_name
240 returnTc (local_ty, (sel_id, dm_info))
244 %************************************************************************
246 \subsection[Default methods]{Default methods}
248 %************************************************************************
250 The default methods for a class are each passed a dictionary for the
251 class, so that they get access to the other methods at the same type.
252 So, given the class decl
256 op2 :: Ord b => a -> b -> b -> b
259 op2 x y z = if (op1 x) && (y < z) then y else z
261 we get the default methods:
263 defm.Foo.op1 :: forall a. Foo a => a -> Bool
264 defm.Foo.op1 = /\a -> \dfoo -> \x -> True
266 defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
267 defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
268 if (op1 a dfoo x) && (< b dord y z) then y else z
271 When we come across an instance decl, we may need to use the default
274 instance Foo Int where {}
278 const.Foo.Int.op1 :: Int -> Bool
279 const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
281 const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
282 const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
284 dfun.Foo.Int :: Foo Int
285 dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
287 Notice that, as with method selectors above, we assume that dictionary
288 application is curried, so there's no need to mention the Ord dictionary
289 in const.Foo.Int.op2 (or the type variable).
292 instance Foo a => Foo [a] where {}
294 dfun.Foo.List :: forall a. Foo a -> Foo [a]
296 = /\ a -> \ dfoo_a ->
298 op1 = defm.Foo.op1 [a] dfoo_list
299 op2 = defm.Foo.op2 [a] dfoo_list
300 dfoo_list = (op1, op2)
305 The function @tcClassDecls2@ just arranges to apply @tcClassDecl2@ to
306 each local class decl.
309 tcClassDecls2 :: Module -> [RenamedTyClDecl] -> NF_TcM (LIE, TcMonoBinds, [Id])
311 tcClassDecls2 this_mod decls
313 (returnNF_Tc (emptyLIE, EmptyMonoBinds, []))
314 [tcClassDecl2 cls_decl | cls_decl@(ClassDecl {tcdMeths = Just _}) <- decls]
315 -- The 'Just' picks out source ClassDecls
317 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1, ids1) ->
318 tc2 `thenNF_Tc` \ (lie2, binds2, ids2) ->
319 returnNF_Tc (lie1 `plusLIE` lie2,
320 binds1 `AndMonoBinds` binds2,
324 @tcClassDecl2@ generates bindings for polymorphic default methods
325 (generic default methods have by now turned into instance declarations)
328 tcClassDecl2 :: RenamedTyClDecl -- The class declaration
329 -> NF_TcM (LIE, TcMonoBinds, [Id])
331 tcClassDecl2 (ClassDecl {tcdName = class_name, tcdSigs = sigs,
332 tcdMeths = Just default_binds, tcdLoc = src_loc})
333 = -- The 'Just' picks out source ClassDecls
334 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds, [])) $
335 tcAddSrcLoc src_loc $
336 tcLookupClass class_name `thenNF_Tc` \ clas ->
338 -- We make a separate binding for each default method.
339 -- At one time I used a single AbsBinds for all of them, thus
340 -- AbsBind [d] [dm1, dm2, dm3] { dm1 = ...; dm2 = ...; dm3 = ... }
341 -- But that desugars into
342 -- ds = \d -> (..., ..., ...)
343 -- dm1 = \d -> case ds d of (a,b,c) -> a
344 -- And since ds is big, it doesn't get inlined, so we don't get good
345 -- default methods. Better to make separate AbsBinds for each
347 (tyvars, _, _, op_items) = classBigSig clas
348 prags = filter isPragSig sigs
349 tc_dm = tcDefMeth clas tyvars default_binds prags
351 mapAndUnzip3Tc tc_dm op_items `thenTc` \ (defm_binds, const_lies, dm_ids_s) ->
353 returnTc (plusLIEs const_lies, andMonoBindList defm_binds, concat dm_ids_s)
356 tcDefMeth clas tyvars binds_in prags (_, NoDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
357 tcDefMeth clas tyvars binds_in prags (_, GenDefMeth) = returnTc (EmptyMonoBinds, emptyLIE, [])
358 -- Generate code for polymorphic default methods only
359 -- (Generic default methods have turned into instance decls by now.)
360 -- This is incompatible with Hugs, which expects a polymorphic
361 -- default method for every class op, regardless of whether or not
362 -- the programmer supplied an explicit default decl for the class.
363 -- (If necessary we can fix that, but we don't have a convenient Id to hand.)
365 tcDefMeth clas tyvars binds_in prags op_item@(sel_id, DefMeth dm_name)
366 = tcInstTyVars ClsTv tyvars `thenNF_Tc` \ (clas_tyvars, inst_tys, _) ->
368 dm_ty = idType sel_id -- Same as dict selector!
369 -- The default method's type should really come from the
370 -- iface file, since it could be usage-generalised, but this
371 -- requires altering the mess of knots in TcModule and I'm
372 -- too scared to do that. Instead, I have disabled generalisation
373 -- of types of default methods (and dict funs) by annotating them
374 -- TyGenNever (in MkId). Ugh! KSW 1999-09.
376 theta = [mkClassPred clas inst_tys]
377 dm_id = mkDefaultMethodId dm_name dm_ty
378 local_dm_id = setIdLocalExported dm_id
379 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
380 xtve = tyvars `zip` clas_tyvars
382 newDicts origin theta `thenNF_Tc` \ [this_dict] ->
384 mkMethodBind origin clas inst_tys binds_in op_item `thenTc` \ (dm_inst, meth_info) ->
385 tcMethodBind xtve clas_tyvars theta
386 [this_dict] meth_info `thenTc` \ (defm_bind, insts_needed) ->
388 tcAddErrCtxt (defltMethCtxt clas) $
392 (ptext SLIT("class") <+> ppr clas)
395 insts_needed `thenTc` \ (const_lie, dict_binds) ->
397 -- Simplification can do unification
398 checkSigTyVars clas_tyvars `thenTc` \ clas_tyvars' ->
404 [(clas_tyvars', local_dm_id, instToId dm_inst)]
405 emptyNameSet -- No inlines (yet)
406 (dict_binds `andMonoBinds` defm_bind)
408 returnTc (full_bind, const_lie, [dm_id])
410 origin = ClassDeclOrigin
415 %************************************************************************
417 \subsection{Typechecking a method}
419 %************************************************************************
421 @tcMethodBind@ is used to type-check both default-method and
422 instance-decl method declarations. We must type-check methods one at a
423 time, because their signatures may have different contexts and
428 :: [(TyVar,TcTyVar)] -- Bindings for type environment
429 -> [TcTyVar] -- Instantiated type variables for the
430 -- enclosing class/instance decl.
431 -- They'll be signature tyvars, and we
432 -- want to check that they don't get bound
433 -- Always equal the range of the type envt
434 -> TcThetaType -- Available theta; it's just used for the error message
435 -> [Inst] -- Available from context, used to simplify constraints
436 -- from the method body
437 -> (Id, TcSigInfo, RenamedMonoBinds) -- Details of this method
438 -> TcM (TcMonoBinds, LIE)
440 tcMethodBind xtve inst_tyvars inst_theta avail_insts
441 (sel_id, meth_sig, meth_bind)
443 -- Check the bindings; first adding inst_tyvars to the envt
444 -- so that we don't quantify over them in nested places
445 tcExtendTyVarEnv2 xtve (
446 tcAddErrCtxt (methodCtxt sel_id) $
447 tcMonoBinds meth_bind [meth_sig] NonRecursive
448 ) `thenTc` \ (meth_bind, meth_lie, _, _) ->
450 -- Now do context reduction. We simplify wrt both the local tyvars
451 -- and the ones of the class/instance decl, so that there is
454 -- op :: Eq a => a -> b -> a
456 -- We do this for each method independently to localise error messages
459 TySigInfo meth_id meth_tvs meth_theta _ local_meth_id _ _ = meth_sig
461 tcAddErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $
462 newDicts SignatureOrigin meth_theta `thenNF_Tc` \ meth_dicts ->
464 all_tyvars = meth_tvs ++ inst_tyvars
465 all_insts = avail_insts ++ meth_dicts
468 (ptext SLIT("class or instance method") <+> quotes (ppr sel_id))
469 all_tyvars all_insts meth_lie `thenTc` \ (lie, lie_binds) ->
471 checkSigTyVars all_tyvars `thenTc` \ all_tyvars' ->
474 meth_tvs' = take (length meth_tvs) all_tyvars'
475 poly_meth_bind = AbsBinds meth_tvs'
476 (map instToId meth_dicts)
477 [(meth_tvs', meth_id, local_meth_id)]
478 emptyNameSet -- Inlines?
479 (lie_binds `andMonoBinds` meth_bind)
481 returnTc (poly_meth_bind, lie)
484 mkMethodBind :: InstOrigin
485 -> Class -> [TcType] -- Class and instance types
486 -> RenamedMonoBinds -- Method binding (pick the right one from in here)
488 -> TcM (Inst, -- Method inst
489 (Id, -- Global selector Id
490 TcSigInfo, -- Signature
491 RenamedMonoBinds)) -- Binding for the method
493 mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info)
494 = tcGetSrcLoc `thenNF_Tc` \ loc ->
495 newMethod origin sel_id inst_tys `thenNF_Tc` \ meth_inst ->
497 meth_id = instToId meth_inst
498 meth_name = idName meth_id
500 -- Figure out what method binding to use
501 -- If the user suppplied one, use it, else construct a default one
502 (case find_bind (idName sel_id) meth_name meth_binds of
503 Just user_bind -> returnTc user_bind
504 Nothing -> mkDefMethRhs origin clas inst_tys sel_id loc dm_info `thenTc` \ rhs ->
505 returnTc (FunMonoBind meth_name False -- Not infix decl
506 [mkSimpleMatch [] rhs placeHolderType loc] loc)
507 ) `thenTc` \ meth_bind ->
509 mkTcSig meth_id loc `thenNF_Tc` \ meth_sig ->
511 returnTc (meth_inst, (sel_id, meth_sig, meth_bind))
514 -- The user didn't supply a method binding,
515 -- so we have to make up a default binding
516 -- The RHS of a default method depends on the default-method info
517 mkDefMethRhs origin clas inst_tys sel_id loc (DefMeth dm_name)
518 = -- An polymorphic default method
519 returnTc (HsVar dm_name)
521 mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth
522 = -- No default method
523 -- Warn only if -fwarn-missing-methods
524 doptsTc Opt_WarnMissingMethods `thenNF_Tc` \ warn ->
525 warnTc (isInstDecl origin && warn)
526 (omittedMethodWarn sel_id) `thenNF_Tc_`
529 error_rhs = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
530 (HsLit (HsString (_PK_ error_msg)))
531 error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
534 mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
535 = -- A generic default method
536 -- If the method is defined generically, we can only do the job if the
537 -- instance declaration is for a single-parameter type class with
538 -- a type constructor applied to type arguments in the instance decl
539 -- (checkTc, so False provokes the error)
540 ASSERT( isInstDecl origin ) -- We never get here from a class decl
542 checkTc (isJust maybe_tycon)
543 (badGenericInstance sel_id (notSimple inst_tys)) `thenTc_`
544 checkTc (isJust (tyConGenInfo tycon))
545 (badGenericInstance sel_id (notGeneric tycon)) `thenTc_`
547 ioToTc (dumpIfSet opt_PprStyle_Debug "Generic RHS" stuff) `thenNF_Tc_`
550 rhs = mkGenericRhs sel_id clas_tyvar tycon
552 stuff = vcat [ppr clas <+> ppr inst_tys,
553 nest 4 (ppr sel_id <+> equals <+> ppr rhs)]
555 -- The tycon is only used in the generic case, and in that
556 -- case we require that the instance decl is for a single-parameter
557 -- type class with type variable arguments:
558 -- instance (...) => C (T a b)
559 clas_tyvar = head (classTyVars clas)
560 Just tycon = maybe_tycon
561 maybe_tycon = case inst_tys of
562 [ty] -> case tcSplitTyConApp_maybe ty of
563 Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
567 isInstDecl InstanceDeclOrigin = True
568 isInstDecl ClassDeclOrigin = False
573 -- The renamer just puts the selector ID as the binder in the method binding
574 -- but we must use the method name; so we substitute it here. Crude but simple.
575 find_bind sel_name meth_name (FunMonoBind op_name fix matches loc)
576 | op_name == sel_name = Just (FunMonoBind meth_name fix matches loc)
577 find_bind sel_name meth_name (AndMonoBinds b1 b2)
578 = find_bind sel_name meth_name b1 `seqMaybe` find_bind sel_name meth_name b2
579 find_bind sel_name meth_name other = Nothing -- Default case
581 -- Find the prags for this method, and replace the
582 -- selector name with the method name
583 find_prags sel_name meth_name [] = []
584 find_prags sel_name meth_name (SpecSig name ty loc : prags)
585 | name == sel_name = SpecSig meth_name ty loc : find_prags sel_name meth_name prags
586 find_prags sel_name meth_name (InlineSig sense name phase loc : prags)
587 | name == sel_name = InlineSig sense meth_name phase loc : find_prags sel_name meth_name prags
588 find_prags sel_name meth_name (prag:prags) = find_prags sel_name meth_name prags
596 = ptext SLIT("When checking the default methods for class") <+> quotes (ppr clas)
599 = ptext SLIT("In the definition for method") <+> quotes (ppr sel_id)
602 = hsep [ptext SLIT("Class"), quotes (ppr clas),
603 ptext SLIT("does not have a method"), quotes (ppr op)]
605 omittedMethodWarn sel_id
606 = ptext SLIT("No explicit method nor default method for") <+> quotes (ppr sel_id)
608 badGenericInstance sel_id because
609 = sep [ptext SLIT("Can't derive generic code for") <+> quotes (ppr sel_id),
613 = vcat [ptext SLIT("because the instance type(s)"),
614 nest 2 (ppr inst_tys),
615 ptext SLIT("is not a simple type of form (T a b c)")]
618 = vcat [ptext SLIT("because the instance type constructor") <+> quotes (ppr tycon) <+>
619 ptext SLIT("was not compiled with -fgenerics")]
622 = ptext SLIT("Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)