\begin{code}
module TcClassDcl ( tcClassSigs, tcClassDecl2,
- getGenericInstances,
- MethodSpec, tcMethodBind, mkMethId,
+ findMethodBind, tcMethodBind,
+ mkGenericDefMethBind, getGenericInstances, mkDefMethRdrName,
tcAddDeclCtxt, badMethodErr, badATErr, omittedATWarn
) where
import TcEnv
import TcBinds
import TcHsType
-import TcSimplify
-import TcUnify
import TcMType
import TcType
import TcRnMonad
let
(tyvars, _, _, op_items) = classBigSig clas
rigid_info = ClsSkol clas
- origin = SigOrigin rigid_info
prag_fn = mkPragFun sigs
sig_fn = mkTcSigFun sigs
clas_tyvars = tcSkolSigTyVars rigid_info tyvars
- tc_dm = tcDefMeth origin clas clas_tyvars
- default_binds sig_fn prag_fn
+ tc_dm = tcDefMeth clas_tyvars default_binds
+ sig_fn prag_fn
+ -- tc_dm is called only for a sel_id
+ -- that has a binding in default_binds
dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
-- Generate code for polymorphic default methods only
-- the programmer supplied an explicit default decl for the class.
-- (If necessary we can fix that, but we don't have a convenient Id to hand.)
- (defm_binds, dm_ids_s) <- mapAndUnzipM tc_dm dm_sel_ids
- return (listToBag defm_binds, concat dm_ids_s)
+ (defm_binds, dm_ids) <- mapAndUnzipM tc_dm dm_sel_ids
+ return (unionManyBags defm_binds, dm_ids)
tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
-tcDefMeth :: InstOrigin -> Class -> [TyVar] -> LHsBinds Name
+tcDefMeth :: [TyVar] -> LHsBinds Name
-> TcSigFun -> TcPragFun -> Id
- -> TcM (LHsBindLR Id Var, [Id])
-tcDefMeth origin clas tyvars binds_in sig_fn prag_fn sel_id
- = do { dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_id)
- ; let inst_tys = mkTyVarTys tyvars
- dm_ty = idType sel_id -- Same as dict selector!
- cls_pred = mkClassPred clas inst_tys
- local_dm_id = mkDefaultMethodId dm_name dm_ty
-
- ; loc <- getInstLoc origin
- ; this_dict <- newDictBndr loc cls_pred
- ; (_, meth_id) <- mkMethId origin clas sel_id inst_tys
- ; (defm_bind, insts_needed) <- getLIE $
- tcMethodBind origin tyvars [cls_pred] this_dict []
- sig_fn prag_fn binds_in
- (sel_id, DefMeth) meth_id
-
- ; addErrCtxt (defltMethCtxt clas) $ do
-
- -- Check the context
- { dict_binds <- tcSimplifyCheck
- loc
- tyvars
- [this_dict]
- insts_needed
-
- -- Simplification can do unification
- ; checkSigTyVars tyvars
-
- -- Inline pragmas
- -- We'll have an inline pragma on the local binding, made by tcMethodBind
- -- but that's not enough; we want one on the global default method too
- -- Specialisations, on the other hand, belong on the thing inside only, I think
- ; let sel_name = idName sel_id
- inline_prags = filter isInlineLSig (prag_fn sel_name)
- ; prags <- tcPrags meth_id inline_prags
-
- ; let full_bind = AbsBinds tyvars
- [instToId this_dict]
- [(tyvars, local_dm_id, meth_id, prags)]
- (dict_binds `unionBags` defm_bind)
- ; return (noLoc full_bind, [local_dm_id]) }}
-
-mkDefMethRdrName :: Id -> RdrName
-mkDefMethRdrName sel_id = mkDerivedRdrName (idName sel_id) mkDefaultMethodOcc
-\end{code}
+ -> TcM (LHsBinds Id, Id)
+tcDefMeth tyvars binds_in sig_fn prag_fn sel_id
+ = do { let sel_name = idName sel_id
+ ; dm_name <- lookupTopBndrRn (mkDefMethRdrName sel_name)
+ ; uniq <- newUnique
+ ; let dm_ty = idType sel_id -- Same as dict selector!
+ local_dm_name = setNameUnique sel_name uniq
+ local_dm_id = mkLocalId local_dm_name dm_ty
+ top_dm_id = mkDefaultMethodId dm_name dm_ty
+ all_tvs = map tyVarName tyvars ++ (sig_fn sel_name `orElse` [])
+ -- Tyvars in scope are *both* the ones from the
+ -- class decl *and* ones from the method sig
+
+ ; let meth_bind = findMethodBind sel_name local_dm_name binds_in
+ `orElse` pprPanic "tcDefMeth" (ppr sel_id)
+ -- We only call tcDefMeth on selectors for which
+ -- there is a binding in binds_in
+
+ ; tc_meth_bind <- tcMethodBind all_tvs (prag_fn sel_name)
+ local_dm_id meth_bind
+
+ -- See Note [Silly default-method bind]
+ ; let loc = getLoc meth_bind
+ top_bind = L loc $ VarBind top_dm_id $
+ L loc $ HsWrap (WpLet tc_meth_bind) $
+ HsVar local_dm_id
+
+ ; return (unitBag top_bind, top_dm_id) }
+
+mkDefMethRdrName :: Name -> RdrName
+mkDefMethRdrName sel_name = mkDerivedRdrName sel_name mkDefaultMethodOcc
+---------------------------
+-- The renamer just puts the selector ID as the binder in the method binding
+-- but we must use the method name; so we substitute it here. Crude but simple.
+findMethodBind :: Name -> Name -- Selector and method name
+ -> LHsBinds Name -- A group of bindings
+ -> Maybe (LHsBind Name) -- The binding, with meth_name replacing sel_name
+findMethodBind sel_name meth_name binds
+ = foldlBag mplus Nothing (mapBag f binds)
+ where
+ f (L loc1 bind@(FunBind { fun_id = L loc2 op_name }))
+ | op_name == sel_name
+ = Just (L loc1 (bind { fun_id = L loc2 meth_name }))
+ f _other = Nothing
-%************************************************************************
-%* *
-\subsection{Typechecking a method}
-%* *
-%************************************************************************
-
-@tcMethodBind@ is used to type-check both default-method and
-instance-decl method declarations. We must type-check methods one at a
-time, because their signatures may have different contexts and
-tyvar sets.
-
-\begin{code}
-type MethodSpec = (Id, -- Global selector Id
- Id, -- Local Id (class tyvars instantiated)
- LHsBind Name) -- Binding for the method
-
-tcMethodBind
- :: InstOrigin
- -> [TcTyVar] -- Skolemised type variables for the
- -- enclosing class/instance decl.
- -- They'll be signature tyvars, and we
- -- want to check that they don't get bound
- -- Also they are scoped, so we bring them into scope
- -- Always equal the range of the type envt
- -> TcThetaType -- Available theta; it's just used for the error message
- -> Inst -- Current dictionary (this_dict)
- -> [Inst] -- Other stuff available from context, used to simplify
- -- constraints from the method body (exclude this_dict)
- -> TcSigFun -- For scoped tyvars, indexed by sel_name
- -> TcPragFun -- Pragmas (e.g. inline pragmas), indexed by sel_name
- -> LHsBinds Name -- Method binding (pick the right one from in here)
- -> ClassOpItem
- -> TcId -- The method Id
- -> TcM (LHsBinds Id)
-
-tcMethodBind origin inst_tyvars inst_theta
- this_dict extra_insts
- sig_fn prag_fn meth_binds
- (sel_id, dm_info) meth_id
- | Just user_bind <- find_bind sel_name meth_name meth_binds
- = -- If there is a user-supplied method binding, typecheck it
- tc_method_bind inst_tyvars inst_theta (this_dict:extra_insts)
- sig_fn prag_fn
- sel_id meth_id user_bind
-
- | otherwise -- The user didn't supply a method binding, so we have to make
- -- up a default binding, in a way depending on the default-method info
- = case dm_info of
- NoDefMeth -> do { warn <- doptM Opt_WarnMissingMethods
- ; warnTc (isInstDecl origin
- && warn -- Warn only if -fwarn-missing-methods
- && reportIfUnused (getOccName sel_id))
- -- Don't warn about _foo methods
- (omittedMethodWarn sel_id)
- ; return (unitBag $ L loc (VarBind meth_id error_rhs)) }
-
- DefMeth -> do { -- An polymorphic default method
- -- Might not be imported, but will be an OrigName
- dm_name <- lookupImportedName (mkDefMethRdrName sel_id)
- ; dm_id <- tcLookupId dm_name
- -- Note [Default methods in instances]
- ; return (unitBag $ L loc (VarBind meth_id (mk_dm_app dm_id))) }
-
- GenDefMeth -> ASSERT( isInstDecl origin ) -- We never get here from a class decl
- do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id meth_name
- ; tc_method_bind inst_tyvars inst_theta (this_dict:extra_insts)
- sig_fn prag_fn
- sel_id meth_id meth_bind }
-
- where
- meth_name = idName meth_id
- sel_name = idName sel_id
- loc = getSrcSpan meth_id
- (clas, inst_tys) = getDictClassTys this_dict
+---------------------------
+tcMethodBind :: [Name] -> [LSig Name] -> Id
+ -> LHsBind Name -> TcM (LHsBinds Id)
+tcMethodBind tyvars prags meth_id bind
+ = do { let sig_fn _ = Just tyvars
+ prag_fn _ = prags
+
+ -- Typecheck the binding, first extending the envt
+ -- so that when tcInstSig looks up the meth_id to find
+ -- its signature, we'll find it in the environment
+ --
+ -- If scoped type variables is on, they are brought
+ -- into scope by tcPolyBinds (via sig_fn)
+ --
+ -- See Note [Polymorphic methods]
+ ; traceTc (text "tcMethodBind" <+> ppr meth_id <+> ppr tyvars)
+ ; (tc_binds, ids) <- tcExtendIdEnv [meth_id] $
+ tcPolyBinds TopLevel sig_fn prag_fn
+ NonRecursive NonRecursive
+ (unitBag bind)
+
+ ; ASSERT( ids == [meth_id] ) -- Binding for ONE method
+ return (unionManyBags tc_binds) }
+\end{code}
- this_dict_id = instToId this_dict
- error_id = L loc (HsVar nO_METHOD_BINDING_ERROR_ID)
- error_id_app = mkLHsWrap (WpTyApp (idType meth_id)) error_id
- error_rhs = mkHsApp error_id_app $ L loc $
- HsLit (HsStringPrim (mkFastString error_msg))
- error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
+Note [Polymorphic methods]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ class Foo a where
+ op :: forall b. Ord b => a -> b -> b -> b
+ instance Foo c => Foo [c] where
+ op = e
- mk_dm_app dm_id -- dm tys inst_dict
- = mkLHsWrap (WpApp this_dict_id `WpCompose` mkWpTyApps inst_tys)
- (L loc (HsVar dm_id))
+When typechecking the binding 'op = e', we'll have a meth_id for op
+whose type is
+ op :: forall c. Foo c => forall b. Ord b => [c] -> b -> b -> b
+So tcPolyBinds must be capable of dealing with nested polytypes;
+and so it is. See TcBinds.tcMonoBinds (with type-sig case).
----------------------------
-tc_method_bind :: [TyVar] -> TcThetaType -> [Inst] -> (Name -> Maybe [Name])
- -> (Name -> [LSig Name]) -> Id -> Id -> LHsBind Name
- -> TcRn (LHsBindsLR Id Var)
-tc_method_bind inst_tyvars inst_theta avail_insts sig_fn prag_fn
- sel_id meth_id meth_bind
- = recoverM (return emptyLHsBinds) $
- -- If anything fails, recover returning no bindings.
- -- This is particularly useful when checking the default-method binding of
- -- a class decl. If we don't recover, we don't add the default method to
- -- the type enviroment, and we get a tcLookup failure on $dmeth later.
-
- -- Check the bindings; first adding inst_tyvars to the envt
- -- so that we don't quantify over them in nested places
-
- do { let sel_name = idName sel_id
- meth_name = idName meth_id
- meth_sig_fn name = ASSERT( name == meth_name ) sig_fn sel_name
- -- The meth_bind metions the meth_name, but sig_fn is indexed by sel_name
-
- ; ((meth_bind, mono_bind_infos), meth_lie)
- <- tcExtendTyVarEnv inst_tyvars $
- tcExtendIdEnv [meth_id] $ -- In scope for tcInstSig
- addErrCtxt (methodCtxt sel_id) $
- getLIE $
- tcMonoBinds [meth_bind] meth_sig_fn Recursive
-
- -- Now do context reduction. We simplify wrt both the local tyvars
- -- and the ones of the class/instance decl, so that there is
- -- no problem with
- -- class C a where
- -- op :: Eq a => a -> b -> a
- --
- -- We do this for each method independently to localise error messages
+Note [Silly default-method bind]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When we pass the default method binding to the type checker, it must
+look like op2 = e
+not $dmop2 = e
+otherwise the "$dm" stuff comes out in the interface file. So we
+typecheck the former, and wrap it in a let, thus
+ $dmop2 = let op2 = e in op2
+This makes the error messages right.
- ; let [(_, Just sig, local_meth_id)] = mono_bind_infos
- loc = sig_loc sig
- ; addErrCtxtM (sigCtxt sel_id inst_tyvars inst_theta (idType meth_id)) $ do
- { meth_dicts <- newDictBndrs loc (sig_theta sig)
- ; let meth_tvs = sig_tvs sig
- all_tyvars = meth_tvs ++ inst_tyvars
- all_insts = avail_insts ++ meth_dicts
+%************************************************************************
+%* *
+ Extracting generic instance declaration from class declarations
+%* *
+%************************************************************************
- ; lie_binds <- tcSimplifyCheck loc all_tyvars all_insts meth_lie
+@getGenericInstances@ extracts the generic instance declarations from a class
+declaration. For exmaple
- ; checkSigTyVars all_tyvars
+ class C a where
+ op :: a -> a
- ; prags <- tcPrags meth_id (prag_fn sel_name)
- ; let poly_meth_bind = noLoc $ AbsBinds meth_tvs
- (map instToId meth_dicts)
- [(meth_tvs, meth_id, local_meth_id, prags)]
- (lie_binds `unionBags` meth_bind)
+ op{ x+y } (Inl v) = ...
+ op{ x+y } (Inr v) = ...
+ op{ x*y } (v :*: w) = ...
+ op{ 1 } Unit = ...
- ; return (unitBag poly_meth_bind) }}
+gives rise to the instance declarations
+ instance C (x+y) where
+ op (Inl v) = ...
+ op (Inr v) = ...
+
+ instance C (x*y) where
+ op (v :*: w) = ...
----------------------------
-mkMethId :: InstOrigin -> Class
- -> Id -> [TcType] -- Selector, and instance types
- -> TcM (Maybe Inst, Id)
-
--- mkMethId instantiates the selector Id at the specified types
-mkMethId origin clas sel_id inst_tys
- = let
- (tyvars,rho) = tcSplitForAllTys (idType sel_id)
- rho_ty = ASSERT( length tyvars == length inst_tys )
- substTyWith tyvars inst_tys rho
- (preds,tau) = tcSplitPhiTy rho_ty
- first_pred = ASSERT( not (null preds)) head preds
- in
- -- The first predicate should be of form (C a b)
- -- where C is the class in question
- ASSERT( not (null preds) &&
- case getClassPredTys_maybe first_pred of
- { Just (clas1, _tys) -> clas == clas1 ; Nothing -> False }
- )
- if isSingleton preds then do
- -- If it's the only one, make a 'method'
- inst_loc <- getInstLoc origin
- meth_inst <- newMethod inst_loc sel_id inst_tys
- return (Just meth_inst, instToId meth_inst)
- else do
- -- If it's not the only one we need to be careful
- -- For example, given 'op' defined thus:
- -- class Foo a where
- -- op :: (?x :: String) => a -> a
- -- (mkMethId op T) should return an Inst with type
- -- (?x :: String) => T -> T
- -- That is, the class-op's context is still there.
- -- BUT: it can't be a Method any more, because it breaks
- -- INVARIANT 2 of methods. (See the data decl for Inst.)
- uniq <- newUnique
- loc <- getSrcSpanM
- let
- real_tau = mkPhiTy (tail preds) tau
- meth_id = mkUserLocal (getOccName sel_id) uniq real_tau loc
-
- return (Nothing, meth_id)
+ instance C 1 where
+ op Unit = ...
----------------------------
--- The renamer just puts the selector ID as the binder in the method binding
--- but we must use the method name; so we substitute it here. Crude but simple.
-find_bind :: Name -> Name -- Selector and method name
- -> LHsBinds Name -- A group of bindings
- -> Maybe (LHsBind Name) -- The binding, with meth_name replacing sel_name
-find_bind sel_name meth_name binds
- = foldlBag mplus Nothing (mapBag f binds)
- where
- f (L loc1 bind@(FunBind { fun_id = L loc2 op_name })) | op_name == sel_name
- = Just (L loc1 (bind { fun_id = L loc2 meth_name }))
- f _other = Nothing
----------------------------
+\begin{code}
mkGenericDefMethBind :: Class -> [Type] -> Id -> Name -> TcM (LHsBind Name)
mkGenericDefMethBind clas inst_tys sel_id meth_name
= -- A generic default method
_ -> Nothing
_ -> Nothing
-isInstDecl :: InstOrigin -> Bool
-isInstDecl (SigOrigin InstSkol) = True
-isInstDecl (SigOrigin (ClsSkol _)) = False
-isInstDecl o = pprPanic "isInstDecl" (ppr o)
-\end{code}
-
-
-Note [Default methods]
-~~~~~~~~~~~~~~~~~~~~~~~
-The default methods for a class are each passed a dictionary for the
-class, so that they get access to the other methods at the same type.
-So, given the class decl
-
- class Foo a where
- op1 :: a -> Bool
- op2 :: forall b. Ord b => a -> b -> b -> b
-
- op1 x = True
- op2 x y z = if (op1 x) && (y < z) then y else z
-
-we get the default methods:
-
- $dmop1 :: forall a. Foo a => a -> Bool
- $dmop1 = /\a -> \dfoo -> \x -> True
-
- $dmop2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
- $dmop2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
- if (op1 a dfoo x) && (< b dord y z) then y else z
-
-When we come across an instance decl, we may need to use the default methods:
-
- instance Foo Int where {}
-
- $dFooInt :: Foo Int
- $dFooInt = MkFoo ($dmop1 Int $dFooInt)
- ($dmop2 Int $dFooInt)
-
-Notice that, as with method selectors above, we assume that dictionary
-application is curried, so there's no need to mention the Ord dictionary
-in the application of $dmop2.
-
- instance Foo a => Foo [a] where {}
-
- $dFooList :: forall a. Foo a -> Foo [a]
- $dFooList = /\ a -> \ dfoo_a ->
- let rec
- op1 = defm.Foo.op1 [a] dfoo_list
- op2 = defm.Foo.op2 [a] dfoo_list
- dfoo_list = MkFoo ($dmop1 [a] dfoo_list)
- ($dmop2 [a] dfoo_list)
- in
- dfoo_list
-
-Note [Default methods in instances]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider this
-
- class Baz v x where
- foo :: x -> x
- foo y = y
-
- instance Baz Int Int
-
-From the class decl we get
-
- $dmfoo :: forall v x. Baz v x => x -> x
-
-Notice that the type is ambiguous. That's fine, though. The instance decl generates
-
- $dBazIntInt = MkBaz ($dmfoo Int Int $dBazIntInt)
-
-BUT this does mean we must generate the dictionary translation directly, rather
-than generating source-code and type-checking it. That was the bug ing
-Trac #1061. In any case it's less work to generate the translated version!
-
-
-%************************************************************************
-%* *
-\subsection{Extracting generic instance declaration from class declarations}
-%* *
-%************************************************************************
-@getGenericInstances@ extracts the generic instance declarations from a class
-declaration. For exmaple
-
- class C a where
- op :: a -> a
-
- op{ x+y } (Inl v) = ...
- op{ x+y } (Inr v) = ...
- op{ x*y } (v :*: w) = ...
- op{ 1 } Unit = ...
-
-gives rise to the instance declarations
-
- instance C (x+y) where
- op (Inl v) = ...
- op (Inr v) = ...
-
- instance C (x*y) where
- op (v :*: w) = ...
-
- instance C 1 where
- op Unit = ...
-
-
-\begin{code}
+---------------------------
getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
getGenericInstances class_decls
= do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
ctxt = hsep [ptext (sLit "In the"), text thing,
ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
-defltMethCtxt :: Class -> SDoc
-defltMethCtxt clas
- = ptext (sLit "When checking the default methods for class") <+> quotes (ppr clas)
-
-methodCtxt :: Var -> SDoc
-methodCtxt sel_id
- = ptext (sLit "In the definition for method") <+> quotes (ppr sel_id)
-
badMethodErr :: Outputable a => a -> Name -> SDoc
badMethodErr clas op
= hsep [ptext (sLit "Class"), quotes (ppr clas),
= hsep [ptext (sLit "Class"), quotes (ppr clas),
ptext (sLit "does not have an associated type"), quotes (ppr at)]
-omittedMethodWarn :: Id -> SDoc
-omittedMethodWarn sel_id
- = ptext (sLit "No explicit method nor default method for") <+> quotes (ppr sel_id)
-
omittedATWarn :: Name -> SDoc
omittedATWarn at
= ptext (sLit "No explicit AT declaration for") <+> quotes (ppr at)
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