module TcClassDcl ( tcClassSigs, tcClassDecl2,
getGenericInstances,
- MethodSpec, tcMethodBind, mkMethodBind,
+ MethodSpec, tcMethodBind, mkMethId,
tcAddDeclCtxt, badMethodErr, badATErr, omittedATWarn
) where
%************************************************************************
%* *
-\subsection[Default methods]{Default methods}
+ Class Declarations
%* *
%************************************************************************
-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
-\begin{verbatim}
-class Foo a where
- op1 :: a -> Bool
- op2 :: Ord b => a -> b -> b -> b
-
- op1 x = True
- op2 x y z = if (op1 x) && (y < z) then y else z
-\end{verbatim}
-we get the default methods:
-\begin{verbatim}
-defm.Foo.op1 :: forall a. Foo a => a -> Bool
-defm.Foo.op1 = /\a -> \dfoo -> \x -> True
-
-defm.Foo.op2 :: forall a. Foo a => forall b. Ord b => a -> b -> b -> b
-defm.Foo.op2 = /\ a -> \ dfoo -> /\ b -> \ dord -> \x y z ->
- if (op1 a dfoo x) && (< b dord y z) then y else z
-\end{verbatim}
-
-When we come across an instance decl, we may need to use the default
-methods:
-\begin{verbatim}
-instance Foo Int where {}
-\end{verbatim}
-gives
-\begin{verbatim}
-const.Foo.Int.op1 :: Int -> Bool
-const.Foo.Int.op1 = defm.Foo.op1 Int dfun.Foo.Int
-
-const.Foo.Int.op2 :: forall b. Ord b => Int -> b -> b -> b
-const.Foo.Int.op2 = defm.Foo.op2 Int dfun.Foo.Int
-
-dfun.Foo.Int :: Foo Int
-dfun.Foo.Int = (const.Foo.Int.op1, const.Foo.Int.op2)
-\end{verbatim}
-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 const.Foo.Int.op2 (or the type variable).
-
-\begin{verbatim}
-instance Foo a => Foo [a] where {}
-
-dfun.Foo.List :: forall a. Foo a -> Foo [a]
-dfun.Foo.List
- = /\ a -> \ dfoo_a ->
- let rec
- op1 = defm.Foo.op1 [a] dfoo_list
- op2 = defm.Foo.op2 [a] dfoo_list
- dfoo_list = (op1, op2)
- in
- dfoo_list
-\end{verbatim}
-
-@tcClassDecls2@ generates bindings for polymorphic default methods
-(generic default methods have by now turned into instance declarations)
-
\begin{code}
tcClassDecl2 :: LTyClDecl Name -- The class declaration
-> TcM (LHsBinds Id, [Id])
cls_pred = mkClassPred clas inst_tys
local_dm_id = mkDefaultMethodId dm_name dm_ty
- ; (_, meth_info) <- mkMethodBind origin clas inst_tys binds_in (sel_id, DefMeth)
; loc <- getInstLoc origin
; this_dict <- newDictBndr loc cls_pred
- ; (defm_bind, insts_needed) <- getLIE (tcMethodBind tyvars [cls_pred] [this_dict]
- sig_fn prag_fn meth_info)
+ ; (_, 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
-- 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 (_,dm_inst_id,_) = meth_info
- sel_name = idName sel_id
+ ; let sel_name = idName sel_id
inline_prags = filter isInlineLSig (prag_fn sel_name)
- ; prags <- tcPrags dm_inst_id inline_prags
+ ; prags <- tcPrags meth_id inline_prags
; let full_bind = AbsBinds tyvars
[instToId this_dict]
- [(tyvars, local_dm_id, dm_inst_id, prags)]
+ [(tyvars, local_dm_id, meth_id, prags)]
(dict_binds `unionBags` defm_bind)
; return (noLoc full_bind, [local_dm_id]) }}
LHsBind Name) -- Binding for the method
tcMethodBind
- :: [TcTyVar] -- Skolemised type variables for the
+ :: 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] -- Available from context, used to simplify constraints
- -- from the method body
+ -> 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
- -> MethodSpec -- Details of this method
+ -> LHsBinds Name -- Method binding (pick the right one from in here)
+ -> ClassOpItem
+ -> TcId -- The method Id
-> TcM (LHsBinds Id)
-tcMethodBind inst_tyvars inst_theta avail_insts sig_fn prag_fn
- (sel_id, meth_id, meth_bind)
- = recoverM (return emptyLHsBinds) $ do
+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
+
+ 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 ])
+
+ mk_dm_app dm_id -- dm tys inst_dict
+ = mkLHsWrap (WpApp this_dict_id `WpCompose` mkWpTyApps inst_tys)
+ (L loc (HsVar dm_id))
+
+
+---------------------------
+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
-- Check the bindings; first adding inst_tyvars to the envt
-- so that we don't quantify over them in nested places
-
- let sel_name = idName sel_id
- meth_sig_fn meth_name = ASSERT( meth_name == idName meth_id ) 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
-
- 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
-
- lie_binds <- tcSimplifyCheck loc all_tyvars all_insts meth_lie
-
- checkSigTyVars all_tyvars
-
- prags <- tcPrags meth_id (prag_fn sel_name)
- let
- poly_meth_bind = noLoc $ AbsBinds meth_tvs
+ 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
+
+ ; 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
+
+ ; lie_binds <- tcSimplifyCheck loc all_tyvars all_insts meth_lie
+
+ ; checkSigTyVars all_tyvars
+
+ ; 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)
- return (unitBag poly_meth_bind)
-
+ ; return (unitBag poly_meth_bind) }}
-mkMethodBind :: InstOrigin
- -> Class -> [TcType] -- Class and instance types
- -> LHsBinds Name -- Method binding (pick the right one from in here)
- -> ClassOpItem
- -> TcM (Maybe Inst, -- Method inst
- MethodSpec)
--- Find the binding for the specified method, or make
--- up a suitable default method if it isn't there
-
-mkMethodBind origin clas inst_tys meth_binds (sel_id, dm_info) = do
- (mb_inst, meth_id) <- mkMethId origin clas sel_id inst_tys
- let
- meth_name = idName meth_id
-
- -- Figure out what method binding to use
- -- If the user suppplied one, use it, else construct a default one
- loc <- getSrcSpanM
- meth_bind
- <- case find_bind (idName sel_id) meth_name meth_binds of
- Just user_bind -> return user_bind
- Nothing -> do
- rhs <- mkDefMethRhs origin clas inst_tys sel_id loc dm_info
- -- Not infix decl
- return (noLoc $ mkFunBind (noLoc meth_name) [mkSimpleMatch [] rhs])
-
- return (mb_inst, (sel_id, meth_id, meth_bind))
+---------------------------
mkMethId :: InstOrigin -> Class
-> Id -> [TcType] -- Selector, and instance types
-> TcM (Maybe Inst, Id)
return (Nothing, meth_id)
- -- The user didn't supply a method binding,
- -- so we have to make up a default binding
- -- The RHS of a default method depends on the default-method info
-mkDefMethRhs origin clas inst_tys sel_id loc DefMeth = do
- -- An polymorphic default method
- dm_name <- lookupImportedName (mkDefMethRdrName sel_id)
- -- Might not be imported, but will be an OrigName
- traceRn (text "mkDefMeth" <+> ppr dm_name)
- return (nlHsVar dm_name)
-
-mkDefMethRhs origin clas inst_tys sel_id loc NoDefMeth = do
- -- No default method
- -- Warn only if -fwarn-missing-methods
- warn <- doptM Opt_WarnMissingMethods
- warnTc (isInstDecl origin
- && warn
- && reportIfUnused (getOccName sel_id))
- (omittedMethodWarn sel_id)
- return error_rhs
- where
- error_rhs = noLoc $ HsLam (mkMatchGroup [mkSimpleMatch wild_pats simple_rhs])
- simple_rhs = nlHsApp (nlHsVar (getName nO_METHOD_BINDING_ERROR_ID))
- (nlHsLit (HsStringPrim (mkFastString error_msg)))
- error_msg = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
-
- -- When the type is of form t1 -> t2 -> t3
- -- make a default method like (\ _ _ -> noMethBind "blah")
- -- rather than simply (noMethBind "blah")
- -- Reason: if t1 or t2 are higher-ranked types we get n
- -- silly ambiguity messages.
- -- Example: f :: (forall a. Eq a => a -> a) -> Int
- -- f = error "urk"
- -- Here, tcSub tries to force (error "urk") to have the right type,
- -- thus: f = \(x::forall a. Eq a => a->a) -> error "urk" (x t)
- -- where 't' is fresh ty var. This leads directly to "ambiguous t".
- --
- -- NB: technically this changes the meaning of the default-default
- -- method slightly, because `seq` can see the lambdas. Oh well.
- (_,_,tau1) = tcSplitSigmaTy (idType sel_id)
- (_,_,tau2) = tcSplitSigmaTy tau1
- -- Need two splits because the selector can have a type like
- -- forall a. Foo a => forall b. Eq b => ...
- (arg_tys, _) = tcSplitFunTys tau2
- wild_pats = [nlWildPat | ty <- arg_tys]
-
-mkDefMethRhs origin clas inst_tys sel_id loc GenDefMeth
+---------------------------
+-- 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
+
+---------------------------
+mkGenericDefMethBind clas inst_tys sel_id meth_name
= -- A generic default method
-- If the method is defined generically, we can only do the job if the
-- instance declaration is for a single-parameter type class with
-- a type constructor applied to type arguments in the instance decl
-- (checkTc, so False provokes the error)
- ASSERT( isInstDecl origin ) -- We never get here from a class decl
do { checkTc (isJust maybe_tycon)
(badGenericInstance sel_id (notSimple inst_tys))
; checkTc (tyConHasGenerics tycon)
-- Rename it before returning it
; (rn_rhs, _) <- rnLExpr rhs
- ; return rn_rhs }
+ ; return (noLoc $ mkFunBind (noLoc meth_name) [mkSimpleMatch [] rn_rhs]) }
where
rhs = mkGenericRhs sel_id clas_tyvar tycon
-- case we require that the instance decl is for a single-parameter
-- type class with type variable arguments:
-- instance (...) => C (T a b)
- clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
- Just tycon = maybe_tycon
- maybe_tycon = case inst_tys of
+ clas_tyvar = ASSERT (not (null (classTyVars clas))) head (classTyVars clas)
+ Just tycon = maybe_tycon
+ maybe_tycon = case inst_tys of
[ty] -> case tcSplitTyConApp_maybe ty of
Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
other -> Nothing
\end{code}
-\begin{code}
--- 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 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
-\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!
%************************************************************************
projects / ghc-hetmet.git / commitdiff