Typechecking class declarations
\begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
module TcClassDcl ( tcClassSigs, tcClassDecl2,
- getGenericInstances,
- MethodSpec, tcMethodBind, mkMethId,
+ findMethodBind, instantiateMethod, tcInstanceMethodBody,
+ mkGenericDefMethBind, getGenericInstances,
tcAddDeclCtxt, badMethodErr, badATErr, omittedATWarn
) where
import HsSyn
import RnHsSyn
import RnExpr
-import RnEnv
import Inst
import InstEnv
+import TcPat( addInlinePrags )
import TcEnv
import TcBinds
-import TcHsType
-import TcSimplify
import TcUnify
+import TcHsType
import TcMType
import TcType
import TcRnMonad
+import BuildTyCl( TcMethInfo )
import Generics
-import PrelInfo
import Class
import TyCon
-import Type
import MkId
import Id
import Name
+import Var
import NameEnv
import NameSet
-import OccName
-import RdrName
import Outputable
import PrelNames
import DynFlags
import ErrUtils
import Util
-import Unique
import ListSetOps
import SrcLoc
import Maybes
-import List
import BasicTypes
import Bag
import FastString
import Control.Monad
+import Data.List
\end{code}
-> LHsBinds Name
-> TcM [TcMethInfo]
-type TcMethInfo = (Name, DefMeth, Type) -- A temporary intermediate, to communicate
- -- between tcClassSigs and buildClass
tcClassSigs clas sigs def_methods
- = do { dm_env <- checkDefaultBinds clas op_names def_methods
- ; mapM (tcClassSig dm_env) op_sigs }
+ = do { dm_env <- mapM (addLocM (checkDefaultBind clas op_names))
+ (bagToList def_methods)
+ ; mapM (tcClassSig (mkNameEnv dm_env)) op_sigs }
where
op_sigs = [sig | sig@(L _ (TypeSig _ _)) <- sigs]
- op_names = [n | sig@(L _ (TypeSig (L _ n) _)) <- op_sigs]
-
+ op_names = [n | (L _ (TypeSig (L _ n) _)) <- op_sigs]
-checkDefaultBinds :: Name -> [Name] -> LHsBinds Name -> TcM (NameEnv Bool)
+checkDefaultBind :: Name -> [Name] -> HsBindLR Name Name -> TcM (Name, DefMethSpec)
-- Check default bindings
-- a) must be for a class op for this class
-- b) must be all generic or all non-generic
- -- and return a mapping from class-op to Bool
- -- where True <=> it's a generic default method
-checkDefaultBinds clas ops binds
- = do dm_infos <- mapM (addLocM (checkDefaultBind clas ops)) (bagToList binds)
- return (mkNameEnv dm_infos)
-
checkDefaultBind clas ops (FunBind {fun_id = L _ op, fun_matches = MatchGroup matches _ })
= do { -- Check that the op is from this class
- checkTc (op `elem` ops) (badMethodErr clas op)
+ checkTc (op `elem` ops) (badMethodErr clas op)
-- Check that all the defns ar generic, or none are
- ; checkTc (all_generic || none_generic) (mixedGenericErr op)
-
- ; return (op, all_generic)
+ ; case (none_generic, all_generic) of
+ (True, _) -> return (op, VanillaDM)
+ (_, True) -> return (op, GenericDM)
+ _ -> failWith (mixedGenericErr op)
}
where
n_generic = count (isJust . maybeGenericMatch) matches
none_generic = n_generic == 0
all_generic = matches `lengthIs` n_generic
+checkDefaultBind _ _ b = pprPanic "checkDefaultBind" (ppr b)
-tcClassSig :: NameEnv Bool -- Info about default methods;
+
+tcClassSig :: NameEnv DefMethSpec -- Info about default methods;
-> LSig Name
-> TcM TcMethInfo
tcClassSig dm_env (L loc (TypeSig (L _ op_name) op_hs_ty))
= setSrcSpan loc $ do
{ op_ty <- tcHsKindedType op_hs_ty -- Class tyvars already in scope
- ; let dm = case lookupNameEnv dm_env op_name of
- Nothing -> NoDefMeth
- Just False -> DefMeth
- Just True -> GenDefMeth
+ ; let dm = lookupNameEnv dm_env op_name `orElse` NoDM
; return (op_name, dm, op_ty) }
+tcClassSig _ s = pprPanic "tcClassSig" (ppr s)
\end{code}
\begin{code}
tcClassDecl2 :: LTyClDecl Name -- The class declaration
- -> TcM (LHsBinds Id, [Id])
+ -> TcM (LHsBinds Id)
tcClassDecl2 (L loc (ClassDecl {tcdLName = class_name, tcdSigs = sigs,
tcdMeths = default_binds}))
- = recoverM (return (emptyLHsBinds, [])) $
- setSrcSpan loc $ do
- clas <- tcLookupLocatedClass class_name
+ = recoverM (return emptyLHsBinds) $
+ setSrcSpan loc $
+ do { clas <- tcLookupLocatedClass class_name
-- We make a separate binding for each default method.
-- At one time I used a single AbsBinds for all of them, thus
-- dm1 = \d -> case ds d of (a,b,c) -> a
-- And since ds is big, it doesn't get inlined, so we don't get good
-- default methods. Better to make separate AbsBinds for each
- 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
-
- dm_sel_ids = [sel_id | (sel_id, DefMeth) <- op_items]
- -- Generate code for polymorphic default methods only
- -- (Generic default methods have turned into instance decls by now.)
- -- This is incompatible with Hugs, which expects a polymorphic
- -- default method for every class op, regardless of whether or not
- -- 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)
-
-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}
+ ; let
+ (tyvars, _, _, op_items) = classBigSig clas
+ rigid_info = ClsSkol clas
+ prag_fn = mkPragFun sigs default_binds
+ sig_fn = mkSigFun sigs
+ clas_tyvars = tcSkolSigTyVars rigid_info tyvars
+ pred = mkClassPred clas (mkTyVarTys clas_tyvars)
+ ; this_dict <- newEvVar pred
+ ; let tc_dm = tcDefMeth clas clas_tyvars
+ this_dict default_binds
+ sig_fn prag_fn
-%************************************************************************
-%* *
-\subsection{Typechecking a method}
-%* *
-%************************************************************************
+ ; dm_binds <- tcExtendTyVarEnv clas_tyvars $
+ mapM tc_dm op_items
-@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.
+ ; return (listToBag (catMaybes dm_binds)) }
-\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
+tcClassDecl2 d = pprPanic "tcClassDecl2" (ppr d)
+
+tcDefMeth :: Class -> [TyVar] -> EvVar -> LHsBinds Name
+ -> SigFun -> PragFun -> ClassOpItem
+ -> TcM (Maybe (LHsBind Id))
+-- Generate code for polymorphic default methods only (hence DefMeth)
+-- (Generic default methods have turned into instance decls by now.)
+-- This is incompatible with Hugs, which expects a polymorphic
+-- default method for every class op, regardless of whether or not
+-- 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.)
+tcDefMeth clas tyvars this_dict binds_in sig_fn prag_fn (sel_id, dm_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 }
-
+ NoDefMeth -> return Nothing
+ GenDefMeth -> return Nothing
+ DefMeth dm_name -> do
+ { let sel_name = idName sel_id
+ ; local_dm_name <- newLocalName sel_name
+ -- Base the local_dm_name on the selector name, because
+ -- type errors from tcInstanceMethodBody come from here
+
+ -- See Note [Silly default-method bind]
+ -- (possibly out of date)
+
+ ; let meth_bind = findMethodBind sel_name binds_in
+ `orElse` pprPanic "tcDefMeth" (ppr sel_id)
+ -- dm_info = DefMeth dm_name only if there is a binding in binds_in
+
+ dm_sig_fn _ = sig_fn sel_name
+ dm_id = mkDefaultMethodId sel_id dm_name
+ local_dm_type = instantiateMethod clas sel_id (mkTyVarTys tyvars)
+ local_dm_id = mkLocalId local_dm_name local_dm_type
+ prags = prag_fn sel_name
+
+ ; dm_id_w_inline <- addInlinePrags dm_id prags
+ ; spec_prags <- tcSpecPrags dm_id prags
+
+ ; warnTc (not (null spec_prags))
+ (ptext (sLit "Ignoring SPECIALISE pragmas on default method")
+ <+> quotes (ppr sel_name))
+
+ ; liftM Just $
+ tcInstanceMethodBody (ClsSkol clas)
+ tyvars
+ [this_dict]
+ Nothing
+ dm_id_w_inline local_dm_id
+ dm_sig_fn IsDefaultMethod meth_bind }
+
+---------------
+tcInstanceMethodBody :: SkolemInfo -> [TcTyVar] -> [EvVar]
+ -> Maybe EvBind
+ -> Id -> Id
+ -> SigFun -> TcSpecPrags -> LHsBind Name
+ -> TcM (LHsBind Id)
+tcInstanceMethodBody skol_info tyvars dfun_ev_vars
+ this_dict meth_id local_meth_id
+ meth_sig_fn specs
+ (L loc bind)
+ = do { -- Typecheck the binding, first extending the envt
+ -- so that when tcInstSig looks up the local_meth_id to find
+ -- its signature, we'll find it in the environment
+ let full_given = case this_dict of
+ Nothing -> dfun_ev_vars
+ Just (EvBind dict _) -> dict : dfun_ev_vars
+ lm_bind = L loc (bind { fun_id = L loc (idName local_meth_id) })
+ -- Substitue the local_meth_name for the binder
+ -- NB: the binding is always a FunBind
+
+ ; (ev_binds, (tc_bind, _))
+ <- checkConstraints skol_info tyvars full_given $
+ tcExtendIdEnv [local_meth_id] $
+ tcPolyBinds TopLevel meth_sig_fn no_prag_fn
+ NonRecursive NonRecursive
+ [lm_bind]
+
+ -- Add the binding for this_dict, if we have one
+ ; ev_binds' <- case this_dict of
+ Nothing -> return ev_binds
+ Just (EvBind self rhs) -> extendTcEvBinds ev_binds self rhs
+
+ ; let full_bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
+ , abs_exports = [(tyvars, meth_id, local_meth_id, specs)]
+ , abs_ev_binds = ev_binds'
+ , abs_binds = tc_bind }
+
+ ; return (L loc full_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))
-
+ no_prag_fn _ = [] -- No pragmas for local_meth_id;
+ -- they are all for meth_id
+\end{code}
----------------------------
-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
-
- ; 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)
+\begin{code}
+instantiateMethod :: Class -> Id -> [TcType] -> TcType
+-- Take a class operation, say
+-- op :: forall ab. C a => forall c. Ix c => (b,c) -> a
+-- Instantiate it at [ty1,ty2]
+-- Return the "local method type":
+-- forall c. Ix x => (ty2,c) -> ty1
+instantiateMethod clas sel_id inst_tys
+ = ASSERT( ok_first_pred ) local_meth_ty
+ where
+ (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id)
+ rho_ty = ASSERT( length sel_tyvars == length inst_tys )
+ substTyWith sel_tyvars inst_tys sel_rho
- ; return (unitBag poly_meth_bind) }}
+ (first_pred, local_meth_ty) = tcSplitPredFunTy_maybe rho_ty
+ `orElse` pprPanic "tcInstanceMethod" (ppr sel_id)
+ ok_first_pred = case getClassPredTys_maybe first_pred of
+ Just (clas1, _tys) -> clas == clas1
+ Nothing -> False
+ -- The first predicate should be of form (C a b)
+ -- where C is the class in question
----------------------------
-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)
---------------------------
--- 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
+findMethodBind :: Name -- Selector name
+ -> LHsBinds Name -- A group of bindings
+ -> Maybe (LHsBind Name) -- The binding
+findMethodBind sel_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)
- do { checkTc (isJust maybe_tycon)
- (badGenericInstance sel_id (notSimple inst_tys))
- ; checkTc (tyConHasGenerics tycon)
- (badGenericInstance sel_id (notGeneric tycon))
-
- ; dflags <- getDOpts
- ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
- (vcat [ppr clas <+> ppr inst_tys,
- nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
-
- -- Rename it before returning it
- ; (rn_rhs, _) <- rnLExpr rhs
- ; return (noLoc $ mkFunBind (noLoc meth_name) [mkSimpleMatch [] rn_rhs]) }
- where
- rhs = mkGenericRhs sel_id clas_tyvar tycon
-
- -- The tycon is only used in the generic case, and in that
- -- 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
- [ty] -> case tcSplitTyConApp_maybe ty of
- Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
- other -> Nothing
- other -> Nothing
-
-isInstDecl (SigOrigin InstSkol) = True
-isInstDecl (SigOrigin (ClsSkol _)) = False
+ f bind@(L _ (FunBind { fun_id = L _ op_name }))
+ | op_name == sel_name
+ = Just bind
+ 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
-
+Note [Polymorphic methods]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
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 {}
+ op :: forall b. Ord b => a -> b -> b -> b
+ instance Foo c => Foo [c] where
+ op = e
- $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
+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
-Note [Default methods in instances]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider this
+So tcPolyBinds must be capable of dealing with nested polytypes;
+and so it is. See TcBinds.tcMonoBinds (with type-sig case).
- 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!
+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 error messages. But we want the
+"$dm" to come 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.
%************************************************************************
%* *
-\subsection{Extracting generic instance declaration from class declarations}
+ Extracting generic instance declaration from class declarations
%* *
%************************************************************************
instance C 1 where
op Unit = ...
-
\begin{code}
-getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo]
+mkGenericDefMethBind :: Class -> [Type] -> Id -> TcM (LHsBind Name)
+mkGenericDefMethBind clas inst_tys sel_id
+ = -- 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)
+ do { checkTc (isJust maybe_tycon)
+ (badGenericInstance sel_id (notSimple inst_tys))
+ ; checkTc (tyConHasGenerics tycon)
+ (badGenericInstance sel_id (notGeneric tycon))
+
+ ; dflags <- getDOpts
+ ; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Filling in method body"
+ (vcat [ppr clas <+> ppr inst_tys,
+ nest 2 (ppr sel_id <+> equals <+> ppr rhs)]))
+
+ -- Rename it before returning it
+ ; (rn_rhs, _) <- rnLExpr rhs
+ ; return (noLoc $ mkFunBind (noLoc (idName sel_id))
+ [mkSimpleMatch [] rn_rhs]) }
+ where
+ rhs = mkGenericRhs sel_id clas_tyvar tycon
+
+ -- The tycon is only used in the generic case, and in that
+ -- 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
+ [ty] -> case tcSplitTyConApp_maybe ty of
+ Just (tycon, arg_tys) | all tcIsTyVarTy arg_tys -> Just tycon
+ _ -> Nothing
+ _ -> Nothing
+
+
+---------------------------
+getGenericInstances :: [LTyClDecl Name] -> TcM [InstInfo Name]
getGenericInstances class_decls
= do { gen_inst_infos <- mapM (addLocM get_generics) class_decls
; let { gen_inst_info = concat gen_inst_infos }
(vcat (map pprInstInfoDetails gen_inst_info)))
; return gen_inst_info }}
+get_generics :: TyClDecl Name -> TcM [InstInfo Name]
get_generics decl@(ClassDecl {tcdLName = class_name, tcdMeths = def_methods})
| null generic_binds
= return [] -- The comon case: no generic default methods
--
-- The class should be unary, which is why simpleInstInfoTyCon should be ok
let
- tc_inst_infos :: [(TyCon, InstInfo)]
+ tc_inst_infos :: [(TyCon, InstInfo Name)]
tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
group `lengthExceeds` 1]
get_uniq (tc,_) = getUnique tc
- mapM (addErrTc . dupGenericInsts) bad_groups
+ mapM_ (addErrTc . dupGenericInsts) bad_groups
-- Check that there is an InstInfo for each generic type constructor
let
where
generic_binds :: [(HsType Name, LHsBind Name)]
generic_binds = getGenericBinds def_methods
+get_generics decl = pprPanic "get_generics" (ppr decl)
---------------------------------
-- them in finite map indexed by the type parameter in the definition.
getGenericBinds binds = concat (map getGenericBind (bagToList binds))
+getGenericBind :: LHsBindLR Name Name -> [(HsType Name, LHsBindLR Name Name)]
getGenericBind (L loc bind@(FunBind { fun_matches = MatchGroup matches ty }))
= groupWith wrap (mapCatMaybes maybeGenericMatch matches)
where
= []
groupWith :: ([a] -> b) -> [(HsType Name, a)] -> [(HsType Name, b)]
-groupWith op [] = []
+groupWith _ [] = []
groupWith op ((t,v):prs) = (t, op (v:vs)) : groupWith op rest
where
- vs = map snd this
- (this,rest) = partition same_t prs
- same_t (t',v) = t `eqPatType` t'
+ vs = map snd this
+ (this,rest) = partition same_t prs
+ same_t (t', _v) = t `eqPatType` t'
eqPatLType :: LHsType Name -> LHsType Name -> Bool
eqPatLType t1 t2 = unLoc t1 `eqPatType` unLoc t2
-- A very simple equality function, only for
-- type patterns in generic function definitions.
eqPatType (HsTyVar v1) (HsTyVar v2) = v1==v2
-eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2
-eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t2 `eqPatLType` t2 && unLoc op1 == unLoc op2
+eqPatType (HsAppTy s1 t1) (HsAppTy s2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2
+eqPatType (HsOpTy s1 op1 t1) (HsOpTy s2 op2 t2) = s1 `eqPatLType` s2 && t1 `eqPatLType` t2 && unLoc op1 == unLoc op2
eqPatType (HsNumTy n1) (HsNumTy n2) = n1 == n2
eqPatType (HsParTy t1) t2 = unLoc t1 `eqPatType` t2
eqPatType t1 (HsParTy t2) = t1 `eqPatType` unLoc t2
---------------------------------
mkGenericInstance :: Class
-> (HsType Name, LHsBinds Name)
- -> TcM InstInfo
+ -> TcM (InstInfo Name)
mkGenericInstance clas (hs_ty, binds) = do
-- Make a generic instance declaration
-- and wrap them as forall'd tyvars, so that kind inference
-- works in the standard way
let
- sig_tvs = map (noLoc.UserTyVar) (nameSetToList (extractHsTyVars (noLoc hs_ty)))
+ sig_tvs = userHsTyVarBndrs $ map noLoc $ nameSetToList $
+ extractHsTyVars (noLoc hs_ty)
hs_forall_ty = noLoc $ mkExplicitHsForAllTy sig_tvs (noLoc []) (noLoc hs_ty)
-- Type-check the instance type, and check its form
dfun_id = mkDictFunId dfun_name tyvars inst_theta clas [inst_ty]
ispec = mkLocalInstance dfun_id overlap_flag
- return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] })
+ return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds [] False })
\end{code}
%************************************************************************
\begin{code}
+tcAddDeclCtxt :: TyClDecl Name -> TcM a -> TcM a
tcAddDeclCtxt decl thing_inside
= addErrCtxt ctxt thing_inside
where
then "newtype" ++ maybeInst
else "data type" ++ maybeInst
| isFamilyDecl decl = "family"
+ | otherwise = panic "tcAddDeclCtxt/thing"
maybeInst | isFamInstDecl decl = " instance"
| otherwise = ""
ctxt = hsep [ptext (sLit "In the"), text thing,
ptext (sLit "declaration for"), quotes (ppr (tcdName decl))]
-defltMethCtxt clas
- = ptext (sLit "When checking the default methods for class") <+> quotes (ppr clas)
-
-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),
ptext (sLit "does not have a method"), quotes (ppr op)]
+badATErr :: Class -> Name -> SDoc
badATErr clas at
= hsep [ptext (sLit "Class"), quotes (ppr clas),
ptext (sLit "does not have an associated type"), quotes (ppr at)]
-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)
+badGenericInstance :: Var -> SDoc -> SDoc
badGenericInstance sel_id because
= sep [ptext (sLit "Can't derive generic code for") <+> quotes (ppr sel_id),
because]
+notSimple :: [Type] -> SDoc
notSimple inst_tys
= vcat [ptext (sLit "because the instance type(s)"),
nest 2 (ppr inst_tys),
ptext (sLit "is not a simple type of form (T a1 ... an)")]
+notGeneric :: TyCon -> SDoc
notGeneric tycon
= vcat [ptext (sLit "because the instance type constructor") <+> quotes (ppr tycon) <+>
- ptext (sLit "was not compiled with -fgenerics")]
+ ptext (sLit "was not compiled with -XGenerics")]
+badGenericInstanceType :: LHsBinds Name -> SDoc
badGenericInstanceType binds
= vcat [ptext (sLit "Illegal type pattern in the generic bindings"),
- nest 4 (ppr binds)]
+ nest 2 (ppr binds)]
+missingGenericInstances :: [Name] -> SDoc
missingGenericInstances missing
= ptext (sLit "Missing type patterns for") <+> pprQuotedList missing
+dupGenericInsts :: [(TyCon, InstInfo a)] -> SDoc
dupGenericInsts tc_inst_infos
= vcat [ptext (sLit "More than one type pattern for a single generic type constructor:"),
- nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
+ nest 2 (vcat (map ppr_inst_ty tc_inst_infos)),
ptext (sLit "All the type patterns for a generic type constructor must be identical")
]
where
ppr_inst_ty (_,inst) = ppr (simpleInstInfoTy inst)
+mixedGenericErr :: Name -> SDoc
mixedGenericErr op
= ptext (sLit "Can't mix generic and non-generic equations for class method") <+> quotes (ppr op)
\end{code}
projects / ghc-hetmet.git / blobdiff