import Class
import Type
+import Coercion
import ErrUtils
import MkId
import DataCon
import Outputable
import FastString
import Bag
+
+import Control.Monad
\end{code}
%************************************************************************
, ds_cls :: Class
, ds_tys :: [Type]
, ds_tc :: TyCon
+ , ds_tc_args :: [Type]
, ds_newtype :: Bool }
-- This spec implies a dfun declaration of the form
-- df :: forall tvs. theta => C tys
-- The tyvars bind all the variables in the theta
-- For family indexes, the tycon in
-- in ds_tys is the *family* tycon
- -- in ds_tc is the *representation* tycon
+ -- in ds_tc, ds_tc_args is the *representation* tycon
-- For non-family tycons, both are the same
-- ds_newtype = True <=> Newtype deriving
when the dict is constructed in TcInstDcls.tcInstDecl2
-
+Note [Unused constructors and deriving clauses]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+See Trac #3221. Consider
+ data T = T1 | T2 deriving( Show )
+Are T1 and T2 unused? Well, no: the deriving clause expands to mention
+both of them. So we gather defs/uses from deriving just like anything else.
%************************************************************************
%* *
-> [LInstDecl Name] -- All instance declarations
-> [LDerivDecl Name] -- All stand-alone deriving declarations
-> TcM ([InstInfo Name], -- The generated "instance decls"
- HsValBinds Name) -- Extra generated top-level bindings
+ HsValBinds Name, -- Extra generated top-level bindings
+ DefUses)
tcDeriving tycl_decls inst_decls deriv_decls
- = recoverM (return ([], emptyValBindsOut)) $
+ = recoverM (return ([], emptyValBindsOut, emptyDUs)) $
do { -- Fish the "deriving"-related information out of the TcEnv
-- And make the necessary "equations".
is_boot <- tcIsHsBoot
; overlap_flag <- getOverlapFlag
; let (infer_specs, given_specs) = splitEithers early_specs
- ; insts1 <- mapM (genInst overlap_flag) given_specs
+ ; insts1 <- mapM (genInst True overlap_flag) given_specs
; final_specs <- extendLocalInstEnv (map (iSpec . fst) insts1) $
inferInstanceContexts overlap_flag infer_specs
- ; insts2 <- mapM (genInst overlap_flag) final_specs
+ ; insts2 <- mapM (genInst False overlap_flag) final_specs
-- Generate the generic to/from functions from each type declaration
; gen_binds <- mkGenericBinds is_boot
- ; (inst_info, rn_binds) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
+ ; (inst_info, rn_binds, rn_dus) <- renameDeriv is_boot gen_binds (insts1 ++ insts2)
; dflags <- getDOpts
; liftIO (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
(ddump_deriving inst_info rn_binds))
- ; return (inst_info, rn_binds) }
+ ; return (inst_info, rn_binds, rn_dus) }
where
ddump_deriving :: [InstInfo Name] -> HsValBinds Name -> SDoc
ddump_deriving inst_infos extra_binds
renameDeriv :: Bool -> LHsBinds RdrName
-> [(InstInfo RdrName, DerivAuxBinds)]
- -> TcM ([InstInfo Name], HsValBinds Name)
+ -> TcM ([InstInfo Name], HsValBinds Name, DefUses)
renameDeriv is_boot gen_binds insts
| is_boot -- If we are compiling a hs-boot file, don't generate any derived bindings
-- The inst-info bindings will all be empty, but it's easier to
-- just use rn_inst_info to change the type appropriately
- = do { rn_inst_infos <- mapM rn_inst_info inst_infos
- ; return (rn_inst_infos, emptyValBindsOut) }
+ = do { (rn_inst_infos, fvs) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, emptyValBindsOut, usesOnly (plusFVs fvs)) }
| otherwise
= discardWarnings $ -- Discard warnings about unused bindings etc
; let aux_binds = listToBag $ map (genAuxBind loc) $
rm_dups [] $ concat deriv_aux_binds
; rn_aux_lhs <- rnTopBindsLHS emptyFsEnv (ValBindsIn aux_binds [])
- ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs)
+ ; let aux_names = map unLoc (collectHsValBinders rn_aux_lhs)
; bindLocalNames aux_names $
- do { (rn_aux, _dus) <- rnTopBindsRHS aux_names rn_aux_lhs
- ; rn_inst_infos <- mapM rn_inst_info inst_infos
- ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen) } }
+ do { (rn_aux, dus_aux) <- rnTopBindsRHS (mkNameSet aux_names) rn_aux_lhs
+ ; (rn_inst_infos, fvs_insts) <- mapAndUnzipM rn_inst_info inst_infos
+ ; return (rn_inst_infos, rn_aux `plusHsValBinds` rn_gen,
+ dus_gen `plusDU` dus_aux `plusDU` usesOnly (plusFVs fvs_insts)) } }
where
(inst_infos, deriv_aux_binds) = unzip insts
| otherwise = rm_dups (b:acc) bs
- rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
- = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived })
+ rn_inst_info (InstInfo { iSpec = inst, iBinds = NewTypeDerived co })
+ = return (InstInfo { iSpec = inst, iBinds = NewTypeDerived co }, emptyFVs)
- rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs })
+ rn_inst_info (InstInfo { iSpec = inst, iBinds = VanillaInst binds sigs standalone_deriv })
= -- Bring the right type variables into
-- scope (yuk), and rename the method binds
ASSERT( null sigs )
bindLocalNames (map Var.varName tyvars) $
- do { (rn_binds, _fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds
- ; return (InstInfo { iSpec = inst, iBinds = VanillaInst rn_binds [] }) }
+ do { (rn_binds, fvs) <- rnMethodBinds clas_nm (\_ -> []) [] binds
+ ; let binds' = VanillaInst rn_binds [] standalone_deriv
+ ; return (InstInfo { iSpec = inst, iBinds = binds' }, fvs) }
where
(tyvars,_,clas,_) = instanceHead inst
clas_nm = className clas
(arg_kinds, _) = splitKindFunTys kind
n_args_to_drop = length arg_kinds
n_args_to_keep = tyConArity tc - n_args_to_drop
- inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
- inst_ty_kind = typeKind inst_ty
-
+ args_to_drop = drop n_args_to_keep tc_args
+ inst_ty = mkTyConApp tc (take n_args_to_keep tc_args)
+ inst_ty_kind = typeKind inst_ty
+ dropped_tvs = mkVarSet (mapCatMaybes getTyVar_maybe args_to_drop)
+ univ_tvs = (mkVarSet tvs `extendVarSetList` deriv_tvs)
+ `minusVarSet` dropped_tvs
+
-- Check that the result really is well-kinded
; checkTc (n_args_to_keep >= 0 && (inst_ty_kind `eqKind` kind))
(derivingKindErr tc cls cls_tys kind)
+ ; checkTc (sizeVarSet dropped_tvs == n_args_to_drop && -- (a)
+ tyVarsOfTypes (inst_ty:cls_tys) `subVarSet` univ_tvs) -- (b)
+ (derivingEtaErr cls cls_tys inst_ty)
+ -- Check that
+ -- (a) The data type can be eta-reduced; eg reject:
+ -- data instance T a a = ... deriving( Monad )
+ -- (b) The type class args do not mention any of the dropped type
+ -- variables
+ -- newtype T a s = ... deriving( ST s )
+
-- Type families can't be partially applied
- -- e.g. newtype instance T Int a = ... deriving( Monad )
+ -- e.g. newtype instance T Int a = MkT [a] deriving( Monad )
+ -- Note [Deriving, type families, and partial applications]
; checkTc (not (isOpenTyCon tc) || n_args_to_drop == 0)
(typeFamilyPapErr tc cls cls_tys inst_ty)
- ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys inst_ty Nothing } }
+ ; mkEqnHelp DerivOrigin (varSetElems univ_tvs) cls cls_tys inst_ty Nothing } }
where
-- Tiresomely we must figure out the "lhs", which is awkward for type families
-- E.g. data T a b = .. deriving( Eq )
deriveTyData _other
= panic "derivTyData" -- Caller ensures that only TyData can happen
+\end{code}
-------------------------------------------------------------------
+Note [Deriving, type families, and partial applications]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+When there are no type families, it's quite easy:
+
+ newtype S a = MkS [a]
+ -- :CoS :: S ~ [] -- Eta-reduced
+
+ instance Eq [a] => Eq (S a) -- by coercion sym (Eq (coMkS a)) : Eq [a] ~ Eq (S a)
+ instance Monad [] => Monad S -- by coercion sym (Monad coMkS) : Monad [] ~ Monad S
+
+When type familes are involved it's trickier:
+
+ data family T a b
+ newtype instance T Int a = MkT [a] deriving( Eq, Monad )
+ -- :RT is the representation type for (T Int a)
+ -- :CoF:R1T a :: T Int a ~ :RT a -- Not eta reduced
+ -- :Co:R1T :: :RT ~ [] -- Eta-reduced
+
+ instance Eq [a] => Eq (T Int a) -- easy by coercion
+ instance Monad [] => Monad (T Int) -- only if we can eta reduce???
+
+The "???" bit is that we don't build the :CoF thing in eta-reduced form
+Henc the current typeFamilyPapErr, even though the instance makes sense.
+After all, we can write it out
+ instance Monad [] => Monad (T Int) -- only if we can eta reduce???
+ return x = MkT [x]
+ ... etc ...
+
+\begin{code}
mkEqnHelp :: InstOrigin -> [TyVar] -> Class -> [Type] -> Type
-> Maybe ThetaType -- Just => context supplied (standalone deriving)
-- Nothing => context inferred (deriving on data decl)
className cls `elem` typeableClassNames)
(derivingHiddenErr tycon)
- ; mayDeriveDataTypeable <- doptM Opt_DeriveDataTypeable
- ; newtype_deriving <- doptM Opt_GeneralizedNewtypeDeriving
-
+ ; dflags <- getDOpts
; if isDataTyCon rep_tc then
- mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
+ mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
else
- mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving
- tvs cls cls_tys
+ mkNewTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta }
| otherwise
= failWithTc (derivingThingErr cls cls_tys tc_app
%************************************************************************
\begin{code}
-mkDataTypeEqn :: InstOrigin -> Bool -> [Var] -> Class -> [Type]
- -> TyCon -> [Type] -> TyCon -> [Type] -> Maybe ThetaType
- -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
-
-mkDataTypeEqn orig mayDeriveDataTypeable tvs cls cls_tys
+mkDataTypeEqn :: InstOrigin
+ -> DynFlags
+ -> [Var] -- Universally quantified type variables in the instance
+ -> Class -- Class for which we need to derive an instance
+ -> [Type] -- Other parameters to the class except the last
+ -> TyCon -- Type constructor for which the instance is requested (last parameter to the type class)
+ -> [Type] -- Parameters to the type constructor
+ -> TyCon -- rep of the above (for type families)
+ -> [Type] -- rep of the above
+ -> Maybe ThetaType -- Context of the instance, for standalone deriving
+ -> TcRn EarlyDerivSpec -- Return 'Nothing' if error
+
+mkDataTypeEqn orig dflags tvs cls cls_tys
tycon tc_args rep_tc rep_tc_args mtheta
- = case checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc of
- -- NB: pass the *representation* tycon to checkSideConditions
- CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
- NonDerivableClass -> bale_out (nonStdErr cls)
- DerivableClassError msg -> bale_out msg
+ | isJust mtheta = go_for_it -- Do not test side conditions for standalone deriving
+ | otherwise = case checkSideConditions dflags cls cls_tys rep_tc of
+ -- NB: pass the *representation* tycon to checkSideConditions
+ CanDerive -> go_for_it
+ NonDerivableClass -> bale_out (nonStdErr cls)
+ DerivableClassError msg -> bale_out msg
where
+ go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
bale_out msg = failWithTc (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) msg)
mk_data_eqn, mk_typeable_eqn
| otherwise
= do { dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
- ; let ordinary_constraints
- = [ mkClassPred cls [arg_ty]
- | data_con <- tyConDataCons rep_tc,
- arg_ty <- ASSERT( isVanillaDataCon data_con )
- dataConInstOrigArgTys data_con rep_tc_args,
- not (isUnLiftedType arg_ty) ]
- -- No constraints for unlifted types
- -- Where they are legal we generate specilised function calls
-
- -- See Note [Superclasses of derived instance]
- sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
- (classSCTheta cls)
- inst_tys = [mkTyConApp tycon tc_args]
-
- stupid_subst = zipTopTvSubst (tyConTyVars rep_tc) rep_tc_args
- stupid_constraints = substTheta stupid_subst (tyConStupidTheta rep_tc)
- all_constraints = stupid_constraints ++ sc_constraints ++ ordinary_constraints
-
+ ; let inst_tys = [mkTyConApp tycon tc_args]
+ inferred_constraints = inferConstraints tvs cls inst_tys rep_tc rep_tc_args
spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = tvs
- , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tc
- , ds_theta = mtheta `orElse` all_constraints
+ , ds_cls = cls, ds_tys = inst_tys
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
+ , ds_theta = mtheta `orElse` inferred_constraints
, ds_newtype = False }
; return (if isJust mtheta then Right spec -- Specified context
else Left spec) } -- Infer context
-mk_typeable_eqn orig tvs cls tycon tc_args rep_tc _rep_tc_args mtheta
+mk_typeable_eqn orig tvs cls tycon tc_args rep_tc rep_tc_args mtheta
-- The Typeable class is special in several ways
-- data T a b = ... deriving( Typeable )
-- gives
; loc <- getSrcSpanM
; return (Right $
DS { ds_loc = loc, ds_orig = orig, ds_name = dfun_name, ds_tvs = []
- , ds_cls = cls, ds_tys = [mkTyConApp tycon []], ds_tc = rep_tc
+ , ds_cls = cls, ds_tys = [mkTyConApp tycon []]
+ , ds_tc = rep_tc, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` [], ds_newtype = False }) }
+
+inferConstraints :: [TyVar] -> Class -> [TcType] -> TyCon -> [TcType] -> ThetaType
+-- Generate a sufficiently large set of constraints that typechecking the
+-- generated method definitions should succeed. This set will be simplified
+-- before being used in the instance declaration
+inferConstraints tvs cls inst_tys rep_tc rep_tc_args
+ = ASSERT2( equalLength rep_tc_tvs all_rep_tc_args, ppr cls <+> ppr rep_tc )
+ stupid_constraints ++ extra_constraints
+ ++ sc_constraints ++ con_arg_constraints
+ where
+ -- Constraints arising from the arguments of each constructor
+ con_arg_constraints
+ = [ mkClassPred cls [arg_ty]
+ | data_con <- tyConDataCons rep_tc,
+ arg_ty <- ASSERT( isVanillaDataCon data_con )
+ get_constrained_tys $
+ dataConInstOrigArgTys data_con all_rep_tc_args,
+ not (isUnLiftedType arg_ty) ]
+ -- No constraints for unlifted types
+ -- Where they are legal we generate specilised function calls
+
+ -- For functor-like classes, two things are different
+ -- (a) We recurse over argument types to generate constraints
+ -- See Functor examples in TcGenDeriv
+ -- (b) The rep_tc_args will be one short
+ is_functor_like = getUnique cls `elem` functorLikeClassKeys
+
+ get_constrained_tys :: [Type] -> [Type]
+ get_constrained_tys tys
+ | is_functor_like = concatMap (deepSubtypesContaining last_tv) tys
+ | otherwise = tys
+
+ rep_tc_tvs = tyConTyVars rep_tc
+ last_tv = last rep_tc_tvs
+ all_rep_tc_args | is_functor_like = rep_tc_args ++ [mkTyVarTy last_tv]
+ | otherwise = rep_tc_args
+
+ -- Constraints arising from superclasses
+ -- See Note [Superclasses of derived instance]
+ sc_constraints = substTheta (zipOpenTvSubst (classTyVars cls) inst_tys)
+ (classSCTheta cls)
+
+ -- Stupid constraints
+ stupid_constraints = substTheta subst (tyConStupidTheta rep_tc)
+ subst = zipTopTvSubst rep_tc_tvs all_rep_tc_args
+
+ -- Extra constraints
+ -- The Data class (only) requires that for
+ -- instance (...) => Data (T a b)
+ -- then (Data a, Data b) are among the (...) constraints
+ -- Reason: that's what you need to typecheck the method
+ -- dataCast1 f = gcast1 f
+ extra_constraints
+ | cls `hasKey` dataClassKey = [mkClassPred cls [mkTyVarTy tv] | tv <- tvs]
+ | otherwise = []
+
------------------------------------------------------------------
-- Check side conditions that dis-allow derivability for particular classes
-- This is *apart* from the newtype-deriving mechanism
-- family tycon (with indexes) in error messages.
data DerivStatus = CanDerive
- | NonDerivableClass
- | DerivableClassError SDoc
-
-checkSideConditions :: Bool -> Class -> [TcType] -> TyCon -> DerivStatus
-checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tc
- | notNull cls_tys
- = DerivableClassError ty_args_why -- e.g. deriving( Foo s )
- | otherwise
- = case sideConditions cls of
- Nothing -> NonDerivableClass
- Just cond -> case (cond (mayDeriveDataTypeable, rep_tc)) of
- Nothing -> CanDerive
- Just err -> DerivableClassError err
+ | DerivableClassError SDoc -- Standard class, but can't do it
+ | NonDerivableClass -- Non-standard class
+
+checkSideConditions :: DynFlags -> Class -> [TcType] -> TyCon -> DerivStatus
+checkSideConditions dflags cls cls_tys rep_tc
+ | Just cond <- sideConditions cls
+ = case (cond (dflags, rep_tc)) of
+ Just err -> DerivableClassError err -- Class-specific error
+ Nothing | null cls_tys -> CanDerive
+ | otherwise -> DerivableClassError ty_args_why -- e.g. deriving( Eq s )
+ | otherwise = NonDerivableClass -- Not a standard class
where
ty_args_why = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "is not a class")
sideConditions :: Class -> Maybe Condition
sideConditions cls
- | cls_key == eqClassKey = Just cond_std
- | cls_key == ordClassKey = Just cond_std
- | cls_key == showClassKey = Just cond_std
- | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs)
- | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
- | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
- | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
- | cls_key == dataClassKey = Just (cond_mayDeriveDataTypeable `andCond` cond_std `andCond` cond_noUnliftedArgs)
- | getName cls `elem` typeableClassNames = Just (cond_mayDeriveDataTypeable `andCond` cond_typeableOK)
+ | cls_key == eqClassKey = Just cond_std
+ | cls_key == ordClassKey = Just cond_std
+ | cls_key == showClassKey = Just cond_std
+ | cls_key == readClassKey = Just (cond_std `andCond` cond_noUnliftedArgs)
+ | cls_key == enumClassKey = Just (cond_std `andCond` cond_isEnumeration)
+ | cls_key == ixClassKey = Just (cond_std `andCond` cond_enumOrProduct)
+ | cls_key == boundedClassKey = Just (cond_std `andCond` cond_enumOrProduct)
+ | cls_key == dataClassKey = Just (checkFlag Opt_DeriveDataTypeable `andCond`
+ cond_std `andCond` cond_noUnliftedArgs)
+ | cls_key == functorClassKey = Just (checkFlag Opt_DeriveFunctor `andCond`
+ cond_functorOK True) -- NB: no cond_std!
+ | cls_key == foldableClassKey = Just (checkFlag Opt_DeriveFoldable `andCond`
+ cond_functorOK False) -- Functor/Fold/Trav works ok for rank-n types
+ | cls_key == traversableClassKey = Just (checkFlag Opt_DeriveTraversable `andCond`
+ cond_functorOK False)
+ | getName cls `elem` typeableClassNames = Just (checkFlag Opt_DeriveDataTypeable `andCond` cond_typeableOK)
| otherwise = Nothing
where
cls_key = getUnique cls
-type Condition = (Bool, TyCon) -> Maybe SDoc
- -- Bool is whether or not we are allowed to derive Data and Typeable
+type Condition = (DynFlags, TyCon) -> Maybe SDoc
+ -- first Bool is whether or not we are allowed to derive Data and Typeable
+ -- second Bool is whether or not we are allowed to derive Functor
-- TyCon is the *representation* tycon if the
-- data type is an indexed one
-- Nothing => OK
cond_std :: Condition
cond_std (_, rep_tc)
- | any (not . isVanillaDataCon) data_cons = Just existential_why
- | null data_cons = Just no_cons_why
- | otherwise = Nothing
+ | null data_cons = Just no_cons_why
+ | not (null con_whys) = Just (vcat con_whys)
+ | otherwise = Nothing
where
data_cons = tyConDataCons rep_tc
no_cons_why = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "has no data constructors")
- existential_why = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "has non-Haskell-98 constructor(s)")
+
+ con_whys = mapCatMaybes check_con data_cons
+
+ check_con :: DataCon -> Maybe SDoc
+ check_con con
+ | isVanillaDataCon con
+ , all isTauTy (dataConOrigArgTys con) = Nothing
+ | otherwise = Just (badCon con (ptext (sLit "does not have a Haskell-98 type")))
cond_enumOrProduct :: Condition
cond_enumOrProduct = cond_isEnumeration `orCond`
where
bad_cons = [ con | con <- tyConDataCons tc
, any isUnLiftedType (dataConOrigArgTys con) ]
- why = ptext (sLit "Constructor") <+> quotes (ppr (head bad_cons))
- <+> ptext (sLit "has arguments of unlifted type")
+ why = badCon (head bad_cons) (ptext (sLit "has arguments of unlifted type"))
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
fam_inst = quotes (pprSourceTyCon rep_tc) <+>
ptext (sLit "is a type family")
-cond_mayDeriveDataTypeable :: Condition
-cond_mayDeriveDataTypeable (mayDeriveDataTypeable, _)
- | mayDeriveDataTypeable = Nothing
- | otherwise = Just why
+
+functorLikeClassKeys :: [Unique]
+functorLikeClassKeys = [functorClassKey, foldableClassKey, traversableClassKey]
+
+cond_functorOK :: Bool -> Condition
+-- OK for Functor class
+-- Currently: (a) at least one argument
+-- (b) don't use argument contravariantly
+-- (c) don't use argument in the wrong place, e.g. data T a = T (X a a)
+-- (d) optionally: don't use function types
+cond_functorOK allowFunctions (dflags, rep_tc)
+ | not (dopt Opt_DeriveFunctor dflags)
+ = Just (ptext (sLit "You need -XDeriveFunctor to derive an instance for this class"))
+ | otherwise
+ = msum (map check_con data_cons) -- msum picks the first 'Just', if any
+ where
+ data_cons = tyConDataCons rep_tc
+ check_con con = msum (check_vanilla con : foldDataConArgs (ft_check con) con)
+
+ check_vanilla :: DataCon -> Maybe SDoc
+ check_vanilla con | isVanillaDataCon con = Nothing
+ | otherwise = Just (badCon con existential)
+
+ ft_check :: DataCon -> FFoldType (Maybe SDoc)
+ ft_check con = FT { ft_triv = Nothing, ft_var = Nothing
+ , ft_co_var = Just (badCon con covariant)
+ , ft_fun = \x y -> if allowFunctions then x `mplus` y
+ else Just (badCon con functions)
+ , ft_tup = \_ xs -> msum xs
+ , ft_ty_app = \_ x -> x
+ , ft_bad_app = Just (badCon con wrong_arg)
+ , ft_forall = \_ x -> x }
+
+ existential = ptext (sLit "has existential arguments")
+ covariant = ptext (sLit "uses the type variable in a function argument")
+ functions = ptext (sLit "contains function types")
+ wrong_arg = ptext (sLit "uses the type variable in an argument other than the last")
+
+checkFlag :: DynFlag -> Condition
+checkFlag flag (dflags, _)
+ | dopt flag dflags = Nothing
+ | otherwise = Just why
where
- why = ptext (sLit "You need -XDeriveDataTypeable to derive an instance for this class")
+ why = ptext (sLit "You need -X") <> text flag_str
+ <+> ptext (sLit "to derive an instance for this class")
+ flag_str = case [ s | (s, f, _) <- xFlags, f==flag ] of
+ [s] -> s
+ other -> pprPanic "checkFlag" (ppr other)
std_class_via_iso :: Class -> Bool
std_class_via_iso clas -- These standard classes can be derived for a newtype
-- using the isomorphism trick *even if no -fglasgow-exts*
- = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
+ = classKey clas `elem` [eqClassKey, ordClassKey, ixClassKey, boundedClassKey]
-- Not Read/Show because they respect the type
-- Not Enum, because newtypes are never in Enum
; newDFunName clas [mkTyConApp tycon []] loc }
-- The type passed to newDFunName is only used to generate
-- a suitable string; hence the empty type arg list
+
+badCon :: DataCon -> SDoc -> SDoc
+badCon con msg = ptext (sLit "Constructor") <+> quotes (ppr con) <+> msg
\end{code}
Note [Superclasses of derived instance]
%************************************************************************
\begin{code}
-mkNewTypeEqn :: InstOrigin -> Bool -> Bool -> [Var] -> Class
+mkNewTypeEqn :: InstOrigin -> DynFlags -> [Var] -> Class
-> [Type] -> TyCon -> [Type] -> TyCon -> [Type]
-> Maybe ThetaType
-> TcRn EarlyDerivSpec
-mkNewTypeEqn orig mayDeriveDataTypeable newtype_deriving tvs
+mkNewTypeEqn orig dflags tvs
cls cls_tys tycon tc_args rep_tycon rep_tc_args mtheta
+-- Want: instance (...) => cls (cls_tys ++ [tycon tc_args]) where ...
| can_derive_via_isomorphism && (newtype_deriving || std_class_via_iso cls)
= do { traceTc (text "newtype deriving:" <+> ppr tycon <+> ppr rep_tys)
; dfun_name <- new_dfun_name cls tycon
; loc <- getSrcSpanM
; let spec = DS { ds_loc = loc, ds_orig = orig
, ds_name = dfun_name, ds_tvs = varSetElems dfun_tvs
- , ds_cls = cls, ds_tys = inst_tys, ds_tc = rep_tycon
+ , ds_cls = cls, ds_tys = inst_tys
+ , ds_tc = rep_tycon, ds_tc_args = rep_tc_args
, ds_theta = mtheta `orElse` all_preds
, ds_newtype = True }
; return (if isJust mtheta then Right spec
else Left spec) }
+ | isJust mtheta = go_for_it -- Do not check side conditions for standalone deriving
| otherwise
- = case check_conditions of
- CanDerive -> mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
- -- Use the standard H98 method
- DerivableClassError msg -> bale_out msg -- Error with standard class
+ = case checkSideConditions dflags cls cls_tys rep_tycon of
+ CanDerive -> go_for_it -- Use the standard H98 method
+ DerivableClassError msg -> bale_out msg -- Error with standard class
NonDerivableClass -- Must use newtype deriving
| newtype_deriving -> bale_out cant_derive_err -- Too hard, even with newtype deriving
| otherwise -> bale_out non_std_err -- Try newtype deriving!
where
- check_conditions = checkSideConditions mayDeriveDataTypeable cls cls_tys rep_tycon
- bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg)
+ newtype_deriving = dopt Opt_GeneralizedNewtypeDeriving dflags
+ go_for_it = mk_data_eqn orig tvs cls tycon tc_args rep_tycon rep_tc_args mtheta
+ bale_out msg = failWithTc (derivingThingErr cls cls_tys inst_ty msg)
non_std_err = nonStdErr cls $$
ptext (sLit "Try -XGeneralizedNewtypeDeriving for GHC's newtype-deriving extension")
nt_eta_arity = length (fst (newTyConEtadRhs rep_tycon))
-- For newtype T a b = MkT (S a a b), the TyCon machinery already
- -- eta-reduces the represenation type, so we know that
+ -- eta-reduces the representation type, so we know that
-- T a ~ S a a
-- That's convenient here, because we may have to apply
-- it to fewer than its original complement of arguments
-- See Note [Newtype deriving superclasses] above
cls_tyvars = classTyVars cls
- dfun_tvs = tyVarsOfTypes tc_args
+ dfun_tvs = tyVarsOfTypes inst_tys
inst_ty = mkTyConApp tycon tc_args
inst_tys = cls_tys ++ [inst_ty]
sc_theta = substTheta (zipOpenTvSubst cls_tyvars inst_tys)
-------------------------------------------------------------------
-- Figuring out whether we can only do this newtype-deriving thing
- right_arity = length cls_tys + 1 == classArity cls
+ can_derive_via_isomorphism
+ = not (non_iso_class cls)
+ && arity_ok
+ && eta_ok
+ && ats_ok
+-- && not (isRecursiveTyCon tycon) -- Note [Recursive newtypes]
- -- Never derive Read,Show,Typeable,Data this way
+ -- Never derive Read,Show,Typeable,Data by isomorphism
non_iso_class cls = className cls `elem` ([readClassName, showClassName, dataClassName] ++
typeableClassNames)
- can_derive_via_isomorphism
- = not (non_iso_class cls)
- && right_arity -- Well kinded;
- -- eg not: newtype T ... deriving( ST )
- -- because ST needs *2* type params
- && eta_ok -- Eta reduction works
- && not (isRecursiveTyCon tycon) -- Does not work for recursive tycons:
- -- newtype A = MkA [A]
- -- Don't want
- -- instance Eq [A] => Eq A !!
- -- Here's a recursive newtype that's actually OK
- -- newtype S1 = S1 [T1 ()]
- -- newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
- -- It's currently rejected. Oh well.
- -- In fact we generate an instance decl that has method of form
- -- meth @ instTy = meth @ repTy
- -- (no coerce's). We'd need a coerce if we wanted to handle
- -- recursive newtypes too
+
+ arity_ok = length cls_tys + 1 == classArity cls
+ -- Well kinded; eg not: newtype T ... deriving( ST )
+ -- because ST needs *2* type params
-- Check that eta reduction is OK
- eta_ok = (nt_eta_arity <= length rep_tc_args)
- -- (a) the newtype can be eta-reduced to match the number
+ eta_ok = nt_eta_arity <= length rep_tc_args
+ -- The newtype can be eta-reduced to match the number
-- of type argument actually supplied
-- newtype T a b = MkT (S [a] b) deriving( Monad )
-- Here the 'b' must be the same in the rep type (S [a] b)
-- And the [a] must not mention 'b'. That's all handled
-- by nt_eta_rity.
- && (tyVarsOfTypes cls_tys `subVarSet` dfun_tvs)
- -- (c) the type class args do not mention any of the dropped type
- -- variables
- -- newtype T a b = ... deriving( Monad b )
-
- cant_derive_err = vcat [ptext (sLit "even with cunning newtype deriving:"),
- if isRecursiveTyCon tycon then
- ptext (sLit "the newtype may be recursive")
- else empty,
- if not right_arity then
- quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
- else empty,
- if not eta_ok then
- ptext (sLit "cannot eta-reduce the representation type enough")
- else empty
- ]
+ ats_ok = null (classATs cls)
+ -- No associated types for the class, because we don't
+ -- currently generate type 'instance' decls; and cannot do
+ -- so for 'data' instance decls
+
+ cant_derive_err
+ = vcat [ ptext (sLit "even with cunning newtype deriving:")
+ , if arity_ok then empty else arity_msg
+ , if eta_ok then empty else eta_msg
+ , if ats_ok then empty else ats_msg ]
+ arity_msg = quotes (ppr (mkClassPred cls cls_tys)) <+> ptext (sLit "does not have arity 1")
+ eta_msg = ptext (sLit "cannot eta-reduce the representation type enough")
+ ats_msg = ptext (sLit "the class has associated types")
\end{code}
+Note [Recursive newtypes]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Newtype deriving works fine, even if the newtype is recursive.
+e.g. newtype S1 = S1 [T1 ()]
+ newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
+Remember, too, that type families are curretly (conservatively) given
+a recursive flag, so this also allows newtype deriving to work
+for type famillies.
+
+We used to exclude recursive types, because we had a rather simple
+minded way of generating the instance decl:
+ newtype A = MkA [A]
+ instance Eq [A] => Eq A -- Makes typechecker loop!
+But now we require a simple context, so it's ok.
+
%************************************************************************
%* *
| otherwise
= do { -- Extend the inst info from the explicit instance decls
-- with the current set of solutions, and simplify each RHS
- let inst_specs = zipWithEqual "add_solns" (mkInstance2 oflag)
+ let inst_specs = zipWithEqual "add_solns" (mkInstance oflag)
current_solns infer_specs
; new_solns <- checkNoErrs $
extendLocalInstEnv inst_specs $
; return (sortLe (<=) theta) } -- Canonicalise before returning the solution
------------------------------------------------------------------
-mkInstance1 :: OverlapFlag -> DerivSpec -> Instance
-mkInstance1 overlap_flag spec = mkInstance2 overlap_flag (ds_theta spec) spec
-
-mkInstance2 :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
-mkInstance2 overlap_flag theta
+mkInstance :: OverlapFlag -> ThetaType -> DerivSpec -> Instance
+mkInstance overlap_flag theta
(DS { ds_name = dfun_name
, ds_tvs = tyvars, ds_cls = clas, ds_tys = tys })
= mkLocalInstance dfun overlap_flag
-- Representation tycons differ from the tycon in the instance signature in
-- case of instances for indexed families.
--
-genInst :: OverlapFlag -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
-genInst oflag spec
+genInst :: Bool -- True <=> standalone deriving
+ -> OverlapFlag
+ -> DerivSpec -> TcM (InstInfo RdrName, DerivAuxBinds)
+genInst standalone_deriv oflag spec
| ds_newtype spec
- = return (InstInfo { iSpec = mkInstance1 oflag spec
- , iBinds = NewTypeDerived }, [])
+ = return (InstInfo { iSpec = mkInstance oflag (ds_theta spec) spec
+ , iBinds = NewTypeDerived co }, [])
| otherwise
- = do { let loc = getSrcSpan (ds_name spec)
- inst = mkInstance1 oflag spec
- clas = ds_cls spec
- rep_tycon = ds_tc spec
+ = do { let loc = getSrcSpan (ds_name spec)
+ inst = mkInstance oflag (ds_theta spec) spec
+ clas = ds_cls spec
-- In case of a family instance, we need to use the representation
-- tycon (after all, it has the data constructors)
; fix_env <- getFixityEnv
; let (meth_binds, aux_binds) = genDerivBinds loc fix_env clas rep_tycon
-
- -- Build the InstInfo
- ; return (InstInfo { iSpec = inst,
- iBinds = VanillaInst meth_binds [] },
- aux_binds)
+ binds = VanillaInst meth_binds [] standalone_deriv
+ ; return (InstInfo { iSpec = inst, iBinds = binds }, aux_binds)
}
+ where
+ rep_tycon = ds_tc spec
+ rep_tc_args = ds_tc_args spec
+ co1 = case tyConFamilyCoercion_maybe rep_tycon of
+ Nothing -> IdCo
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co2 = case newTyConCo_maybe rep_tycon of
+ Nothing -> IdCo -- The newtype is transparent; no need for a cast
+ Just co_con -> ACo (mkTyConApp co_con rep_tc_args)
+ co = co1 `mkTransCoI` co2
+
+-- Example: newtype instance N [a] = N1 (Tree a)
+-- deriving instance Eq b => Eq (N [(b,b)])
+-- From the instance, we get an implicit newtype R1:N a = N1 (Tree a)
+-- When dealing with the deriving clause
+-- co1 : N [(b,b)] ~ R1:N (b,b)
+-- co2 : R1:N (b,b) ~ Tree (b,b)
genDerivBinds :: SrcSpan -> FixityEnv -> Class -> TyCon -> (LHsBinds RdrName, DerivAuxBinds)
genDerivBinds loc fix_env clas tycon
,(showClassKey, gen_Show_binds fix_env)
,(readClassKey, gen_Read_binds fix_env)
,(dataClassKey, gen_Data_binds)
+ ,(functorClassKey, gen_Functor_binds)
+ ,(foldableClassKey, gen_Foldable_binds)
+ ,(traversableClassKey, gen_Traversable_binds)
]
\end{code}
2 (ptext (sLit "Class") <+> quotes (ppr cls)
<+> ptext (sLit "expects an argument of kind") <+> quotes (pprKind cls_kind))
+derivingEtaErr :: Class -> [Type] -> Type -> Message
+derivingEtaErr cls cls_tys inst_ty
+ = sep [ptext (sLit "Cannot eta-reduce to an instance of form"),
+ nest 2 (ptext (sLit "instance (...) =>")
+ <+> pprClassPred cls (cls_tys ++ [inst_ty]))]
+
typeFamilyPapErr :: TyCon -> Class -> [Type] -> Type -> Message
typeFamilyPapErr tc cls cls_tys inst_ty
= hang (ptext (sLit "Derived instance") <+> quotes (pprClassPred cls (cls_tys ++ [inst_ty])))
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