#include "HsVersions.h"
-import HsSyn ( HsBinds(..), MonoBinds(..), collectLocatedMonoBinders )
+import HsSyn ( HsBinds(..), MonoBinds(..), TyClDecl(..),
+ collectLocatedMonoBinders )
import RdrHsSyn ( RdrNameMonoBinds )
-import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds )
+import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds, RenamedTyClDecl, RenamedHsPred )
import CmdLineOpts ( DynFlag(..), DynFlags )
import TcMonad
-import TcEnv ( TcEnv, tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo )
+import TcEnv ( tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo,
+ tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv
+ )
import TcGenDeriv -- Deriv stuff
import InstEnv ( InstEnv, simpleDFunClassTyCon, extendInstEnv )
+import TcMonoType ( tcHsPred )
import TcSimplify ( tcSimplifyThetas )
import RnBinds ( rnMethodBinds, rnTopMonoBinds )
import RnEnv ( bindLocatedLocalsRn )
-import RnMonad ( --RnNameSupply,
- renameSourceCode, thenRn, mapRn, returnRn )
+import RnMonad ( renameDerivedCode, thenRn, mapRn, returnRn )
import HscTypes ( DFunId, PersistentRenamerState )
-import BasicTypes ( Fixity )
-import Class ( classKey, Class )
+import BasicTypes ( Fixity, NewOrData(..) )
+import Class ( className, classKey, classTyVars, Class )
import ErrUtils ( dumpIfSet_dyn, Message )
import MkId ( mkDictFunId )
-import DataCon ( dataConArgTys, isNullaryDataCon, isExistentialDataCon )
+import DataCon ( dataConRepArgTys, isNullaryDataCon, isExistentialDataCon )
import PrelInfo ( needsDataDeclCtxtClassKeys )
import Maybes ( maybeToBool, catMaybes )
import Module ( Module )
-import Name ( Name, isFrom, getSrcLoc )
+import Name ( Name, getSrcLoc, nameUnique )
import RdrName ( RdrName )
-import TyCon ( tyConTyVars, tyConDataCons, tyConDerivings,
+import TyCon ( tyConTyVars, tyConDataCons, tyConArity, newTyConRep,
tyConTheta, maybeTyConSingleCon, isDataTyCon,
isEnumerationTyCon, TyCon
)
-import Type ( TauType, PredType(..), mkTyVarTys, mkTyConApp, isUnboxedType )
-import Var ( TyVar )
+import TcType ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
+ isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys,
+ tcSplitTyConApp_maybe, tcEqTypes )
+import Var ( TyVar, tyVarKind )
+import VarSet ( mkVarSet, subVarSet )
import PrelNames
-import Util ( zipWithEqual, sortLt, thenCmp )
+import Util ( zipWithEqual, sortLt )
import ListSetOps ( removeDups, assoc )
import Outputable
+import Maybe ( isJust )
+import List ( nub )
+import FastString ( FastString )
\end{code}
%************************************************************************
-- The Name is the name for the DFun we'll build
-- The tyvars bind all the variables in the RHS
-type DerivRhs = [(Class, [TauType])] -- Same as a ThetaType!
- --[PredType] -- ... | Class Class [Type==TauType]
-
+type DerivRhs = ThetaType
type DerivSoln = DerivRhs
\end{code}
-> Module -- name of module under scrutiny
-> InstEnv -- What we already know about instances
-> (Name -> Maybe Fixity) -- used in deriving Show and Read
- -> [TyCon] -- All type constructors
+ -> [RenamedTyClDecl] -- All type constructors
-> TcM ([InstInfo], -- The generated "instance decls".
RenamedHsBinds) -- Extra generated bindings
-tcDeriving prs mod inst_env_in get_fixity tycons
+tcDeriving prs mod inst_env get_fixity tycl_decls
= recoverTc (returnTc ([], EmptyBinds)) $
+ getDOptsTc `thenNF_Tc` \ dflags ->
-- Fish the "deriving"-related information out of the TcEnv
-- and make the necessary "equations".
- makeDerivEqns mod tycons `thenTc` \ eqns ->
- if null eqns then
- returnTc ([], EmptyBinds)
- else
+ makeDerivEqns tycl_decls `thenTc` \ (ordinary_eqns, newtype_inst_info) ->
+ let
+ -- Add the newtype-derived instances to the inst env
+ -- before tacking the "ordinary" ones
+ inst_env1 = extend_inst_env dflags inst_env
+ (map iDFunId newtype_inst_info)
+ in
+ deriveOrdinaryStuff mod prs inst_env1 get_fixity
+ ordinary_eqns `thenTc` \ (ordinary_inst_info, binds) ->
+ let
+ inst_info = newtype_inst_info ++ ordinary_inst_info
+ in
- -- Take the equation list and solve it, to deliver a list of
+ ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
+ (ddump_deriving inst_info binds)) `thenTc_`
+
+ returnTc (inst_info, binds)
+
+ where
+ ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
+ ddump_deriving inst_infos extra_binds
+ = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
+
+
+-----------------------------------------
+deriveOrdinaryStuff mod prs inst_env_in get_fixity [] -- Short cut
+ = returnTc ([], EmptyBinds)
+
+deriveOrdinaryStuff mod prs inst_env_in get_fixity eqns
+ = -- Take the equation list and solve it, to deliver a list of
-- solutions, a.k.a. the contexts for the instance decls
-- required for the corresponding equations.
solveDerivEqns inst_env_in eqns `thenTc` \ new_dfuns ->
-- generate extra not-one-inst-decl-specific binds, notably
-- "con2tag" and/or "tag2con" functions. We do these
-- separately.
-
gen_taggery_Names new_dfuns `thenTc` \ nm_alist_etc ->
tcGetEnv `thenNF_Tc` \ env ->
- getDOptsTc `thenTc` \ dflags ->
+ getDOptsTc `thenNF_Tc` \ dflags ->
let
extra_mbind_list = map gen_tag_n_con_monobind nm_alist_etc
extra_mbinds = foldr AndMonoBinds EmptyMonoBinds extra_mbind_list
-- The only tricky bit is that the extra_binds must scope over the
-- method bindings for the instances.
(rn_method_binds_s, rn_extra_binds)
- = renameSourceCode dflags mod prs (
+ = renameDerivedCode dflags mod prs (
bindLocatedLocalsRn (ptext (SLIT("deriving"))) mbinders $ \ _ ->
rnTopMonoBinds extra_mbinds [] `thenRn` \ (rn_extra_binds, _) ->
mapRn rn_meths method_binds_s `thenRn` \ rn_method_binds_s ->
returnRn (rn_method_binds_s, rn_extra_binds)
)
-
new_inst_infos = zipWith gen_inst_info new_dfuns rn_method_binds_s
in
-
- ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Derived instances"
- (ddump_deriving new_inst_infos rn_extra_binds)) `thenTc_`
-
returnTc (new_inst_infos, rn_extra_binds)
- where
- ddump_deriving :: [InstInfo] -> RenamedHsBinds -> SDoc
- ddump_deriving inst_infos extra_binds
- = vcat (map pprInstInfo inst_infos) $$ ppr extra_binds
- where
+ where
-- Make a Real dfun instead of the dummy one we have so far
gen_inst_info :: DFunId -> RenamedMonoBinds -> InstInfo
gen_inst_info dfun binds
- = InstInfo { iLocal = True, iDFunId = dfun,
- iBinds = binds, iPrags = [] }
+ = InstInfo { iDFunId = dfun, iBinds = binds, iPrags = [] }
- rn_meths meths = rnMethodBinds [] meths `thenRn` \ (meths', _) -> returnRn meths'
- -- Ignore the free vars returned
+ rn_meths (cls, meths) = rnMethodBinds cls [] meths `thenRn` \ (meths', _) ->
+ returnRn meths' -- Ignore the free vars returned
\end{code}
all those.
\begin{code}
-makeDerivEqns :: Module -> [TyCon] -> TcM [DerivEqn]
+makeDerivEqns :: [RenamedTyClDecl]
+ -> TcM ([DerivEqn], -- Ordinary derivings
+ [InstInfo]) -- Special newtype derivings
-makeDerivEqns this_mod tycons
- = let
- think_about_deriving = need_deriving tycons
- (derive_these, _) = removeDups cmp_deriv think_about_deriving
- in
- if null think_about_deriving then
- returnTc [] -- Bale out now
- else
- mapTc mk_eqn derive_these `thenTc` \ maybe_eqns ->
- returnTc (catMaybes maybe_eqns)
+makeDerivEqns tycl_decls
+ = mapAndUnzipTc mk_eqn derive_these `thenTc` \ (maybe_ordinaries, maybe_newtypes) ->
+ returnTc (catMaybes maybe_ordinaries, catMaybes maybe_newtypes)
where
------------------------------------------------------------------
- need_deriving :: [TyCon] -> [(Class, TyCon)]
- -- find the tycons that have `deriving' clauses;
-
- need_deriving tycons_to_consider
- = [ (clas,tycon) | tycon <- tycons_to_consider,
- isFrom this_mod tycon,
- clas <- tyConDerivings tycon ]
-
- ------------------------------------------------------------------
- cmp_deriv :: (Class, TyCon) -> (Class, TyCon) -> Ordering
- cmp_deriv (c1, t1) (c2, t2)
- = (c1 `compare` c2) `thenCmp` (t1 `compare` t2)
+ derive_these :: [(NewOrData, Name, RenamedHsPred)]
+ -- Find the (nd, TyCon, Pred) pairs that must be `derived'
+ -- NB: only source-language decls have deriving, no imported ones do
+ derive_these = [ (nd, tycon, pred)
+ | TyData {tcdND = nd, tcdName = tycon, tcdDerivs = Just preds} <- tycl_decls,
+ pred <- preds ]
------------------------------------------------------------------
- mk_eqn :: (Class, TyCon) -> NF_TcM (Maybe DerivEqn)
- -- we swizzle the tyvars and datacons out of the tycon
+ mk_eqn :: (NewOrData, Name, RenamedHsPred) -> NF_TcM (Maybe DerivEqn, Maybe InstInfo)
+ -- We swizzle the tyvars and datacons out of the tycon
-- to make the rest of the equation
- mk_eqn (clas, tycon)
- = case chk_out clas tycon of
- Just err -> addErrTc err `thenNF_Tc_`
- returnNF_Tc Nothing
- Nothing -> newDFunName this_mod clas [ty] locn `thenNF_Tc` \ dfun_name ->
- returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints))
+ mk_eqn (new_or_data, tycon_name, pred)
+ = tcLookupTyCon tycon_name `thenNF_Tc` \ tycon ->
+ tcAddSrcLoc (getSrcLoc tycon) $
+ tcAddErrCtxt (derivCtxt tycon) $
+ tcExtendTyVarEnv (tyConTyVars tycon) $ -- Deriving preds may (now) mention
+ -- the type variables for the type constructor
+ tcHsPred pred `thenTc` \ pred' ->
+ case getClassPredTys_maybe pred' of
+ Nothing -> bale_out (malformedPredErr tycon pred)
+ Just (clas, tys) -> mk_eqn_help new_or_data tycon clas tys
+
+ ------------------------------------------------------------------
+ mk_eqn_help DataType tycon clas tys
+ | Just err <- chk_out clas tycon tys
+ = bale_out (derivingThingErr clas tys tycon tyvars err)
+ | otherwise
+ = new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
+ returnNF_Tc (Just (dfun_name, clas, tycon, tyvars, constraints), Nothing)
where
- clas_key = classKey clas
tyvars = tyConTyVars tycon
- tyvar_tys = mkTyVarTys tyvars
- ty = mkTyConApp tycon tyvar_tys
data_cons = tyConDataCons tycon
- locn = getSrcLoc tycon
+ constraints = extra_constraints ++
+ [ mkClassPred clas [arg_ty]
+ | data_con <- tyConDataCons tycon,
+ arg_ty <- dataConRepArgTys data_con,
+ -- Use the same type variables
+ -- as the type constructor,
+ -- hence no need to instantiate
+ not (isUnLiftedType arg_ty) -- No constraints for unlifted types?
+ ]
- constraints = extra_constraints ++ concat (map mk_constraints data_cons)
+
+ -- "extra_constraints": see notes above about contexts on data decls
+ extra_constraints | offensive_class = tyConTheta tycon
+ | otherwise = []
+
+ offensive_class = classKey clas `elem` needsDataDeclCtxtClassKeys
- -- "extra_constraints": see notes above about contexts on data decls
- extra_constraints
- | offensive_class = tyConTheta tycon
- | otherwise = []
- where
- offensive_class = clas_key `elem` needsDataDeclCtxtClassKeys
- mk_constraints data_con
- = [ (clas, [arg_ty])
- | arg_ty <- instd_arg_tys,
- not (isUnboxedType arg_ty) -- No constraints for unboxed types?
- ]
- where
- instd_arg_tys = dataConArgTys data_con tyvar_tys
+ mk_eqn_help NewType tycon clas tys
+ = doptsTc Opt_GlasgowExts `thenTc` \ gla_exts ->
+ if can_derive_via_isomorphism && (gla_exts || standard_instance) then
+ -- Go ahead and use the isomorphism
+ new_dfun_name clas tycon `thenNF_Tc` \ dfun_name ->
+ returnTc (Nothing, Just (NewTypeDerived (mk_dfun dfun_name)))
+ else
+ if standard_instance then
+ mk_eqn_help DataType tycon clas [] -- Go via bale-out route
+ else
+ bale_out cant_derive_err
+ where
+ -- Here is the plan for newtype derivings. We see
+ -- newtype T a1...an = T (t ak...an) deriving (C1...Cm)
+ -- where aj...an do not occur free in t, and the Ci are *partial applications* of
+ -- classes with the last parameter missing
+ --
+ -- We generate the instances
+ -- instance Ci (t ak...aj) => Ci (T a1...aj)
+ -- where T a1...aj is the partial application of the LHS of the correct kind
+ --
+ -- Running example: newtype T s a = MkT (ST s a) deriving( Monad )
+
+ kind = tyVarKind (last (classTyVars clas))
+ -- Kind of the thing we want to instance
+ -- e.g. argument kind of Monad, *->*
+
+ (arg_kinds, _) = tcSplitFunTys kind
+ n_args_to_drop = length arg_kinds
+ -- Want to drop 1 arg from (T s a) and (ST s a)
+ -- to get instance Monad (ST s) => Monad (T s)
+
+ (tyvars, rep_ty) = newTyConRep tycon
+ maybe_rep_app = tcSplitTyConApp_maybe rep_ty
+ Just (rep_tc, rep_ty_args) = maybe_rep_app
+
+ n_tyvars_to_keep = tyConArity tycon - n_args_to_drop
+ tyvars_to_drop = drop n_tyvars_to_keep tyvars
+ tyvars_to_keep = take n_tyvars_to_keep tyvars
+
+ n_args_to_keep = tyConArity rep_tc - n_args_to_drop
+ args_to_drop = drop n_args_to_keep rep_ty_args
+ args_to_keep = take n_args_to_keep rep_ty_args
+
+ ctxt_pred = mkClassPred clas (tys ++ [mkTyConApp rep_tc args_to_keep])
+
+ mk_dfun dfun_name = mkDictFunId dfun_name clas tyvars
+ (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars_to_keep)] )
+ [ctxt_pred]
+
+ -- We can only do this newtype deriving thing if:
+ standard_instance = null tys && classKey clas `elem` derivableClassKeys
+
+ can_derive_via_isomorphism
+ = not (clas `hasKey` readClassKey) -- Never derive Read,Show this way
+ && not (clas `hasKey` showClassKey)
+ && n_tyvars_to_keep >= 0 -- Well kinded;
+ -- eg not: newtype T = T Int deriving( Monad )
+ && isJust maybe_rep_app -- The rep type is a type constructor app
+ && n_args_to_keep >= 0 -- Well kinded:
+ -- eg not: newtype T a = T Int deriving( Monad )
+ && eta_ok -- Eta reduction works
+
+ -- Check that eta reduction is OK
+ -- (a) the dropped-off args are identical
+ -- (b) the remaining type args mention
+ -- only the remaining type variables
+ eta_ok = (args_to_drop `tcEqTypes` mkTyVarTys tyvars_to_drop)
+ && (tyVarsOfTypes args_to_keep `subVarSet` mkVarSet tyvars_to_keep)
+
+ cant_derive_err = derivingThingErr clas tys tycon tyvars_to_keep
+ SLIT("too hard for cunning newtype deriving")
+
+
+ bale_out err = addErrTc err `thenNF_Tc_` returnNF_Tc (Nothing, Nothing)
------------------------------------------------------------------
- chk_out :: Class -> TyCon -> Maybe Message
- chk_out clas tycon
- | clas `hasKey` enumClassKey && not is_enumeration = bog_out nullary_why
- | clas `hasKey` boundedClassKey && not is_enumeration_or_single = bog_out single_nullary_why
- | clas `hasKey` ixClassKey && not is_enumeration_or_single = bog_out single_nullary_why
- | any isExistentialDataCon (tyConDataCons tycon) = Just (existentialErr clas tycon)
- | otherwise = Nothing
+ chk_out :: Class -> TyCon -> [TcType] -> Maybe FastString
+ chk_out clas tycon tys
+ | not (null tys) = Just non_std_why
+ | not (getUnique clas `elem` derivableClassKeys) = Just non_std_why
+ | clas `hasKey` enumClassKey && not is_enumeration = Just nullary_why
+ | clas `hasKey` boundedClassKey && not is_enumeration_or_single = Just single_nullary_why
+ | clas `hasKey` ixClassKey && not is_enumeration_or_single = Just single_nullary_why
+ | null data_cons = Just no_cons_why
+ | any isExistentialDataCon data_cons = Just existential_why
+ | otherwise = Nothing
where
+ data_cons = tyConDataCons tycon
is_enumeration = isEnumerationTyCon tycon
is_single_con = maybeToBool (maybeTyConSingleCon tycon)
is_enumeration_or_single = is_enumeration || is_single_con
- single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
- nullary_why = SLIT("data type with all nullary constructors expected")
+ single_nullary_why = SLIT("one constructor data type or type with all nullary constructors expected")
+ nullary_why = SLIT("data type with all nullary constructors expected")
+ no_cons_why = SLIT("type has no data constructors")
+ non_std_why = SLIT("not a derivable class")
+ existential_why = SLIT("it has existentially-quantified constructor(s)")
- bog_out why = Just (derivingThingErr clas tycon why)
+new_dfun_name clas tycon -- Just a simple wrapper
+ = newDFunName clas [mkTyConApp tycon []] (getSrcLoc tycon)
+ -- The type passed to newDFunName is only used to generate
+ -- a suitable string; hence the empty type arg list
\end{code}
%************************************************************************
iterateOnce current_solns
= -- Extend the inst info from the explicit instance decls
-- with the current set of solutions, giving a
- getDOptsTc `thenTc` \ dflags ->
- let (new_dfuns, inst_env) =
- add_solns dflags inst_env_in orig_eqns current_solns
+ getDOptsTc `thenNF_Tc` \ dflags ->
+ let
+ new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
+ inst_env = extend_inst_env dflags inst_env_in new_dfuns
+ -- the eqns and solns move "in lockstep"; we have the eqns
+ -- because we need the LHS info for addClassInstance.
in
-- Simplify each RHS
tcSetInstEnv inst_env (
- listTc [ tcAddErrCtxt (derivCtxt tc) $
+ listTc [ tcAddSrcLoc (getSrcLoc tc) $
+ tcAddErrCtxt (derivCtxt tc) $
tcSimplifyThetas deriv_rhs
| (_, _,tc,_,deriv_rhs) <- orig_eqns ]
) `thenTc` \ next_solns ->
\end{code}
\begin{code}
-add_solns :: DynFlags
- -> InstEnv -- The global, non-derived ones
- -> [DerivEqn] -> [DerivSoln]
- -> ([DFunId], InstEnv)
- -- the eqns and solns move "in lockstep"; we have the eqns
- -- because we need the LHS info for addClassInstance.
-
-add_solns dflags inst_env_in eqns solns
- = (new_dfuns, inst_env)
- where
- new_dfuns = zipWithEqual "add_solns" mk_deriv_dfun eqns solns
- (inst_env, _) = extendInstEnv dflags inst_env_in new_dfuns
+extend_inst_env dflags inst_env new_dfuns
+ = new_inst_env
+ where
+ (new_inst_env, _errs) = extendInstEnv dflags inst_env new_dfuns
-- Ignore the errors about duplicate instances.
-- We don't want repeated error messages
-- They'll appear later, when we do the top-level extendInstEnvs
- mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
- = mkDictFunId dfun_name clas tyvars [mkTyConApp tycon (mkTyVarTys tyvars)]
- (map pair2PredType theta)
-
- pair2PredType (clas, tautypes) = Class clas tautypes
+mk_deriv_dfun (dfun_name, clas, tycon, tyvars, _) theta
+ = mkDictFunId dfun_name clas tyvars
+ [mkTyConApp tycon (mkTyVarTys tyvars)]
+ theta
\end{code}
%************************************************************************
\begin{code}
-- Generate the method bindings for the required instance
--- (paired with class name, as we need that when generating dict
--- names.)
-gen_bind :: (Name -> Maybe Fixity) -> DFunId -> RdrNameMonoBinds
+-- (paired with class name, as we need that when renaming
+-- the method binds)
+gen_bind :: (Name -> Maybe Fixity) -> DFunId -> (Name, RdrNameMonoBinds)
gen_bind get_fixity dfun
- | clas `hasKey` showClassKey = gen_Show_binds get_fixity tycon
- | clas `hasKey` readClassKey = gen_Read_binds get_fixity tycon
- | otherwise
- = assoc "gen_bind:bad derived class"
- [(eqClassKey, gen_Eq_binds)
- ,(ordClassKey, gen_Ord_binds)
- ,(enumClassKey, gen_Enum_binds)
- ,(boundedClassKey, gen_Bounded_binds)
- ,(ixClassKey, gen_Ix_binds)
- ]
- (classKey clas)
- tycon
+ = (cls_nm, binds)
where
+ cls_nm = className clas
(clas, tycon) = simpleDFunClassTyCon dfun
+
+ binds = assoc "gen_bind:bad derived class" gen_list
+ (nameUnique cls_nm) tycon
+
+ gen_list = [(eqClassKey, gen_Eq_binds)
+ ,(ordClassKey, gen_Ord_binds)
+ ,(enumClassKey, gen_Enum_binds)
+ ,(boundedClassKey, gen_Bounded_binds)
+ ,(ixClassKey, gen_Ix_binds)
+ ,(showClassKey, gen_Show_binds get_fixity)
+ ,(readClassKey, gen_Read_binds get_fixity)
+ ]
\end{code}
con2tag_Foo :: Foo ... -> Int#
tag2con_Foo :: Int -> Foo ... -- easier if Int, not Int#
-maxtag_Foo :: Int -- ditto (NB: not unboxed)
+maxtag_Foo :: Int -- ditto (NB: not unlifted)
We have a @con2tag@ function for a tycon if:
\end{code}
\begin{code}
-derivingThingErr :: Class -> TyCon -> FAST_STRING -> Message
-
-derivingThingErr clas tycon why
- = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr clas)],
- hsep [ptext SLIT("for the type"), quotes (ppr tycon)],
+derivingThingErr clas tys tycon tyvars why
+ = sep [hsep [ptext SLIT("Can't make a derived instance of"), quotes (ppr pred)],
parens (ptext why)]
+ where
+ pred = mkClassPred clas (tys ++ [mkTyConApp tycon (mkTyVarTys tyvars)])
-existentialErr clas tycon
- = sep [ptext SLIT("Can't derive any instances for type") <+> quotes (ppr tycon),
- ptext SLIT("because it has existentially-quantified constructor(s)")]
+malformedPredErr tycon pred = ptext SLIT("Illegal deriving item") <+> ppr pred
derivCtxt tycon
= ptext SLIT("When deriving classes for") <+> quotes (ppr tycon)
\end{code}
+
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