rg :: (String -> DynFlags -> DynFlags) -> OptKind (CmdLineP DynFlags)
sepArg fn = SepArg (upd . fn)

in
sepArg :: (String -> DynFlags -> DynFlags) -> OptKind (CmdLineP DynFlags)
sepArg fn = SepArg (upd . fn)
sepArg fn = SepArg (upd . fn)