macro_rules! handlers {
(
$system_name:ident {
$($handler_name:ident {
$($signal_name:ident ( $($arg_name:ident : $arg_type:ty),* ) => $slot_name:ident);*
})*
}
) => { ... };
(
DEFINE_HANDLERS $system_name:ident
$($handler_name:ident {
$($signal_name:ident ( $($arg_name:ident : $arg_type:ty),* ) => $slot_name:ident);*
})*
) => { ... };
}