Macro hopper_dispatch 

macro_rules! hopper_dispatch {
    (
        $program_id:expr, $accounts:expr, $data:expr;
        $( $tag:literal => $handler:expr ),+ $(,)?
    ) => { ... };
}

Macro for instruction dispatch.

hopper_dispatch! {
    program_id, accounts, instruction_data;
    0 => process_init,
    1 => process_deposit,
    2 => process_withdraw,
}