pub struct PaxosEnvironment {
    pub get_message_type: IOFunc,
    pub current_number_is_greater: IOFunc,
    pub send_accept_request: IOFunc,
    pub send_promise: IOFunc,
    pub generate_new_proposal_number: IOFunc,
    pub extract_highest_proposed_value: IOFunc,
    pub promise_valid: IOFunc,
    pub mark_value_as_chosen: IOFunc,
    pub report_chosen_to_leader: IOFunc,
    pub state_rejected: IOFunc,
    pub determine_next_consensus_instance: IOFunc,
    pub propose_command_value: IOFunc,
    pub state_expecting_acknowledgment: IOFunc,
    pub execute_known_commands: IOFunc,
    pub continue_loop: IOFunc,
}