instructions.md

Instructions

You are writing an embedded system for a Take-A-Number machine. It is a very simple model. It can give out consecutive numbers and report what was the last number given out.

1. Start the machine

Implement the start/0 function. It should spawn a new process and return the process's PID. The new process doesn't need to do anything yet.

TakeANumber.start()
# => #PID<0.138.0>

Note that each time you run this code, the PID may be different.

2. Report the machine state

Modify the machine so that the newly spawned process is ready to receive messages (start a receive loop) with an initial state of 0. It should be able to receive {:report_state, sender_pid} messages. As a response to those messages, it should send its current state (the last given out ticket number) to sender_pid and then wait for more messages.

machine_pid = TakeANumber.start()

# a client sending a message to the machine
send(machine_pid, {:report_state, self()})

# a client receiving a message from the machine
receive do
  msg -> msg
end

# => 0

3. Give out numbers

Modify the machine so that it can receive {:take_a_number, sender_pid} messages. It should increase its state by 1, send the new state to sender_pid, and then wait for more messages.

machine_pid = TakeANumber.start()

# a client sending a message to the machine
send(machine_pid, {:take_a_number, self()})

# a client receiving a message from the machine
receive do
  msg -> msg
end

# => 1

4. Stop the machine

Modify the machine so that it can receive a :stop message. It should stop waiting for more messages.

5. Ignore unexpected messages

Modify the machine so that when it receives an unexpected message, it ignores it and continues waiting for more messages.