dog_state_machine.erl

-module(dog_state_machine).
-export([start/0, squirrel/1, pet/1]).

%% states 1) barks, 2) sits 3) wags tails

% sits sees -> squirrel -> barks -> gets petted ->wags tails -> sits

start() -> spawn(fun() -> bark() end).

squirrel(Pid) -> Pid ! squirrel.

pet(Pid) -> Pid ! pet.

bark() ->
  io:format("Dog says: BARK! BARK!~n"),
  receive
    pet ->
      wag_tail();
    _ ->
      io:format("Dog is confused~n"),
      bark()
  after 2000 ->
    bark()
  end.
            
wag_tail() ->
  io:format("Dog wags its tail~n"),
  receive
    pet ->
      sit();
    _ ->
      io:format("Dog is confused~n"),
      wag_tail()
  after 30000 ->
      bark()
  end.

sit() ->
  io:format("Dog is sitting. Gooooood boy!~n"),
  receive
    squirrel ->
      bark();
    _ ->
      io:format("Dog is confused~n"),
      sit()
  end.