Creates two processes that will bounce back and forth to count up to the input value

bouncing_counter.exs

defmodule BouncingCounter do

    def even(max, main_pid) do
        receive do
            {:inc, odd_pid, n} when n <= max -> 
                IO.puts("EVEN: Count currently at #{n}")
                send(odd_pid, {:inc, self(), n + 1})
                even(max, main_pid)
           
            {:inc, even_pid, n} when n > max ->
                send(even_pid, {:done})
                
            {:done} -> send(main_pid, {:done})
        end
    end
    
    def odd(max, main_pid) do
        receive do
            {:inc, even_pid, n} when n <= max -> 
                IO.puts("ODD: Count currently at #{n}")
                send(even_pid, {:inc, self(), n + 1})
                odd(max, main_pid)
            
            {:inc, even_pid, n} when n > max ->
                send(even_pid, {:done})
            
            {:done} -> send(main_pid, {:done})
        end
    end


    def main do
        {max, _} = IO.gets("Enter the max value: ") |> Integer.parse
        
        odd_pid = spawn(BouncingCounter, :odd, [max, self()])
        even_pid = spawn(BouncingCounter, :even, [max, self()])
        
        IO.puts "Starting counter... 1 to #{max}"
        send(odd_pid, {:inc, even_pid, 1})
        
        receive do
            {:done} -> IO.puts("Count complete!")
        end
    end
end

BouncingCounter.main