webserver.exs

cmd = ~S"""
  ruby -e '
    require "bundler"
    require "erlang/etf"
    require "stringio"
    require "sinatra"

    @input = IO.new(3)
    @output = IO.new(4)
    @output.sync = true

    def receive_input
      encoded_length = @input.read(4)
      return nil unless encoded_length
      length = encoded_length.unpack("N").first
      Erlang.binary_to_term(@input.read(length))
    end

    def send_response(value)
      response = Erlang.term_to_binary(Erlang::Tuple[:response, value])
      @output.write([response.bytesize].pack("N"))
      @output.write(response)
      true
    end

    context = binding

    get "/" do
      "hello"
    end

    while (cmd = receive_input) do
      if cmd.is_a?(Erlang::Tuple) && cmd[0] == :eval
        puts "Ruby: #{cmd[1]}"
        res = eval(cmd[1], context)
        puts "Ruby: => #{res.inspect}\n\n"
      end
    end
  '
"""

send_eval = fn(port, command) ->
  Port.command(port, :erlang.term_to_binary({:eval, command}))
end

port = Port.open({:spawn, cmd}, [:binary, {:packet, 4}, :nouse_stdio])