TCP example, rewritten from: http://www.erlang.org/doc/man/gen_tcp.html

client.exs

host = 'localhost' # host needs to be a charlist
{:ok, sock} = :gen_tcp.connect(host, 5678, [:binary, {:packet, 0}])
:ok = :gen_tcp.send(sock, "Some Data")
:ok = :gen_tcp.close(sock)

server.exs

defmodule Server do
  def run do
    { :ok, lsock } = :gen_tcp.listen(5678, [:binary, {:packet, 0}, {:active, false}])
    { :ok, sock  } = :gen_tcp.accept(lsock)
    { :ok, bin }   = do_recv(sock, [])
    :ok = :gen_tcp.close(sock)
    IO.puts(bin)
  end

  defp do_recv(sock, bs) do
    case :gen_tcp.recv(sock, 0) do
      { :ok, b } ->
        do_recv(sock, [bs, b])
      { :error, :closed } ->
        { :ok, list_to_binary(bs) }
    end
  end
end

Server.run