IPv4address =
  dec-octet "."
  dec-octet "."
  dec-octet "."
  dec-octet !!!
    state = Map.put state, :ipv4address, rule
    {:ok, state, "Your ip address is: #{rule}"}
  !!!

dec-octet = DIGIT         ; 0-9
  / %x31-39 DIGIT         ; 10-99
  / "1" 2DIGIT            ; 100-199
  / "2" %x30-34 DIGIT     ; 200-249
  / "25" %x30-35          ; 250-255

DIGIT = %x30-39
