My First Lisp Program

by 12/13/2009 10:11:00 PM 0 comments

My First Lisp Program

I wrote a simple timecode generator for testing of the Video Annotation and Reference System in Groovy. The program listens for requests on a UDP port and responds with a String formated as a timecode. For grins, I converted the program to Clojure

Groovy

#!/usr/bin/env groovy

/**
 * Script for simulation of a udp VCR
 */

def port = (args.size() > 0) ? Integer.valueOf(args[0]) : 9000

println("Localtime timecode generator attached to port ${port}")

 
def socket = new DatagramSocket(port)
def buffer = (' ' * 4096) as byte[]
while(true) {
    def incoming = new DatagramPacket(buffer, buffer.length)
    socket.receive(incoming)
    def c = new GregorianCalendar()
    def f = c.get(Calendar.MILLISECOND) / 1000.0 * 29.97;
    String reply = String.format('%tT:%02d', c, Math.round(f))
    outgoing = new DatagramPacket(reply.bytes, reply.size(),
            incoming.address, incoming.port);
    socket.send(outgoing)
}

Clojure

(import 
  '(java.net DatagramPacket DatagramSocket)
  '(java.util GregorianCalendar Calendar))
  
(defn fmt-time 
  "Format a java Calendar as a timecode"
  [cal] 
  (let [frames (* (/ (. cal get (Calendar/MILLISECOND)) 1000) 29.97)]
    (format "%tT:%02d" cal (Math/round frames))))
  
(defn run-generator 
  "Function for simulation of a udp VCR"
  [port] 
  (println (str "Localtime timecode generator attached to port " port))
  (let [socket (new DatagramSocket port)
        buffer (make-array (Byte/TYPE) 4096)]
    (while true 
      (let [incoming (new DatagramPacket buffer 4096) 
            reply (fmt-time (new GregorianCalendar))]
         (. socket receive incoming)
         (let [outgoing (new DatagramPacket (. reply getBytes) (. reply length) (. incoming getAddress) (. incoming getPort))]
           (. socket send outgoing))))))
  
 (run-generator (Integer/parseInt (first *command-line-args*)))

Brian Schlining

Developer

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