static double autoRestartOnSnippetChange_interval = 10;
static bool autoRestartOnSnippetChange_on, autoRestartOnSnippetChange_debug, autoRestartOnSnippetChange_simulate;
sS autoRestartOnSnippetChange_snippetID;
static java.util.Timer autoRestartOnSnippetChange_timer;
sS autoRestartOnSnippetChange_localMD5;

static void autoRestartOnSnippetChange(double interval, S snippetID) {
  autoRestartOnSnippetChange_interval = interval;
  autoRestartOnSnippetChange(snippetID);
}

static void autoRestartOnSnippetChange(S snippetID) {
  snippetID = fsI(snippetID);
  if (autoRestartOnSnippetChange_on)
    if (eq(autoRestartOnSnippetChange_snippetID, snippetID)) ret;
    else fail("Watching multiple snippets not implemented");
  autoRestartOnSnippetChange_snippetID = snippetID;
  set autoRestartOnSnippetChange_on;
  autoRestartOnSnippetChange_schedule();
  preloadProgramTitle();
}

static void autoRestartOnSnippetChange_off() {
  if (!autoRestartOnSnippetChange_on) ret;
  stopTimer(autoRestartOnSnippetChange_timer);
  autoRestartOnSnippetChange_timer = null;
}

svoid autoRestartOnSnippetChange_schedule {
  autoRestartOnSnippetChange_timer = doLater_daemon(toMS(autoRestartOnSnippetChange_interval), f autoRestartOnSnippetChange_check);
}

svoid autoRestartOnSnippetChange_check ctex {
  try {
    S newMD5 = getSnippetMD5Silently(autoRestartOnSnippetChange_snippetID);
    if (!isMD5(newMD5)) { if (autoRestartOnSnippetChange_debug) print("autoRestartOnSnippetChange: no server value"); ret; }
    if (autoRestartOnSnippetChange_localMD5 == null)
      autoRestartOnSnippetChange_localMD5 = md5(DiskSnippetCache_get(psI(autoRestartOnSnippetChange_snippetID)));

    S localMD5 = autoRestartOnSnippetChange_localMD5;
    if (neq(localMD5, newMD5)) {
      if (autoRestartOnSnippetChange_simulate)
        print("Would upgrade now. " + localMD5 + " -> " + newMD5);
      else {
        infoBox("Upgrading " + programTitle() + " on snippet change");
        restartWithDelay(1000);
        sleep();
      }
    }
  } finally {
    if (autoRestartOnSnippetChange_debug) print("autoRestartOnSnippetChange: Done");
    autoRestartOnSnippetChange_schedule();
  }
}

Began life as a copy of #1010683