Array.prototype.toString = function() {
  var r = "["
  for (var idx = 0; idx < this.length; idx = idx + 1) {
    if (idx > 0)
      r = r + ", "
    r = r + this[idx].toString()
  }
  return r + "]"
}
Array.prototype.push = function(x) {
  this[this.length] = x
  this.length = this.length + 1
  return x
}
Array.prototype.pop = function() {
  var r = this[this.length - 1]
  this[this.length - 1] = undefined
  this.length = this.length - 1
  return r
}
Array.prototype.join = function(delim) {
  var r = ""
  for (var idx = 0; idx < this.length; idx++) {
    if (idx > 0)
      r += delim
    r += this[idx]
  }
  return r  
}
Array.prototype.concat = function(xs) {
  for (var idx = 0; idx < xs.length; idx++)
    this.push(xs[idx])
  return this
}