list.js

var reverseArray = function(a) {
  var r = []
  for(var i = a.length-1; i>=0 ; i--) {
    r.push(a[i])
  }
  return r
}
var prepend = function (v, l) {
  return {value:v, rest:l}
}
var arrayToList = function(a) {
  var l = null
  var r = reverseArray(a)
  for (var i = 0; i < r.length ; i++) {
    l = prepend(r[i], l)
  }
  return l
}
var listToArray = function (l) {
  var a = []
  for(var n = l ; n ; n = n.rest) {
    a.push(n.value)
  }
  return a
}
var nth = function (l, i) {
  if (l == null) return undefined
  var loop = function(l, i, c) {
    if (c == i && l != null) return l.value
    else if (c < i) return loop(l.rest, i, c+1)
    else return undefined
  }
  return loop(l, i, 0)
}