Lazy evaluation implemented in Javascript (well just because it has strict evalution)

lazy.js

function empty_list() {
  return null;
}

// concat :: [[a]] -> [a]
function concat(xs) {
  return foldr(append, empty_list, xs);
}

// foldr :: (a -> b -> b) -> b -> [a] -> b
function foldr(f, z, xs) {
  if (xs == empty_list) {
    return z;
  } else {
    return f(car(xs), foldr(f, z, cdr(xs)));
  }
}

// (++) :: [a] -> [a] -> [a]
function append(xs, ys) {
  if (xs == empty_list) {
    return ys;
  } else {
    return cons(function() {
      return car(xs);
    }, function() {
      return append(cdr(xs), ys);
    });
  }
}

var head = car;
var tail = cdr;

function tail(list) {
  return cdr(list);
}

function map(f, xs) {
  if (xs == empty_list) {
    return empty_list;
  } else {
    return cons(function() {
      return f(car(xs));
    }, function() {
      return map(f, cdr(xs));
    });
  }
}

function cons(x, y) {
  return function _cons(m) {
    return m(x, y);
  };
}

function fst(x) {
  return apply(x);
}

function snd(_, y) {
  return apply(y);
}

function car(z) {
  return z(fst);
}

function cdr(z) {
  return z(snd);
}

function apply(expr) {
  if (typeof expr === 'function') {
    if (expr.name == "_cons") {
      // the expr is a list (current a workaround)
      // probably apply should be called as eval
      return expr;
    } else {
      return expr();
    }
  } else {
    return expr;
  }
}

function take(n, xs) {
  if (n === 0) {
    return empty_list;
  } else if (xs === empty_list) {
    return empty_list;
  } else {
    return cons(function() {
      return car(xs);
    }, function() {
      return take(n - 1, cdr(xs));
    });
  }
}

function drop(n, xs) {
  if (n === 0) {
    return xs;
  } else if (xs === empty_list) {
    return empty_list;
  } else {
    return drop(n - 1, cdr(xs));
  }
}

function list() {
  var args = Array.prototype.slice.call(arguments);
  return args.reduceRight(function(acc, n) {
    return cons(function() { return apply(n); }, function() { return acc });
  }, empty_list);
}

function doAll(f, list) {
  if (list !== empty_list) {
    f(car(list));
    doAll(f, cdr(list));
  }
}

function one() {
  console.log('called 1');
  return 1;
}

function two() {
  console.log('called 2');
  return 2;
}

function three() {
  console.log('called 3');
  return 3;
}

function four() {
  console.log('called 4');
  return 4;
}

l = concat(list(list(one), list(two)));
ll = list(three, four);
lll = append(l, ll);

function double(x) { return x * 2; }
function log(x) { console.log(x); }
function sum(a, b) { return a + b };

//doAll(log, concat(list(list(one), list(two))));
//console.log(foldr(sum, 0, list(1,2,3,4)));
//doAll(log, l);
doAll(log, take(3, map(double, lll)));
// called 1
// 2
// called 2
// 4
// called 3
// 6