Lisp list functions in CoffeeScript

lisp.coffee

cons = (h, t) -> (m) -> m(h, t)
car = (x) -> x((h, t) -> h)
cdr = (x) -> if x then x((h, t) -> t) else null

map = (ls, f) ->
  cons (f car ls), if cdr ls then map cdr(ls), f else null

foldl = (ls, f, n) ->
  f (car ls), if cdr ls then foldl (cdr ls), f, n else n

foldr = (ls, f, n) ->
  f (if cdr ls then foldr (cdr ls), f, n else n), car ls

filter = (ls, fn) ->
  if fn car ls
    cons (car ls), if cdr ls then filter (cdr ls), fn else null
  else
    filter (cdr ls), fn

append = (ls1, ls2) ->
  if ls1 == null
    ls2
  else
    cons (car ls1), append (cdr ls1), ls2

length = (ls, n=0) ->
  if ls == null
    n
  else
    length (cdr ls), n + 1

index = (l, i) ->
  if i == 0
    car l
  else
    index (cdr l), i - 1

a = cons 1, cons 2, cons 3, cons 4, null
b = cons 5, cons 6, cons 7, cons 8, null
z = append a, b
y = map z, (x) -> x * x
x = filter z, (x) -> x > 2

tostring = (l) -> foldl l, ((x, y) -> String(x) + ',' + String(y)), "nil"

alert (tostring z) + ' has length ' + (length z)
alert 'The 4th element of ' + (tostring y) + ' is ' + (index y, 3)
alert tostring x