Continuation-passing style

cps.coffee

#Direct style
factorial = (n) ->
  return 1 if n is 0
  n * factorial(n-1)

console.log factorial(3)
#6

#Continuation-passing style
eq_ = (n1, n2, fn) ->
  fn(n1 is n2)

sub_ = (n1, n2, fn) ->
  fn(n1 - n2)

mul_ = (n1, n2, fn) ->
  fn(n1 * n2)

factorial_ = (n, fn) ->
  eq_ n, 0, (isEqual) ->
    return fn(1) if isEqual
    sub_ n, 1, (nm1) ->
      factorial_ nm1, (facNm1) ->
        mul_(n, facNm1, fn)
    
factorial_ 3, (result) ->
  console.log result
#6