Que asynchronous flow control coffeescript micro library

Que.coffee

Que = new: ->
  Q = []
  Q.then = (fn, args...) -> Q.push(-> args.push Q.next; fn.apply null, args); @
  Q.next = (err) -> Q.splice 0, Q.length-1 if err; Q.shift()?.apply null, arguments
  Q.finally = (fn, args...) -> Q.push(-> fn.apply null, args); Q.next()
  Q

# --

Q = Que.new()

fn1 = (a, cb) -> setTimeout (-> console.log a; cb()), 400
end = (err) -> console.log 'd, err:', err

console.log '--'
Q.then(fn1, 'hello')
Q.then(fn1, 'again')
Q.push ->
  console.log 'a'
  Q.next()
Q.push ->
  console.log 'b'
  Q.next()
Q.push ->
  console.log 'c'
  Q.next()
Q.then fn1, 'goodbye'
Q.finally(end)