p.coffee

class P
	notify = (d, value) ->
		P.run -> d.fulfil(d.onFulfil?(value))
	fulfil: (value) ->
		@value = value
		@dependencies.forEach (d) ->
			notify(d, value)
		return this
	then: (d) ->
		wrapped = new P(d)
		if @value? then notify(wrapped, @value)
		else @dependencies = @dependencies.concat(wrapped)
		return wrapped
	constructor: (@onFulfil) ->
		@dependencies = []
	@combine: (args...) ->
		remaining = args.length
		waiting = new P
		args.forEach (promise) -> promise.then(->
			remaining = remaining - 1
			if remaining == 0
				waiting.fulfil(args.map((p) -> p.value))
		)
		return waiting
	@run: (f) -> setTimeout f, 0

count_to = (n) ->
	while n > 0
		n = n - 1

a = new P()
b = a.then (v) -> console.log('b'); v + 1
c = b.then (v) -> console.log('c'); count_to 100000; v ** 2
d = P.combine(a,b,c).then((args) -> console.log 'd'; args)
logStatus = -> console.log [a, b, c, d].map((v) -> v.value)
logStatus()
a.fulfil (-> console.log 'a'; 5)()
setTimeout (->
	count_to 10000000;
	setTimeout(logStatus, 0)
	setTimeout(logStatus, 1000)
	logStatus()), 0
logStatus()