class fn
  @id         = 0
  @observable = []

  @watch: (val = null) ->
    value = @observable[@id++]

    class getSet
      constructor: (val) ->
        value or=
          value:  undefined
          before: []
          after:  []

        return if val?
          fn value.value, val for fn in value.before
          value.value = val
          fn value.value, val for fn in value.after
        else
          value.value

      @before: (cb) ->
        value.before.push cb
        @
      @after: (cb) ->
        value.after.push cb
        @
      @subscribe: (cb) -> @after(cb)


    if val? then getSet(val)
    return getSet
window.watch = fn.watch





a = fn.watch 42
b = fn.watch 111111
console.log 'a: ' + a()
b(2222222)
a(23)
console.log 'b: ' + b()
console.log 'a: ' + a()
a.before (from, to) ->
  alert 'change from: ' + from + ' to: ' + to
a(55)
console.log 'a: ' + a()