JS computed and observable variables

obs.coffee

frames = []
addFrame = (frame) -> frames.push frame || []
addToStack = (obs) -> if frames.length > 0 then frames[frames.length-1].push obs
mergeFrame = (obs) -> if frames.length > 0 then frames[frames.length-1] = frames[frames.length-1].concat obs
popFrame = ->
    popped = unique frames.pop()
    mergeFrame popped
    return popped

unique = (frame) ->
    set = {}
    nframe = []
    for obs in frame
        if obs.id not of set
            set[obs.id] = true
            nframe.push obs
    return nframe

notify = (bindings,value) ->
    newbindings = []
    for call in bindings
        if call value
            newbindings.push call
    return newbindings

obsids = 0
computed = (tocompute) ->
    watched = []
    cached  = null
    dirty   = true
    evaluate = ->
        if dirty
            dirty = false
            addFrame()
            value = tocompute()
            watched = popFrame()
            if value != cached
                for obs in watched
                    obs.bind -> dirty = true; false;
                cached = value
        else mergeFrame watched
        return cached
    evaluate.bind = (call) -> obs.bind(-> call evaluate()) for obs in watched
    evaluate.tocompute = tocompute
    evaluate()
    return evaluate

observable = (value) ->
    if value.id
        return value
    cached = value
    bindings = []
    evaluate = (value) ->
        addToStack evaluate
        if value? and value != cached
            cached = value
            bindings = notify bindings, value
        return cached
    evaluate.id = obsids++
    evaluate.bind = (call) -> bindings.push call
    return evaluate