Super naive impl of a Clojure-style atom in CoffeeScript

atom.coffee

class Atom
    __state:
        initial: null
        current: null

    constructor: (state) ->
        @__state['current'] = state
        @__state['initial'] = state

    _cloneState: (phase = 'current') ->
        ###
        Returns a copy of a particular phase (i.e. either current or initial)
        of the atom state.
        ###
        obj = @__state[phase]
        if typeof(obj) == 'object'
            tmp_obj = {}
            for k, v of obj
                tmp_obj[k] = v
            return tmp_obj
        else if typeof(obj) == 'array'
            return obj.slice()
        else
            return obj

    _deref: ->
        @_cloneState()

    _swap: (fn, args...) ->
        curr_state = @_deref()
        @__state['last'] = curr_state
        args.splice 0, 0, curr_state
        @__state['current'] = fn.apply(fn, args)
        @

    _reset: (new_val = null) ->
        new_state = @_cloneState('initial')
        if new_val?
           new_state = new_val
        @__state['current'] = new_state
        @

deref = (atom) ->
    ###
    Return a copy of the current state of the atom. Modifications to the
    value returned will not update the state of the atom. Use 'swap' for
    that.
    ###
    atom._deref()

swap = (atom, fn, args...) ->
    ###
    Transform the current state of the atom by calling 'fn' with arguments
    'args'.
    ###
    atom._swap fn, args

reset = (atom, new_val) ->
    ###
    Set the value of atom without regard to its current value. If
    'new_val' is not provided, then resets value of atom to its
    initial value.
    ###
    atom._reset(new_val)

app_state = new Atom
    foo: "bar"
    baz: "qux"

###
Example:

Adds a new key to 'app_state'.

Obviously this requires some knowledge of the shape of the app state in the
atom.

###

_func_for_swap = (state_val) ->
    # 'state_val' will be the value of a dereferenced atom.
    state_val['quux'] = 'quuux'
    state_val

# Look at the current state
console.log deref(app_state)
# Modify the atom state
swap app_state, _func_for_swap
# Should have 'quux' key now
console.log deref(app_state)
# Set it back to its original value
reset app_state
# Should match initial state
console.log deref(app_state)