Different flow control ideas for CoffeeScript ("normal", "step", and "hop")

steps.coffee

# odd synchronus patterns -- purported 'monadic' flow control

events = require 'events'

step = (callback) ->
  first = true
  queue = []
  emitter = new events.EventEmitter
  
  this.step = (callback) ->  
    queue.push callback
    
    if queue.length == 1
      emitter.emit 'ready'
    next = ->
      c = queue.shift()
      if c
        c next
      else
        listener = (e) ->
          emitter.removeListener 'ready', listener
          c = queue.shift()
          c next
        emitter.on 'ready', listener
    process.nextTick ->
      if first
        first = false
        next()
    this
  this.step callback

hop = (callback) ->
  first = true
  queue = []
  emitter = new events.EventEmitter

  f = (callback) ->
    queue.push callback
    
    if queue.length == 1
      emitter.emit 'ready'
    next = ->
      c = queue.shift()
      if c
        c next
      else
        listener = (e) ->
          emitter.removeListener 'ready', listener
          c = queue.shift()
          c next
        emitter.on 'ready', listener
    process.nextTick ->
      if first
        first = false
        next()
    f
  f callback

module.exports = {
  step: step
  hop: hop
}

# examples of using various flow controls to sequence asynchronous events
if process.argv.indexOf 'test' > -1
  # an example of 'normal' sequenced flow control, aka "boomerang code"
  console.log 'normal'
  
  (->
    console.log 1
    (->
      console.log 2
      
      (-> console.log 3)()
    )()
  )()
  
  # monadic, somewhat jQuery-ish idiom. Chained methods become sequenced
  console.log 'step'
  
  step((next) -> console.log 1; next()).
    step((next) -> console.log 2; next()).
    step((next) -> console.log 3)
  
  # combinatorial idiom. Each function returns a new function
  timer = ->
    console.log 'hop'
  
    hop(
      (next) -> console.log 1; next()
    )(
      (next) -> console.log 2; next()
    )(
      (next) -> console.log 3; next()
    )
  setTimeout timer, 1

# outputs:
#   
#   normal
#   1
#   2
#   3
#   step
#   1
#   2
#   3
#   hop
#   1
#   2
#   3