Serial/Parallel functions in CoffeeScript

async.coffee

# Asynchronous DSL for CoffeeScript

serial = (f) ->
  next = -> arr.shift().apply(null, arguments) if arr.length
  arr = (v for k, v of f(next))
  next()
  null

parallel = (f, after = ->) ->
  res = {}; arrc = 0
  arrc++ for k, v of f
  for k, v of f
    do (k, v) ->
      v (args...) -> 
        res[k] = args
        if not --arrc then after(res)
  null

#########################
# serial test w/ mock fs

fs =
  open: (_, _, cb) -> console.log('[fs.open]'); cb(0, {a_fake: 'file object'})
  write: (f, _, cb) ->  console.log('[fs.write]', f); cb(0, f)
  close: (f, cb) -> console.log('[fs.close]', f); cb(0, f)

# serial accepts a function with one "next" continuation,
# which returns a list of steps to execute in order
# you can label your steps anything, but numbers look good:

serial (next) ->
  1: -> fs.open('file', 'w', next)
  2: (err, f) -> fs.write(f, 'Apples', (a...) -> next(a..., f))
  3: (err, written, f) -> fs.close(f, next)
  last: -> console.log 'Serial test complete.'

##############################
# parallel test with timeouts

console.log('Waiting for parallel test...')

# parallel accepts a list of steps to execute in any order
# (each step is passed a "done" continuation to call when finished)
# and an (optional) last function to call with results of each step

parallel
  A: (done) -> setTimeout((-> done(new Date)), 1000)
  B: (done) -> setTimeout((-> done(new Date)), 3000)
  C: (done) -> setTimeout((-> done(new Date)), 2000)
  (res) -> console.log 'Parallel results:', JSON.stringify(res)