Sequential execution

Use of creationix Step library to control the execution flow in case of deeply nested callbacks may be difficult in coffee. Step() treats non-undefined values returned from steps as immediate (sync) result for the subsequent callback. Since coffee treats anything as expression, and implicit values are often returned from functions, subtle and hard to track logic errors may occur.

In particular, one must ensure undefined is returned from async steps.

In my pattern I try to not throw too much, so I must write such ugly (and not coffee-y) constructs: if err next err return

instead of beautiful return next err if err

Another issue with Step() is that is completely spoils @ (it's set to point to the next step), while it's feasible to have kinda "context" object available in steps as @.

Thus, assuming that, and that sync functions are rarely used in Step() (and can be easily mimicked as next null, immediate-result, if needed), wrote a barebone analog called Next:

Next = (context, steps...) ->
	next = (err, result) ->
		unless steps.length
			throw err if err
			return
		fn = steps.shift()
		try
			fn.call context, err, result, next
		catch err
			next err
		return
	next()

Below is example:

exec = () -> Next {foo: 'bar'},
	(err, result, next) ->
		console.log 'first', arguments
		return next err if err
		throw 'Catch me1!'
		next 'err1', 'res1'
	(err, result, next) ->
		console.log 'second', arguments
		return next err if err
		next 'err2', 'res2'
	(err, result, next) ->
		console.log 'third', arguments
		return next err if err
		next 'err3', 'res3'

try
	exec()
catch err
	console.log 'CAUGHT', err

Feedback and critisism is welcome.

Have fun!

--Vladimir Dronnikov