Promise in lua

promise.lua

local P = {}

P.reject = function (err)
	return P.new(function (fulfill, reject) 
		reject(err)
	end)
end

P.resolve = function (r)
	return P.new(function (fulfill, reject) 
		fulfill(r)
	end)
end

P.new = function (start)
	local p = {}

	p._fulfill = function (r)
		if p._next then p._next._startOk(r) end
	end

	p._reject = function (err)
		if p._next then p._next._startErr(err) end
	end

	if start then
		set_immediate(function ()
			start(p._fulfill, p._reject)
		end)
	end

	local callNext = function (cb, prevRes)
		if cb == nil then return end

		local ok, r = pcall(function () 
			return cb(prevRes)
		end)

		if not ok then
			if type(r) ~= 'table' then
				error(r)
			end
			r = Promise.reject(r)
		elseif not (r and type(r) == 'table' and r._isPromise) then
			r = Promise.resolve(r)
		end

		r.thenDo(function (r)
			p._fulfill(r)
		end, function (err)
			p._reject(err)
		end)
	end

	p._startOk = function (r)
		callNext(p._cbOk, r)
	end

	p._startErr = function (err)
		callNext(p._cbErr, err)
	end

	p._isPromise = true

	p.catch = function (cbErr)
		return p.thenDo(nil, cbErr)
	end

	p.thenDo = function (cbOk, cbErr)
		local _next = P.new()
		p._next = _next
		_next._cbOk = cbOk
		_next._cbErr = cbErr
		return _next
	end

	return p
end

Promise = P

test.lua

require('promise')

Promise.new(function (fulfill, reject)
	reject(42)
end).thenDo(function (r)
	info('fulfill', r)
end, function (err)
	info('reject', err)
	return 43
end).thenDo(function (r)
	info('step3', r)
	return 44
end).thenDo(function (r)
	info('step4', r)
end).thenDo(function ()
	return Promise.reject(52).thenDo(function ()
	end, function ()
		return Promise.resolve(53).thenDo(function ()
			return 33
		end)
	end).thenDo(function (r) 
		info('last', r)
	end)
end)