Convert callback-based APIs to promises

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Promisify: Convert callback-based APIs to promises
Promises are a popular solution to some of the drawbacks of the callback-style async APIs dominant in node.js libraries. But it's awkward to write an node.js application using promises when all the libraries you want to use are callback-based.
Hence Promisify. It converts callback-style APIs to use promises instead. To use it, you provide a concise description of the structure of the API to tell Promisify what to convert. For example, here is a sample which converts a substantial portion of the MongoDB driver API to Promises:
var promisify = require('promisify');

var promisify_collection = promisify.object({
    insert: promisify.cb_func(),
    remove: promisify.cb_func(),
    findOne: promisify.cb_func(),
    find: promisify.func(promisify.object({
        stream: promisify.func(promisify.read_stream())

var promisify_connection = promisify.object({
    collection: promisify.cb_func(promisify_collection),
    createCollection: promisify.cb_func(promisify_collection),
    dropCollection: promisify.cb_func()

var promisify_mongodb = promisify.object({
    connect: promisify.cb_func(promisify_connection)

var mongodb = promisify_mongodb(require('mongodb'));