Monadic wrapper for Express API

index.js

var express = require('express')
var app = require('./wrapper')(express())

require('./routes')(app)

app.listen(8080)
console.log('Listening on http://localhost:8080')

routes.sjs

module.exports = function(app) {
  app.get('/', function(req, res) {
    return $do {
      html <- app.render('index')
      return { status: 200, body: html }
    }
  })
}

wrapper.js

var curry  = require('core.lambda').curry
var Future = require('data.future')

module.exports = function(app) {
  var slice   = Function.call.bind([].slice)
  var methods = ['get', 'post', 'put', 'delete', 'all']

  /**
   * Renders the given view `name`.
   *
   * @method
   * @summary String → Object → Future[Error, String]
   */
  var _oldRender = app.render
  app.render = curry(2, render)
  function render(name, options) {
    return new Future(function(reject, resolve) {
                        _oldRender.call( app
                                       , name
                                       , options || {}
                                       , function(error, html) {
                                           if (error)  reject(error)
                                           else        resolve(html) })})
  }

  /**
   * Handles requests.
   *
   * @method
   * @summary String, Function... → Express
   */
  methods.forEach(function(method) {
    var original = app[method]
    app[method] = function Router(route) {
      // `app.get()` is overloaded
      if (method === 'get' && arguments.length === 1)  return original.call(app, route)

      var middlewares = slice(arguments, 1, -1)
      var fn          = arguments[arguments.length - 1]
      var args        = [route].concat(middlewares).concat(handler)

      original.apply(this, args)
      return app

      function handler(req, res) {
        fn(req, res).fork(handleError(res), send(res)) }
    }
  })

  /**
   * Sends some response to the user.
   *
   * @method
   * @summary Response → Contents → Void
   */
  send = curry(2, send)
  function send(res, contents) {
    res.set(contents.headers)
    res.send(contents.status || 200, contents.body)
  }

  /**
   * Handles errors.
   *
   * @method
   * @summary Response → Error → Void
   */
  handleError = curry(2, handleError)
  function handleError(res, error) {
    throw error
  }

  // -- Exports --------------------------------------------------------
  return app
}