loicdescotte

Scala for comprehension translation helper

"For comprehension" is a another syntaxe to use map, flatMap and withFilter (or filter) methods.

yield keyword is used to aggregate values in the resulting structure.

This composition can be used on any type implementing this methods, like List, Option, Future...

sadache

This post aims to document a practical design implementation we came up with when designing some APIs in Scala. Of course the concept is not Scala specific and applies to other functional languages.

If you don't want to go into the full introduction, this post talks about how Applicatives are too restrictive and breaking them into two independent components can be interesting for Contravariant and Invariant Functors. Jump to implementation attached.

We are taking JSON serialization/deserialization as a motivating example.

JsValue is the name of the type that represents the JSON AST. What we need is to be able to read a JsValue and produce an A:

trait Reads[A]{

guillaumebort

def Secured[A](username: String, password: String)(action: Action[A]) = Action(action.parser) { request =>
  request.headers.get("Authorization").flatMap { authorization =>
    authorization.split(" ").drop(1).headOption.filter { encoded =>
      new String(org.apache.commons.codec.binary.Base64.decodeBase64(encoded.getBytes)).split(":").toList match {
        case u :: p :: Nil if u == username && password == p => true
        case _ => false
      }
    }.map(_ => action(request))
  }.getOrElse {
    Unauthorized.withHeaders("WWW-Authenticate" -> """Basic realm="Secured"""")

oodavid

Deploy your site with git

This gist assumes:

• you have a local git repo
• with an online remote repository (github / bitbucket etc)
• and a cloud server (Rackspace cloud / Amazon EC2 etc)
  • your (PHP) scripts are served from /var/www/html/
  • your webpages are executed by apache
• apache's home directory is /var/www/

dcsobral

dcs@ayanami:~/tmp$ scala BenchCode 100000 5 100
Warming up Adrian, functional/indexOf
Warming up Adrian, functional/span
Warming up Adrian, imperative/ArrayBuffer
Warming up Adrian, imperative/ListBuffer
Warming up user unknown, recursive
Warming up user unknown, fold
Warming up paradigmatic, recursive
Warming up paradigmatic, fold
Warming up soc

dcsobral

// Question at http://stackoverflow.com/q/7084212/53013
// Results at https://gist.github.com/1152764

import scala.collection.mutable.{ArrayBuffer, ListBuffer}
import scala.util.Random

object BenchCode extends scala.testing.Benchmark with Algorithms {
  var xs: List[Int] = Nil
  var acc = 0
  var code: List[Int] => List[Int] = (identity _)