Gerbrand on ICT » scala

Scala and Java

gerbrand — Fri, 05 Mar 2010 12:53:22 +0000

When you say Ruby, you say Rails. When you say Groovy, you say unit-tests, scripting and integration. Well that might be over-acted, but that’s what most people make of it.
Some people remark Scala is best-suited for backend-code, or very good at parallel code, but apart from that I’ve never heard that Scala is the language for the Lift framework. Or the language to use when you want to create multi-threaded code. What I hear mostly, Scala is the new Java.

Would that be true: could you use Scala as a dropin replacement for Java, as, let’s say, a Java 2.0 or Java 8?

In the coming postings I want to investigate that claim using my knowledge of experience in Java/J2EE and my complete lack of experience in Scala. Can you say to you’re developers, or yourself, from this day on, we’ll use Scala instead of Java to do our development?

For now, I found this nice presentation I want to share: Introduction To Scala For Java Developers by Miles Sabin.

Internal DSLs in Scala

gerbrand — Sun, 15 Mar 2009 20:42:30 +0000

The language Ruby is very extendible, making the language very suitable for designing internal DSL’s – custom languages for domain, or single purpose as you could call it. Togetter with a collegue I wrote on Internal DSLs in Ruby some time ago for my company’s website and newsletter. Scala is also quite extensible, and type safe. How good will Scala be on the creation on Internal DSL? Bill Venners write about this subject on Artima: Comparing DSLs in Ruby and Scala.

Scala and Twitter update

gerbrand — Sun, 15 Mar 2009 12:50:40 +0000

Recently wrote about a presentation on the interesest in Scala of tech-lead at Twitter. On another site a Twitter developer wrote half a year ago that several people at his company are learning Scala. On the Twitter dev site I found a client-application for Twitter written in Scala. The application looks simple, but I make to little use of Twitter to know how good it compares. According to another article I found via Google, part of Twitter is (re)implemented in Scala!

Scala and twitter

gerbrand — Wed, 04 Mar 2009 16:01:42 +0000

By stumbled on a presentation by API lead of Twitter on Scala. For a moment I hoped Twitter was developed, but the language used at Twitter is Ruby. The speaker investigated a few current-date programming languages and found Scala met his needs best. See Why Scala.

Combining Flex and Scala using Liftweb and BlazeDS

gerbrand — Sun, 18 Jan 2009 17:05:03 +0000

I wanted to setup a sample project that uses Flex and Scala. I followed the excellent tutorial on FlexOnRails: Integrating Flex, BlazeDS, and Scala/Lift. The tutorial helps a lot explaining how to set up your sample project. Unfortunately the tutorial is a bit outdated with regard to latest versions. Fortunately I could solve all problems! I’ll list the problems I had. Also, I’ll post my project. I won’t redo the tutorial, as I certainly couldn’t to a better job then Derek Wischusen.

First problem I had, was getting my backend compiled. The liftweb has changed slightly, as a result the class Boot.scala didn’t work anymore. I could solve it by downloading the latest Liftweb framework, version 0.9. I copied & pasted the Boot.scala from the sites/examples dir. After a few tweaks (removing code I didn’t need), the project compiled successfully!
Then I wanted to setup the flex project. That was quite easy, using the latest version of Flexbuilder (version 3.0.2.214193).
I setup flexbuilder to deploy in the backend/webapp directly, as is explained in the tutorial.
I ran the project by running the following maven commands in the backend subdir:
mvn package
mvn jetty:run
While running the example, I got a AbstractMethodError. I wasn’t the first person to get that error, as I found on the Liftmailinglist. I could fix the problem by using Scala version 2.7.1 for my own project. All in all, when using bleeding-edge technologies, having the latest version isn’t good always!
After that I ran the project again. Now I get a NullPointerException, seems the line val msgBroker = MessageBroker.getMessageBroker(null) returns Null.
Turned out I forgot to update the web.xml, the Flex servlet and other configuration has to be added.

I named the sample project Elegante. Download the source here: elegante.zip. For explanation see the original tutorial.

Scala release

gerbrand — Wed, 14 Jan 2009 23:36:47 +0000

The final release of Scala 2.7.3 is out! You can download the release from the scala-download page.

Some background: Scala is a elegant language that runs on the JavaVM. Unlike languages like Ruby and Groovy, Scala is statically typed. One of the reasons a lot of people like dynamic languages more than Java, is because Java is very verbose. That verbosity is, amongst others, because of its type-system.
However, unlike Java the typing-system is much more elegant and flexible. Because Scala can infer types, you’ll have to define types only when necessary. Look for example at the following code (taken from the Scala website):

object Maps {
  val colors = Map("red" -> 0xFF0000,
                   "turquoise" -> 0x00FFFF,
                   "black" -> 0xFFFFFF,
                   "orange" -> 0xFF8040,
                   "brown" -> 0x804000)

  def main(args: Array[String]) {
    for (name <- args) println(
      colors.get(name) match {
        case Some(code) =>
          name + " has code: " + code
        case None =>
          "Unknown color: " + name
      }
    )
  }
}

There are no explicit type definitions, eventhough every defined value is statically typed. The scala compiler can infer that the val colors should have type scala.collection.immutable.Map[java.lang.String,Int]. Compare that to Java, where you’d have to use Map several times.
Minor sidenote: there are languages that have an even more advanced typing system, see, this nice article.

Furthermore, another what’s very much to like about new dynamic languages is it’s extendibily. You can extent a language like Ruby or Groovy, and create a new internal language. Eventhough Scala is statically typed, in Scala this is possible as well.
Let’s say you want a sort method for the general Array type. This can be accomplished with the following code:

/* Defines a new method 'sort' for array objects */
object implicits extends Application {
  implicit def arrayWrapper[A](x: Array[A]) =
    new {
      def sort(p: (A, A) => Boolean) = {
        util.Sorting.stableSort(x, p); x
      }
    }
  val x = Array(2, 3, 1, 4)
  println("x = "+ x.sort((x: Int, y: Int) => x < y))
}

There’s a lot more exciting, as a last example, I put a code-snippet that demonstrates how XML is integrated in Scala:

  val header =
    
      </span>
        { <span class="str" style="color: red;">"My Address Book"</span> }
      <span class="tag" style="color: blue;">
    ;

  val people = new AddressBook(
    Person("Tom", 20),
    Person("Bob", 22),
    Person("James", 19));

  val page =
    
      { header }
      
       { people.toXHTML }
      
    ;

Finally, an example of a quicksort taken from this sample website. Impressive, but I am to much unexperienced in Scala to grasp that code immediately:

  def sort[A <% Ordered[A]](xs: List[A]): List[A] = {
    xs match {
        case List() => xs
        case _ =>  sort(for(item <- xs.tail if item < xs.head) yield item) ::: List(xs.head) ::: sort(for(item <- xs.tail if item >= xs.head) yield item)
    }
  }

Below a book about Scala I recently read