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Short intro to Scala

Welcome!

You’re probably here because you’ve heard that Scala is a cool programming language and you’d like to learn more about it. Because, hey, it’s object-oriented and functional at the same time!

I’ll show you something very basic at first: a bit more “personal” version of the famous “Hello World” program.

The following little Scala program will ask for your name and then it’ll print “Hello, <Your name>!” to the console.

object WordApp extends App {
  val name = scala.io.StdIn.readLine("What's your name? \n")
  println("Hello " + name + "!")
}

In case this is really your very first Scala program, you might ask: how do I make the above example App come alive? Well, you have more than one option. (Btw, you’ll have to get used to this in the world of Scala – usually there is more than one way to do things. I admit that this fact is not very beginner-friendly, but later it will come handy.)

At first let’s not complicate things with IDEs and GUIs, let’s just use the console tools available. Another post will show you how to use Eclipse or IntelliJ IDEA for Scala development.

Setting up our first Scala project with SBT

SBT stands for the “Scala Build Tool”. It’s like ‘gradle’ or ‘maven’ for Java. If you are not familiar with build tools, then consult the Internet :)

Installing SBT

Check the latest install documentation here: http://www.scala-sbt.org/release/docs/Setup.html

Creating the “Hello” project

It won’t be as painful as it might seem at first :)

It’s really just two steps: writing the source files to an appropriate location, and give some hints to SBT about how it should do its work.

The source tree

SBT expects the source Scala files (and tests, but we won’t have any for now) to be in a specific folder. So, let’s go ahead and create them (I’m assuming you have soma basic experience with the Linux command line):

mkdir -p src/main/scala
mkdir -p src/test/scala

Within these two directories we’ll usually have somewhat parallel sub-directories with packages for our main source files and tests. Now we won’t have any packages or tests, for simplicity.

The source file we’ll edit must be in the “src/main/scala/” folder. Let’s name it “App.scala”. (You can use another name, but it wouldn’t be a good idea to change the “.scala” extension.) And its contents, as above: 

object WordApp extends App {
  val name = scala.io.StdIn.readLine("What's your name? \n")
  println("Hello " + name + "!")
}
So, just save this into a file “src/main/scala/App.scala”.

The “build.sbt” file

This little confg-like file will set some useful settings for your project, and also contains a list of dependencies.

It should be saved to the top-level directory of your project, next to the “src” folder.

And its contents:

name := "01_grader_app"

version := "0.1"

exportJars := true

scalaVersion := "2.11.8"

Note the empty lines! Looks stupid, but they are actually necessary, if you are using an older SBT version, prior to 0.13.7. (Here is an explanation.)

To check which version you have, run: 

sbt 'inspect sbtVersion'

With newer versions (from 0.13.7 up) you don’t need the empty lines.

More help with SBT

Let’s run it already!

Standing in the root of your project, just say: 

sbt run

I hope it works for all of you now! :)

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