The REPL

These days, most languages provide an interactive shell, and Kotlin is no exception. If you want to quickly write some code that you won't use again, then the REPL is a good tool to have. Some prefer to quickly test their methods, but you should always write unit tests rather than using the REPL to validate that the output is correct.

You can start the REPL by adding dependencies to the classpath in order to make them available within the instance. To give an example, we will use the Joda library to deal with the date and time. First, we need to download the JAR. In a terminal window, use the following commands:

$ wget https://github.com/JodaOrg/joda-time/releases/download/v2.9.4/joda-time-2.9.4-dist.tar.gz
$ tar xvf joda-time-2.9.4-dist.tar.gz

Now you are ready to start the REPL, attach the Joda library to its running instance, and import and use the classes it provides:

$ kotlinc-jvm -cp joda-time-2.9.4/joda-time-2.9.4.jar
Welcome to Kotlin version 1.1-M04 (JRE 1.8.0_66-internal-b17)
Type :help for help, :quit for quit
>>> import org.joda.time.DateTime
>>> DateTime.now()
2016-08-25T22:53:41.017+01:00