Basic function declaration and usage

The most common first program that programmers write to test a programming language is the Hello, World! program. It is a full program that just displays Hello, World! as text on the console. We are also going to start with this program, because in Kotlin it is based on a function and only on a function (no class is needed). So the Kotlin Hello, World! program looks as follows:

    // SomeFile.kt 
    fun main(args: Array<String>) {     // 1 
        println("Hello, World!")        // 2, Prints: Hello, World! 
    } 

1. A function defines a single parameter, args, which contains an array of all arguments used to run the program (from the command line). It is defined as non-nullable, because an empty array is passed to a method when the program is started without any arguments.
2. The println function is a Kotlin function defined in the Kotlin standard library that is equivalent to the Java function System.out.println.

This program tells us a lot about Kotlin...