Kotlin from the ground up, Part 2 - the REPL

In part 1 you set up a barebones command-line Kotlin environment with proper PATH settings and learned how to compile Kotlin source into a runnable .class or .jar file. Now, let's explore the interactive REPL.

Invoke as below:

> kotlinc
Welcome to Kotlin version 1.3.72 (JRE 1.8.0_181-b13)
Type :help for help, :quit for quit
>>>

and let's try a few cool & useful things such as how to check what a Kotlin object's class is via reflection :

>>> System.getProperties()
res0: java.util.Properties! = { ....
..... }

/* What type of object is this returning? */
>>> val sp = System.getProperties()

/* It's not a string, it's a Properties object */
>>> sp::class.simpleName
res1: kotlin.reflect.KClass<out java.util.Properties!> = class java.util.Properties

/* Compare to an integer */
>>> val x = 5
>>> x::class
res3: kotlin.reflect.KClass<out kotlin.Int> = class kotlin.Int

/* You can reflect directly on literals, not just variables */
>>> 42::class
res4: kotlin.reflect.KClass<out kotlin.Int> = class kotlin.Int

>>> "hello there"::class
res5: kotlin.reflect.KClass<out kotlin.String> = class kotlin.String

/* What members does the class provide? Let's make a helper 
  function to show them properly */
>>> fun listMembers(x:Any) { println(); for (m in x::class.members) println(m) }

>>> listMembers("I'm a string")
val kotlin.String.length: kotlin.Int
fun kotlin.String.compareTo(kotlin.String): kotlin.Int
fun kotlin.String.get(kotlin.Int): kotlin.Char
fun kotlin.String.plus(kotlin.Any?): kotlin.String
fun kotlin.String.subSequence(kotlin.Int, kotlin.Int): kotlin.CharSequence
fun kotlin.String.chars(): java.util.stream.IntStream!
fun kotlin.String.codePoints(): java.util.stream.IntStream!
fun kotlin.String.equals(kotlin.Any?): kotlin.Boolean
fun kotlin.String.hashCode(): kotlin.Int
fun kotlin.String.toString(): kotlin.String

I might add more REPL stuff to do here, but for now, you can head on to Part 3 where you finally build a GUI app using Kotlin and the TornadoFX framework!