if (x != null) {

if

x

null

@Given("^We want to execute a constraint graph 10000 times$")
    fun `We want to execute a constraint graph 10000 times`(){
        TODO()
    }

@Given

val x: Any = Unit
if (x is Int && x is String) {
  x.length + x
}

if (not isEmpty())
if (!isEmpty())
if (isNotEmpty())
if (isEmpty().not())

sealed class Expression
data class Const(val value: Int) : Expression()
data class Add(val left: Expression, val right: Expression) : Expression()
data class Neg(val expr: Expression) : Expression()

fun eval(expr: Expression): Int = when (expr) {
    is Const -> expr.value
    is Add -> eval(expr.left) + eval(expr.right)
    is Neg -> -eval(expr.expr)
}

fun main(args: Array<String>) {
    println(eval(Add(Const(1), Neg(Const(2)))))
}

Add(left, Const(0))

left