The Y combinator in Kotlin. A single argument Y combinator is used to find the factorial of a number.

YCombinator.kt

fun main(args: Array<String>) {
    if (args.count() == 0) {
        println("Please input a number")    
    } else {
        try {
            val n = args[0].toInt()
            val factorial = y<Int,Int> {f-> { n->
                            if (n == 0)  1
                            else n * f(n - 1)
                            } }
            val fact = factorial(n)
            println("Factorial of $n is $fact")
        } catch(e: NumberFormatException) {
            println("Please input a number")        
        }
    }
}
fun <In, Out> y(f: (_:(n: In) -> Out)->(n: In) -> Out) : (n: In) -> Out {
        return {
            f(y(f))(it)
        }
    }

This is simply lovely. Thank you. ❤️

In my opinion, it is more understandable this way: fun <In, Out> y(f: (_: (n: In) -> Out) -> (n: In) -> Out): (n: In) -> Out = { p -> f(y(f))(p) }, but still great