Simple Pipe forward operator in Kotlin

function_composition_in_kotlin.kt

infix fun<R,S,T> ((R) -> S).andThen(f : ((S) -> T)): ((R) -> T) = { f(this(it)) }

val toUpperCase = { x: String -> x.toUpperCase()}
val exclaim = { x: String -> x + "!"}

val reverse = {r: List<String> -> r.asReversed() }
val head = { l: List<String> -> l[0]}

val shout = exclaim andThen toUpperCase

val last = reverse andThen head

val shoutLast = reverse andThen head andThen exclaim andThen toUpperCase

fun main(args: Array<String>){
	println(
		shoutLast(listOf("First", "Second", "Third", "Last"))
    	)
	// prints LAST!
}

PipeForward.md

Here I try to implement a simple pipe forward operator similar to |> operator in Elixir or the andThen operator in Scala

Let's say you have a need for doing something like this

val x = f("something")
val y = g(x)
val z = h(y)

This is also equivalent to saying:

val z = h(g(f("something"))) // Ugly

You can rewrite the above like this:

val z = (f andThen g andThen h)("something") // Better

OR if you want to reuse the composed function again:

// Much Better
val newFunc = f andThen g andThen h
val z = newFunc("something")
val a = newFunc("else)