Let's reimplement while and for loops in Kotlin with its omit-parens-around-last-function-argument syntax

README.md

Runnable version: http://try.kotlinlang.org/#/UserProjects/h98israna39btvnahdbghp21jm/ke0lmunnpg0ncu9gvkj8fihpna

Kotlin's function invocation syntax lets you close the parens early and supply the last function argument as a block like so:

foo(bar, baz) { it > squiggle }

Which is equivalent to:

foo(bar, baz, { it > squiggle })

Note that for this to work, the last argument passed to the function must be another function.

I thought, hey, why not use this to build my own loops...

FakeLoops.kt

fun wwhile (cond: () -> Boolean, body: () -> Unit) {
    if (cond()) {
        body()
        wwhile(cond, body)
    }
}

fun <T> ffor(initialise: () -> T, check: (T) -> Boolean, step: (T) -> T, body: (T) -> Unit) {
    var loopvar = initialise()
    wwhile({check(loopvar)}) {
        body(loopvar)
        loopvar = step(loopvar)
    }
}

fun main(args: Array<String>) {
    var counter = 0
    wwhile ({ counter < 5 }) {
        counter += 1
        print("While iteration $counter\n")
    }
    
    ffor({1}, {it <= 5}, {it + 1}) {
        i ->
        print("For iteration $i\n")
    }
}