Playing with kotlin: Implementing the Caesar Cipher

Caesar.kt

package aaa

import java.util.concurrent.ThreadLocalRandom

private fun caesar(key: Int) : (Char) -> Char {
    val seq = generateSequence('a' + key) { last -> if (last + 1 > 'z') 'a' else last + 1}
    return { c -> seq.elementAt(c - 'a') }
}

private fun unCaesar(key: Int) : (Char) -> Char {
    val seq = generateSequence('z' - (key - 1)) { last -> if (last + 1 > 'z') 'a' else last + 1}
    return { c -> seq.elementAt((c - 'a')) }
}

fun translate(translate: (Char) -> Char) : (String) -> String {
    return { input -> input
            .map { it.toLowerCase() }
            .map { if (it == ' ') it else translate(it) }
            .fold("") { acc, c -> acc + c } }
}

fun main(args: Array<String>) {

    val encode = { key: Int -> translate(caesar(key)) }
    val decode = { key: Int -> translate(unCaesar(key)) }

    val key = ThreadLocalRandom.current().nextInt(1, 26)

    check("askrible doxz" == decode(key)(encode(key)("askrible doxz"))) { "decoded encoded string matches input" }

    val phrase = "a fox ran aCroSS thE plAIN in the moonlight and said hi"
    val encodedPhrase = encode(key)(phrase)

    println("Phrase to find: $encodedPhrase\n\nVariations:")

    (1..25).forEach {
        val phraseByThisKey = encode(it)(phrase)
        if (encodedPhrase == phraseByThisKey)  {
            println("Found under key: $it, \"$phraseByThisKey\"  decoded: ${decode(it)(encodedPhrase)}")
        }
    }

    println("\nKey was: $key")
}