String Parser 2

common.kt

fun <T> List<T>.headTail(): Pair<T, List<T>> = Pair(first(), drop(1))

typealias Result = List<Pair<String, Int>>

fun iterString(rest: List<Char>, stringAcc: String, numberAcc: String, acc: Result): Result {
    if (rest.isEmpty()) {
        throw IllegalStateException()
    }
    val (head, tail) = rest.headTail()
    if (head.isLetter()) {
        return iterString(tail, stringAcc + head, numberAcc, acc)
    }
    return iterNumber(tail, stringAcc, "" + head, acc)
}

fun iterNumber(rest: List<Char>, stringAcc: String, numberAcc: String, acc: Result): Result {
    if (rest.isEmpty()) {
        return acc + Pair(stringAcc, numberAcc.toInt())
    }
    val (head, tail) = rest.headTail()
    if (head.isLetter()) {
        return iterString(tail, "" + head, "", acc + Pair(stringAcc, numberAcc.toInt()))
    }
    return iterNumber(tail, stringAcc, numberAcc + head, acc)
}

fun parseString(string: String): Result {
    return iterString(string.toList(), "", "", listOf())
}

fun main(args: Array<String>) {
    println(parseString("abc2edf4ee7"))
    
    assert("[(abc, 2), (edf, 4), (ee, 7)]"      == parseString("abc2edf4ee7").toString())
    assert("[(foo, 45), (bar, 99), (baz, 100)]" == parseString("foo45bar99baz100").toString())
    assert("[(bit, 0), (been, 1), (b, 0)]"      == parseString("bit000been1b0").toString())
}