Fibonacci Sequence in Kotlin (2)

gistfile1.kt

import java.math.BigInteger
import kotlin.math.plus

fun main(args: Array<String>) {
    fibo().take(10).forEach { println(it) }
}

data class FiboEntry(val cur : BigInteger, val next : BigInteger)
private fun fibo() : FunctionStream<BigInteger> {
    var tmp = FiboEntry(BigInteger.ZERO, BigInteger.ONE)
    return FunctionStream({() ->
        val (cur, next) = tmp
        tmp = tmp.copy(next, cur plus next)
        cur
    })
}