[Kotlin] fold / reduce

In kotlin, "fold" is same in Javascript's reduce. "fold" has initial value

"reduce" in kotlin, you don't give initial value

val colors = listOf("red", "blue", "green", "black")

    println(colors.reduce {
        acc, curr -> "$acc, $curr"
    }) // red, blue, green, black

    println(colors.map {it.length}.fold(0) {
            acc, curr -> acc + curr
    }) // 17