Some helpers for working with immutable collections in Kotlin

ImmutableHelpers.kt

/**
 * Returns a new List with the element at [fromIndex] moved to [toIndex]
 */
private fun <T> List<T>.move(fromIndex: Int, toIndex: Int) = this.mapIndexed { index, element -> when {
    index == toIndex -> this[fromIndex]
    fromIndex < toIndex && index in fromIndex..toIndex -> this[index + 1]
    fromIndex > toIndex && index in toIndex..fromIndex -> this[index - 1]
    else -> element
} }

/**
 * Returns a pair of the head and the tail of this iterable.
 */
fun <T> Iterable<T>.pop(): Pair<T, List<T>> = this.first() to this.drop(1)