> For the complete documentation index, see [llms.txt](https://gold.gitbook.io/kotlin/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gold.gitbook.io/kotlin/collections/aggregate-operations/reduceright.md).

# reduceRight

```kotlin
public inline fun <S, T: S> List<T>.reduceRight(operation: (T, acc: S) -> S): S {
    val iterator = listIterator(size)
    if (!iterator.hasPrevious)
        throw UnsupportedOperationException("Empty list can't be reduced.")
    var accumulator: S = iterator.previous()
    while (iterator.hasPrevious()) {
        accumulator = operation(iterator.previous(), accumulator)
    }
    return accumulator
}


val list = listOf(1, 2, 3, 4, 5)
println(list.reduceRight{ before, acc -> before + acc })  // 15
```