fn main() {
    println!("{:?}", scanl(|x, y| x + y, 0, &[1, 2, 3, 4, 5]));
}

fn scanl<T, F>(op: F, initial: T, list: &[T]) -> Vec<T>
where
    F: Fn(&T, &T) -> T,
{
    let mut acc = Vec::with_capacity(list.len());
    acc.push(initial);

    list.iter().fold(acc, |mut acc, val| {
        acc.push(op(val, acc.last().unwrap()));
        acc
    })
}