fn main(){
    let mut a = (1..10).peekable();
    let b = std::iter::repeat(()).map(|()| {
        let mut current = a.next();
        if let Some(current) = current.as_mut() {
            if let Some(next) = a.peek() {
                if next % 2 == 1 { *current *= 2 }
            }
        }
        current
    });
}