Function choice2

pub fn choice2<'arn, 'grm: 'arn, 'a, O, E: ParseError>(
    p1: &'a impl Parser<'arn, 'grm, O, E>,
    p2: &'a impl Parser<'arn, 'grm, O, E>,
) -> impl Parser<'arn, 'grm, O, E> + 'a