Function select_random 

pub fn select_random<'rule, T, M, R>(
    _: &T,
    rs: &mut dyn Iterator<Item = (&'rule R, Update<T, M>)>,
) -> Option<(&'rule R, Update<T, M>)>
where
    T: Uniplate,
    R: Rule<T, M>,

Selects a random (Rule, Update) from the iterator.

See the module-level documentation for more information.