Function with_card 

pub fn with_card<R>(
    readers: &dyn Readers,
    ident: &str,
    work: impl FnOnce(&mut dyn Card, &CardInfo) -> Result<R, CardError>,
) -> Result<R, CardError>

Opens the key ident for work, given what it says; Absent when it is not there, Busy when another program holds a key Sioul could not open.