[racket] formlets with radio button & checkbox example?

Hi all,

could someone perhaps point me to a simple formlet example including not just text inputs, but also radio buttons and check boxes?
>From the formlet syntax shown in Continue and the Formlets chapter, unfortunately I have problems understanding how the syntax for radio buttons and check boxes works, especially how to get back the values (that is, how to construct the second argument to formlet, for use by formlet-process).

(Sorry for the dumb question, but I have so much less time for Racket than I'd like to, and so I sometimes have problems understanding / inferring from the documentation...)

Many thanks in advance!
Sigrid