arc> ([(prn "You entered " _)] 34)
You entered 34
Error: "car: expects argument of type <pair>; given ()"
That's good investigation. Note the work described in this thread uses Arc 3.1, not Anarki.
Btw do you mean there's something wrong with defop, or that the example I wrote is incorrect? I had gotten that example from: http://arcfn.com/doc/srv.html