What is the correct contract for an on-tick handler in the universe teachpack? I'm playing with the universe teachpack, and I'm having trouble writing an on-tick clause for a universe. The help files says clearly: (on-tick tick-expr) tick-expr : (-> [listof world?] UniverseState bundle?) The one example I could find of a universe with an on-tick handler (in universe.ss) says (universe '() (on-new nu) (on-msg process) #; (on-tick (lambda (u x) (printf "hello!\n") (list u)) 1))) This clearly supplies a function of 2 arguments, though not one that apparently matches the contract in the help file. But when I try to say (define (on-tick-fn worlds s-state) (make-bundle worlds s-state empty)) (define (run-server d) (universe '* (on-new on-new-fn) (on-msg on-msg-fn) (on-tick on-tick-fn 1) )) I get: > (run-server 1) on-tick: procedure of one argument expected as first argument; given procedure of 2 arguments What's up with this? What values are actually sent to the on-tick handler? --Mitch