Hi all, I'd like to refactor and extend the code below, such that r is either defined to be an instance of an item-representer% or a multi-item-representer%, depending on whether param-a is a single item or a list. The solution that springs to mind is to choose which class to instantiate with (if (list? param-a) ,,,) but then I'd have to state the parameter lists twice. It seems to me there's got to be a better way in Racket to do this. Thanks in advance for any suggestions on how to proceed. Cheers, Kieron. **** #lang racket (define text-item "hello world") (define text-item-list (list "alpha bravo" "charlie delta" "echo foxtrot")) (define x% (class object% (super-new) )) (define item-representer% (class x% (init param-a param-b param-c) (super-new) (field (item param-a)) (define/public (print) (printf "item:~a~n" item)) )) (define multi-item-representer% (class x% (init param-a param-b param-c) (super-new) (field (item-list (map (lambda (item) (new item-representer% [param-a item] [param-b param-b] [param-c param-c])) param-a))) (define/public (print) (printf "multi-item:~n") (map (lambda (item) (send item print)) item-list) ) )) (define r1 (new item-representer% [param-a text-item] [param-b 10] [param-c "red"])) (define r2 (new multi-item-representer% [param-a text-item-list] [param-b 20] [param-c "green"])) (send r1 print) (send r2 print) ;(define r (some-representer% [param-a x] [param-b 50] [param-c "yellow"])) ;(send r print)