On Tue, May 31, 2011 at 6:29 PM, Todd O'Bryan <[email protected]> wrote: > I have a structure with a guard function. It works well. > > However, I want to use it in a (shared ...) construct, and when the > guard runs, a value is #<undefined>. I'm fine with letting the guard > accept #<undefined> as a legal value, but I can't figure out any way > to test for it. > > Is there such a beast, or is #<undefined> untouchable? > > Todd
I believe the "undefined" value is eq? to itself, so you should be able to use the following: (define undefined (letrec ([x x]) x)) (define (undefined? x) (eq? x undefined)) --Carl _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
