Hi all - it seems that prop:evt and prop:procedure do not work well together - when prop:procedure is specified the struct will no longer be an event. See the code below for example. This is in v4.2.3. Thanks, yc (define-struct s1 (evt) #:property prop:evt 0) (define-struct s2 (evt) #:property prop:evt 0 #:property prop:procedure (lambda ($s) 1)) > (define a1 (make-s1 (make-channel))) > (evt? a1) #t > (define a2 (make-s2 (make-channel))) > (evt? a2) #f