Went for a walk and had an idea. I think this sample illustrates the answer to my own question:
#lang slideshow (define (retract-up-to s retracted) (let ([newly-retracted (retract-most-recent-slide)]) (if (eq? newly-retracted s) (cons newly-retracted retracted) (retract-up-to s (cons newly-retracted retracted))))) (slide #:title "Slide 1") (slide #:title "Slide 2") (slide #:title "Slide 3") (slide #:title "Branching slide" (clickback (t "1") (λ () (let* ([remainder (retract-up-to remainder-start (list))] [branch-start #f] [_ (begin (slide #:title "1" (clickback (t "a") (λ () (slide #:title "a" (clickback (t "resume remainder") (λ () (retract-up-to branch-start '()) (re-slide (car remainder)) (start-at-recent-slide) (for ([rem-sl (cdr remainder)]) (re-slide rem-sl))))) (start-at-recent-slide)))) (set! branch-start (most-recent-slide)))]) (start-at-recent-slide))))) (define branching-slide (most-recent-slide)) (slide #:title "Remainder 1") (define remainder-start (most-recent-slide)) (slide #:title "Remainder 2") (slide #:title "Remainder 3") -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.