I read docs, played with examples, and (re-)discovered, that the position of #:break or #:final in the iterator clauses (of course) matters. So this, e.g. (for/fold ([j-found? #f] [pos 0]) ([ch ch-stream] [ch-idx (in-naturals 1)] #:break j-found?)
solves my problem. On Tuesday, December 13, 2022 at 8:40:06 AM UTC+1 tbh...@gmail.com wrote: > I haven't asked any questions here for a long time, so hope it's OK to > cross-post here: > > > https://racket.discourse.group/ > > (which I just discovered.) > > > Cheers, > > Tim > > On Monday, December 12, 2022 at 10:28:22 PM UTC+1 tbh...@gmail.com wrote: > >> hi, I'm trying to do something slightly harder than what the attached >> example tries to do, but this example suffices to show that I, evidently, >> am missing something about how for/fold and/or #:break work together. >> >> (I have used both before, but have gotten out of practice with racket of >> late and am stuck longer on this than seems reasonable.) >> >> I expect both tests to pass, but both fail (the "j" for jewel in "xxjxx") >> is seen but not "found", as it were. >> >> I'd be grateful for a bug fix and/or explanation. >> >> Cheers, >> >> Tim Hanson >> >> -------- >> >> #lang racket >> >> (require rackunit) >> >> (define (port->char-stream aport) >> (printf "(port->char-stream aport)~n") >> (define (process-next-ch-iter) >> (let ([ch (read-char aport)]) >> (printf "p->cs ch: ~a~n" ch) >> (if (eof-object? ch) >> empty-stream >> (stream-cons >> ch >> (process-next-ch-iter))))) >> >> (process-next-ch-iter)) >> >> >> (let ([my-port >> (open-input-string "xxjxx")]) >> >> (let ([ch-stream (port->char-stream my-port)]) >> (let-values ([(pos-found? pos) >> (for/fold ([j-found? #f] >> [pos 0]) >> (#:break j-found? >> ;#:final j-found? >> [ch ch-stream] >> [ch-idx (in-naturals 1)]) >> (begin >> (printf "ch: ~a~n" ch) >> (printf "ch-idx: ~a~n" ch-idx) >> (printf "(eq? ch #\\j): ~a~n" (eq? ch #\j)) >> (values >> (eq? ch #\j) >> ch-idx)))]) >> >> (check-equal? pos-found? #t) >> >> (check-equal? pos 3) >> >> (close-input-port my-port)))) >> >> >> -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/beaa2ef6-afd2-4686-829a-390eb69f5620n%40googlegroups.com. Beyond the Racket Users Google Group, Racket Discussions take place on Discourse ( https://racket.discourse.group/ ) and Discord ( https://discord.gg/6Zq8sH5 ). Discussion (but less active) also takes place on the Racket Slack https://racket.slack.com/ ( sign up at https://racket-slack.herokuapp.com/ ), and IRC #racket https://kiwiirc.com/nextclient/irc.libera.chat/#racket --- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/2fa4a1a8-32ad-4c03-9194-e4b856fd4ae3n%40googlegroups.com.