hi, folks, I posted this question here: https://groups.google.com/g/racket-users/c/LblfrTvKVx4 yestereve, but just discovered this discourse group. I hope it's OK to cross-post here, so to speak.
--tbh
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))))