Re: Weird behaviour of SRFI-127 lseq in a multithreaded program

;; Eagerly apply a proc to the elements of lseqs
;; Included because it's a common operation, even though it is trivial
(define (lseq-for-each proc . lseqs)
  (apply for-each proc (map lseq-realize lseqs)))

lseq-for-each* applies the proc before processing the remaining list, not the egg source.


> On Feb 22, 2026, at 10:22 AM, Stanislav Kljuhhin via Chicken-users <[email protected]> wrote:
> 
> Hello,
> 
> Consider the following minimal example:
> 
> ---8<---
> (import srfi-18)
> (import srfi-121)
> (import srfi-127)
> 
> (define (emit yield)
>  (let loop ((i 1))
>    (thread-sleep! 1)
>    (yield "hello")
>    (when (< i 10)
>      (loop (add1 i)))))
> 
> (define (collect s)
>  (display s)
>  (newline))
> 
> (define (lseq-for-each* proc lseq)
>  (unless (null? lseq)
>    (proc (lseq-car lseq))
>    (lseq-for-each* proc (lseq-cdr lseq))))
> 
> (lseq-for-each collect (generator->lseq (make-coroutine-generator emit)))
> ---8<—--
> 
> When I run this program (compiled or interpreted, makes no difference), nothing
> happens for 10 seconds, then 10 hello's are printed at once. But if I use the
> in-place implementation lseq-for-each*, then the program behaves as one might
> expect, i.e. hello's are printed with a 1-second interval.
> 
> Here I used a simplified implementation of lseq-for-each*, just for brevity, but
> we can copy the SRFI-127 implementation verbatim, and it still works the same.
> 
> Can you help me understand what is going on, please?
> 
> —
> Stan