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

OK, I should probably have figured this out earlier myself.

The egg sources are not entirely up-to-date with upstream and miss this commit:
https://github.com/scheme-requests-for-implementation/srfi-127/commit/7976fce401da8ac368ada1914c5fbaba715aa246

https://srfi-email.schemers.org/srfi-127/msg/21875262/

—
Stan


> On 22 Feb 2026, at 20:20, Kon Lovett <[email protected]> wrote:
> 
> ;; 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
>