Re: make-thread with lambda form instead of function symbol

[Eric Abrahamsen]

Noam Postavsky <address@hidden> writes:

> On Sun, Apr 16, 2017 at 2:11 PM, Eric Abrahamsen
> <address@hidden> wrote:
>>
>> (setq lexical-binding t)
>>
>> (let ((threads
>>        (mapcar
>>         (lambda (el)
>>           (make-thread
>>            (lambda ()
>>              (push (cl-incf el) results))))
>>         '(1 2 3)))
>>       results)
>>   (mapc #'thread-join threads)
>>   results)
>>
>> This gives me nil.
>>
>> (Incidentally, if I put this in a function and edebug it, it tells me
>> edebug will stop at the next break point, and then enters a level of
>> recursive editing I can't escape from: C-M-c gives me "No catch for tag:
>> exit, nil".)
>>
>> Should the above example work?
>
> No, check the compile warnings:
>
> a.el:7:33:Warning: reference to free variable ‘results’
> a.el:9:7:Warning: assignment to free variable ‘results’

Aha! That makes sense now that I see it. The thread function starts
executing immediately, so of course it needs to be able to see
"results". Thanks for that.

> Not sure about the edebug thing, probably it doesn't handle
> cross-thread stepping.

I can imagine it would be complicated.

Thanks again,
Eric