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

From: Eric Abrahamsen
Subject: Re: make-thread with lambda form instead of function symbol
Date: Sun, 16 Apr 2017 13:02:54 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

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,

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