From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Tomas Hlavaty <tom@logand.com>
Cc: Jim Porter <jporterbugs@gmail.com>,
Karthik Chikmagalur <karthikchikmagalur@gmail.com>,
Thomas Koch <thomas@koch.ro>,
"emacs-devel@gnu.org" <emacs-devel@gnu.org>
Subject: Re: continuation passing in Emacs vs. JUST-THIS-ONE
Date: Thu, 16 Mar 2023 23:08:25 -0400 [thread overview]
Message-ID: <jwvpm98nlqz.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87mt4c6xju.fsf@logand.com> (Tomas Hlavaty's message of "Fri, 17 Mar 2023 01:17:41 +0100")
>> ;; (futur-let*
>> ;; (exitcode <- (futur-process-make :command cmd :buffer t))
>> ;; (out (buffer-string)) ;; Get the process's output.
>> ;; (cmd2 (build-second-arg-list exitcode out))
>> ;; (otherexit <- (futur-process-make :command cmd2 :buffer t)))
>> ;; (futur-pure (buffer-string)))
>
> Seems like beautiful lisp code has no futur. :-)
BTW the above code can't work right now. Part of the issue is the
management of `current-buffer`: should the composition of futures with
`futur-let*` save&restore `current-buffer` to mimic more closely the
behavior one would get with plain old sequential execution? If so,
should we do the same with `point`? What about other such state?
> There is something very ugly about this code.
> It looks like assembly, 1 dimensional vertical code.
> It is hard to see the structure of the code and what it actually does.
> I do not think it is practical to write non-trivial code in this style.
:-)
> Nice lisp code is usually 2 dimensional,
> with indentation and top-left to bottom-right direction.
> It is usually much clearer to see what is an argument to what
> based on the position in the syntax tree.
>
> Is it possible to make the syntax more structured (lispy)?
> Meaning tree-like, not list-like?
> Something in the spirit of:
>
> (futur-progn
> (futur-process-make
> :command (futur-let ((exitcode (futur-process-make
> :command (build-arg-list)
> :buffer t)))
> (build-second-arg-list exitcode (buffer-string)))
> :buffer t)
> (buffer-string))
The `futur-progn` is just:
(defmacro futur-progn (form &rest forms)
(if (null forms) form
`(futur-let* ((_ ,form)) (futur-progn ,@forms))))
As for passing the result of `futur-let` to `:command` it just requires
writing `futur-process-make` in a way that is tolerant of this
`:command` arg being a future rather than a string, which should be
fairly easy (it's basically always easy when done within a function
which itself returns a future).
> or would it need some fancy syntax rewriting like other async/cps
> syntax rewriting libraries?
I don't think so, no. But you would need fancy rewriting if you wanted
to allow
(concat foo (futur-let* (...) ...))
But as you point out at the beginning, as a general rule, if you want to
avoid rewritings in the style of `generator.el`, then the code will tend
to feel less like a tree and more "linear/imperative/sequential",
because you fundamentally have to compose your operations "manually"
with a monadic "bind" operation that forces you to *name* the
intermediate value.
> Second question: I see that futur-wait blocks the whole Emacs due to
> the while loop. How can one use futur without blocking Emacs?
Don't use `futur-wait` and instead use `futur-let*`.
IOW: instead of waiting, return immediately a future.
> Last question: How would similar functionality be implemented
> using futur?
Good question.
To a large extent I guess it could be implemented in basically the same
way: you'd use futures only for the timer part of the code, and leave
the process's output to fill the buffer just like you do.
I think the difference would be very small and cosmetic like replacing
(defun stream-pull-in-background (stream &optional secs repeat)
(let (timer)
(setq timer (run-with-timer
(or secs 1)
(or repeat 1)
(lambda ()
;;(message "@@@ polling!")
(unless (funcall stream)
(cancel-timer timer)))))))
with something like:
(defun stream-pull-in-background (stream &optional secs repeat)
(futur-run-with-timer
(or secs 1)
(lambda ()
;;(message "@@@ polling!")
(when (and (funcall stream) repeat)
(stream-pull-in-background stream secs repeat)))))
The only benefit I could see is that it returns a future, i.e. a kind of
standardized representation of that async computation so the caller can
use things like `futur-wait` or `futur-let*` without having to care
about whether the function is using timers or something else.
And, there's also the benefit of standardized error-signaling.
Stefan
next prev parent reply other threads:[~2023-03-17 3:08 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-11 12:53 continuation passing in Emacs vs. JUST-THIS-ONE Thomas Koch
2023-03-12 1:45 ` Jim Porter
2023-03-12 6:33 ` tomas
2023-03-14 6:39 ` Karthik Chikmagalur
2023-03-14 18:58 ` Jim Porter
2023-03-15 17:48 ` Stefan Monnier
2023-03-17 0:17 ` Tomas Hlavaty
2023-03-17 3:08 ` Stefan Monnier [this message]
2023-03-17 5:37 ` Jim Porter
2023-03-25 18:42 ` Tomas Hlavaty
2023-03-26 19:35 ` Tomas Hlavaty
2023-03-28 7:23 ` Tomas Hlavaty
2023-03-29 19:00 ` Stefan Monnier
2023-04-03 0:39 ` Tomas Hlavaty
2023-04-03 1:44 ` Emanuel Berg
2023-04-03 2:09 ` Stefan Monnier
2023-04-03 4:03 ` Po Lu
2023-04-03 4:51 ` Jim Porter
2023-04-10 21:47 ` Tomas Hlavaty
2023-04-11 2:53 ` Stefan Monnier
2023-04-11 19:59 ` Tomas Hlavaty
2023-04-11 20:22 ` Stefan Monnier
2023-04-11 23:07 ` Tomas Hlavaty
2023-04-12 6:13 ` Eli Zaretskii
2023-04-17 20:51 ` Tomas Hlavaty
2023-04-18 2:25 ` Eli Zaretskii
2023-04-18 5:01 ` Tomas Hlavaty
2023-04-18 10:35 ` Konstantin Kharlamov
2023-04-18 15:31 ` [External] : " Drew Adams
2023-03-29 18:47 ` Stefan Monnier
2023-04-17 3:46 ` Lynn Winebarger
2023-04-17 19:50 ` Stefan Monnier
2023-04-18 2:56 ` Lynn Winebarger
2023-04-18 3:48 ` Stefan Monnier
2023-04-22 2:48 ` Lynn Winebarger
2023-04-18 6:19 ` Jim Porter
2023-04-18 9:52 ` Po Lu
2023-04-18 12:38 ` Lynn Winebarger
2023-04-18 13:14 ` Stefan Monnier
2023-04-19 0:28 ` Basil L. Contovounesios
2023-04-19 2:59 ` Stefan Monnier
2023-04-19 13:25 ` [External] : " Drew Adams
2023-04-19 13:34 ` Robert Pluim
2023-04-19 14:19 ` Stefan Monnier
2023-04-21 1:33 ` Richard Stallman
2023-04-19 1:11 ` Po Lu
2023-04-17 21:00 ` Tomas Hlavaty
2023-03-14 3:58 ` Richard Stallman
2023-03-14 6:28 ` Jim Porter
2023-03-16 21:35 ` miha
2023-03-16 22:14 ` Jim Porter
2023-03-25 21:05 ` Tomas Hlavaty
2023-03-26 23:50 ` Tomas Hlavaty
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