From: "Garreau\, Alexandre" <galex-713@galex-713.eu>
To: Yuri Khan <yurivkhan@gmail.com>
Cc: Stefan Monnier <monnier@iro.umontreal.ca>,
Emacs developers <emacs-devel@gnu.org>
Subject: Re: Why is there no `until' in elisp?
Date: Wed, 17 Oct 2018 11:23:15 +0200 [thread overview]
Message-ID: <87lg6xgc58.fsf@portable.galex-713.eu> (raw)
In-Reply-To: <CAP_d_8XqerNmDMGpXT=yLAaEk8Zh7FXbJjHut5cBPZ-J4A3VQw@mail.gmail.com> (Yuri Khan's message of "Wed, 17 Oct 2018 15:04:43 +0700")
On 2018-10-17 at 15:04, Yuri Khan wrote:
> In both these implementations, ‘until’ is still a pre-condition loop
> (same as ‘while’, but with the condition negated).
Something such as the C “do” construct might overcomplicate the
language, while I think normal `while' and `until' are not only simpler
but also superior: with those you have the case of 0 loops, in which
basically works as a when.
> However, in many languages that have an ‘until’ loop as a language
> construct, it is a post-condition loop. The body is executed first,
> then the condition is evaluated.
Which languages? I looked again in bash to be sure, and bash doesn’t do
that.
> Of course, that raises additional questions…
>
> * Should a hypothetical ELisp ‘until’ macro implement a post-condition loop?
I find this a useless discrepancy, coming from inconsistent languages,
that shouldn’t be imported in elisp. Which is less bad than others in
this respect.
> * If so, should the condition be passed as the last argument?
I guess so, it’d be confusing otherwise. Yet from a low level
standpoint it’s not trivial (you need last arg of the linked list, but
you might just as well delay the problem by just using `progn'), but
this time I feel this stays elegant enough as the other form present no
real advantages.
> * If so, how should indentation work? (indent the body 4 spaces,
> condition 2 spaces?)
I guess… can (indent …) declaration constructs allow that?
> * The macro will then have to take body and condition as a single
> &rest list, and split it, right?
Yes I think. Since here it’s a lot more crucial and important than a
basic side-effects / not-always-used thing such as `progn' (though if I
wanted to make `progn' look more functional I’d do the same for it, as
an option).
I’ve alway found sad that `defun' &args specs were not powerful enough
for this kind of things (&rest rest &optional last), or even supporting
docstrings (although that requires typing so…).
next prev parent reply other threads:[~2018-10-17 9:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 17:42 Why is there no `until' in elisp? Garreau, Alexandre
2018-10-16 19:16 ` Eric Abrahamsen
2018-10-16 19:31 ` Garreau, Alexandre
2018-10-16 20:23 ` Eric Abrahamsen
2018-10-16 23:00 ` Garreau, Alexandre
2018-10-19 15:28 ` Stefan Monnier
2018-10-16 21:28 ` Stefan Monnier
2018-10-17 0:12 ` Garreau, Alexandre
2018-10-17 2:04 ` Stefan Monnier
2018-10-17 9:14 ` Garreau, Alexandre
2018-10-17 15:06 ` Stefan Monnier
2018-10-17 16:51 ` Garreau, Alexandre
2018-10-19 15:34 ` Stefan Monnier
2018-10-19 18:08 ` Garreau, Alexandre
2018-10-17 8:04 ` Yuri Khan
2018-10-17 9:23 ` Garreau, Alexandre [this message]
2018-10-17 9:46 ` Yuri Khan
2018-10-17 11:06 ` Garreau, Alexandre
2018-10-17 17:50 ` Paul Eggert
2018-10-17 21:15 ` Garreau, Alexandre
2018-10-17 21:35 ` Paul Eggert
2018-10-17 21:49 ` Garreau, Alexandre
2018-10-17 22:33 ` Paul Eggert
2018-10-17 22:54 ` Garreau, Alexandre
2018-10-17 12:41 ` Elias Mårtenson
2018-10-17 15:03 ` Stefan Monnier
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