From: Andrew Hyatt <ahyatt@gmail.com>
To: rms@gnu.org
Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
Subject: Re: pcase defuns
Date: Tue, 21 Dec 2021 00:20:41 -0500 [thread overview]
Message-ID: <m2r1a68rfa.fsf@andrews-mbp.lan> (raw)
In-Reply-To: <E1mzWYH-0000dL-GI@fencepost.gnu.org>
On Mon, Dec 20, 2021 at 11:15 PM Richard Stallman <rms@gnu.org>
wrote:
> [[[ To any NSA and FBI agents reading my email: please consider
> ]]] [[[ whether defending the US Constitution against all
> enemies, ]]] [[[ foreign or domestic, requires you to follow
> Snowden's example. ]]]
>
> The idea of defining a function in pieces, scattered around one
> or more files, is attractive as regards writing them. But it
> creates an inconvenience for subsequent maintenance by other
> people.
>
> The first thing you're likely to do when you see a call to a
> function you don't know about is to find its definition. For a
> piecewise-defined function, "the" definition doesn't exist. It
> has a number of partial definitions, scattered around one file
> or perhaps multiple files.
>
> If you think it is helpful for clarity to put the code for
> handling various cases in various places in the file, no new
> construct is needed for that. You can define a function for
> handling each case, and put its definition in the place you want
> it. Then define one overall function (you can think of it as
> "generic") which detects the cases and calls those.
>
> This works with our tools.
>
> Let's contrast this with generic functions.
>
> A generic function has a single central definition which
> describes how to call it. It is easy to find that.
>
> Finding the definitions of all the methods may be difficult.
> You may need to grep for them.
>
> Calling the generic function selects a method by data types, and
> you can generally tell, for given arguments, what data types
> they have. You can probably tell that one method is the right
> one without seeing all the others and comparing them.
>
> Thus, generic functions cause one kind of inconvenience for
> studying a program, but avoids the other kinds.
>
> Let's not add any constructs that increase the level of
> complexity of genericness beyond this.
These are all good points, thanks.
I agree that just implementing everything in a function is
reasonable. For that, just using pcase seems good enough,
although it might be interesting to have a very different way of
writing a function such as
(pcase-defun mytest
"Demonstrates a way of writing defuns via pcase matching."
((a b _) "a b match")
(`(c ,v _) (format "c %s match" v)))
Not sure if I like this syntax, it does seem to lend itself to the
idea of a pcase-centric way of programming, but it's also a bit
odd, and doesn't seem to buy much. However, it does at least
answer the objections raised to my initial proposal. Of course, so
does not doing anything.
>
>
> --
> Dr Richard Stallman (https://stallman.org)
> Chief GNUisance of the GNU Project (https://gnu.org)
> Founder, Free Software Foundation (https://fsf.org)
> Internet Hall-of-Famer (https://internethalloffame.org)
next prev parent reply other threads:[~2021-12-21 5:20 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-19 4:53 pcase defuns Andrew Hyatt
2021-12-19 8:34 ` Tassilo Horn
2021-12-19 15:33 ` Andrew Hyatt
2021-12-19 17:16 ` Tassilo Horn
2021-12-19 19:05 ` Stefan Monnier
2021-12-20 5:56 ` Tassilo Horn
2021-12-22 14:07 ` LdBeth
2021-12-19 17:23 ` Stefan Monnier
2021-12-19 21:08 ` Andrew Hyatt
2021-12-21 4:15 ` Richard Stallman
2021-12-21 5:20 ` Andrew Hyatt [this message]
2021-12-22 4:18 ` Richard Stallman
2021-12-23 1:52 ` Andrew Hyatt
2021-12-24 4:13 ` Richard Stallman
2021-12-21 15:32 ` Stefan Monnier
2021-12-20 4:43 ` Richard Stallman
2021-12-23 2:30 ` Po Lu
2022-03-26 17:41 ` Andrew Hyatt
2022-03-27 9:31 ` Stefan Monnier
2022-03-27 18:17 ` Andrew Hyatt
2022-03-28 4:15 ` Richard Stallman
2022-03-30 1:28 ` Andrew Hyatt
2022-03-31 4:27 ` Richard Stallman
2022-04-17 22:09 ` Andrew Hyatt
2022-04-19 3:48 ` Richard Stallman
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