From: Ted Zlatanov <tzz@lifelogs.com>
To: help-gnu-emacs@gnu.org
Subject: Re: plists, alists, and hashtables
Date: Thu, 06 Aug 2015 21:53:36 -0400 [thread overview]
Message-ID: <87lhdnsw2n.fsf@lifelogs.com> (raw)
In-Reply-To: jwv8u9o3ygd.fsf-monnier+gnu.emacs.help@gnu.org
On Thu, 06 Aug 2015 17:31:29 -0400 Stefan Monnier <monnier@iro.umontreal.ca> wrote:
SM> So, IIUC you want to signal errors for invalid maps.
That's what I meant, yes. The syntax to specify an invalid map would be
invalid at the reader level and generate an error when the source code
is parsed.
>> (mapcar #'car '((a) (b 1) (c . 2) d))
-> Debugger entered--Lisp error: (wrong-type-argument listp d)
>> ...and that's just a simple edge case.
SM> So, now you don't want to signal errors for invalid maps?
SM> Make up your mind.
I am showing how extracting the keys of an alist can generate *runtime*
errors, when the alist has already been read in. Which makes actual
maps more appealing, I thought, because they could avoid that problem at
the reader level.
SM> Reality check: Have you looked at the definition of hash-table-keys?
SM> Better yet: have you looked at how often hash-table-keys is used?
SM> The efficiency of map-keys is largely irrelevant.
Right. I agree. My point was different: there is no "keys" function for
alists and plists. Keys in those two formats are a convention.
SM> More importantly, mathematical maps are persistent, whereas your
SM> apparently favorite implementation (the hash-table) is not persistent,
SM> contrary to (e.g.) alists.
>> I am not sure what you mean. Perhaps it's a problem with the
>> terminology. Could you explain?
SM> alists can be functional, whereas hash-tables are by nature imperative.
SM> For example,
SM> (cons (cons k v) m)
SM> returns a new alist with a new mapping from "k" to "v" without changing
SM> the map "m". Whereas after
SM> (puthash k v m)
SM> "m" has necessarily been modified.
I certainly see the advantages of appending instead of modifying in
place. I think that's an artifact of the current hashtable API, not a
fundamental property of maps or hashtables. Would it be useful if, in
addition to the reader syntax, "maps" (backed by hashtables or something
else) were made cons-able as you describe? Or is that fundamentally
impossible in your opinion?
Ted
next prev parent reply other threads:[~2015-08-07 1:53 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-31 21:42 How to iterate over properties in a plist? Marcin Borkowski
2015-07-31 22:18 ` Stefan Monnier
2015-07-31 22:29 ` Marcin Borkowski
2015-07-31 22:42 ` Dmitry Gutov
2015-08-01 13:34 ` Michael Heerdegen
[not found] ` <mailman.7705.1438381807.904.help-gnu-emacs@gnu.org>
2015-07-31 23:33 ` Pascal J. Bourguignon
2015-08-01 22:49 ` Stefan Monnier
[not found] ` <mailman.7750.1438469396.904.help-gnu-emacs@gnu.org>
2015-08-04 10:15 ` plists, alists, and hashtables (was: How to iterate over properties in a plist?) Ted Zlatanov
2015-08-04 10:29 ` Nicolas Petton
[not found] ` <mailman.7809.1438684158.904.help-gnu-emacs@gnu.org>
2015-08-04 11:23 ` plists, alists, and hashtables Ted Zlatanov
2015-08-05 4:36 ` plists, alists, and hashtables (was: How to iterate over properties in a plist?) Rusi
2015-08-05 6:12 ` plists, alists, and hashtables Pascal J. Bourguignon
2015-08-05 9:47 ` Ted Zlatanov
2015-08-05 12:20 ` Rusi
2015-08-06 19:16 ` Stefan Monnier
[not found] ` <mailman.7892.1438888819.904.help-gnu-emacs@gnu.org>
2015-08-07 16:33 ` Rusi
2015-08-05 17:24 ` Pascal J. Bourguignon
2015-08-05 18:31 ` Ted Zlatanov
2015-08-05 19:30 ` Barry Margolin
2015-08-05 19:40 ` Robert Thorpe
2015-08-05 21:11 ` Pascal J. Bourguignon
2015-08-06 15:17 ` Ted Zlatanov
2015-08-06 18:46 ` Pascal J. Bourguignon
2015-08-06 20:19 ` Drew Adams
2015-08-06 21:08 ` Ted Zlatanov
2015-08-07 0:23 ` Pascal J. Bourguignon
2015-08-06 19:35 ` Stefan Monnier
2015-08-05 13:48 ` Drew Adams
2015-08-06 19:12 ` Stefan Monnier
[not found] ` <mailman.7890.1438888393.904.help-gnu-emacs@gnu.org>
2015-08-06 20:00 ` Pascal J. Bourguignon
2015-08-06 20:57 ` Ted Zlatanov
2015-08-06 21:10 ` Drew Adams
[not found] ` <mailman.7902.1438895429.904.help-gnu-emacs@gnu.org>
2015-08-06 21:15 ` Ted Zlatanov
2015-08-06 21:31 ` Stefan Monnier
2015-08-07 1:53 ` Ted Zlatanov [this message]
2015-08-07 7:34 ` Pascal J. Bourguignon
2015-08-07 16:32 ` Stefan Monnier
[not found] ` <mailman.7941.1438965165.904.help-gnu-emacs@gnu.org>
2015-08-08 3:48 ` Pascal J. Bourguignon
2015-08-08 13:42 ` Stefan Monnier
2015-08-08 14:51 ` Rusi
2015-08-07 0:08 ` Pascal J. Bourguignon
2015-08-07 2:14 ` Ted Zlatanov
2015-08-07 7:53 ` Pascal J. Bourguignon
2015-08-07 11:21 ` Ted Zlatanov
2015-08-07 11:47 ` Pascal J. Bourguignon
2015-08-07 17:21 ` Ted Zlatanov
2015-08-07 19:21 ` Stefan Monnier
[not found] ` <mailman.7952.1438975314.904.help-gnu-emacs@gnu.org>
2015-08-08 3:52 ` Pascal J. Bourguignon
2015-08-07 16:35 ` Stefan Monnier
[not found] <mailman.7856.1438803631.904.help-gnu-emacs@gnu.org>
2015-08-05 20:08 ` Ted Zlatanov
2015-08-05 20:45 ` Stefan Monnier
2015-08-05 21:36 ` Drew Adams
2015-08-05 21:41 ` Pascal J. Bourguignon
[not found] ` <mailman.7860.1438807554.904.help-gnu-emacs@gnu.org>
2015-08-06 1:32 ` Ted Zlatanov
[not found] ` <mailman.7862.1438810623.904.help-gnu-emacs@gnu.org>
2015-08-06 1:36 ` Ted Zlatanov
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