From: "Clément Pit--Claudel" <clement.pit@gmail.com>
To: Michael Heerdegen <michael_heerdegen@web.de>
Cc: emacs-devel@gnu.org
Subject: Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams
Date: Tue, 13 Sep 2016 21:24:34 -0400 [thread overview]
Message-ID: <27962aa1-ae40-99f8-64ad-ae21012fb36e@gmail.com> (raw)
In-Reply-To: <8737l3a4ab.fsf@web.de>
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Hi Michael,
On 2016-09-13 17:17, Michael Heerdegen wrote:
> Yes, I want to forbid them, unless there are realistic use cases.
> No, we don't have something like `tail' for streams. If you want
> something like that, you are in general better done with lists (i.e.
> convert the stream into a list), I think.
I don't think converting to list would be a good idea. When operating on text files, for example, it's often convenient to get the last n lines of a file. If the file is represented as a stream of lines, then tail makes sense. Doesn't it? Converting the file to a list of lines beforehand sounds like a bad idea, memory wise.
> Streams are a mean to program in a certain way (called data flow
> control or something like that). Negative indexes for `seq-subseq'
> collide with this model.
I don't see why; isn't it common to implement slyding-window-style algorithms on data streams? 'tail' is just one such example.
I do agree, however, that the return value of these silding-window algorithms is not commonly a stream (rather a list, or a function of that list). But I'm not sure that this is enough to make subseq with negative arguments irrelevant. Otherwise, what's a point of subseq vs. e.g. drop + take?
Let me know what you think of the 'last n lines of a file' example. Maybe I'm missing something :)
Cheers,
Clément.
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next prev parent reply other threads:[~2016-09-14 1:24 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-13 16:23 [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams Michael Heerdegen
2016-09-13 18:02 ` Clément Pit--Claudel
2016-09-13 21:17 ` Michael Heerdegen
2016-09-14 1:24 ` Clément Pit--Claudel [this message]
2016-09-14 15:05 ` Michael Heerdegen
2016-09-14 23:26 ` Clément Pit--Claudel
2016-09-15 0:51 ` John Mastro
2016-09-15 2:00 ` Clément Pit--Claudel
2016-09-15 17:01 ` John Mastro
2016-09-15 21:07 ` Michael Heerdegen
2016-09-15 22:18 ` Clément Pit--Claudel
2016-09-15 22:28 ` Michael Heerdegen
2016-09-15 22:52 ` Clément Pit--Claudel
2016-09-15 0:58 ` Michael Heerdegen
2016-09-15 3:47 ` Clément Pit--Claudel
2016-09-15 8:42 ` Nicolas Petton
2016-09-15 22:30 ` Michael Heerdegen
2016-09-15 23:08 ` Nicolas Petton
2016-09-15 21:29 ` Michael Heerdegen
2016-09-14 1:28 ` John Wiegley
2016-09-14 15:15 ` Michael Heerdegen
2016-09-13 22:20 ` Nicolas Petton
2016-09-13 22:40 ` Michael Heerdegen
2016-09-14 8:25 ` Nicolas Petton
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