From: Michael Heerdegen <michael_heerdegen@web.de>
To: "Clément Pit--Claudel" <clement.pit@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: [PATCH] Elpa: Pinpoint semantics of `seq-subseq' for streams
Date: Thu, 15 Sep 2016 23:29:39 +0200 [thread overview]
Message-ID: <87oa3oam2k.fsf@web.de> (raw)
In-Reply-To: <63ebf6ee-d623-e863-42a8-bc802d3df54d@gmail.com> ("Clément Pit--Claudel"'s message of "Wed, 14 Sep 2016 23:47:47 -0400")
Clément Pit--Claudel <clement.pit@gmail.com> writes:
> Ok. But how do you refer to the file's contents from elisp, then?
> As a string?
I didn't have a string in mind. More something like running `cat` in
a subprocess maybe?
I have a question: AFAIK there is no mean to delay Emacs from accepting
output from a process (or is there? sorry if i missed it then). But
when we must collect the complete process output when it arrives...and
we don't have asynchronity in Emacs etc...of what use is the usage of a
delayed structure (stream) in this case at all, and how would it be
different from the string case?
>> Sure, but with what I mean, the error (inefficiency) would already
>> be inthe "I have..." part.
> I don't think so :) These sound like reasonable streams to me ^^The
> second one in particular is one that I used recently: I wanted to
> enumerate all spans with constant text properties, and I didn't need
> to keep the whole list of spans in memory. On the other hand, I
> didn't want to put the buffer segmentation in each function that
> iterated over the spans. Using a stream for that was quite convenient.
Here I again would chime in: it's convenient, but not efficient. Search
backwards from the end of the buffer, don't enumerate from the beginning
if you are only interested in the last n, and start building a stream if
you have found the right place to start.
> > And should we add `stream'method implementations for building
> > streams from files and/or processes to stream.el if such stuff is
> > useful?
>
> I think this would be great.
Maybe you want to give it a try? Then we will at least know how useful
that would be ;-)
> > But I guess I'm beginning to understand: if you have a string (or
> > something "similar") consisting of multiple lines (or records or
> > whatever), and you are interested in the last n lines, in contrast to a
> > buffer, the "go to the end and then n times backwards" approach might
> > not even be possible, so there is no alternative to dissect the complete
> > string into entities from the start until you hit the end (and throw
> > away most of the stuff without accumulation) -- i.e. to the sliding
> > window approach implemented by seq-subseq with negative indexes.
>
> Yes, essentially. In the string case, though, you could copy the
> string into a buffer and apply the trick that you mentioned.
Well, I learned some time ago that because a buffer is more complicated
than a string, most operations are slower for a buffer than for an
equivalent string.
> But more generally streams are good at producing their contents
> lazily, so an implementation that requires forcing the entire stream
> and then searching from the end of the resulting list is non-optimal.
Yes, but that's was not my argument: I wanted to avoid this stream
entirely in such cases. For your use case (of the negative indexes),
forcing the entire stream is unavoidable. That's the point I criticize.
> In any case, I don't think this should hold the previous patch; we can
> always extend the functionality of seq-subseq later.
Ok, so I think I'll just install the patch for now.
Michael.
next prev parent reply other threads:[~2016-09-15 21:29 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
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 [this message]
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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