From: Stefan Monnier <monnier@iro.umontreal.ca>
To: "Mattias Engdegård" <mattiase@acm.org>
Cc: "Basil L. Contovounesios" <contovob@tcd.ie>,
Ag Ibragimov <agzam.ibragimov@gmail.com>,
Emacs developers <emacs-devel@gnu.org>
Subject: Re: Pattern matching on match-string groups #elisp #question
Date: Sun, 28 Feb 2021 10:37:25 -0500 [thread overview]
Message-ID: <jwv7dmsurzz.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <62A88DEE-5BFD-4479-AB15-1A43DC2B299D@acm.org> ("Mattias Engdegård"'s message of "Sun, 28 Feb 2021 14:46:42 +0100")
> I went with dotted lists (a b c . d) because benchmarking showed it to be
> faster than either proper lists or vectors, the generated code is smaller
> than for lists, and the case of a single variable reduces naturally to no
> consing at all.
Nice.
> Looking a bit closer it gets more nuanced: one reason why
>
> (pcase (list 1 2 3) (`(,a ,b ,c) (+ a b c)))
>
> is faster than
>
> (pcase (vector 1 2 3) (`[,a ,b ,c] (+ a b c)))
>
> is that the latter contains three general function calls: to `vector`,
> `vectorp`, and `eql` (for checking the length), whereas the list version has
> byte-ops for everything.
Very good point. The choice of which primitives deserve their own
bytecode was made many many years ago and it likely deserves
a serious reconsideration [ we still have dedicated byte codes for
Btemp_output_buffer_show and Btemp_output_buffer_setup ;-( ]
Personally, I'd vote to start by making the `eq` byte code return the
value of `Feql` ;-)
Stefan
prev parent reply other threads:[~2021-02-28 15:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 5:11 Pattern matching on match-string groups #elisp #question Ag Ibragimov
2021-02-25 14:55 ` Basil L. Contovounesios
2021-02-25 15:32 ` Stefan Monnier
2021-02-25 18:28 ` Mattias Engdegård
2021-02-26 4:31 ` Stefan Monnier
2021-02-26 10:24 ` Mattias Engdegård
2021-02-26 19:38 ` Stefan Monnier
2021-02-27 10:17 ` Mattias Engdegård
2021-02-27 14:39 ` Stefan Monnier
2021-02-27 18:10 ` Mattias Engdegård
2021-02-27 20:32 ` Stefan Monnier
2021-02-28 13:46 ` Mattias Engdegård
2021-02-28 15:37 ` Stefan Monnier [this message]
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