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From: Dan Cross <crossd@gmail.com>
To: Dave Horsfall <dave@horsfall.org>
Cc: Computer Old Farts Followers <coff@tuhs.org>
Subject: [COFF] Re: Requesting thoughts on extended regular expressions in grep.
Date: Fri, 3 Mar 2023 12:13:13 -0500	[thread overview]
Message-ID: <CAEoi9W7hjvuTF=g-3B1E=1-z_o_nBJzre+LqGiKOdPpzna46vA@mail.gmail.com> (raw)
In-Reply-To: <alpine.BSF.2.21.9999.2303040254050.4881@aneurin.horsfall.org>

On Fri, Mar 3, 2023 at 11:12 AM Dave Horsfall <dave@horsfall.org> wrote:
> [snip]
>     # Yes, I have a warped sense of humour here.
>     /^[JFMAMJJASOND][aeapauuuecoc][nbrrynlgptvc] [ 0123][0-9] / \
>     {
>         date = sprintf("%4d/%.2d/%.2d",
>             year, months[substr($0, 1, 3)], substr($0, 5, 2))

If I may, I'd like to point out something fairly subtle here that, I
think, bears on the original question (paraphrased as, "where does one
draw the line between concision and understandability?").

Note Dave's class to match the first letter of the month:
`[JFMAMJJASOND]`. One may notice that a few letters are repeated (J,
M, A), and one _could_ shorten this to: `[JFMASOND]`. But I can see a
serious argument where that may be regarded as a mistake; in
particular, the original is easy to validate by just saying the names
of the month out loud as one scans the list. For the shorter version,
I'd worry that I would miss something or make a mistake. The lesson
here is keep it simple and don't over-optimize!

> Etc.  The idea is not to validate so much as to grab a line of interest to
> me and extract the bits that I want.
> [snip]

Too true.

A few years ago, Rob Pike gave a talk about lexing in Go that bears on
this that's worth a listen:
https://www.youtube.com/watch?v=HxaD_trXwRE

        - Dan C.

  reply	other threads:[~2023-03-03 17:13 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-02 18:54 [COFF] " Grant Taylor via COFF
2023-03-02 19:23 ` [COFF] " Clem Cole
2023-03-02 19:38   ` Grant Taylor via COFF
2023-03-02 23:01   ` Stuff Received
2023-03-02 23:46     ` Steffen Nurpmeso
2023-03-03  1:08     ` Grant Taylor via COFF
2023-03-03  2:10       ` Dave Horsfall
2023-03-03  3:34         ` Grant Taylor via COFF
2023-03-02 21:53 ` Dan Cross
2023-03-03  1:05   ` Grant Taylor via COFF
2023-03-03  3:04     ` Dan Cross
2023-03-03  3:53       ` Grant Taylor via COFF
2023-03-03 13:47         ` Dan Cross
2023-03-03 19:26           ` Grant Taylor via COFF
2023-03-03 10:59 ` Ralph Corderoy
2023-03-03 13:11   ` Dan Cross
2023-03-03 13:42     ` Ralph Corderoy
2023-03-03 19:19       ` Grant Taylor via COFF
2023-03-04 10:15         ` [COFF] Reading PDFs on a mobile. (Was: Requesting thoughts on extended regular expressions in grep.) Ralph Corderoy
2023-03-07 21:49           ` [COFF] " Tomasz Rola
2023-03-07 22:46             ` Tomasz Rola
2023-06-20 16:02           ` Michael Parson
2023-06-20 21:26             ` Tomasz Rola
2023-06-22 15:45               ` Michael Parson
2023-07-10  9:08                 ` [COFF] Re: Reader, paper, tablet, phone (was: Re: Reading PDFs on a mobile. (Was: Requesting thoughts on extended regular expressions in grep.)) Tomasz Rola
2023-03-03 16:12   ` [COFF] Re: Requesting thoughts on extended regular expressions in grep Dave Horsfall
2023-03-03 17:13     ` Dan Cross [this message]
2023-03-03 17:38       ` Ralph Corderoy
2023-03-03 19:09         ` Dan Cross
2023-03-03 19:36     ` Grant Taylor via COFF
2023-03-04 10:26       ` Ralph Corderoy
2023-03-03 19:06 ` Grant Taylor via COFF
2023-03-03 19:31   ` Dan Cross
2023-03-04 10:07   ` Ralph Corderoy
2023-03-06 10:01 ` Ed Bradford
2023-03-06 21:01   ` Dan Cross
2023-03-06 21:49     ` Steffen Nurpmeso
2023-03-07  1:43     ` Larry McVoy
2023-03-07  4:01       ` Ed Bradford
2023-03-07 11:39         ` [COFF] " Ralph Corderoy
2023-03-07 18:31           ` [COFF] " Grant Taylor via COFF
2023-03-08 11:22           ` Ed Bradford
2023-03-07 16:14         ` Dan Cross
2023-03-07 17:34           ` [COFF] " Ralph Corderoy
2023-03-07 18:33             ` [COFF] " Dan Cross
2023-03-07  4:19     ` Ed Bradford

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