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From: Rob Pike <robpike@gmail.com>
To: markus schnalke <meillo@marmaro.de>
Cc: TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] RegExp decision for meta characters: Circumflex
Date: Fri, 17 Sep 2021 19:32:00 +1000	[thread overview]
Message-ID: <CAKzdPgyos3psLGBiVde3M0OkpR2FW7483+5NFnM0XX316Cp_4g@mail.gmail.com> (raw)
In-Reply-To: <1mR9bE-8RG-00@marmaro.de>

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You'd have to ask ken why he chose the characters he did, but I can answer
the second question. The beginning and end of line are the same. If you
make ^ mean both beginning and end of line, what does this ed command do:

s/^/x/

Which end gets the x?

-rob


On Fri, Sep 17, 2021 at 7:00 PM markus schnalke <meillo@marmaro.de> wrote:

> Hoi,
>
> I'm interested in the early design decisions for meta characters
> in REs, mainly regarding Ken's RE implementation in ed.
>
> Two questions:
>
> 1) Circumflex
>
> As far as I see, the circumflex (^) is the only meta character that
> has two different special meanings in REs: First being the
> beginning of line anchor and second inverting a character class.
> Why was it chosen for the second one? Why not the exclamation mark
> in that case? (Sure, C didn't exist by then, but the bang probably
> was used to negate in other languages of the time, I think.)
>
> 2) Symbol for the end of line anchor
>
> What is the reason that the beginning of line and end of line
> anchors are different symbols? Is there a reason why not only one
> symbol, say the circumflex, was chosen to represent both? I
> currently see no disadvantages of such a design. (Circumflexes
> aren't likely to end lines of text, neither.)
>
> I would appreciate if you could help me understand these design
> decisions better. Maybe there existed RE notations that were simply
> copied ...
>
>
> meillo
>

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  reply	other threads:[~2021-09-17  9:32 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  8:52 markus schnalke
2021-09-17  9:32 ` Rob Pike [this message]
2021-09-17  9:32   ` Rob Pike
2021-09-17 10:10   ` markus schnalke
2021-09-17 16:40 Douglas McIlroy
2021-09-17 20:40 ` Chris Torek
2021-09-18  1:03   ` Greg 'groggy' Lehey
2021-09-18  1:23     ` Bakul Shah

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