From: Rob Pike <firstname.lastname@example.org> To: markus schnalke <email@example.com> Cc: TUHS main list <firstname.lastname@example.org> Subject: Re: [TUHS] RegExp decision for meta characters: Circumflex Date: Fri, 17 Sep 2021 19:32:28 +1000 [thread overview] Message-ID: <CAKzdPgzRreiFGdChnfQsZnv0E+sc_TJGVxJme8V9CgVtcQF7aQ@mail.gmail.com> (raw) In-Reply-To: <CAKzdPgyos3psLGBiVde3M0OkpR2FW7483+5NFnM0XX316Cp_4g@mail.gmail.com> [-- Attachment #1: Type: text/plain, Size: 1631 bytes --] *NOT* the same. Sorry.... I hope the example explains better than my prose. -rob On Fri, Sep 17, 2021 at 7:32 PM Rob Pike <email@example.com> wrote: > 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 <firstname.lastname@example.org> 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 >> > [-- Attachment #2: Type: text/html, Size: 2413 bytes --]
next prev parent reply other threads:[~2021-09-17 9:34 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 2021-09-17 9:32 ` Rob Pike [this message] 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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