[TUHS] v7 K&R C [really lexers]

[Warner Losh]

On Sat, May 16, 2020, 6:05 PM Brantley Coile <brantley at coraid.com> wrote:

> “The asteroid to kill this dinosaur is still in orbit.“
>
>     —- Plan 9 lex man page
>
>
> I always hand craft my lexers and use yacc to parse. Most  code on plan 9
> does that as well.
>

Wow! That is the most awesome thing I've seen in a while....

Warner


  Brantley
>
>
> On May 16, 2020, at 8:00 PM, Jon Steinhart <jon at fourwinds.com> wrote:
>
> Steffen Nurpmeso writes:
>
> Tony Finch wrote in
>
> <alpine.DEB.2.20.2005142316170.3374 at grey.csi.cam.ac.uk>:
>
> |Larry McVoy <lm at mcvoy.com> wrote:
>
> |>
>
> |> It's got some perl goodness, regexps are part of the syntax, ....
>
> |
>
> |I got into Unix after perl and I've used it a lot. Back in the 1990s I saw
>
> |Henry Spencer's joke that perl was the Swiss Army Chainsaw of Unix, as a
>
> |riff on lex being its Swiss Army Knife. I came to appreciate lex
>
> |regrettably late: lex makes it remarkably easy to chew through a huge pile
>
> |of text and feed the pieces to some library code written in C. I've been
>
> |using re2c recently (http://re2c.org/), which is differently weird than
>
> |lex, though it still uses YY in all its variable names. It's remarkable
>
> |how much newer lexer/parser generators can't escape from the user
>
> |interface of lex/yacc. Another YY example: http://www.hwaci.com/sw/lemon/
>
>
> P.S.: i really hate automated lexers.  I never ever got used to
>
> use them.  For learning i once tried to use flex/bison, but
>
> i failed really hard.  I like that blood, sweat and tears thing,
>
> and using a lexer seems so shattered, all the pieces.  And i find
>
> them really hard to read.
>
>
> If you can deal with them they are surely a relief, especially in
>
> rapidly moving syntax situations.  But if i look at settled source
>
> code which uses it, for example usr.sbin/ospfd/parse.y, or
>
> usr.sbin/smtpd/parse.y, both of OpenBSD, then i feel lost and am
>
> happy that i do not need to maintain that code.
>
>
> --steffen
>
>
> Wow, I've had the opposite experience.  I find lex/yacc/flex/bison really
> easy to use.  The issue, which I believe was covered in the early docs,
> is that some languages are not designed with regularity in mind which makes
> for ugly code.  But to be fair, that code is at least as ugly with
> hand-crafted
> code.
>
> I believe that the original wisecrack was directed towards FORTRAN.  My
> ancient
> experience was that it was using lex/yacc for HSPICE was not going to work
> so I
> had to hand-craft code for that.
>
> Jon
>
>
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