Re: Tiny regular expressions code

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.lang.forth
Subject	Re: Tiny regular expressions code
Date	2014-10-18 15:43 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<2014Oct18.174324@mips.complang.tuwien.ac.at> (permalink)
References	<543bfa10$0$2928$e4fe514c@news2.news.xs4all.nl> <6a35de1e-64e4-426c-b9d9-e3c70ab2eeee@googlegroups.com> <544139de$0$2964$e4fe514c@news2.news.xs4all.nl> <54414f47$0$2922$e4fe514c@news2.news.xs4all.nl>

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Hans Bezemer <the.beez.speaks@gmail.com> writes:
>Hans Bezemer wrote:
>
>If you think the previous version (which kept the state in stack values) was
>some heavy duty code, here is a recursive version which is cleaner:
> 
>---8<---
>: chop 1- swap char+ swap ;            ( a n -- a+1 n-1)
>: 4drop 2drop 2drop ;                  ( a b c d --)
>
>: match-wild
>  begin
>    dup                                \ exit when match string is exhausted
>  while
>    over c@ [char] ? =                 \ match any character
>    if                                 \ except empty string
>      >r over r> swap 0= if 4drop false exit then
>      2>r chop 2r> chop                \ okay, next one please
>    else
>      over c@ [char] * =               \ match zero or more characters
>      if                               \ because we eat one character
>        2over 2over chop recurse if 4drop true exit then
>        >r over r> swap if 2over chop 2over recurse else false then
>        >r 4drop r> exit               \ from match string, recursion stops
>      else                             \ nothing worked with this wildcard
>        2over if                       \ not an empty string?
>          c@ >r over c@ r> =           \ if so, compare both characters
>          if 2>r chop 2r> chop else 4drop false exit then
>        else                           \ otherwise, it's no use going on
>          drop 4drop false exit
>        then
>      then
>    then
>  repeat                               \ get next character
>  >r drop nip r> or 0=                 \ only a match if both are at the end
>;

Related to an adjacent discussion: I think that this serves nicely as
a demonstration that lack of locals does not automatically lead to
well-factored code (especially if you use 'the magical "seven, plus or
minus two" words' *maximum* as the definition of "well-factored").

- anton
-- 
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
     New standard: http://www.forth200x.org/forth200x.html
   EuroForth 2014: http://www.euroforth.org/ef14/

Thread

Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-13 18:15 +0200
  Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-13 18:18 +0200
    Re: Tiny regular expressions code Pablo Hugo Reda <pabloreda@gmail.com> - 2014-10-13 09:32 -0700
    Re: Tiny regular expressions code Howerd <howerdo@yahoo.co.uk> - 2014-10-13 11:18 -0700
      Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-13 20:36 +0200
        Re: Tiny regular expressions code Howerd <howerdo@yahoo.co.uk> - 2014-10-13 11:53 -0700
  Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-13 22:14 +0200
  Re: Tiny regular expressions code mhx@iae.nl (Marcel Hendrix) - 2014-10-13 22:59 +0200
    Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-13 23:11 +0200
  Re: Tiny regular expressions code albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-14 09:22 +0000
    Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-14 17:43 +0200
      Re: Tiny regular expressions code albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-14 16:27 +0000
        Re: Tiny regular expressions code albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-15 09:48 +0000
          Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-15 17:38 +0200
            Re: Tiny regular expressions code albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-16 09:20 +0000
  Re: Tiny regular expressions code josv@planet.nl - 2014-10-17 05:03 -0700
    Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-17 17:48 +0200
      Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-17 19:20 +0200
        Re: Tiny regular expressions code anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-18 15:43 +0000
          Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-18 18:53 +0200
          Re: Tiny regular expressions code hughaguilar96@yahoo.com - 2014-10-18 19:19 -0700
            Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-19 14:52 +0200
              Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-19 15:25 +0200
                Re: Tiny regular expressions code Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-19 21:14 +0200
                Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-20 00:17 +0200
              Re: Tiny regular expressions code albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-19 17:10 +0000
                Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-19 19:59 +0200
          Re: Tiny regular expressions code Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-19 09:31 -0500
            The magical number seven (was: Tiny regular expressions code) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-20 09:10 +0000
              Re: The magical number seven (was: Tiny regular expressions code) m.a.m.hendrix@tue.nl - 2014-10-20 03:13 -0700
                Re: The magical number seven (was: Tiny regular expressions code) mhx@iae.nl (Marcel Hendrix) - 2014-10-20 20:19 +0200
                Re: The magical number seven Lars Brinkhoff <lars.spam@nocrew.org> - 2014-10-21 08:56 +0200
                Re: The magical number seven Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-21 11:44 +0200
                Re: The magical number seven (was: Tiny regular expressions code) Just Ian <superian@gmail.com> - 2014-10-21 07:06 -0700
                Re: The magical number seven (was: Tiny regular expressions code) mhx@iae.nl (Marcel Hendrix) - 2014-10-21 20:11 +0200
                Re: The magical number seven Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 04:27 -0500
              Re: The magical number seven (was: Tiny regular expressions code) Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-20 17:28 +0200
                Re: The magical number seven (was: Tiny regular expressions code) anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2014-10-20 16:25 +0000
                Re: The magical number seven (was: Tiny regular expressions code) "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-20 16:36 -0400
                Re: The magical number seven "Elizabeth D. Rather" <erather@forth.com> - 2014-10-20 12:19 -1000
                Re: The magical number seven "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-21 01:47 -0400
                Re: The magical number seven "Elizabeth D. Rather" <erather@forth.com> - 2014-10-20 20:31 -1000
                Re: The magical number seven albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-10-21 09:06 +0000
                Re: The magical number seven "Elizabeth D. Rather" <erather@forth.com> - 2014-10-21 08:47 -1000
                Re: The magical number seven "Rod Pemberton" <buzzoff@nonamewhichexists.cmm> - 2014-10-22 02:21 -0400
                Re: The magical number seven (was: Tiny regular expressions code) Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-21 10:29 +0200
                Re: The magical number seven (was: Tiny regular expressions code) Bernd Paysan <bernd.paysan@gmx.de> - 2014-10-21 11:34 +0200
                Re: The magical number seven Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 04:41 -0500
                Re: The magical number seven Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-26 12:07 +0100
                Re: The magical number seven Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 13:58 -0500
                Re: The magical number seven (was: Tiny regular expressions code) hughaguilar96@yahoo.com - 2014-10-20 16:34 -0700
                Re: The magical number seven Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 04:33 -0500
                Re: The magical number seven Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-26 12:12 +0100
              Re: The magical number seven Andrew Haley <andrew29@littlepinkcloud.invalid> - 2014-10-26 04:24 -0500
          Re: Tiny regular expressions code mhx@iae.nl (Marcel Hendrix) - 2014-10-19 17:10 +0200
      Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-18 16:02 +0200
        Re: Tiny regular expressions code josv@planet.nl - 2014-10-18 07:50 -0700
  Re: Tiny regular expressions code Hans Bezemer <the.beez.speaks@gmail.com> - 2014-10-18 17:27 +0200
  Re: Tiny regular expressions code the_gavino_himself <visphatesjava@gmail.com> - 2014-11-08 19:24 -0800
  Re: Tiny regular expressions code the_gavino_himself <visphatesjava@gmail.com> - 2014-11-08 20:42 -0800

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