Re: syntax complexity

From	anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups	comp.compilers
Subject	Re: syntax complexity
Date	2023-02-21 18:39 +0000
Organization	Institut fuer Computersprachen, Technische Universitaet Wien
Message-ID	<23-02-059@comp.compilers> (permalink)
References	(3 earlier) <23-02-050@comp.compilers> <29156_1676600565_63EEE4F4_29156_1009_1_23-02-051@comp.compilers> <23-02-052@comp.compilers> <23-02-053@comp.compilers> <23-02-055@comp.compilers>

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anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:
>Regular expression syntax is missing an operator that signifies the
>intersection of the sets recognized by the operand regexps.  Let's
>call this operator "&".  Then this requirement for an FP number can be
>expressed as:
>
>([0-9.]*&.*[0-9].*)(E[0-9]+)?&.*[.E].*
...
>[Wouldn't that pattern allow 1.2.3 ? -John]

Good point.  The & operator makes it easy to fix this bug (once you
have found it):

([0-9.]*&.*[0-9].*)(E[0-9]+)?&.*[.E].*&[^.]*[.]?[^.]*

But it suggests that I tried to put too many requirements into the
first part, so let's try again:

At most one "." in front of at most one "E":  [0-9]*[.]?[0-9]*E?[0-9]*
At least one of "." or "E":                   .*[.E].*
At least one digit in front of and after "E": .*[0-9].*E[0-9]+

In total:

[0-9]*[.]?[0-9]*E?[0-9]*&.*[.E].*&.*[0-9].*E[0-9]+

- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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syntax complexity gah4 <gah4@u.washington.edu> - 2023-02-15 15:08 -0800
  Re: syntax complexity Thomas Koenig <tkoenig@netcologne.de> - 2023-02-16 06:32 +0000
  Re: syntax complexity Hans-Peter Diettrich <DrDiettrich1@netscape.net> - 2023-02-16 12:03 +0100
    Re: syntax complexity gah4 <gah4@u.washington.edu> - 2023-02-16 11:33 -0800
      Re: syntax complexity gah4 <gah4@u.washington.edu> - 2023-02-16 16:08 -0800
      Re: syntax complexity Roger L Costello <costello@mitre.org> - 2023-02-20 15:09 +0000
        Re: syntax complexity gah4 <gah4@u.washington.edu> - 2023-02-20 09:57 -0800
          Re: syntax complexity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2023-02-21 08:14 +0000
            Re: syntax complexity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2023-02-21 18:39 +0000
              Re: ireegular expressions, syntax complexity anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2023-02-22 10:55 +0000
            Re: irregular expressions, syntax complexity arnold@freefriends.org (Aharon Robbins) - 2023-02-22 08:53 +0000
            Re: irregular expressions, syntax complexity Kaz Kylheku <864-117-4973@kylheku.com> - 2023-02-23 00:34 +0000
        Re: syntax complexity George Neuner <gneuner2@comcast.net> - 2023-02-20 13:49 -0500
      syntax complexity Christopher F Clark <christopher.f.clark@compiler-resources.com> - 2023-02-21 20:54 +0200

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