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Re: re2c-1.0 released!

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From	Ulya Trofimovich <skvadrik@gmail.com>
Newsgroups	comp.compilers
Subject	Re: re2c-1.0 released!
Date	Sun, 3 Sep 2017 17:58:33 +0100
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> In fact we can do it all in standard lex.
> [...]
> Pseudo-code, including a mechanism for returning to the INITIAL
> state without parser involvement:
> [...]

The thing is, the new algorithm is both more *efficient* and *elegant*.
Consider how parsing date in format 'YYYY-MM-DD' would look like in re2c:


@y [0-9]{4} [-] @m [0-9]{2} [-] @d [0-9]{2} {
    unsigned year
        = (y[0] - '0') * 1000
        + (y[1] - '0') * 100
        + (y[2] - '0') * 10
        + (y[3] - '0');
    unsigned month
        = (m[0] - '0') * 10
        + (m[1] - '0');
    unsigned day
        = (m[0] - '0') * 10
        + (m[1] - '0');
}


Here re2c will optimize out all dynamic variables, because @d is always
2 characters behind the end of input, and @m is 3 characters behind @d,
and @y is 5 characters behind @m. So all three variables will be
calculated using static offsets from cursor when it points to the end of
input.


If comments and whitespace are allowed between date components, we could
change the above example like this (now re2c will use variables to track
submatch positions, since components have variable length):


com = "/*" ([^*] | ("*" [^/]))* "*""/";
wsp = [ \t\n\r]* | com;
hyp = wsp [-] wsp;

@y [0-9]{4} hyp @m [0-9]{2} hyp @d [0-9]{2} {
    unsigned year
        = (y[0] - '0') * 1000
        + (y[1] - '0') * 100
        + (y[2] - '0') * 10
        + (y[3] - '0');
    unsigned month
        = (m[0] - '0') * 10
        + (m[1] - '0');
    unsigned day
        = (m[0] - '0') * 10
        + (m[1] - '0');
}

Thread

re2c-1.0 released! Ulya Trofimovich <skvadrik@gmail.com> - 2017-08-27 18:25 +0100
  Re: re2c-1.0 released! Kaz Kylheku <398-816-0742@kylheku.com> - 2017-09-02 11:18 -0400
    Re: re2c-1.0 released! anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-09-02 17:02 +0000
      Re: re2c-1.0 released! Kaz Kylheku <398-816-0742@kylheku.com> - 2017-09-03 15:14 +0000
      Re: re2c-1.0 released! Ulya Trofimovich <skvadrik@gmail.com> - 2017-09-03 17:58 +0100
      Re: re2c-1.0 released! Ulya Trofimovich <skvadrik@gmail.com> - 2017-09-03 18:31 +0100
        Re: re2c-1.0 released! Ben Hanson <jamin.hanson@googlemail.com> - 2017-09-04 05:19 -0700
          Re: re2c-1.0 released! Ulya Trofimovich <skvadrik@gmail.com> - 2017-09-08 23:40 +0100
  Re: re2c-1.0 released! Kaz Kylheku <398-816-0742@kylheku.com> - 2017-09-02 11:18 -0400
  Re: re2c-1.0 released! George Neuner <gneuner2@comcast.net> - 2017-09-02 14:11 -0400
    Re: re2c-1.0 released! Ulya Trofimovich <skvadrik@gmail.com> - 2017-09-03 09:00 +0100
    Re: re2c-1.0 released! Ben Hanson <jamin.hanson@googlemail.com> - 2017-09-03 03:13 -0700
  Re: re2c-1.0 released! Ben Hanson <jamin.hanson@googlemail.com> - 2017-09-03 03:16 -0700

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