On Fri, Feb 28, 2003 at 08:43:49AM -0600, Jack L. Stone wrote:
> I know this was discussed many months ago, but I've forgotten what Bison is
> used for....??

        'bison' is the GNU version of 'yacc'.
        'yacc' (Yet Another Compiler Compiler) is a massively-useful
but evidently forgotten tool for generating parsers.
        Yacc reads a file containing a BNF-like grammar that describes
the syntax of whatever it is that you want to parse, and outputs C
code that parses input in that format. For instance, if you wanted to
parse timestamps, you might specify the grammar as

                date time               /* Date and time */
                | date                  /* Just a date, no time */
                NUMBER '/' NUMBER '/' NUMBER    /* YYYY/MM/DD */
                | DAY_ABBR ' ' MON_ABBR ' ' NUMBER      /* "Mon Jan 13" */
                NUMBER ':' NUMBER ':' NUMBER    /* HH:MM:SS */
                | NUMBER ':' NUMBER             /* HH:MM */

Yacc is most often used in conjunction with 'lex' (or the GNU version,
'flex') which reads an input stream recognizes individual tokens (in
this example: "NUMBER", "DAY_ABBR", and "MON_ABBR") and feeds them back to

Andrew Arensburger, Systems guy         University of Maryland
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