Re: Source locations with Flex+Bison

On Fri, 31 Mar 2005, Bjarni Juliusson wrote:


> The problem:
> I have a lexer, written for Flex, and a parser, written for Bison. Now I
> want the source code locations of the tokens to be propagated up to the
> parser to allow meaningful error messages.
[...]


> I have no reason to make the parser pure, by the way.


I recommend always generating a pure parser. Even if you don't want
to use multiple threads or processes now, you might want to in the
future. I find the extra effort of making functions (including
`yylex()' and `yyparse()') thread-safe and/or reentrant is minimal in
comparison to the potential benefits. In addition, with Bison, you
can pass a parameter to `yyparse()' when you generate a pure parser; a
feature I find extremely useful.


I don't remember the details of using locations, since I haven't been
working on this part of my package lately. However, if you want an
example, you may examine my code. It's available at:
http://savannah.gnu.org/cgi-bin/viewcvs/3dldf/3dldf/Group/


I define `YYLTYPE' in the file
http://savannah.gnu.org/cgi-bin/viewcvs/3dldf/3dldf/Group/CWEB/pbsndecl.w
It's also used in the files `pfuncfin.w', `scan.web',
and `scanprsf.web' in the same directory.
You can find examples of using locations in parser rules in
the files `pcondit.w' and `pnumexpr.w'.


Laurence Finston
http://www.gnu.org/software/3dldf/LDF.html

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