Re: re-entrant parsers, pure_parser, bison, flex

Hi,


I did something of this nature to create a thread-safe interpreter that
accepts arbitrary commands at runtime from a one-liner to an entire file.
I used pure-parser in bison and flex. A GUI can send this parser commands
at runtime and then call yyparse to run the interpreter.


Eliminate globals...


Use %pure_parser
Carry a parameter through the parser calls
#define YYPARSE_PARAM param
#define YYLEX_PARAM param
I had to write a awk script to change the yacc/lex generated files
so that they would carry the 'param' through every
function call. This was important b/c I was using string
input.


Use string input instead of file input...but remember that it's
multithreaded, so you have to have a buffer for each possible thread...


#ifdef HAVE_FLEX
#undef YY_INPUT
#define YY_INPUT(b,r,ms) (r=_fake_parser_input_with_string(b,ms,param))
#endif


#undef YY_DECL
#define YY_DECL int yylex(lvalp,param)YYSTYPE*lvalp;void*param;


....There's lots of interactions here. Please send me a note if you want a
copy of the files or such...The O'Reilly lex/yacc book is a must when your
doing this kind of stuff too. Good luck.


-Jeffrey Vetter




On 21 Jul 1997, Brian W. Inglis wrote:


> PJ Mealy writes:
> > As the GUI is structured around an event processing loop
> > I can't just go ahead and do the full parse in one go.
> > I need to have the event loop active periodically to process
> > progress bar updates and respond to a click on the CANCEL button.
>
> Sure you can. Just invert the approach. Think INPUT.
> Add whatever you need into the yylex() function. ...
--

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