From: krand AT ican DOT net (Andrew Ellem)
Newsgroups: comp.os.msdos.djgpp
Subject: Flex, Bison & How to use them
Followup-To: comp.os.msdos.djgpp
Date: Sat, 31 Jan 1998 03:46:02 GMT
Organization: ACC TelEnterprises Ltd.
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Reply-To: krand AT ican DOT net
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To: djgpp AT delorie DOT com
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I've been experimenting with embeddable languages for
extensions to my program (a RPG if you're interested),
and so far I've simply been parsing text files (as text).
But I've found this to be too slow and my "language" is
too inflexable, so I decided to look at Flex & Bison.

I've looked around the docs and info files and I belive
I understand their input and what it represents.  But
I don't understand what to do with the output...

Here's what I know : 
Flex takes its input file (which contains the tokens 
& symbols used by the language) and creates a .c file
which has the function yylex().

Bison takes a grammar file and creates a parser function, 
yyparse(), from it.  I create a .o file from this, which
I link into my program.

Here's what I don't know :
What do I do with the yyparse() function within my 
program?  What setup does it require?  (This is probably
in the info file, but I might have missed it...)

What exactly does the parser do?  I got the impression
that it's basically a virtual machine of sorts, but is
it completly self-contained?  What I mean is, is it 
possible for me to alter variables from within the 
parser?

e.g.
I have an object :
class Foo
{
int x, y, z;
char *scriptFile;  // A pointer to the "compiled" script
}

Could I have the script (Foo::scriptFile) alter the 
variables of class Foo?  Am I making any sense? Am I
posting in the correct news group?

Any help is appreciated...
--
Andrew Ellem
krand AT ican DOT net