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Gabriele Farina on January 15, 2009 in actionscript

AsYacc - first alpha release

Before going further with discussing how to add runtime scripting support to a Flash applications, I'd like to share with you the source code of a porting of Yacc I did a while ago. I did some simple modification to make Yacc able to generate ActionScript 3.0 source code instead of C. It works quite well and supports a lot standard Yacc features. There might be some issues - report them to me and I'll try to fix them :)

You can easilly find documentation about Yacc searching Google (you can start here for example).

Usually Yacc is used in conjunction with a Scanner generator (like Lex/Flex), but I didn't to any porting of commonly used Scanner generators yet.

Here you can download the sources. The source code should be portable and compilable on all the most common platform, but I didn't tested it on Windows yet. To compile the source code on Mac or Linux, cd to the source code directory and type use:

gcc *.c -o AsYacc

Once you have the compiled binary file, you can run the Parser generator using:

./AsYacc -Hpackage=it.sephiroth.test grammar.y

Where grammar.y is a text file that contains the grammar of a language defined using the proper syntax (see the docs online for all the detailed information you may need).

Here you can download a simple calculator example that uses the RegexLexer described previously to implement the Scanner. For the ones who might be interested, here is the grammar used:

/* Infix notation calculator. */ 

%token NUM 
%left '-' '+' 
%left '*' '/' 
%left NEG 
%right '^' /* exponentiation */
	exp			{ trace( $1 ); }

	 NUM 			{ $$ = $1; }
	| exp '+' exp 		{ $$ = $1 + $3; } 
	| exp '-' exp 		{ $$ = $1 - $3; }
	| exp '*' exp 		{ $$ = $1 * $3; } 
	| exp '/' exp 		{ $$ = $1 / $3; } 
	| '-' exp %prec NEG 	{ $$ = -$2; } 
	| exp '^' exp 		{ $$ = Math.pow( $1, $3 ); } 
	| '(' exp ')' 		{ $$ = $2; } 


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first release? quite great.
Hi Max, sorry but I didn't see your comment before. I've never had this kind of issue, but probably you can avoid the problem by grouping some rules togheter (ie: keywords or symbols), and then generate different tokens using custom rules. Could you please explain me more in depth your situation ? Maybe I can help you more
Hi Gabriele,
thanks four your code, I can use it very well.
But I have one problem: If I add more than 31 rules to the class ExprLexer it does not work anymore. It seems that there is a restriction to 32 patterns. The pattern becomes too large which is built in RegexLexer::buildRegExp(). Do you have any idea?

Best Regards

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