[antlr-interest] Problems parsing real numbers

[mzukowski at bco.com]

By the way, look at the generated code, this is the way to learn ANTLR.  It
will be obvious what the problem is, even if the solution isn't so obvious.


Monty

> -----Original Message-----
> From: aliguori123 [mailto:ajl13 at bellatlantic.net]
> Sent: Monday, January 21, 2002 3:14 PM
> To: antlr-interest at yahoogroups.com
> Subject: [antlr-interest] Problems parsing real numbers
> 
> 
> Hi,
> 
> I just started using ANTLR from using bison/flex.  I really like ANTLR
> over these two tools but I am struggling when trying to parse real
> numbers.  Specifically, floating point numbers that do not have an
> explicit whole number portion (i.e. '.5', '.3').
> 
> The strange thing is that in attempting to figure out how to
> accomplish this in ANTLR, I pulled in the grammars from the java,
> pascal, and GNUC examples and they all seem to have the same problem. 
> I've included a sample below that reproduces the problem.  From what I
> can tell - and that doesn't mean much of course - it should do the
> job, but the parser will bug out that '.' is an illegal character if
> one of these numbers are inputted.  I am using ANTLR v2.7.1.
> 
> Otherwise, I am finding ANTLR to be incredibly useful.  I was able to
> translate all the expression parsing stuff from lex/yacc to ANTLR with
> no problems.  It actually turned out alot better because ANTLR handles
> things a bit nicer than lex/yacc do.  ANTLR is really a great tool.
> 
> Thanks,
> Anthony
> 
> <-- BEGIN SNIPPET -->
> 
> options {
>     language="Cpp";
> }
> 
> class NumberParser extends Parser;
> options {
>     buildAST = true;
> }
> 
> expr: (NUM_INT | NUM_REAL) EOL! ;
> 
> class NumberLexer extends Lexer;
> options {
> k=4;
> }
> 
> WS_	:	(' '
> 	|	'\t'
> 	|	'\r')
> 		{ _ttype = ANTLR_USE_NAMESPACE(antlr)Token::SKIP; }
> 	;
> 
> DOT: '.';
> EOL: '\n';
> 
> NUM_INT
> 	{bool isDecimal=false; /* changed to bool for C++ */}
> 	:/*	".." {_ttype = DOTDOT;} 
>         |*/   '.'  {_ttype = DOT;}
> 		(('0'..'9')+ (EXPONENT)? { _ttype = NUM_REAL; })?
> 	|	(	'0' {isDecimal = true;} 
>                 // special case for just '0'
> 		|	('1'..'9') ('0'..'9')*  
> {isDecimal=true;}		// non-zero decimal
> 		)
> 		(	{ LA(2)!='.' && LA(3)!='.' && isDecimal}?
> 			(	'.' ('0'..'9')* (EXPONENT)?
> 			|	EXPONENT
> 			)
> 			{ _ttype = NUM_REAL; }
> 		)?
> 	;
> 
> EXPONENT
> 	:	('e') ('+'|'-')? ('0'..'9')+
> 	;
> 
> class NumberTreeWalker extends TreeParser;
> options {
> 	buildAST = true;
> }
> 
> expr returns [double r]
> {
> 	r=0.0;
> }
> 	: ni:NUM_INT		{r=atoi(ni->getText().c_str());}
> 	| nf:NUM_REAL		{r=atof(nf->getText().c_str());}
> 	;
> 
> <-- END SNIPPET -->
> 
> 
>  
> 
> Your use of Yahoo! Groups is subject to 
http://docs.yahoo.com/info/terms/ 



 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/