[antlr-interest] Problems parsing real numbers

[mzukowski at bco.com]

DOT needs to be a "protected" method, it is conflicting with your NUM_INT
rule.  Or since you don't reference DOT from any other rule, it could be in
the tokens section, just like DOTDOT is, presumably.  Or in your real parser
you reference DOT an DOTDOT which implicitly defines it for the lexer.

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 -->
> 
> 
>  
> 
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