[antlr-interest] Ambiguous grammar

[Jim Idle]

Please see the FAQ:

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Jim


> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Ondrej Krc-Jediny
> Sent: Wednesday, May 26, 2010 1:34 PM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] Ambiguous grammar
> 
> Hello,
> 
> I am new to ANTLR and I'd appreciate help with my problem. At first
> some grammar rules I am going to talk about:
> 
> DIGIT: '0'..'9';
> LETTER: 'a'..'z'|'A'..'Z';
> 
> REAL
>     :   (DIGIT)+ '.' (DIGIT)* EXPONENT?
>     |   '.' (DIGIT)+ EXPONENT?
>     |   (DIGIT)+ EXPONENT
>     ;
> 
> INTEGER: DIGIT+;
> 
> IDENTIFIER: LETTER+;
> 
> range_expr:
>   expr ('..' expr)?;
> 
> expr: expratom ('+' expratom)?;
> 
> expratom: INTEGER | REAL | IDENTIFIER;
> 
> This grammar allows '1.' and .1' as correct real numbers. Also, it
> allows range expression '1..2', which gets parsed incorrectly as two
> real numbers 1. and .2. Redefining token
> INTEGER: DIGIT '..'?;
> doesn't help, because then also valid range expression 'i + 1..2'. Is
> there any way how to parse the '..' correctly in all cases?
> 
> Thank you very much,
> 
> Ondrej.
> 
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