[antlr-interest] How does INTEGER+ '.' INTEGER+ match "2."?

[Kevin J. Cummings]

On 08/08/2010 08:35 PM, Ken Klose wrote:
> Thanks for replying.
> 
> 2. is not a valid PRICE.  PRICE should have at least 1 digit following the
> '.'.  In the context of the string that I am trying to match "2." doesn't
> have any particular significance, it is neither an INTEGER nor a PRICE.  It
> is simply an INTEGER following by an SYMBOL token.  What I don't understand
> is why ANTLR is getting hung up trying to match it as a PRICE when it
> doesn't conform to the PRICE specification.  PRICE specifies another INTEGER
> following the '.' which this input doesn't have.

Ken,
	What you are missing is that PRICE is that PRICE is a token.  Tokens
get matched based on longest possible match.  Once the lexer sees that
it has an INTEGER followed by a '.', its path is chosen.  Its either a
PRICE or its an error (which you are seeing).  If that is not your
intent, then you need to fix your lexer so that it knows better.

Gerald poses a possible solution.  But, perhaps he doesn't go far
enough.  Would the following work for you?

INTEGER: DIGIT+ ( '.' DIGIT+ { $type=PRICE; } )?
       ;

Now, if the lexer sees an INTEGER followed by a '.', it *must* be
followed by DIGITs otherwise, it will just lex an INTEGER, and then try
and deal with the '.' character....

> On Sun, Aug 8, 2010 at 7:28 PM, Gerald Rosenberg <gerald at certiv.net> wrote:
> 
>>
>> ------ Original Message (Sunday, August 08, 2010 6:42:55 PM) From: Ken
>> Klose ------
>> Subject: [antlr-interest] How does INTEGER+ '.' INTEGER+ match "2."?
>>
>>  INTEGER: DIGIT+;
>>> PRICE: INTEGER '.' INTEGER;
>>>
>> Integer and price are ambiguous and, if "2." is a valid price, need to make
>> the decimal field optional.
>>
>> Try:
>>
>> INTEGER : DIGIT+
>>                        (  '.' (DIGIT+)? { $type=PRICE; }  // define PRICE
>>  in the token block
>>                         |  // just an integer
>>                        )
>>                ;
>>
>>
>>
>>
> 
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-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)