[antlr-interest] Keywords Vs Identifiers.

[Monty Zukowski]

If you want to handle that in the lexer you need to do it by calling 
the rule that tests the literals table, here's an example from the C 
grammar:

IDMEAT
         :
                 i:ID                {

                                         if ( i.getType() == 
LITERAL___extension__ ) {
                                                 $setType(Token.SKIP);
                                         }
                                         else {
                                                 $setType(i.getType());
                                         }

                                     }
         ;

protected ID
         options
                 {
                 testLiterals = true;
                 }
         :       ( 'a'..'z' | 'A'..'Z' | '_' | '$')
                 ( 'a'..'z' | 'A'..'Z' | '_' | '$' | '0'..'9' )*
         ;

It's actually tricky to figure out how to lex the following whitespace 
and integer without using a syntactic predicate, but a syn pred here 
will be a performance problem.  I would actually recommend using a 
parser filter see http://www.codetransform.com/filterexample.html

By the way your parser solution works just fine too, is probably the 
easiest.

Monty

On May 19, 2004, at 2:55 PM, Bharath wrote:

> Hi Monty,
>
> I did. I figured a way out too but I am not sure if it's an efficient
> solution. I set a rule in the parser which accepts an identifier and I
> extracted the identifier input into a string. If the string is not 
> "TIME", I
> throw an exception, otherwise I accept it. (using getText() method).
>
> Please let me know if this is bad practice.
>
> Thanks!
>
> Bharath.
>
> -----Original Message-----
> From: Monty Zukowski [mailto:monty at codetransform.com]
> Sent: Wednesday, May 19, 2004 4:41 PM
> To: antlr-interest at yahoogroups.com
> Cc: Monty Zukowski
> Subject: Re: [antlr-interest] Keywords Vs Identifiers.
>
> See the documentation about "literals"
>
> Monty
>
> On May 19, 2004, at 8:25 AM, Bharath S wrote:
>
>> Hi Antlers,
>>
>> I have some rules in my grammar, for time literals which require that
>> 'TIME'
>> or "time" be appended to the front of the rule. For eg., time can
>> represented as TIME 99secs. The problem is, "TIME" is not a keyword
>> and so I
>> cant have it in the parser. If I throw it in the lexer, it causes a
>> clash
>> with IDENTIFIER rule, because the lexer sees the rule as
>>
>> TIME: 'T' 'I' 'M' 'E' (Integer) ; and
>> IDENTIFIER: ('a'..'z'|'A'..'Z')+;
>>
>> as expected. Is there a common workaround for this?
>>
>> I can solve this problem by moving a whole bunch of rules in the
>> parser back
>> to the lexer, just to make the TIME rule protected. But it doesnt make
>> sense, at all.
>>
>> Any comments are most welcome.
>>
>> Bharath.
> Monty Zukowski
>
> ANTLR & Java Consultant -- http://www.codetransform.com
> ANSI C/GCC transformation toolkit --
> http://www.codetransform.com/gcc.html
> Embrace the Decay -- http://www.codetransform.com/EmbraceDecay.html
>
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Monty Zukowski

ANTLR & Java Consultant -- http://www.codetransform.com
ANSI C/GCC transformation toolkit -- 
http://www.codetransform.com/gcc.html
Embrace the Decay -- http://www.codetransform.com/EmbraceDecay.html



 
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