[antlr-interest] Distinguish between number and value

[Jim Idle]

Usually, you would do such things in the parser, but in this instance you
can actually do it in the lexer if you want. If you leave it to the pasere
then you would need a keyword 'px', which may be awkward elsewhere of
course:

 

tokens

{

 PIXELS;

}

 

// Parser goes here

 

 

NUMBER 

      : ('0'..'9')+ 

           ( 

                (('px')=> 'px') { $type = PIXELS; } 

              | // Just a number after all

           )

      ;

 

 

Should work fine for you and will avoid lexing errors if the input is 89p by
mistake, that would go back to the parser as two tokens and it will error
out gracefully. Note, that you may get a warning about the PIXELS token,
which you can ignore.

 

There are other approaches of course, such as leaveing the px to go back as
a token like ID, then in the parser allowing:

 

NUMBER ID { see if ID text is 'px' else error}

 

Hope that helps,

 

Jim

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Adrian Ber
Sent: Friday, November 02, 2007 10:07 AM
To: antlr-interest at antlr.org
Subject: [antlr-interest] Distinguish between number and value

 

I'm using a CSS grammar and wondering how can I write a rule to distinguish
between a number and a value. If I have the input "123" and "123px" I want
to know that "123" is a number and "123px" is a length. 

I'm new to ANTLR and using v3. 

 

Thanks a lot,

A.


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