[antlr-interest] Re: Regular expression "repetition"

[peg_ericsson]

Thanks Mark,

I think your approach is right: "write the grammar to accept any 
number at all ,and then generate an error for the user if the limits 
are exceeded or not met."

My original problem was that I wanted an easy way to translate the 
following piece of protocol syntax presented in ABNF:

AuthData   = "0x" 24*64(HEXDIG)
domainName = (...) *63(ALPHA / DIGIT / "-" / ".") (...)

to ANTLR syntax. I will just write it like:

AuthData : "0x" (HEXDIG)+;

and then check if the string length is within 24..64.

Thanks,
Per

--- In antlr-interest at yahoogroups.com, Mark Lentczner <markl at g...> 
wrote:
> 
> I have found that it is often much more useful, both for the 
grammar 
> and for the user to express size limits (on characters in 
identifiers, 
> in number of digits for numbers, or repeats of some rule) as 
semantic 
> constraints: Write the grammar to accept any number at all, and 
then 
> generate an error for the user if the limits are exceeded or not 
met.  
> Consider:
> 
> ID: LETTER{1,8} ;
> protected LETTER: 'a'..'z' ;
> 
> Does anyone expect "subtotals" to parse as two IDs?
> 
> In your case, have you considered what a run of 64 r structures 
should 
> be?  It is just an error, or is really a structure of 63 r.s 
followed 
> by 1 r?
> 
> 	- Mark
> 
> Mark Lentczner
> markl at w...
> http://www.wheatfarm.org/



 
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