[antlr-interest] Java.g grammar issues & potential fix

[Terence Parr]

On Apr 7, 2004, at 1:10 AM, Vincent Mallet wrote:
>  1. the grammar won't accept octal-looking floats or doubles
>     (09d for example)
>  2. the grammar will accept hexadecimal numbers with a fractional
>     part (0x12.34 for example)
>
> I have seen a fix for problem #1 in java.g version 1.21-october-2003
> but #2 is definitely broken.
>
> In an attempt to clarify that part of the grammar I came up with a
> version of the NUM_INT lexer rule which seems to be more correct and
> potentially easier to read (indentation might need some work).


>
> If you have an opinion on the new rule I would love to hear it.
>

It seems easier to read, but you've added a syntactic predicate that 
will execute upon every numeric value I think.  Given that this could 
cause lots of exceptions, I'm guessing it would seriously degrade the 
lexer's speed (probably bad as it is). ;)

It is often the case that being super precise in the grammar can cost 
you.  Probably best to leave this syntactic hole as there are always 
holes like this.


Regards,
Terence
--
Professor Comp. Sci., University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
Cofounder, http://www.jguru.com
Cofounder, http://www.knowspam.net enjoy email again!
Cofounder, http://www.peerscope.com pure link sharing





 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
     http://groups.yahoo.com/group/antlr-interest/

<*> To unsubscribe from this group, send an email to:
     antlr-interest-unsubscribe at yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
     http://docs.yahoo.com/info/terms/