[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH] Do not allow identifiers that start with a negative number.

From: Joel E. Denny
Subject: Re: [PATCH] Do not allow identifiers that start with a negative number.
Date: Mon, 24 Jan 2011 22:47:02 -0500 (EST)
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)


On Wed, 19 Jan 2011, Paul Eggert wrote:

> On 01/19/2011 12:13 AM, Alex Rozenman wrote:
> > it is impossible to obtain an unambiguous grammar with syntax extensions
> > like id '[' c_id ']' without involving the ';' requirement.
> Yes, but that's OK; that's what I'm proposing.  That is, I'm proposing that
> if a user wants to use the new syntax extensions, the user also must put ';'
> at the end of each rule.
> It's OK to require ';' for new grammars.  Omitting ';' has been deprecated
> for many years, and no new grammars should be omitting ';'.

I also agree that the code here is hard to read and that something should 
be done eventually.  However, unless there's a bug, can we postpone this 
work until after the 2.5 release?  Named references are experimental, and 
omitting semicolons is deprecated, so I don't see any pressing need to 
address this now.  I feel it would be more beneficial to spend our scarce 
time on the problems already raised in this thread.

Also, as you probably recall, the reason scan-gram.l has to be so messy in 
order to support omitting semicolons is because Bison-generated parsers 
support only one token of lookahead.  However, after 2.5, I'd like to 
propose a mechanism that enables a user to cleanly extend lookahead at 
particular points in a grammar.  About a year ago, I implemented that 
mechanism offline and successfully used it to clean up this area of the 
grammar without changing the functionality.  So, whenever we return to 
this issue, if we find that there's no other nice way to clean up this 
code without losing important backward compatibility, we'll still have a 
decent way out.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]