From: Eric Mahurin <eric_mahurin@...>
Date: 2005-10-14T04:03:17+09:00
Subject: Re: Default argument values for blocks



--- Austin Ziegler <halostatue@gmail.com> wrote:

> On 10/13/05, Phil  Tomson <philtomson@gmail.com> wrote:
> > While I tend to agree that there are probably much better
> parser
> > generators available now like ANTLR or even using a
> Ruby-based one like
> > Rockit, I can understand the hesitation to change from
> yacc.  It's a
> > huge amount of work for one, and there would need to be a
> lot of
> > testing to ensure that nothing has broke.  I suspect that a
> change from
> > yacc to another parser generator would delay Ruby2.0 by at
> least
> > several months.  Maybe that would be OK.  Perhaps there
> would be other
> > advantages gained by moving away from yacc that would help
> justify
> > doing so?
> >
> > I'm still in the "It might be a nice feature to have, but
> it's not
> > really needed enough to justify the kinds of changes being
> suggested"
> > category.
> 
> I'm suggesting that it may be time for a parser change
> because the
> proposed language changes IMO are really really really ugly
> -- and I'd
> rather see:
> 
>   foo = lambda { |foo = 1 | 2| puts foo }
> 
> work than not.

How do you interpret the above?

foo = lambda { |foo = 1| (2|puts foo) }

or

foo = lambda { |foo = (1|2)| puts foo }

I think the first interpretation is implementable in most
parsers (including yacc, I think) relatively easily if you just
don't allow "|" directly in the default value (unlike a normal
RHS).  The second interpretation would be more difficult
because it would require an arbitrary amount of lookahead. 
Even if the parser can do it, I think arbitrary amounts of
lookahead should be avoided in a language because it will
result in a performance hit (like backtracking in regular
expressions).



	
		
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