From: Eric Mahurin <eric.mahurin@...>
Date: 2005-11-29T09:18:36+09:00
Subject: Re: String#to_rx ?

On 11/28/05, Nikolai Weibull
<mailing-lists.ruby-talk@rawuncut.elitemail.org> wrote:
> Well, Perl 6 doesn't define the parser as a very complex string.  It's a
> set of regexes - a grammar.

Yep, your right.  Even in perl5, you do it with a set of regexes -
where you can do regex recursion with (??{ $re }).  This is one or two
more languages you have to learn on top of perl - the grammar/regex
language.  And then trying to integrate actions into this becomes a
mess.  I think my approach (no new grammar language - just classes,
objects, and methods) is a more flexible.

> But I'm not saying that that's the best way
> to do it.  I like your grammar package and once namespaces are
> implemented in Ruby I think that it can be made even sweeter (it's a
> little too verbose at the moment).

Thanks.  There are a few things I'm doing for my next release that
will help the verbosity:

- the recommended way to make a parser/lexer will be to sub-class
Grammar (you can do this in the current release - examples in the next
release will do it):

  class Expression < Grammar
    def initialize
       # we don't have to use the Grammar:: prefix all over the place now
       super(expr)
    end
  end
  g = Expression.new
  g.scan(...)

- make Grammar subclasses (in the package) effectively callable
(calling new).  To do this, I just defined class and instance methods
with the same name as the classes that called klass.new.  Before, you
would do something like this Grammar::Code.new {...}, and now (with
the above sub-classing Grammar for parsers), you'd say Code {...}.  I
would have had real callable objects like Python, but this seems like
a good enough hack.