From: "Hal E. Fulton" <hal9000@...>
Date: 2003-04-17T06:31:23+09:00
Subject: Re: regular expressions

----- Original Message ----- 
From: <dblack@superlink.net>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Wednesday, April 16, 2003 12:33 PM
Subject: Re: regular expressions


> I have a few questions -- sort of just "academic" interest, as I am
> (as you know) one of those freaky people who think regular expressions
> are incredibly cool and elegant and have no intention of abandoning
> them :-)
> 

I'll give you my opinion, speaking for no one
else's idea or project.

Regexes are fine, and I wouldn't want to abandon them.

It's the notation that makes my eyes hurt. It looks
like line noise. It's dense, terse, compressed,
cryptic.

> The questions being... what exactly would be happening in the above?
> In what sense is it a "language"?

I'd like to write a complex regex in a more readable 
form which could then be "compiled" to a Ruby regex.
(Now that I think about it, the analogy between regex
notation and machine language is not a bad one.)

Now, I'll be the first to admit that it most cases,
it just doesn't matter much. Most of the time I would
still use a "plain" regualr expression.

But there is a complexity threshold where I would 
rather have a more verbose, readable, multi-line
notation. Whether it's considered a "language" is
debatable -- in fact, the same is true for programming
"languages" in general. ;)

> And at what point would you be
> matching something?  Could you show a mock-up example of a whole real
> case?  

Now you're asking me to invent syntax on the spur of
the moment. I'm not good at that. :)

Here's a very rough first effort. (One too simple really.)

  phone = RegexLang.new(<<EOF)
    string "("
    digits(3,:area_code,Fixnum)
    # Above: Grab three digits, store in area_code
    # as a Fixnum
    string ") "
    match(:rest) do  # Store this stuff in 'rest' as
      digits(3)      # a String
      string "-"
      digits(4)
    end
  EOF

  area_code = rest = nil
  str = "(800) 555-1234"
  phone.match(str)
  puts area_code           # 800
  puts rest                # 555-1234
  area_code.is_a? Fixnum   # true
  puts phone.to_r          # /\((\d{3}) (\d{3}-\d{4})/
    
There are lots of problems here. I just tossed it 
off the top of my head.

> Do you know the way to San Jose?

Take a left turn at Albuquerque, and make sure
Bugs Bunny is following you.

Hal