From: dblack@...
Date: 2003-04-17T07:31:42+09:00
Subject: Re: regular expressions

Hi --

On Thu, 17 Apr 2003, Hal E. Fulton wrote:

> > 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.

Hmmm....  I guess readability is in the eye of the beholder.  Give me
/\((\d{3})\) (\d{3})-(\d{4})/ any day :-)  Or

/
  # Area code: '(' + 3 digits + ') '
    \((\d{3})\)\
  # Number: 3 digits + '-' + 4 digits
    (\d{3})-(\d{4})
/x

though I find the first one much clearer.

The thing with the local variables is kind of unexpected.  Might it be
more idiomatic to have an object with named attributes?

  res = phone.match(str)
  puts res.area_code     # etc.


David

-- 
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav