From: Andreas Launila <ruby-talk@...>
Date: 2008-05-05T23:19:57+09:00
Subject: Re: How would you design regexps in the integer domain?

Eivind Eklund wrote:
> 
> I'd implement this using a generic repeat operator instead of
> hardcoding * and +, and using a generic comparator instead of
> restricting to Integers.
> 
> The declaration for this would be something like
> 
> # Use repeat(0, nil, ...) for *
> # Use repeat(1, nil, ...) for +
> # Use repeat(0, 1, ...) for ?
> def repeat(minimum, maximum, repeated_expression)
> def or(*expressions)
> 
> So you'd convert your example "(17|1 5)*" to repeat(0, nil, or(17, [1, 5]))
> 

I like that idea, especially using the arrays to group integers. It
seems like a rather economic way to do it. I think "any" would fit
better than "or" though (since it can take more than two arguments). The
example in its entirety would then be

  [repeat(0, nil, any(17, [1, 5])), 4711]

I would also consider swapping the position of repeated_expression to
the first argument of repeat, since it seems like a more natural order
to me ("repeat expression between 0 and 4 times"). I'm a bit split on
using nil for infinity, but that is minor.

I will need to explore the idea, but it feels like a good fit to me.
Thank you.

> Actually, as I thought of after I had written the above, I have
> written code that does part of this already, and is generic - it's
> available in types.rb (http://people.freebsd.org/~eivind/ruby/types/).
>  If you want it, I think I can extend that to support repeats tonight.
>  Feel free to use code from it under any license that absolves me of
> legal blame (ie, the only reason I don't put it in the public domain
> is because that expose me to legal liability.)
> 

Thanks for the offer, but there's no need to add additional support. The
important part is the idea, which you have provided.

-- 
Andreas Launila