From: Phrogz <phrogz@...>
Date: 2008-05-06T00:15:07+09:00
Subject: Re: How would you design regexps in the integer domain?

On May 5, 2:24 am, Andreas Launila <ruby-t...@lokorin.org> wrote:
> I'm trying to come up with a clean way to specify regexps in the integer
> domain. I.e. instead of describing a pattern of characters (as in normal
> regexps) one describes patterns of integers ("17 followed by 3 or 15"
> rather than "'a' followed by 'b' or 'c'").

You could specify it as a PEG[1], possibly using Treetop[2] in some
way.

The benefit of the PEG (re-usable sub-expressions) may not outweigh
the multi-line nature. However, you could do something like LPEG[3]
does. Instead of using standard PEG syntax come up with a custom
syntax via operators that allows you to describe an entire grammar in
a single Ruby expression. I'm personally not a fan of the syntax LPEG
uses; you could come up with a better one, perhaps using terse method
names instead of operators in some cases. (Perhaps
"pattern.atleast(5)" instead of LPEG's "pattern^5".)

[1] http://en.wikipedia.org/wiki/Parsing_expression_grammar
[2] http://treetop.rubyforge.org/
[3] http://www.inf.puc-rio.br/~roberto/lpeg.html