From: Anthony Durity <anthony.durity@...>
Date: 2006-02-07T02:24:42+09:00
Subject: Re: Merging regular expressions

Jacob, Brilliant!

But... see my last post, i want to avoid iteration by merging all
regexps into one large regexp. However, this is absolutely beautiful
and correct. Taken with the replies I got earlier this is a great
start.

Question... What would the following code output?

r = []
r << /aaa/
r << /[ab][ab][ab]/
m = Regexp.union( *r )
m =~ "aaa" #  => ?

(I think I basically want to be able to twiddle with the finite
automata the regexps make when they are compiled/created, I dunno if
this is possible)

Later,
    Anthony

On 2/6/06, Jacob Fugal <lukfugl@gmail.com> wrote:
> On 2/6/06, Anthony Durity <anthony.durity@gmail.com> wrote:
> > r[0] = /a/
> > r[1] = /b/
> > m = Regexp.union(r0.source, r1.source)
> > # _but_ when I go to check s with
> > m =~ s
> > # if it matches, i want it to tell me which of the original r[i] would have matched!
>
> How about:
>
>  class Regexp
>    class Union
>      def initialize( *regexen )
>        @regexen = regexen
>      end
>
>      def <<( regex )
>        @regexen << regex
>      end
>
>      def =~( other )
>        regexen = @regexen.select{ |regex| regex =~ other }
>        raise "ambiguous input" if regexen.size > 1
>        return nil if @regexen.empty?
>        return @regexen.index(regexen[0])
>      end
>
>      def []( index )
>        @regexen[index]
>      end
>    end
>
>    def self.union( *regexen )
>      Regexp::Union.new( *regexen )
>    end
>  end
>
> Usage:
>
>  r = []
>  r << /a/
>  r << /b/
>  m = Regexp.union( *r )
>  m =~ "a test" # => 0
>  m =~ "test b" # => 1
>  m =~ "none" # => nil
>  m =~ "ambiguous" # raises "ambiguous input"
>
> Jacob Fugal
>
>