From: "ara.t.howard" <ara.t.howard@...>
Date: 2008-05-06T01:48:00+09:00
Subject: Re: How would you design regexps in the integer domain?


On May 5, 2008, at 2:24 AM, Andreas Launila 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'").
>
> My main objective is to make the syntax intuitive to Ruby users. I  
> have
> been toying around with a few different approaches, but I'm not sure  
> if
> any meet the goal. How would you design the syntax for regexps in the
> integer domain?
>
> The syntax does not need to support especially many operators:
> * Kleene star ('*' in character regexps)
> * "At least once" ('+' in character regexps)
> * Alternation ('|' in character regexps, i.e. "a|b" being "'a' or  
> 'b'")
>
> Below are some of the approaches one could take.


i personally would not bother making a new syntax, rather i'd simply  
use the exiting one and add a new atom builder:



cfp:~ > cat a.rb
N = 0.chr

def N n
   "#{ n }#{ N }"
end

module Enumerable
   def nmatch pattern
     match = pattern.match( select{|i| Fixnum === i}.join(N) )
     if match
       returned = []
       captured = match.to_a.map{|capture| capture.split N}
       returned << captured.first.map{|s| Float(s).to_i}
       captured[1..-1].each do |list|
         returned << Float(list.first).to_i
       end
       returned
     else
       nil
     end
   end
end

pattern = %r/#{ N 42 }#{ N 7 }(#{ N 17 }){2}(#{ N 1 }){1,}/

p [42, 7, 17, 17, 1, 1, 1].nmatch( pattern ).to_a



cfp:~ > ruby a.rb
[[42, 7, 17, 17, 1, 1], 17, 1]




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