From: "Wolfgang Nádasi-Donner" <ed.odanow@...>
Date: 2007-10-09T16:30:32+09:00
Subject: Re: regexp question - look for parentheses then remove them

Jesús Gabriel y Galán wrote:
> I've read that the .NET regex engine has some constructs to recognize
> balanced constructs like parens...

It's possible in Ruby 1.9 or Ruby 1.8 and the Oniguruma library too:

module Matchelements
  def bal(lpar='(', rpar=')')
    raise RegexpError,
      "wrong length of left bracket '#{lpar}' in bal" unless lpar.length 
== 1
    raise RegexpError,
      "wrong length of right bracket '#{rpar}' in bal" unless 
rpar.length == 1
    raise RegexpError,
      "identical left and right bracket '#{lpar}' in bal" if 
lpar.eql?(rpar)
    lclass, rclass = lpar, rpar
    lclass = '\\' + lclass if lclass.match(/[\-\[\]]/)
    rclass = '\\' + rclass if rclass.match(/[\-\[\]]/)
    return "(?<bal>" +
              "[^#{lclass}#{rclass}]*?" +
              "(?:\\#{lpar}\\g<bal>\\#{rpar}" +
                "[^#{lclass}#{rclass}]*?" +
              ")*?" +
           ")"
  end
end
include Matchelements

result = "3 * (2 + (1 + 3)) + (1 * 4)".scan(/\(#{bal()}\)/)

p result # => [["2 + (1 + 3)"], ["1 * 4"]]

Wolfgang Nádasi-Donner
-- 
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