Exercise 2: Parentheses Balancing

parens.rb

# https://class.coursera.org/progfun-004/assignment/view?assignment_id=4
# Exercise 2: Write a recursive function which verifies the balancing of parentheses in a string

def balance(ary, collected = [])
  return collected.length.even? if ary.empty?
  char = ary.shift
  balance(ary, collected + char.scan(/\(|\)/))
end

require 'minitest/autorun'
require 'minitest/pride'

describe 'matching parens' do
  describe 'valid' do
    it '' do
      balance('(if (zero? x) max (/ 1 x))'.split('')).must_equal true
    end

    it '' do
      balance("I told him (that it's not (yet) done). (But he wasn't listening)".split('')).must_equal true
    end
  end

  describe 'invalid' do
    it '' do
      balance(':-)'.split('')).must_equal false
    end
     it '' do
       balance('())()'.split('')).must_equal false
     end
  end
end