small parsing exercise

parse.rb

def parse(name)
  results = []
  tokens = name.split(/(\[[^\]]*\])/).reject{|s| s.empty? }
  permutations = 2**tokens.count{|s| s.start_with?("[") } 
  permutations.times do |permutation|
    result = ""
    opt_count = 1
    tokens.each do |word|
      if word.start_with?("[")
        if (opt_count & permutation) > 0
          result<<word[1..-2]
        end
        opt_count+=1
      else
        result<<word
      end
    end
    results << result
  end
  results
end

describe "parse" do 

  it 'should list all permutations, text in brackets is optional' do
    strings = parse('foo[bar]')
    strings.should include('foo')
    strings.should include('foobar')
    strings.should_not include('bar')
    strings.size.should == 2
  end
  
  it 'should list all permutations, text in brackets is optional' do
    strings = parse('[foo]bar[baz]')
    strings.should include('foobar')
    strings.should include('bar')
    strings.should include('barbaz')
    strings.should include('foobarbaz')
    strings.should_not include('foo')
    strings.should_not include('baz')
    strings.size.should == 4
  end

end