Binary Chop kata

chop1.rb

require 'rspec-given'

# Really, really, really going nowhere with this at the moment :-(
class Chop
  def initialize(list)
    @list = list
  end

  def find(item, start = 0)
    mid_point = @list.length / 2
    next_point = mid_point + 1

    top = @list[next_point..-1]
    bottom = @list[0...next_point]

    return nil if top.nil? || bottom.empty?

    if bottom.last == item
      mid_point + start
    else
      Chop.new(top).find(item, next_point)
    end
  end
end

describe "binary chop" do
  Then { Chop.new([99]).find(99) == 0 }
  Then { Chop.new([98,99]).find(99) == 1 }
  Then { Chop.new([97,98,99]).find(99) == 2 }
  Then { Chop.new([97,98,99]).find(98) == 1 }
  Then { Chop.new([97,98,99]).find(97) == 0 }  # Failing at the moment
  Then { Chop.new([97,98,99]).find(100).nil? }
end