chop implementation, see http://codekata.pragprog.com/2007/01/kata_two_karate.html

chop.rb

def chop(v, values)

  ix = values.length / 2
  m = values[ ix ]

  return ix if v == m
  return nil if values.length < 2

  if v > m
    ix + 1 + chop(v, values[ix+1..-1]) rescue nil
  else
    chop(v, values[0..ix-1]) rescue nil
  end
end

a = [ 1, 4, 7, 13, 54, 88, 102 ]

puts chop(0, a)
puts chop(1, a)
puts chop(4, a)
puts chop(7, a)
puts chop(14, a)
puts chop(88, a)
puts chop(102, a)
puts chop(103, a)