gistfile1.rb

def find_first a, b
  0.upto(a.length-b.length) do |i|
    catch :fail do
      0.upto(b.length-1) do |j|
        throw :fail unless a[i+j] == b[j]
      end
      return i
    end
  end
  nil
end

find_first %w[a b c d], %w[c d]