Non-working lazy version of permutations.rb

permutations_lazy2.rb

def permutations_lazy(list)
  # return [list] if list.size == 1
  en = Enumerator.new do |y|
    if list.size == 1
      # yield instead of returning in the base case of recursion
      y.yield list
    end

    list.each do |locked|
      puts "locking #{locked}"
      list_copy = list.dup
      list_copy.delete locked
      permutations_lazy(list_copy).each do |permutation|
        puts "permutation #{permutation}, locked #{locked}"
        y.yield permutation.insert(0, locked)
      end
    end
  end
  en
end

if __FILE__ == $0
  pl = permutations_lazy %w[a b c d]
  pl.first(5).each {|i| p i}
end

~output.txt

Output:
["a", "b", "c", "d"]
["a", "b", "c", "a", "b", "c", "d"]
["a", "b", "c", "a", "b", "c", "a", "b", "c", "d"]
["a", "b", "c", "a", "b", "c", "a", "b", "c", "a", "b", "c", "d"]
["a", "b", "c", "a", "b", "c", "a", "b", "c", "a", "b", "c", "a", "b", "c", "d"]

My best guess for why this happens is that because the base case is yielding and not returning, the algorithm never exits, and simply adds the locked values over and over again with each solution.  This is just a guess, though.