Ruby recursive Hash search

hash_search.rb

haystack = {
  action: "greeting",
  scope: "world",
  things: [
    { x: "city" },
    { x: "country" },
    { x: "world" },
  ]
}

def search(needle, haystack, path = [], matches = [])
  case haystack
  when Hash
    haystack.each_pair { |k, v| search(needle, v, path + [k], matches) }
  when Array
    haystack.each_with_index { |v, i| search(needle, v, path + [i], matches) }
  else
    matches << path.join(".") if haystack == needle
  end
  matches
end

p search("world", haystack)