#!/usr/bin/env luajit

local json = require 'cjson'
local yaml = require 'lyaml'

local document = json.decode(io.read('*a'))

local function replace(document)
  for key, value in pairs(document) do
    if value == json.null then
      document[key] = yaml.null
    elseif type(value) == 'table' then
      replace(value)
    elseif type(value) == 'userdata' then
      document[key] = '<USERDATA>'
    end
  end
  return document
end

print(yaml.dump({replace(document)}))