# Takes a hash to extract keys from
# - If the first argument is not Hash, print warning and return nil
# - Returns array of hash keys otherwise
#
module Puppet::Parser::Functions
  newfunction(:hash_keys, :type => :rvalue) do |args|
    unless args[0].is_a?(Hash)
      Puppet.warning "hash_keys takes one argument, the input hash"
      nil
    else
      args[0].keys
    end
  end
end