# Test whether a given class or definition is defined
Puppet::Parser::Functions::newfunction(:defined, :type => :rvalue, :doc => "Determine whether a given
  type is defined, either as a native type or a defined type, or whether a class is defined.
  This is useful for checking whether a class is defined and only including it if it is.
  This function can also test whether a resource has been defined, using resource references
  (e.g., ``if defined(File['/tmp/myfile']) { ... }``).  This function is unfortunately
  dependent on the parse order of the configuration when testing whether a resource is defined.") do |vals|
    result = false
    vals = [vals] unless vals.is_a?(Array)
    vals.each do |val|
      case val
      when String
        if Puppet::Type.type(val) or find_definition(val) or find_hostclass(val)
          result = true
          break
        end
      when Puppet::Resource
        if findresource(val.to_s)
          result = true
          break
        end
      else
        raise ArgumentError, "Invalid argument of type '#{val.class}' to 'defined'"
      end
    end
    result
end