def resources_by_type(ast)
      raise_unless_xpath!(ast)
      result = Hash.new { |hash, key| hash[key] = Array.new }
      find_resources(ast).each do |resource|
        result[resource_type(resource)] << resource
      end
      result
    end
def resources_by_type(ast)
      raise_unless_xpath!(ast)
      result = Hash.new { |hash, key| hash[key] = Array.new }
      find_resources(ast).each do |resource|
        result[resource_type(resource)] << resource
      end
      result
    end
Resources in an AST, keyed by type.