def value_of name, type = :normal

      if @definitions.variable?(name)
        ValueExtractor.new(@definitions.variable(name), type)
      else
        raise "Unknown variable #{name}"
      end

    end
def value_of name, type = :normal

      if @definitions.variable?(name)
        ValueExtractor.new(@definitions.variable(name), type)
      else
        raise "Unknown variable #{name}"
      end

    end
type can be :normal, :absolute, :absolute_row, :absolute_column