def add_code( instruction )
      raise "Not an instruction:#{instruction.to_s}:#{instruction.class.name}" unless  instruction.is_a?(Risc::Instruction)
      raise instruction.to_s if( instruction.class.name.split("::").first == "Arm")
      new_current = instruction.last #after insertion this point is lost
      @current.insert(instruction) #insert after current
      @current = new_current
      self
    end
def add_code( instruction )
      raise "Not an instruction:#{instruction.to_s}:#{instruction.class.name}" unless  instruction.is_a?(Risc::Instruction)
      raise instruction.to_s if( instruction.class.name.split("::").first == "Arm")
      new_current = instruction.last #after insertion this point is lost
      @current.insert(instruction) #insert after current
      @current = new_current
      self
    end
add a risc instruction after the current (insertion point)
 the added instruction will become the new insertion point