补充一下，进行调试的话会报错：
Error in (function (srcref)  : unimplemented type (29) in 'eval'
Error: no more error handlers available (recursive errors?); invoking 'abort' restart
Error: INTEGER() can only be applied to a 'integer', not a 'unknown type #29'
In addition: Warning message:
type 29 is unimplemented in 'type2char'