common lisp 的访问器 SUBSEQ

gistfile1.txt

语法
  subseq sequence start &optional end => subsequence
  (setf (subseq sequence start &optional end) new-subsequence)

参数和值
  sequence --- 一个 sequence
  start, end --- 边界描述符, end 默认为nil
  subsequence --- 一个 sequence
  new-subsequence --- 一个 sequence
  
描述
  subseq 创建一个从sequence的start到end的subsequence 

代码
  * (setq str "012345")
  "012345"

  * (subseq str 3 5)
  "34"

  * (setf (subseq str 0 2) "A")
  "A"

  * str
  "A12345"

  * (setf (subseq str 4) "abc")
  "abc"

  * str
  "A123ab"