搜索和替换列表中的 n 个元素 - 方案 [英] Searching and replacing n element on list - scheme

问题描述

做这种代码有问题，不知道如何搜索元素 (a) 并用 (b) 替换 i，怎么做?提前谢谢

have got a problem with do this kind of code , can't figure how to search for a element (a) and replace i by ( b) , how to do it? Thx in advance

推荐答案

试试这个功能:

(define subst
  (lambda (new old l)
    (cond
     ((null? l) (quote ()))
     ((atom? (car l))
      (cond
       ((eq? (car l) old) (cons new
                                (subst new old (cdr l))))
       (else (cons (car l)
                   (subst new old (cdr l))))))
     (else (cons (subst new old (car l))
                 (subst new old (cdr l)))))))

这将搜索 S 表达式列表，并用 new 的出现替换每次出现的 old.

This will search through a list of S expressions and substitute every occurrence of old with an occurrence of new.

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