方案:更改列表中元素的值 [英] Scheme: change value of an element in a list

问题描述

我讨厌使用SO作为查找简单函数的方法，但是我真的在任何地方都找不到这样的函数:

I hate using SO as a way to find simple functions, but I really can't find a function like this anywhere:

给出一个列表(1 2 3 4 5)，我想要相当于(PHP，Perl，Python)

Given a list (1 2 3 4 5), I'd like the equivalent of (PHP's, Perl's, Python's)

$a = array(1, 2, 3, 4, 5);   
$a[3] = 100;  

得出(1 2 3 100 5)

Which results in (1 2 3 100 5)

谢谢！

推荐答案

您可以编写Guile的list-set!，如下所示:

You can write list-set! of Guile, like so:

(define a (list 1 2 3 4))     ; a is '(1 2 3 4)

(define (list-set! list k val)
    (if (zero? k)
        (set-car! list val)
        (list-set! (cdr list) (- k 1) val)))

(list-set! a 2 100)           ; a is '(1 2 100 4)

(在DrRacket中进行了尝试.)

(Tried this in DrRacket.)

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