方案查找列表的平均值 [英] Scheme find average of a list

问题描述

所以我的代码应该可以找到列表的平均值，但我在控制台中没有看到打印值

So I have code that should find the average of a list but I see no printed value in console

#lang racket
(define x (list '10 '60 '3 '55 '15 '45 '40))
(define (average x)
(/ (sum x) (length x)))

(display average (current-output-port))

(define (sum)
(if (null? x)
    0
    (+ (car x) (sum (cdr x)))))

它只是显示

#<procedure:average>

推荐答案

您的代码有以下问题:

1. sum 在定义之前使用.
2. sum 没有带参数.
3. average 函数未在 display 中求值.
4. 我使用了 exact->inexact 因为这就是我认为您的意图.

1. sum was used before it was defined.
2. sum did not take a parameter.
3. average function was not evaluated in display.
4. I have used exact->inexact because that's what I think your intention is.

以下作品.

(define x (list 10 60 3 55 15 45 40))

(define (sum x)
    (if (null? x)
        0
        (+ (car x) (sum (cdr x)))))

(define (average x)
    (/ (sum x) (length x)))

(display (exact->inexact (average x)) (current-output-port))

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