用 Lisp 编写递归 GCD

发布于 2024-10-31 17:06:35 字数 256 浏览 0 评论 0原文

编译此函数时，我不断收到随机错误：

(defun gcd (a b)
  (if (= b 0)
      a
      (gcd b mod (a b))))

最常见的是它显示“未定义的函数 a”。所以我想我需要在那个地方返回 a 。这不起作用。我得到了很多 if 语句错误的参数。知道我在这里做错了什么吗？ Lisp 新手，到目前为止我们的看法还不一致。

在 Windows 7 上的 CLISP 上运行。

原文

I keep getting random errors when compiling this function:

(defun gcd (a b)
  (if (= b 0)
      a
      (gcd b mod (a b))))

The most common is that it says "undefined function a." So I figured I needed return a in that place. This did not work. I get a to many parameters for if statement error. Any idea what I am doing wrong here? New to Lisp and so far we are not seeing eye to eye.

Running on CLISP on Windows 7.

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蓝礼 2024-11-07 17:06:35

在 Lisp 中，函数调用总是*以 '(' 开头，因此该行的

(gcd b mod(a b))

意思是“使用参数 b、mod 调用函数 gcd，使用参数 b 调用函数 a 的结果”。

我怀疑你真的想要这样的东西：

(gcd b (mod a b))

*我有一段时间没有使用 Lisp 了所以我对“总是”的看法可能不是100%正确。

In Lisp a function call always* starts with '(', so the line

(gcd b mod(a b))

means "call the function gcd with arguments b, mod and the result of calling function a with argument b".

I suspect you really want something like:

(gcd b (mod a b))

*I haven't used Lisp for a little while so I might not be 100% correct on the "always".

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记忆里有你的影子 2024-11-07 17:06:35

(gcd b mod(ab)) 应该是 (gcd b (mod ab))

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挽袖吟 2024-11-07 17:06:35

您的 mod 函数调用是错误的。这是我的工作代码：

(defun gcd2(a b)
  (if (= b 0) a (gcd2 b (mod a b))))

You mod function call is wrong. Here's my working code:

(defun gcd2(a b)
  (if (= b 0) a (gcd2 b (mod a b))))

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半衬遮猫 2024-11-07 17:06:35

通常编译器可以为您提供更多信息：

使用 LispWorks：

(defun gcd1 (a b)
  (if (= b 0)
      a
      (gcd1 b mod (a b))))


CL-USER 31 > (compile 'gcd1)
;;;*** Warning in GCD1: GCD1 is called with the wrong number of arguments: Got 3 wanted 2
;;;*** Warning in GCD1: MOD assumed special

The following function is undefined:
A which is referenced by GCD1
GCD1

因此您会看到使用错误数量的参数调用 GCD1，MOD 被假定为一个变量，并且A 被假定为一个函数。

SBCL：

; in: DEFUN GCD1
;     (GCD1 B MOD (A B))
; 
; caught WARNING:
;   The function was called with three arguments, but wants exactly two.

; in: DEFUN GCD1
;     (A B)
; 
; caught STYLE-WARNING:
;   undefined function: A

;     (GCD1 B MOD (A B))
; 
; caught WARNING:
;   undefined variable: MOD

Usually a compiler can give you more information:

Using LispWorks:

(defun gcd1 (a b)
  (if (= b 0)
      a
      (gcd1 b mod (a b))))


CL-USER 31 > (compile 'gcd1)
;;;*** Warning in GCD1: GCD1 is called with the wrong number of arguments: Got 3 wanted 2
;;;*** Warning in GCD1: MOD assumed special

The following function is undefined:
A which is referenced by GCD1
GCD1

So you see that you call GCD1 with the wrong number of arguments, that MOD is assumed to be a variable and that A is assumed to be a function.

SBCL:

; in: DEFUN GCD1
;     (GCD1 B MOD (A B))
; 
; caught WARNING:
;   The function was called with three arguments, but wants exactly two.

; in: DEFUN GCD1
;     (A B)
; 
; caught STYLE-WARNING:
;   undefined function: A

;     (GCD1 B MOD (A B))
; 
; caught WARNING:
;   undefined variable: MOD

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