如何在 Common Lisp 中按顺序创建变量？

发布于 2024-09-26 02:37:40 字数 258 浏览 1 评论 0原文

我在一个正在读取地图文件的函数内有以下代码。我收到一条错误消息，指出 *numrows* 是非法维度。我认为这是因为 lisp 正在并行处理这些变量。我该如何解决这个问题？

(setq *numrows* (read map))
(setq *numcols* (read map))
(setq *map* (make-array '(*numrows* *numcols*) :initial-element nil))

原文

I have the following code inside a function that is reading in a file which is a map. I get an error that *numrows* is an illegal dimension. I think this is because lisp is processing these variables in parallel. How can I fix this?

(setq *numrows* (read map))
(setq *numcols* (read map))
(setq *map* (make-array '(*numrows* *numcols*) :initial-element nil))

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爱格式化 2024-10-03 02:37:40

你误判了问题。您传递给 MAKE-ARRAY 的第一个参数是两个符号的列表：*NUMROWS* 和 *NUMCOLS*。但是，MAKE-ARRAY 的第一个参数应该是非负整数列表。修复示例的最简单方法是使用值创建一个列表：(list *numrows* *numcols*)。因此，代码将如下所示：

(setq *numrows* (read map))
(setq *numcols* (read map))
(setq *map* (make-array (list *numrows* *numcols*) :initial-element nil))

不过，您通常不会像这样使用 setq。根据上下文，使用 LET* 绑定这些变量可能会更好：

(let* ((numrows (read map))
       (numcols (read map))
       (map-array (make-array (list numrows numcols) :initial-element nil))
  ; do something with map-array
  )

You're misdiagnosing the problem. The first argument you're passing to MAKE-ARRAY is a list of two symbols, *NUMROWS* and *NUMCOLS*. However, the first argument to MAKE-ARRAY should be a list of non-negative integers. The easiest way to fix your example is to make a list with the values instead: (list *numrows* *numcols*). So the code would look like this instead:

(setq *numrows* (read map))
(setq *numcols* (read map))
(setq *map* (make-array (list *numrows* *numcols*) :initial-element nil))

You normally wouldn't use setq like this, though. It'd probably be better, depending on the context, to bind those variables with LET*:

(let* ((numrows (read map))
       (numcols (read map))
       (map-array (make-array (list numrows numcols) :initial-element nil))
  ; do something with map-array
  )

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