等同于C枚举的Common Lisp [英] Common Lisp equivalent to C enums

问题描述

我最近正在尝试学习一些Lisp（通用Lisp），我想知道是否有一种方法可以像给C一样通过枚举来给常数命名。

I'm trying to learn some Lisp (Common Lisp) lately, and I wonder if there is a way to give constant numbers a name just like you can do in C via enums.

我不需要枚举的全部功能。最后，我只想拥有快速的和可读代码。

I don't need the full featureset of enums. In the end I just want to have fast and readable code.

我已经尝试了全局变量和小函数，但这总是带有一个性能下降。只需将数字插入代码中总是更快。

I've tried globals and little functions, but that always came with a degration in performance. Just plugging the numbers into the code was always faster.

推荐答案

在Lisp中进行枚举的正常方法是使用符号。符号会被插入（用指向符号表中条目的指针代替），因此它们与整数一样快，并且与其他语言中的枚举常量一样可读。

The normal way to do enumerations in Lisp is to use symbols. Symbols get interned (replaced with pointers to their entries in a symbol table) so they are as fast as integers and as readable as enumerated constants in other languages.

C您可能会这样写：

enum {
   apple,
   orange,
   banana,
};

在Lisp中，您可以只使用'apple ， '橙色和'香蕉直接。

In Lisp you can just use 'apple, 'orange and 'banana directly.

如果需要枚举的类型，则可以使用 deftype ：

If you need an enumerated type, then you can define one with deftype:

(deftype fruit () '(member apple orange banana))

，然后您可以在声明中使用水果类型， typep ， typecase 等，，您可以编写专门用于。

and then you can use the type fruit in declare, typep, typecase and so on, and you can write generic functions that specialize on that type.

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