为什么在Common Lisp中冒号先于变量 [英] Why colons precede variables in Common Lisp

问题描述

Common Lisp中的冒号在变量前的语法是什么意思?我已经看过这样的程序了，在这里，我将介绍大量函数中的一些示例代码.

What does the syntax, colons preceding variable in Common Lisp, mean? I've seen programs with such, and I'll present some sample code here, out of a large set of functions.

(defun expand (successorf node)
    (mapcar (lambda (action-state-cost)
          (let ((action (car action-state-cost))
                (state (cadr action-state-cost))
                (cost (caddr action-state-cost)))
            (make-node :state state :parent node
                       :action action :path-cost (+ (node-path-cost node) cost)
                       :depth (1+ (node-depth node)))
            ))
      (funcall successorf (node-state node))
      ))

推荐答案

实际上，它们不是变量；这些是关键字.它们是一种特殊的有效令牌，类似于其他语言中的原子".这是将命名(几乎总是可选)参数传递给函数调用的便捷内置方法.

They're not variables, actually; those are keywords. They're a special kind of efficient token, similar to "atoms" in other languages. It's a convenient, built-in way to pass named (and, almost always, optional) parameters into a function call.

http://www.gigamonkeys.com/book/functions.html 描述函数调用的语法.

http://www.gigamonkeys.com/book/functions.html describes the syntax of function calls.

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