Common Lisp中的函数名称和动态绑定 [英] Function name and dynamic binding in Common Lisp

问题描述

我正在阅读Peter Norvig的 AI范例.在6.2章中，作者使用如下代码(不是原始代码，我挑选了麻烦的部分):

I'm reading Peter Norvig's Paradigms of AI. In chapter 6.2, the author uses code like below (not the original code, I picked out the troubling part):

代码段:

(progv '(op arg) '(1+ 1)
(eval '(op arg)))

作为作者的初衷，此代码应该返回 2 ，但是在sbcl 1.1.1中，解释器显然没有查找 op 在环境中，丢弃op: undefined function.

As the author's original intent, this code should return 2, but in sbcl 1.1.1, the interpreter is apparently not looking up op in the environment, throwing out op: undefined function.

此实现特定吗?由于该代码必须已经在其他Lisp上进行了测试.

Is this implementation specific? Since the code must have been tested on some other lisp.

p.s 原始代码

推荐答案

您可能是说

(progv '(op arg) '(1+ 1)
  (eval '(funcall op arg)))

编辑(2013-08-21):

PAIP是在ANSI-Common-Lisp之前的时代编写的，因此代码很可能 该标准包含一些不合规之处.我们可以做 这些示例适用于以下版本:

Edit(2013-08-21):

PAIP was written in pre-ANSI-Common-Lisp era, so it's possible the code there contains a few noncompliances wrt the standard. We can make the examples work with the following revision:

(defun match-if (pattern input bindings)
  "Test an arbitrary expression involving variables.
  The pattern looks like ((?if code) . rest)."
  (and (eval (reduce (lambda (code binding)
                       (destructuring-bind (var . val) binding
                         (subst val var code)))
                     bindings :initial-value (second (first pattern))))
       (pat-match (rest pattern) input bindings)))

;; CL-USER> (pat-match '(?x ?op ?y is ?z (?if (eql (?op ?x ?y) ?z))) '(3 + 4 is 7))
;; ((?Z . 7) (?Y . 4) (?OP . +) (?X . 3) (T . T))
;; CL-USER> (pat-match '(?x ?op ?y (?if (?op ?x ?y))) '(3 > 4))
;; NIL

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