什么是“函子中的非法论证”？在普通Lisp中意味着什么？ [英] What does "illegal argument in functor" mean in Common Lisp?

问题描述

注意学习Lisp

我遇到此错误：

Illegal argument in functor position: (EVALEXP (CDR MAIN-LIST) BIND-LIST) 
in ((EVALEXP(CDR   MAIN-LIST) BIND-LIST))

来自此：

(defun evalexp (main-list bind-list)

(if (eq nil (cdr main-list)) 
    (  (if  (eq nil  (atom (car main-list))) (evalexp (car main-list) bind-list) ) )

( (print (car main-list))
  (evalexp (cdr main-list) bind-list) )
)

主列表包含以下列表：

(and 1 (or a b))

绑定列表中的内容无关紧要，因为我还没有使用它。我试图遍历列表以打印出每辆汽车。我为什么会遇到此错误？

What is in bind-list doesn't matter because I am not using it yet. I am trying to loop through the list printing out each car. Any ideas why I am getting this error?

推荐答案

额外的括号。

通常，左括号后的第一件事是函数名称。在某些情况下，您还会看到另一个括号，如您所见，这是语法错误。

Normally the first thing after an opening parenthesis is a function name. You have another opening parenthesis there in some cases, which is a syntax error, as you saw.

您似乎还希望使用语句块。 progn 通常很合适。您可以对内部 if 使用一个块，但这实际上不是必需的，因为它只包含一个语句。

You also seem to want a statement block. progn often fits the bill. You could use a block for the inner if, but it's really not necessary since it would contain only one statement.

(defun evalexp (main-list bind-list)
  (if (eq nil (cdr main-list)) 
      (if  (eq nil (atom (car main-list))) (evalexp (car main-list) bind-list) )
      (progn
        (print (car main-list))
        (evalexp (cdr main-list) bind-list) )
  )
)

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