LISP：謂詞作爲參數

Question

我想要謂詞作爲函數的參數。

(DEFUN per (F L) 
    (cond ((F L) 'working) 
      (T  'anything))) 

(per 'numberp 3) 

因爲導致它提出了一個錯誤：

Undefined operator F in form (F L).

Answer 1

如Technical Issues of Separation in Function Cells and Value Cells解釋， Common Lisp是一個Lisp-2，即，你 需要funcall：

(defun per (F L) 
    (if (funcall F L) 
     'working 
     'other)) 
(per #'numberp 3) 
==> WORKING 
(per #'numberp "3") 
==> OTHER 

見也apply。

Answer 2

遲到了，但這裏有一個例子：

(defun strip-predicate (p list) 
    (cond ((endp list) nil) 
     ((funcall p (first list)) (strip-predicate (rest list))) 
     (T (cons (first list) (strip-Predicate p (rest list)))))) 

這可能對謂語，如原子或numberp使用：

(strip-predicate 'numberp '(a 1 b 2 c 3 d)) 

(a b c d)

或：

(strip-predicate 'atom '(a (a b) b c d)) 

((a b))