Question

我收到错误＆＃34; variable EQ has no value＆＃34;当我运行以下代码时。如何克服这个错误？

(defun add_book(bookref title author publisher)
  (setf (get bookref 'title) title)
  (setf (get bookref 'author) author)
  (setf (get bookref 'publisher) publisher)
  (setq library (cons bookref library))
  bookref)

(defun retrieve_by (property value)
  (setq result nil)
  (do  ((L library (cdr L)))
      ((NULL L) result)
    (cond (EQ (get (car L) property) value)
          (cons (car L) result))))

Answer 1

也许更好的格式化和SBCL编译器的输出将帮助您。请参阅编译器警告。尝试查阅Lisp引用以查找各种构造的语法：http://lispdoc.com

* (defun add_book(bookref title author publisher)
  (setf (get bookref 'title) title)
  (setf (get bookref 'author) author)
  (setf (get bookref 'publisher) publisher)
  (setq library (cons bookref library))
  bookref)
; in: DEFUN ADD_BOOK
;     (SETQ LIBRARY (CONS BOOKREF LIBRARY))
; 
; caught WARNING:
;   undefined variable: LIBRARY
; 
; compilation unit finished
;   Undefined variable:
;     LIBRARY
;   caught 1 WARNING condition

ADD_BOOK
* (defun retrieve_by (property value)
  (setq result nil)
  (do  ((L library (cdr L)))
      ((NULL L) result)
    (cond (EQ (get (car L) property) value)
          (cons (car L) result))))

; in: DEFUN RETRIEVE_BY
;     (COND (EQ (GET (CAR L) PROPERTY) VALUE) (CONS (CAR L) RESULT))
; --> IF COND 
; ==>
;   (IF CONS
;       (PROGN (CAR L) RESULT)
;       NIL)
; 
; caught WARNING:
;   undefined variable: CONS

; ==>
;   (IF EQ
;       (PROGN (GET (CAR L) PROPERTY) VALUE)
;       (COND (CONS (CAR L) RESULT)))
; 
; caught WARNING:
;   undefined variable: EQ

;     (DO ((L LIBRARY (CDR L)))
;         ((NULL L) RESULT)
;       (COND (EQ (GET (CAR L) PROPERTY) VALUE) (CONS (CAR L) RESULT)))
; --> BLOCK 
; ==>
;   (LET ((L LIBRARY))
;     (TAGBODY
;       (GO #:G1)
;      #:G0
;       (TAGBODY (COND (EQ # VALUE) (CONS # RESULT)))
;       (PSETQ L (CDR L))
;      #:G1
;       (UNLESS (NULL L) (GO #:G0))
;       (RETURN-FROM NIL (PROGN RESULT))))
; 
; caught WARNING:
;   undefined variable: LIBRARY

;     (SETQ RESULT NIL)
; 
; caught WARNING:
;   undefined variable: RESULT
; 
; compilation unit finished
;   Undefined variables:
;     CONS EQ LIBRARY RESULT
;   caught 4 WARNING conditions

RETRIEVE_BY
*

常见的lisp编程EQ错误

1 个答案: