清除方案中的列表

Question

(define ls2 '((james (1 2 3) (4 5 6) (8 5 6))
              (daren (7 8 9) (2 6 4))
              ))    
(define (delete name lst clear)
      (if (equal? (caar ls2) name) (clear (cdar lst)) 
       (delete name (cdr lst) clear)))

(define (clear lst)
      (if (null? lst) #t (remove (car lst) lst)))

(delete 'james ls2 clear)

If james is matched with an element of list then (1 2 3) (4 5 6) (8 5 6) must be clear. I can just clear the (1 2 3) and i want to clear (4 5 6) (8 5 6) each by each recursively. However i can't succesive that. I need an emergency help, please.

Answer 1

您编写的 clear 过程将不起作用，remove 创建一个新列表，其中删除的元素不存在，但原始元素保持不变。试试这个：

(define (delete name lst)
  (cond ((null? lst) '())
        ((equal? (caar lst) name)        ; if there's a match
         (cons (list (caar lst))         ; clear all elements at once
               (delete name (cdr lst)))) ; and advance recursion
        (else (cons (car lst) 
                    (delete name (cdr lst))))))

它是这样工作的：它创建一个新的列表，其中的元素被删除，原始列表保持不变 - 这就是我们在 Scheme 中编写程序的方式：

(define lst '((james (1 2 3) (4 5 6) (8 5 6))
              (daren (7 8 9) (2 6 4))))

(delete 'james lst)
=> '((james) (daren (7 8 9) (2 6 4)))

清除方案中的列表

Clear the list in scheme

scheme

list