Question

我写了几个小方案函数

＆＃13;

; Given a list, this should return the maximum value in the list.
(define (maxInt lst)
	(if (empty? lst) 0   ; if the list is empty, return 0
		(max(first lst) (maxInt(rest lst)))))
		; ^ What this line does is recursively take the maximum of pairs in the list.
		; Ex. If the list was (7 3 6 2), this line would take the max of 7 and (the max of 3 and(the max of 2 and 6)),
		; returning a result of 7.  
		
		
; The zip3 function.  Takes three lists of integers and returns a list of ordered triples containing the first, second, or third elements of each original list(i.e. an ordered triple containing the first elements of each list, etc)

(define (zip3 lst1 lst2 lst3)
	(if (or((not(= (length lst1)(length lst2))) (not(= (length lst2)(length lst3))) (not(= (length lst 1)(length lst3))))) (error "Error")
		(append (map car(lst1 lst2 lst3)) (map cadr(lst1 lst2 lst3)) (map caddr(lst1 lst2 lst3)))))
; This says 'if list 1 and 2 are different lengths or list 2 and 3 are different lengths or list 1 and 3 are different lengths, return an error.
; Otherwise, append the list containing the ordered triple of the second element of each list and that containing said triple of the third element
; to the list containing the ordered triple of the first element of each list.'


; The compute function.  takes a list of integers and and integer x and computes a + bx + cx^2 + etc, with a, b, c, etc being the ints in the list.

(define (compute polyLst x)
	(for ([i (length polyLst)])
		(+ (* (list-ref polyLst i) (expt x i)))))
; Recursion was hinted at for this one, but I found it easier to just use a for loop.  This takes the sum of the products of each element of the list and
; x raised to the power of that element's index in the list.

＆＃13;

我使用了完全正确的方案符号（我认为），但这些函数都没有在使用调用它们的测试程序进行测试时起作用。我真的很困惑为什么这些功能不起作用。这对我没有任何意义。我只是想知道我做错了什么。

Answer 1

maxInt似乎有效。

zip3有一些括号错误，必须使用list并且应该阅读

(define (zip3 lst1 lst2 lst3)
  (if (or (not(= (length lst1)(length lst2))) (not(= (length lst2)(length lst3))) (not(= (length lst1)(length lst3))))
      (error "Error")
      (append (map car (list lst1 lst2 lst3)) (map cadr (list lst1 lst2 lst3)) (map caddr (list lst1 lst2 lst3)))))

和compute需要使用for/sum：

(define (compute polyLst x)
  (for/sum ([i (length polyLst)])
    (* (list-ref polyLst i) (expt x i))))

一些重构的想法：

(define (maxInt lst)
  (apply max lst))

(define (zip3 . l) 
  (flatten (apply map list l)))

(define (compute polyLst x)
  (for/sum ([(e n) (in-indexed polyLst)])
    (* e (expt x n))))

我写了一些简单的方案函数，但显然它们都没有用，我想知道为什么

1 个答案: