Question

每次运行此代码时，都会收到错误消息：“define：只需要一个函数体表达式，但找到1个额外部分。”我一次又一次地尝试解决这个问题，但我还没有找到解决方案。有谁知道如何解决它？很抱歉长码，我想我应该把它包括在内，否则就没有意义了。谢谢！

(define MT (empty-scene 50 50))

; A Polygon is one of: 
; – (list Posn Posn Posn)
; – (cons Posn Polygon)

; A NELoP is one of: 
; – (cons Posn empty)
; – (cons Posn NELoP)

; Polygon -> Image 
; adds an image of p to MT
(define (render-polygon p)
  (local 
    [;Polygon -> Posn
     ; extracts the last item from p
     (define (last p) 
       (cond
         [(empty? (rest (rest (rest p)))) (third p)]
         [else (last (rest p))]))]
    [;Image Posn Posn -> Image
     (define (render-line im p q)
       (add-line
        im (posn-x p) (posn-y p) (posn-x q) (posn-y q) "red"))]
    [;NELop -> Image
     ;connects the posns in p in an image
     (define (connect-dots p)
       (cond
         [(empty? (rest p)) MT]
         [else
          (render-line
           (connect-dots (rest p)) (first p) (second p))]))])
  (render-line (connect-dots p) (first p) (last p)))

新代码（仍无效）：

; Polygon -> Image 
; adds an image of p to MT
(define (render-polygon p)
  (local 
    [;Polygon -> Posn
     ; extracts the last item from p
     (define (last p) 
       (cond
         [(empty? (rest (rest (rest p)))) (third p)]
         [else (last (rest p))]))
    ;Image Posn Posn -> Image
     (define (render-line im p q)
       (add-line
        im (posn-x p) (posn-y p) (posn-x q) (posn-y q) "red"))
    ;NELop -> Image
     ;connects the posns in p in an image
     (define (connect-dots p)
       (cond
         [(empty? (rest p)) MT]
         [else
          (render-line
           (connect-dots (rest p)) (first p) (second p))]))
  (render-line (connect-dots p) (first p) (last p))]))

Answer 1

您的render-line表达式必须 local表单，而不是之后。此外，您define的所有local应位于(local [(define (last p) ...) (define (render-line im p q) ...) (define (connect-dots p) ...)] (render-line ...))中的一个子表单中，而不是每个子表单中的每个子表单。所以，它应该看起来像：

{{1}}

为什么我会收到这个身体错误？

1 个答案: