定义:期望变量，但找到一个部分

Question

我正在从下面的函数邻居获得定义错误，我需要使用"let“从定义内部声明吗？

;; Purpose: Produce a maze, being a list of whole numbers (cells) 
;; between 0 and the square of grid-size (grid-size^2)
;; The list prepresenting the maze will start with 0 and be expanded 
;; by randomly picking a cell already in the maze
;;  then randomly selecting a neighbouring cell (horz and vert axis 
;; only) following tests to ensure that the new neighbouring cell is:
;   a) within the grid/maze area
;   b) not already in the maze
;   c) not adjacent to a cell already in the maze (otherwide could block the maze path)
;   d) will likely add tests here to make sure maze does not consume itself
; Grid will lay out as follows (assuming grid-size is 3;
;   0  1  2
;   3  4  5
;   6  7  8

(define grid-size 15)
(define a-maze (list 0))

;Is returned value part of the existing a-maze
(check-expect (member? (random-cell a-maze) a-maze)
          #true)
;Is returned vale a number?
(check-expect (number? (random-cell a-maze))
          #true)

;Is returned value within the limits of the grid
(check-expect (<= 0 (random-cell a-maze) (sqr grid-size))
          #true)

;random-cell: non-empty list -> random number from list
(define (random-cell a-list)
   (list-ref a-list (random (length a-list))))


(check-expect (member? 15 (neighbours (random-cell a-maze))) #true)
(check-expect (member? 1 (neighbours (random-cell a-maze))) #true)
(check-expect (member? -1 (neighbours (random-cell a-maze))) #true)
(check-expect (member? -15 (neighbours (random-cell a-maze))) #true)



(check-expect (= (length (neighbours-in-grid (random-cell a-maze))) 2) #true)

;neighbours: non-empty whole number representing a cell -> list of     
;neighbouring cells - use horz and vert axis only (no diagonals)
(define (neighbours member-cell)
  (list (+ member-cell grid-size) ;cell below
        (+ member-cell 1) ;cell immediate right
        (- member-cell 1) ;cell immediate left
        (- member-cell grid-size) ;cell above
      )

   )

  ;neighbours-in-grid: non-empty list of potential neighbours -> narrowed list of validated neighbours that are in the grid
(define (neighbours-in-grid (neighbours (random-cell a-maze)))
  (cond [(< 0 (first neighbours) > grid-size) (remove (first neighbours))]
        [(< 0 (second neighbours) > grid-size) (remove (second neighbours))]
        [(< 0 (third neighbours) > grid-size) (remove (third neighbours))]
        [(< 0 (fourth neighbours) > grid-size) (remove (fourth neighbours))]
       ))

Answer 1

这里的问题与neighbours-in-grid函数的第一行有关。

具体来说，使用此形状定义了一个函数：

(define (<name-of-function> <name-of-argument> ...)
   <body-of-function>)

函数的第一行如下所示：

(define (neighbours-in-grid (neighbours (random-cell a-maze)))
  (cond ...))

这不符合模式。这些争论的名字是什么？基于这行后面的代码，在我看来，您需要一个名为neighbours的参数。如果是这样的话，这段代码应该改为：

(define (neighbours-in-grid neighbours)
   (cond ...))

我认为，这里的部分混乱可能源于这样一个事实，即单独地，您有一个名为“邻居”的函数。