CODEWITHSUNDEEP
racket
data_pi
data_pi

Reputation: 821

Racket - Function call error

Definitions: 

(define-struct Cell (x y))

(define (count-in cell cells)
(cond
[(member? cell cells) 1]
[else 0]))

(define (touches cell cells)
(+
(count-in
(cell (Cell-x cell) (+ (Cell-y cell) 1)) (list cells))
(count-in
(cell (Cell-x cell) (+ (Cell-y cell) -1))(list cells))
(count-in
(cell (+ (Cell-x cell) -1) (Cell-y cell))(list cells))
(count-in
(cell (+ (Cell-x cell) 1) (Cell-y cell))(list cells))))

The check-expect and where the error occurs:

(check-expect (touches (make-Cell 2 30) 
(list
make-Cell 2 31
make-Cell 1 29
make-Cell 1 30
make-Cell 2 30)) 2)

It is giving me an error saying:

function call: expected a function after the open parenthesis, but received (make-Cell 2 30)

Why is this happening? And how would I go about fixing this?

What the code does: Checks if a cell (with its values adjusted by 1) is presently in the list. So make-cell 2 30, the adjusting values would be 2 31, 2 29, 1 30, 3 30. And if the one of the cells is inside the list, itll produce a 1, if not it'll produce a 0. Then if the code just adds all them up telling me how many of the adjusted cells are in the list.

Upvotes: 0

Views: 6999

Answers (1)

Óscar López
Óscar López

Reputation: 236122

You forgot to surround the calls to make-cell with parentheses, and the touches procedure looks wrong. Assuming that the member? procedure is correctly implemented and works for a list of structures, this should work:

(define (touches cell cells)
  (+
   (count-in
    (make-Cell (Cell-x cell) (+ (Cell-y cell) 1))
    cells)
   (count-in
    (make-Cell (Cell-x cell) (+ (Cell-y cell) -1))
    cells)
   (count-in
    (make-Cell (+ (Cell-x cell) -1) (Cell-y cell))
    cells)
   (count-in
    (make-Cell (+ (Cell-x cell) 1) (Cell-y cell))
    cells)))

(check-expect
 (touches (make-Cell 2 30) 
          (list
           (make-Cell 2 31)
           (make-Cell 1 29)
           (make-Cell 1 30)
           (make-Cell 2 30)))
 2)

Upvotes: 1

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