在方案中，我不断收到“错误：（：1）汽车：参数 1 必须是：对”，为什么？

Question

我发现 this page 解释了一些 gimp 函数不会始终如一地返回值，因此我实现了一个 do while 循环以确保函数在使用 car 之前返回对。尽管如此，我还是收到了错误Error: ( : 1) car: argument 1 must be: pair，但我不确定这怎么可能，因为它应该继续运行该函数，直到它返回一对。

(define (script-fu-scratchpad drawable)
  (let* ((imgHeight 0)
         (imgWidth)
         (bpp)
         (pixel))
    (set! imgHeight (gimp-drawable-height drawable))
    (do ()
        [(pair? imgHeight)]
      (set! imgHeight (gimp-drawable-height drawable)))
    (set! imgHeight (car imgHeight))

    (set! imgWidth (gimp-drawable-width drawable))
    (do ()
        [(pair? imgWidth)]
      (set! imgWidth (gimp-drawable-width drawable)))
    (set! imgWidth (car imgWidth))

    (set! bpp (gimp-drawable-bpp drawable))
    (do ()
        [(pair? bpp)]
      (set! bpp (gimp-drawable-bpp drawable)))
    (set! bpp (car bpp))

    (display bpp) (newline)
    (set! pixel (cons-array bpp 'byte))
    (aset pixel 0 150)
    (aset pixel 1 150)
    (aset pixel 2 150)
    (aset pixel 3 0)

    (gimp-drawable-set-pixel drawable (/ imgHeight 2) (/ imgWidth 2) bpp pixel)
    (gimp-context-set-background '(100 100 100))
    (define county 0)
    (define countx 0)
    (do ()
        [(= countx imgWidth)]
      (do ()
          [(= county imgHeight)]
        (gimp-drawable-set-pixel drawable county countx bpp pixel)
        (set! county (+ county 1)))
      (set! countx (+ countx 1)))))

---

针对 GoZoner，我对其进行了编辑并收到以下错误：Error: (:1) car: argument 1 must be: pair

(define
    (script-fu-scratchpad drawable)
    (let*
        ( 
            (imgHeight 0)
            (imgWidth 0)
            (bpp 0)
            (pixel 0)
        )

        (set! imgHeight (gimp-drawable-height drawable))    
        (set! imgWidth (gimp-drawable-width drawable))

        (set! bpp (gimp-drawable-bpp drawable))
        (do ()
            [(pair? bpp)]
            (set! bpp (gimp-drawable-bpp drawable))
        )
        (set! bpp (car bpp))

        (display bpp) (newline)
        (set! pixel (cons-array bpp 'byte))
        (aset pixel 0 150)
        (aset pixel 1 150)
        (aset pixel 2 150)
        (aset pixel 3 0)

        (gimp-drawable-set-pixel drawable (/ imgHeight 2) (/ imgWidth 2) bpp pixel)
        (gimp-context-set-background '(100 100 100))
        (define county 0)
        (define countx 0)
        (do ()
            [(= countx imgWidth)]
            (do ()
                [(= county imgHeight)]
                (gimp-drawable-set-pixel drawable county countx bpp pixel)
                (set! county (+ county 1))
            )
            (set! countx (+ countx 1))
        )
    )
)

Answer 1

有几件事。

1. 在您的最高级别let* 中，您应该初始化每个 变量，而不仅仅是 imgHeight 或没有。实际的 Scheme 要求全部初始化。

2. 根据名称，我不希望 (gimp-drawable-height drawable) 返回列表/缺点；它应该以数字形式返回高度。因此：

   • 我无法想象(pair? imgHeight) 会是真的

   • 我预计 (car imgHeight) 会失败 - 这显然是基于您报告的错误。

3. 函数aset 大概作用于多维 ((>= rank 2)) 数组。因此，它的“索引”参数应该不止一个整数。但是，aset 可能只是 GIMP 脚本变体中的 vector-ref。

[编辑：更具体地说]我已经注释了你的代码

(set! bpp (gimp-drawable-bpp drawable))         ; bpp is NOT a pair
(do ()
    [(pair? bpp)]                               ; bpp is NOT a pair
 (set! bpp (gimp-drawable-bpp drawable)))
(set! bpp (car bpp))                            ; bpp is NOT a pair => ERROR