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在使用 Steel Bank Common Lisp 通过 SICP 工作时，我取得了相当大的成功，但是我在“图片语言”示例上遇到了障碍。以下似乎不会写入 PPM 文件，而我编写的其他旋转和翻转可以。我怀疑 LAMBDA 在 LABELS 中调用时不知何故没有返回函数？

我已经有 Mx check-parens 并且那里没有任何东西是孤立的或看似不正常的。

(defun below (painter1 painter2)
  "Divides frame along 2nd axis and invokes a painter on each region"
  (let ((split-point (make-vect 0.0 0.5)))
    (labels ((paint-up (fr)
               (transform-painter painter2
                                  (make-vect 0.0 0.0)
                                  (make-vect 1.0 0.0)
                                  split-point))
             (paint-down (fr)
               (transform-painter painter1
                                  split-point
                                  (make-vect 1.0 0.5)
                                  (make-vect 0.0 1.0))))
      #'(lambda (frame)
          (paint-up frame)
          (paint-down frame)))))

(defun krest-below ()
  "Tests BELOW on the KREST-SEGMENTS"
  (init-buffer 400 400)
  (funcall (below (segments->painter krest-segments)
                  (segments->painter krest-segments))
           (make-frame (cons 0 0)
                       (cons 399 0)
                       (cons 0 399)))
  (rgb-buffer->ppm "krest-below.ppm" *buffer*))
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1 回答 1

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根据 Svante 的提示，我发现答案是我需要确保 TRANSFORM-PAINTER 返回的函数实际上是用 FUNCALL调用的，并在调用标签 PAINT-UP 和 PAINT-DOWN 时传递了 FR。更正后的 BELOW 函数如下所示：

(defun below (painter1 painter2)
  "Divides frame along 2nd axis and invokes a painter on each region"
  (let ((split-point (make-vect 0.0 0.5)))
    (labels ((paint-up (fr)
         (funcall (transform-painter painter2
                         (make-vect 0.0 0.0)
                         (make-vect 1.0 0.0)
                         split-point) fr))
       (paint-down (fr)
         (funcall (transform-painter painter1
                         split-point
                         (make-vect 1.0 0.5)
                         (make-vect 0.0 1.0)) fr)))
    #'(lambda (frame)
    (paint-up frame)
    (paint-down frame)))))
于 2012-03-25T01:11:45.413 回答