[plt-scheme] Pasteboard in pasteboard and the error: here: I am

Hi All,


I am still playing around with pasteboards, snips and
friends, but progress is slow.

Can anyone provide a simple example of a
pasteboard containing another pasteboard?
Preferably where the containing pasteboard
is diplayable (via an editor-snip) in the DrScheme REPL?


Anyways, while playing I came upon this error,

     here: I am

which, well, is not too informative.

What does it mean, and why does it occur?


To reproduce the error, run the program below.


#lang scheme/gui
(require mrlib/aligned-pasteboard)

(define current-pasteboard (make-parameter #f))
(define current-editor (make-parameter #f))
(define current-frame (make-parameter #f))
(define current-canvas (make-parameter #f))

;;; COMMON

(define (make-string-snip string)
   (make-object string-snip% string))

(define (make-image-snip filename)
   (make-object image-snip% filename))

(define (insert-snip editor snip)
   (send editor insert snip))

(define (insert-snips editor snips)
   (for-each (? (s) (insert-snip editor s)) snips))

(define (realign aligned-pasteboard)
   (let ([min-width  (send aligned-pasteboard get-aligned-min-width)]
         [min-height (send aligned-pasteboard get-aligned-min-height)])
     (send aligned-pasteboard realign min-width min-height)))

(define (element->snip e f c)
   (cond [(string? e) (make-string-snip e)]
         [(column? e) (column->snip e f c)]
         ;[(row? e) (row->snip e)]
         [(image? e)  (image->snip e)]
         [else (error 'element->snip "Unknown element type")]))

;;; IMAGE

(define (image-writer col port write?)
   (display (image->snip col) port))

(define-struct image  (filename) #:property prop:custom-write image-writer)

(define (image->snip img)
   (make-image-snip (image-filename img)))


;;; COLUMN

(define (column-writer col port write?)
   (display (column->snip col #f #f) port))

(define-struct column (elements) #:property prop:custom-write column-writer)

(define (column->snip col frame canvas)
   (let* ([pasteboard  (new vertical-pasteboard%)]
          [editor-snip (new editor-snip% [editor pasteboard]
                            [min-width 1] [min-height 1])]
          [frame       (if frame frame
                           (new frame% [label
                                     "never shown, needed by canvas"]))]
          [canvas      (if canvas canvas
                           (new aligned-editor-canvas% [parent frame]
                                [editor pasteboard]))])
     (insert-snips pasteboard
                   (reverse (map (? (e) (element->snip e frame canvas))
                                 (column-elements col))))
     (realign pasteboard)
     editor-snip))

#;(define (column->snip col frame canvas)
   (let* ([pasteboard  (new vertical-pasteboard%)]
          [editor-snip (new editor-snip% [editor pasteboard]
                            [min-width 1] [min-height 1])]
          [frame       (new frame% [label
                                     "never shown, needed by canvas"])]
          [canvas      (new aligned-editor-canvas%
                            [parent frame]
                            [editor pasteboard])])
     ;(send editor-snip show-border #f)
     (insert-snips pasteboard
                   (reverse (map (? (e) (element->snip e frame canvas))
                                 (column-elements col))))
     (realign pasteboard)
     editor-snip))



;;; TEST

;; works
(make-column (list "Foo" "Bar" "Baz"))
;(make-row (list "Foo" "Bar" "Baz"))
;(make-image "face-smile.png")

;(make-column (list "FOO" (make-image  "face-smile.png") "BAR"))



; broken
(make-column
  (list "a"
        (make-column (list "1" "2" "3"))
        "b"
        (make-column (list "x" "y" "z"))
        "c"
        (make-column (list "!" "?" "@"))))

#;(make-row (list "Foo"
                 (make-image "face-smile.png")
                 (make-column (list "Foo" "Bar" "Baz"))
                 "Baz"))

;(make-column (list "Foo" (make-row (list "123" "456" "789")) "@@@"))