[plt-scheme] editor snips and replacing the editor with set-editor

> I'm trying to create an editor snip that doesn't allow further edits to it. 
> I tried the following, but the resulting snips that show up on the 
> interaction window continue to allow internal editing.  I'm missing something 
> obvious but I don't quite see the problem yet.

... and, of course, five minutes later, I see the problem.  Doh.  Sorry 
for bothering people.


Summary: I didn't realize that a call to the 'copy' method fires off when 
the snip shows up on the interaction window.  So for any of the custom 
snips I write, I must make sure to define a copy method for them.

The following code does sorta what I want, although I suspect I need to be 
much more careful.  I guess I really do need to look closely at the 
snipclass stuff to preserve my snips under other situations like saving to 
disk.

;;;;;;

#lang scheme/base
(require scheme/gui/base
          scheme/list
          scheme/class
          scheme/sandbox)


(define immutable-text%
   (class text%
     (inherit insert)

     (init content)
     (define after-initialize? #f)

     (define (initialize)
       (super-new)
       (insert content)
       (set! after-initialize? #t))

     (define/augment (can-insert? pos len)
       (not after-initialize?))

     (define/augment (can-delete? pos len)
       (not after-initialize?))

     (initialize)))


(define immutable-editor-snip%
   (class editor-snip%
     (inherit set-editor)
     (init-field content)
     (define (initialize)
       (super-new [editor (new immutable-text% [content content])]))

     (define/override (copy)
       (new immutable-editor-snip% [content content]))

     (initialize)))