[plt-scheme] handling user-breaks in MrEd app...

Have you considered using DrScheme? It solves all of these problems.

Robby

At Wed, 30 Oct 2002 17:58:45 -0600, Jefferson Provost wrote:
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> 
> Hey,
> 
> I'm writing a graphical MrEd app, and though most interaction will be 
> through graphical objects, I want to run a repl for debugging and other 
> stuff.  I don't want to use MrEd's graphical repl, but when I do mred 
> -z, the stdio repl never yields to give events/time to my graphical 
> objects.  My solution is to instantiate my graphical objects, and then 
> run a stdio repl in a separate, as in the code below.
> 
> The problem is that the with-handlers form seems to swallow all 
> exceptions (other than exn:break) without any notification.  Without the 
> with-handlers, breaks (ctrl-C's) send the program into some inscrutable 
> state in which there's still a repl running (the top-level repl?) but 
> the program is basically unusable.
> 
> I guess I don't understand how handlers work, because I assumed that 
> handling one kind of exception wouldn't change how the others were 
> handled, but that's not what's happening.  What's going on?
> 
> J.
> 
> ;;;;;;;;;;;;;;;;;;;;;;;
>    (define (gui-repl)
>      (let ((t (thread read-eval-print-loop)))
>        (let loop ()
> 	(yield)
> 	(sleep 0.01)
> 	(if (thread-running? t) (loop)))))
> 
> ;;;;;;;;;;;;;;;;;;;;;;
> ; instantiate my window(s) here
> 
> (define my-console (instantiate my-graphical-console% () )
> (send my-console show #t)
> 
> ;;;;;;;;;;;;;;;;;;;;;
> ; start the repl
>    (with-handlers ((exn:break? (lambda (x)
>    			       (display (format "\nuser break!\n"))
>   	 
> 	       (exit))))
>    	       (gui-repl)
>    	       (exit))
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> 
> 
> The problem with this is that errors generated from my-console (or the 
> windows it spawns) just vanish.  If I run mred w/o "-z", and comment out 
> everything below ";start the repl", then errors get printed to stdout