[Apologies if some if this is obvious to many of you - kjx]

As some of you may know, I'm trying to write a program visualisation system in Self for a doctoral thesis. This is based upon an mechanism for generating events whenever something interesting happens in a Self program (the events are fed to other Self objects to produce the visualisations - papers available on request :-). Events can be easily generated when messages are received by an object, when methods return normally. Currently, I can't handle non-local method completion, (that is the "^" operator) - these message completions are ignored. This has only been a theoretical problem so far, however, gradually scaling up the size of programs I'm trying to visualise, I seem to have reached a point where I need to be able to handle non-local returns in the event system.

Now several other languages incorporating non-local exits (Smalltalk, Lisp and even VAX Pascal) include an "unwind protect" construct which would trap non-local returns, allowing some action to be taken "on the way up the stack" so to speak. Something like this would allow me to generate the appropriate events and hopefully visualise the programs currently giving me trouble.

So while I try to find ways to avoid the non-local exits in the code in question, this is another plaintive cry asking if anyone has ideas about incorporating unwind-protect into Self. Given that the VM source code is now available, I suppose I could try that - does anyone have any idea how difficult it would be? (in passing - how have people outside the Self group found the VM code to work with). Another alternative would be to move the whole event mechanism inside the VM - but I'm sure that would be even more work.

Another related question, (discovered when poking around these things) is what happens to blocks that perform a non-local return where the method returned to is not in the running process. (Yes, I was attempting a work-around where the protected code would be run in another Self process). However, a non-local return in this case seems to terminate the process without a return value.

Some example code is appended below.

Thanks

James

"what's happening here"

lobby _AddSlots: (| foo = (| parent* = traits oddball.

a = ( 'foo a called' printLine.

'foo a stores magic block' printLine. blk: [ 'blk called' printLine. ^'magic-return'.].

'foo a stores process number' printLine. prc: process this.

'foo a suspends' printLine. process this suspend.

'foo a invokes block' printLine. blk value.

'foo a returns' printLine.).

blk. "holds block" prc. "holds process" |) |)

"Now, run these commands from the prompt"

" foo a

[foo blk value. ^'where does this go?'] value

foo prc resume "