Dynamic scoping (was: Proposal: Squeak-E = Squeak x Kernel-E)
spair at acm.org
Mon Jan 27 19:41:18 UTC 2003
Avi Bryant wrote:
> On Mon, 27 Jan 2003, Stephen Pair wrote:
> > Have you looked at RuntimeEnvironments (on SqueakMap)? They
> > accomplish the same effect, but they are cleaner than using
> > exceptions...
> By whose definition of cleaner? ;)
Well, I consider "Env at: #world" to be more clear about the intent than
"MyWorldEnvironment signal" or similar...don't you? I think you are
looking at the implementation.
> I find using exceptions preferable for at least two reasons:
> - the semantics of dynamic scope are defined by the context
> stack, not by Process. There is not always a one-one
> relationship here.
I agree, but you're speaking about implementation.
> If you use a dynamic scoping mechanism
> that walks the context stack, you get the correct behavior
> for free when working with constructs like Continuation.
> RuntimeEnvironments would require special treatment to work
> across coroutining or continuation invocation.
Yes, your implementation of Continuation has made that clearly evident
to me. ;)
I agree that the runtime environment should be inter-woven in the
context stack. I'm actually working on that change right now.
> - a mechanism based purely on exceptions is likely to be
> fairly portable, and also likely to make good use of primitives
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