Russ Abbott wrote:
Regarding whether variables should be data flow variables, I would
strongly recommend that Oz implement a way to constrain variables to be
non-data-flow and that will result in an exception if an operation that
requires a value is attempted when the variable is undefined. As it now
stands, that's not possible (as far as I know).
You're too dismissive. It's pretty easy to write, in fact. The idea is
to run some code when a thread needs the value of a variable. That's
exactly how we have (re)defined lazy computations in Oz!
proc {DontSuspend X}
thread
{WaitNeeded X}
if {Not {IsDet X}} then
%% put your code here
end
end
end
If X={DontSuspend}, then you have to determine X before trying to use
it. The statement {WaitNeeded X} blocks until some thread needs the
value of X. The conditional after it is necessary because determined
variables are needed by convention (so "being needed" a monotonic property).
Basically, I'm asking for an operation that would constrain an Oz
variable to act like a Prolog variable. If Oz takes its role as a
platform for the explication of programming languages seriously, here's
an important programming language paradigm element that is apparently
impossible to define in Oz.
We don't want to explain other languages in Oz. That could not work.
We want to be able to show useful programming concepts, and those
concepts should be modular. The behavior you ask for is not composable
with concurrency. What you ask for is a debugging tool, IMHO.
Most of the designers of Oz know Prolog well. They know its strengths
and weaknesses. Oz was not designed to be the successor of Prolog. It
was designed to be a general-purpose language. Prolog's paradigm has
some restrictions that do not allow this generality.
Cheers,
raph
_________________________________________________________________________________
mozart-users mailing list
[email protected]
http://www.mozart-oz.org/mailman/listinfo/mozart-users
