Paul Schlie wrote:
From: Dave Korn <[EMAIL PROTECTED]>
----Original Message----
From: Paul Schlie
Sent: 08 June 2005
- Can you give an example of an operation which may yield an undefined
non-deterministic result which is reliably useful for anything?
Random number generation?
randomness has nothing whatever to do with non-determinisn. They
are completely different concepts.
But there are of course many examples.
THere are many examples in concurrent programming where non-determinism
is useful, and in set programming, arbitrary non-deterministic selection
from a set is fundamental.
But this is a complete red herring in this discussion
The reason that for example in Ada we say that
a+b means non-determinisitically either compute a then b, or
b then a, is not that it is useful for these results to be
different, but precisely because we expect NO reasonable
program to ever write an expression a+b in which the two
semantic meanings that are possible are different, and
we want the compiler to take advantage of this to generate
better code.
For example
a + f(b)
we typically expect f(b) to be called first, even though
formally it might be the case that f(b) modifies a, so
this choice could have some effect from the formal
non-determinism of the semantics. Our actual attitude
is that if anyone writes code like this in which f(b)
modifies a, they are highly incompetent and we don't
care what happens.
