Re: Parameter evaluation order

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Nick said

<<None of the constructs being discussed are actually non-deterministic (in
the conventional sense): this is a very esoteric branch of computing indeed!
(Related to natural learning systems, for the curious.) (Oh, and lottery
machines!)
>>


That is completely false. The conventional sense of non-deterministic in
the programming language field is that the effect of a given construct
is a non-deterministic selection from a set of possible outcomes.

Sometimes non-determinism has been used in conjunction with backtracking
semantics, where the model is that the "right" selection is made. Lambert
Meertens suggested some years ago the term "angelic non-determinism" for
this case.

Note that arbitrary selection has NOTHING AT ALL to do with random
selection (I suspect that may be part of Nick's confusion, given that
he mentions lottery machines, where randomness is what is wanted).

So saying that, for example the select statement in Ada 83, makes an
arbitrary selection of which branch to choose among several open branches
does not require or even vaguely imply some kind of "fair" random selection.
(I have been amazed at how many people have been confused on this particular
point, including some supposed experts in Ada :-)

The terms that Nick suggests, e.g. sequential non-determinism, are in my
opinion non-standard and confusing.

As you read the above, you will see that I use non-deterministic selection
and arbitrary selection from a set as synonyms. This is intentional, and
this is the conventional usage.

(related reading: the definition of SETL and its arb operator)