Steven D'Aprano wrote:
On Thu, 20 Nov 2008 14:22:50 +1300, greg wrote:
Antoon Pardon wrote:
You are changing your argument. In a follow up you made the point that
call by value should be as it was intended by the writers of the algol
60 report.
No, I was countering the argument that "call by value" is short for
"call by copying the value". I was pointing out that the inventors of
the term didn't use any such words.
Nor did they define what assignment means, and their definition of
"value" seems to exclude such things as strings.
Arguing that their words were intended to imply copying, as part of the
essence of the idea, is making an even bigger assumption about their
intentions, IMO.
Rather it seems to me that the essence of the idea they had in mind is
that call-by-value is equivalent to assignment.
You've just *assumed* that assignment in Algol 60 doesn't involving
copying. Based on the very little I know about Algol, I think that is a
very unsafe assumption. I know significantly more about Pascal, and in
Pascal, assignment *is* copying.
(I wait now with bated breath for somebody to point out some Python
implementation or feature where assignment doesn't make a copy...)
In stock ALGOL-60, there are only the primitive types, and assignment
of them is a copy. Most useful implementations had strings, and Simula,
which was an ALGOL extension, had objects.
Simula had value parameters, reference parameter, and name parameters.
For assignment, ":=" specified a value assignment, and ":-" specified
a reference assignment.
John Nagle
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