Re: Call by reference vs. call by value

[peterm@senet.com.au (Peter Morris)]

bobduff@world.std.com (Robert A Duff) wrote:

>In article <Pine.SUN.3.91.960723082703.22250A-100000@erlang.praxis.co.uk>,
>Peter Amey  <pna@erlang.praxis.co.uk> wrote:
>>This is another Ada feature well covered by the SPARK subset.  The rules 
>>of SPARK (which are checked by the SPARK Examiner) prohibit all cases 
>>of aliasing where program meaning might be affected by the parameter 
>>passing mechanism used. A SPARK program has copy-in, copy-out semantics 
>>regardless of the compiler used to compile it.

>Right, but you could equally well say that a SPARK program has by-ref
>semantics.  SPARK ensures that the two are equivalent by avoiding
>aliasing, as you said, and also by avoiding exception handlers.

>- Bob

The occam programming language which I have been using for distributed
control systems also prohibits aliasing.  As this seems to be a simple
and efficient way to prevent the problems that aliasing can cause I
wonder if it might not be a good idea for the full version of ADA95 to
prohibit aliasing.

> ... and also by avoiding exception handlers.

Would it be sensible for an implementation of ADA95 to prohibit
aliasing yet allow exception handlers? 



Peter Morris