'goto" gone from computer languages or is it!

[Paul Koning]

>>>>> "John" == John Hogerhuis <jhoger at gmail.com> writes:

 John> Point taken; my first guess was 0 0 0, but it is apparently
 John> left ambiguous by the standards committee. I did use the term
 John> "almost always" to hedge, but still, you're right.

Actually, I don't think the example was "ambiguous".  It's "undefined"
which is actually a term with a precise meaning.  So you were right --
a program is a precise statement.  But for some programs, that precise
statement doesn't define just one possible outcome.

A number of programming languages intentionally make certain things
unspecified, or undefined -- the reason for doing that is to give
implementations more choices and allow more efficient implementation.
The sample program that started this discussion is one example.  

C isn't the only language that does this; Algol 68 is another.  For
example, it quite explicitly and intentionally says that it's
unspecified whether the left or the right side of + (or neither) is
evaluated first.

 John> Nevertheless, for any given compiler there is only one
 John> interpretation.  So I hereby clarify my statement to say that
 John> programming languages as implemented by actual compilers or
 John> interpreters are the most succinct, clear and unambigious
 John> specification languages imaginable.

Not true.  For example, you may have a program in which several things
happen in an order that depends on timing, or interrupts, or things
like that; if so, you may not get the same answer when you run it
twice.  Embedded systems programmers are painfully familiar with this.

To use Algol 68 as an example again:
   int i := 0;
   int j := (i := i+1) + (i := i+1)

(which in C could be written as: j=(++i)+(++i) )

On completion, j might be 1 or 2, and i might be 1 or 2 -- and in
implementations that take advantage of paralellism, the answer might
change from run to run.

       paul