Re: Fun: the Ada assignment operator is an alias of the equivalence operator

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sat, 28 May 2011 10:02:51 +0200, Yannick Duch�ne (Hibou57) wrote:

>> Assignment is not a logical operation, variables are not logical
>> predicates.
> Nor "defined-as" is ;)
> 
> ":=" would be OK for constant, makes Ada looks a bit more functional :p

I think it is a widely shared misconception that immutability has anything
to do with that. [Functional is not an answer, whatever the question was
(:-))]

No, even an initialized constant is not necessarily equivalent to its
initializing expression. Obvious examples:

   I : constant Integer := Get (File);
   X : constant Float := Random (Dice);
   T : constant Time := Clock;

Another point is that equivalence itself is an abstract operation with the
semantics undefined in general.

Mathematical equivalence = is not analogous to "=" operation defined on
objects. Rather it is:

1. Values equivalence (values do not belong to the program). I.e. you can
say that the value of the variable A is equivalent to the value of the
variable B. Which is unrelated [not required] to whether A=B yields True or
False.

2. Program equivalence. You can say that two programs are equivalent in
some [limited] sense, e.g. when the compiler optimizes the code, or when
you modify the program.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de