[Axiom-developer] Re: [Aldor-l] exports and constants

[Christian Aistleitner]

Hello,

On Sun, 23 Jul 2006 08:00:56 +0200, Bill Page  
<address@hidden> wrote:

> > ---BEGIN aaa6.as
> > #include "aldor"
> > #include "aldorio"
> > macro I == MachineInteger;
> > define CatX: Category == with {foo: () -> I}
> > A: CatX == add {foo(): I == 0;}
> > B: CatX == add {foo(): I == 1;}
> >
> > import from MachineInteger;
> > X: CatX == if odd? random(10) then A else B;
> >
> > main(): () == {
> >         import from X;
> >         stdout << foo() << newline;
> > }
> > main();
> > ---END aaa6.as
> >
> > woodpecker:~>aldor -fx -laldor aaa6.as
> > woodpecker:~>aaa6
> > 0
> > woodpecker:~>aaa6
> > 0
> > woodpecker:~>aaa6
> > 0
> > woodpecker:~>aaa6
> > 0
> > woodpecker:~>aaa6
> > 0
> > woodpecker:~>aaa6
> > 1
> > woodpecker:~>aaa6
> > 1
> >
> > [...]
> [...]
>   main(): () == {
>         import from X;
>         stdout << foo() << newline;
>         stdout << foo() << newline;
>         stdout << foo() << newline;
>         stdout << foo() << newline;
>         stdout << foo() << newline;
>         stdout << foo() << newline;
>   }
>   main();
>
> You will see that each time you run the program you will only
> get one *constant* result (all 0's or all 1's). But if you run
> the same program repeatedly (as you did above), then sometimes
> you get one result and sometimes the other! Within a given
> runtime of the program, the result is constant and not variable
> as you might be expecting.

I'd strongly expect it to be constant at runtime! "==" gives a constant.  
So it should be constant.
What kind of concept is a modifyable constant?
Maybe you want to refer to a macro instead of a constant?

A assume that each time you start the program, odd? random(10) is  
evaluated exactly once.
Of course, your whole main function accounts for exactly one program start.

> My conclusion is that Aldor must be sort of "faking" the
> compilation of the constants in the sense that they are not
> fully resolved at compile-time, yet they are indeed constant
> within any run of the program. There must be some kind of
> dynamic initialization phase at the start of the program.

I doubt that. The constant X is compiled to "if odd? random(10) then A  
else B;" and neither A nor B. That's not faking, that's just what's in the  
.as file. However, the value of a constant is (typically) determined only  
once, hence for the whole program execution X acts like either A or B.

--
Kind regards,
Christian