[Axiom-developer] Re: 1: %

[Ralf Hemmecke]

Dear Gaby,

On 02/22/2006 04:00 PM, Gabriel Dos Reis wrote:
> Ralf Hemmecke <address@hidden> writes:
>
> | On 02/22/2006 12:21 AM, Gabriel Dos Reis wrote:
> | > Ralf Hemmecke <address@hidden> writes:
> | > | > | The problem is the "1: %" as a constant (not a nullary
> | > function).
> | > | > The distinction is largely syntactic, not fundamental.
> | > | | I was once told that in Aldor the difference between
> | > |    a: %
> | > | and
> | > |    b: () -> %
> | > | is that
> | > | b() will run a program which might side-effect other things or even
> | > | return something different each time.
> | > expanding on my preivous answer, have a look at the section 5.2 os
> | > the
> | > Aldor user guide on literal forming -- you can define your own function
> | > to interpret a string literal as a constant.
> | 
> | I knew about this Literal stuff before...
>
> I have no doubt about that :-)
>
> | http://lists.gnu.org/archive/html/axiom-developer/2006-02/msg00154.html
> | 
> | But as you see, if you write a domain that has a function
> | string: Literal -> %,
> | it is a function and that means that "1" and "1" need not give
> | identical values.
>
> yes, that is precisely why I said in an earlier message that the
> distinction is largely syntactic.  it is not something fundamental in
> the context of your discussion about axiom and o stuff.
> Underneath, everything is a function in Aldor!

Well, it might depend on which level you look at it. If the generated C 
code is concerned, I have no idea about that.

But if it were really just syntactic, then the output given below is 
strange.

However, this behaviour is exactly, the difference between a constant 
and a nullary function in Aldor.

Aldor computes the value for x at the time the domain is instantiated. 
So it is constant over the lifetime of the domain (unless some dirty 
tricks change that value). For y it is different. That is a function 
constant. But a constant of type ()->% not of type %. Now, of course, if 
you say "y()", you get something of type %. But each time you call y() 
you might get a differen element of %.

I guess, you know all this stuff.

Ralf

aldor -laldor -grun domaintest.as
172443481
172443481
1911439442
1127848893

---domaintest.as
#include "aldor"
DomA: with {
        x: %;
        y: () -> %;
        coerce: % -> Integer;
} == add {
        Rep == Integer;
        import from Rep;
        x  : % == per random();
        y(): % == per random();
        coerce(x: %): Integer == rep x;
}
main(): () == {
  import from TextWriter, Character, Integer;
  a: DomA := x;   stdout << (a::Integer) << newline;
  b: DomA := x;   stdout << (b::Integer) << newline;
  a: DomA := y(); stdout << (a::Integer) << newline;
  b: DomA := y(); stdout << (b::Integer) << newline;
}
main();