[Axiom-developer] Re: conditionally defined functions

[Ralf HEMMECKE]

Hi Martin,

> Hmm, I think it is my point indeed. I don't know Aldor syntax, but my idea was
> roughly
>
>  define A(P: Cat1): Category == with {
>     arg: () -> Cat1
>     f: % -> P;
>  -- the operation arg returns a domain...
>     arg () == P
>  }
>
>
>
>  -- Assume B should be a domain.
>  B(Q: Cat2): Cat3 with {
>     if Q has arg: () -> Cat1 then {g: % -> arg()}
>  }

Oje, I guess that is too much to hope for. I am not one of the language 
designers, but since everything in Aldor/Axiom is first class in 
principle it should work.

There is, however, a little problem which is not so obvious in your 
"argument code arg()". What if I say the following?

DomA(P1: Cat1, P2: Cat1): A(P1) == add {
  b: Boolean := false;
  arg(): Cat1 := {
        free b;
        b := not b;
        if b then P1 else P2;
  }
  ...
}

Now, what is the type of B(DomA(P1,P2))? Does
  B(DomA(P1,P2))
have the same type as
  B(DomA(P1,P2))?

Ralf