[Axiom-developer] Re: conditionally defined functions

[Martin Rubey]

Ralf HEMMECKE writes:
 > Hi Martin,
 > 
 > > Suppose you have a category A, taking as parameter a domain P and 
 > > providing an
 > > operation f: % -> P. Furthermore, you have a category (or a domain, a 
 > > package)
 > > B, taking as parameter a domain Q. Now you want to achieve the following:
 > > 
 > > If Q is a domain in A, provide a function g: % -> P, using f.
 > 
 > Let me translate this into some code...
 > 
 > define A(P: Cat1): Category == with {
 >    f: % -> P;
 > }
 > 
 > -- Assume B should be a domain.
 > B(Q: Cat2): Cat3 with {
 >    if Q has A(???) then {g: % -> ???}
 > }
 > 
 > To me it seems that in order to state that "Q is a domain in A" one 
 > would have to know the parameter of A. Note that A is a function 
 > returning a category. The ??? should be something of type Cat1. And I 
 > don't see this information somewhere available inside the definition of B.
 > 
 > I guess that is not your point. Can you be more precise here?

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()}
 }

Thanks for replying that fast,

Martin