Re: Function pointer in Ada?

["Marc A. Criley" <mcqada95@earthlink.net>]

Kai Schuelke wrote:
> 
> I want a program that can solve every mathematical function (e.g.: z = 2*x +
> sin(x)) for any value (e.g. x=4). It is enough to work with one mathematical
> function at a time. My spec looks like:
> 
> -- Spec
> package math is
>     procedure Set_Function(Func : in STRING);
>     function Calculate(Value : in FLOAT) return FLOAT;
> end math;
> 
> -- Sample program
> with math; use math;
> procedure sample is
>     result : FLOAT;
> begin
>     Set_Function("2*x+sin(x)");
>     result := Calculate(4.0);
> end;
> 
> What would be the Ada way to do this?

If you're going to pass the function in as a String, as your package
shows, then you will have to parse that string into its constituent
operands and operations.. These would be stored perhaps in a tree
structure, then traverse the tree in the proper sequence, doing an
interpretive evaluation as you go.  (And watch for malformed functions!)

Marc A. Criley
Consultant
Quadrus Corporation
www.quadruscorp.com