Parametrically polymorphic operations (Was: Safe C++)

[Jacob Sparre Andersen <sparre@nbi.dk>]

Chad:

> "Brian Rogoff" <bpr@shell5.ba.best.com> wrote in message
[...]
> > Parametrically polymorphic functions

> I'll have to trust you or these three since I have never encountered a
> situation where I was ever wishing for such functionality.

While working on libraries for matrix operations and unit
safe types, I have certainly wanted something very similar
to parametrically polymorphic functions. It would make it
possible to have more extensive compile time checks, than
what is possible with Ada as it is defined today.

An example:

   type Matrix (Left, Right : Positive) is private;

   function "*" (Left  : in Matrix;
                 Right : in Matrix (Height => Left.Width))
     return Matrix (Width  => Right.Width,
                    Height => Left.Height);

(I hope the intention is clear although the syntax isn't
defined)

This would tell the compiler a few things, which would allow
it to
flag type mismatches already at compile time.

The current Ada specification forces us to move these checks
into the body of the functions and procedures.

Jacob
-- 
"an OS that is almost, but not quite, entirely unlike
Windows"