Re: GNAT and Dimension Checking

[AdaMagica <christ-usch.grein@t-online.de>]

Thanks for the chapter - I just overlooked it.

The documentation, though, is rather terse. It doesn't tell you the syntax of the aspect clauses nor anything else than the most basic things.

All in all it looks promising - it's a very clever way to use the new aspects.

What I found out:

  G : constant acceleration := 127137.6 * km/(hour ** 2);
  Put (Sqrt (G), Aft => 2, Exp => 0); Put_Line ("");
yields 3.13 m**(1/2).s**(-1), so it handles fractional powers (at least 1/2).

Math functions except sqrt need dimensionless parameters.
However, sin (t, t0) should be allowed as long as t and t0 have the same dimension. It is not. Also arctan (x, y) is only allowed for dimensionless parameters.

We'll see how it turns out when applied to more complicated formulae, especially with those where parts have fractional dimensions (in SI, there are no items with fractional units, but intermediate ones do).

CGS cannot do without fractions.

Perhaps with some refinement, this could be a theme for Ada 2020 :-)
------------------
PS: Anyone interested in dimensional arithmetics in Ada should have a look at:

Ada Europe Conference 2003
    Christoph Grein, Dmitry A. Kazakov, Fraser Wilson
    A Survey of Physical Unit Handling Techniques in Ada

The conference proceedings have appeared at Springer-Verlag:

    © Springer-Verlag
    Jean-Pierre Rosen, Alfred Strohmeier (Eds)
    Reliable Software Technologies - Ada-Europe 2003
    8th Ada-Europe International Conference on Reliable Software Technologies
    Toulouse, France, June 16-20, 2003
    Proceedings
    Lecture Notes in Computer Science, Vol. 2655, Springer-Verlag, 2003 

The proceedings are also available at Springer-Verlag's web site, but you need to be a subscriber in order to read the full texts:
     http://link.springer.de/link/service/series/0558/tocs/t2655.htm
or
     http://link.springer-ny.com/link/service/series/0558/tocs/t2655.htm

For a quick overview, see
  http://www.christ-usch-grein.homepage.t-online.de/Ada/Dimension.html
where you can also find the full paper.

Have fun :-)