Re: Announce: Grace project site operational

["Martin Dowie" <martin.dowie@nospam.baesystems.com>]

"Ted Dennison" <dennison@telepath.com> wrote in message
news:4519e058.0205140718.3ddb1b2a@posting.google.com...
> That's the biggie. If you try to make separate types for velocities
> and accelerations, you will suddenly find that you also need separate
> types for times and distances, and perhaps even Hz and mass and forces
> and rotational orientations and velocitites and accelerations. Then
> you'll find how annoying it is to have to do type conversions on every
> factor in every formula. A more attractive option may be to write your
> own math operators that return the correct type given their two input
> types. But that causes an exponential growth in operators that you
> have to create every time you add a new unit.
>
> To do this kind of thing *right*, you'd really need a language that
> relies on structural equivalence for types, and automaticly generates
> the proper new type given the operator and the types of its operands.
> In Ada, you just can't do that.
>
> Generally, what I see Ada folk do is use *subtypes* for all this
> stuff. That way ranges are checked, but formulas don't become a chore
> (although you still have to be really careful with intermediate values
> blowing out of subtype constraints).

Can't say I've ever seen these as subtypes and I'm not sure
I like the idea...

The ability to not add volts and metres together is one of
things I like about Ada!

In the same vein as the standard Ada maths library doesn't try to
cover _all_ possible maths packages, an 'elementary SI' package should
be possible (I feel) to cover 99% of project needs (e.g. SI units and
support for powers to the +/- 3 plus a base 'dimensionless' unit).

I have no evidence to support this supposition other than my own experience
that the above would cover every project I've ever work on (and that's
including some heavy duty 3-d geometry type projects).

It might be big, it might not be pretty, but once its there it's not
exactly going to be changing! :-)