Re: Announce: Grace project site operational

[dennison@telepath.com (Ted Dennison)]

"Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org> wrote in message news:<abodqj$3qh$1@nh.pace.co.uk>...
> My point is that you have to give some careful thought to creating types and
> that doing it for every identifiable unique item is not usually smart.
> Decisions should be made with some sensitivity as to what the types
> represent and how much mixing together of the different types is needed. I'd

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).

-- 
T.E.D. 
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