Re: Safe Units Handling in Ada

[Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>]

Fraser <newsfraser@blancolioni.org> writes:

> Someone will have to remind me how the cross product is calculated!

I've got a generic vector package that does everything I need. It's in
SAL at
http://users.erols.com/leakstan/Stephe/Ada/Sal_Packages/index.htm,
file sal-gen_math-gen_vector.ads.

It's instantiated in files sal-gen_math-gen_dof_3.ads and
sal-gen_math-gen_dof_6.ads.

That's what I need adapted to units.

> This is just off the top of my head:
> 
>     unit Meters_Type;
>     unit Seconds_Type;
>     unit Velocity_Type is Meters_Type / Seconds_Type;
> 
>     vector Meters_Cart_Vector_Type is Meters_Type * 3;
>     vector Velocity_Cart_Vector_Type is Velocity_Type * 3;
> 

This looks promising. I think it should be in a second input file, and
produce a second package; some parts of the system need vectors, some
don't.

> There would have to be some sort of syntax for specifying the vector
> index type (or to ask for a record type instead). 

Yes; I use an enumeration type for some vectors, integers for others.

> The operators + and - (binary and unary) would be provided, as well
> as a cross product if it's a 3 vector, and a dot product in any
> case.

And lots more in my package.

> Maybe we don't need a vector keyword, since it's implied by the
> syntax "identifier operator constant-integer", but on the other hand
> there's no need to worry about keyword bloat in a language of this
> size.

Yes, make it easy to parse, and easy to generate friendly error
messages.

-- 
-- Stephe