Re: Question on types conversions - operations

[Martin <martin.dowie@btopenworld.com>]

On Jun 13, 5:59 pm, sjw <simon.j.wri...@mac.com> wrote:
> On Jun 13, 4:51 pm, Olivier Scalbert <olivier.scalb...@algosyn.com>
> wrote:
>
>
>
> > I have the following three types:
> >      type Length is new Float;
> >      type Time   is new Float;
> >      type Speed  is new Float;
>
> > Suppose I need to compute a speed given a length and a time.
>
> >      L: Length := 100.0;
> >      T: Time   :=  10.0;
> >      S: Speed;
>
> > How to do that ?
>
> > With S := Speed(Float(L) / Float(T)) ? Mmmm ... not nice.
>
> > With S := Speed(L / Length(T)), I am also not satisfy as I convert a
> > time in Length ...
>
> You could declare functions such as "*" (s : speed; t : time) return
> length and of course "*" (t : time; s : speed) return length.
>
> Inside, you could use
>   return length (float (s) * float (t));
>
> You could use speed'base, time'base but then what if one is
> long_float?
>
> It's always seemed a lot of work for very little gain to me, I've
> declared them as subtypes rather than types and left checking for the
> right answer to unit test. But then, my world is all about logic and
> there are far more enumerations than reals, and very few calculations.
> Also, we tend to have coordinates (x, y) or (r, theta) so it's a lot
> more useful to define "*", "+" etc.

It would be brilliant if units checking could be built into the
standard language...

Cheers
-- Martin