[racket] Numbers with dimensions

That's a good idea, and it's quite easy to implement using contracts!
Would something like this suit you? (this is currently working as is)
https://gist.github.com/Metaxal/7212740


Laurent



On Tue, Oct 29, 2013 at 11:40 AM, Konrad Hinsen
<konrad.hinsen at fastmail.net>wrote:

> Laurent writes:
>
>  > So I've redesigned it somewhat, and now there are 2 calculation "modes":
>  > - The normal mode is pretty much like Frink (probably the one you
> want), which converts
>  > everything to base SI units. Conversion back to non base units can be
> done afterwards.
>
> Well, what I really want is something else, but this is a useful
> feature nevertheless for a unit calculator. It would be nice though if
> the default units to which everything is converted were modifiable. SI
> units are fine for engineering and daily life, but neither for
> astrophysics nor for atomic-scale measurements.
>
> What I personally care about most is dimensional analysis as a means
> of ensuring program correctness. I want to be able to write
>
>   (define: (kinetic-energy (m : Mass) (v : Velocity) : Energy
>     (m* 1/2 m v v))
>
> and then compute the kinetic energy of a car as
>
>   (kinetic-energy (m 1000 kg) (m 90 km (h -1)))
>
> whereas a typical mistake such as
>
>   (kinetic-energy (m 1000 kg) (m 90 km h))
>
> would get caught by the type checker (ideally) or at run time. With a
> unit-converter approach such as the one you implemented, the erroneous
> call would be accepted and an error would be detected only if the
> result is later converted to an explicitly named energy unit.
>
> Konrad.
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