# [racket] Numbers with dimensions

 From: Matthias Felleisen (matthias at ccs.neu.edu) Date: Sat Oct 26 11:36:10 EDT 2013 Previous message: [racket] Numbers with dimensions Next message: [racket] Numbers with dimensions Messages sorted by: [date] [thread] [subject] [author]

```1. I would hope that some generics might help here.
2. I see a need for struct mixins here because meter isn't a refinement per se but some 'attribute'. Then you could mixin several different units and I may have both m and m-1.

Data representation not fully thought thru. -- Matthias

On Oct 26, 2013, at 11:26 AM, Laurent wrote:

> How would you represents quantities like 2 kg.m^2/s^-2 with that?
> And how would you convert from mi/h to m/s?
>
> Anyway, I've started adding in some converters:
> https://github.com/Metaxal/measures/blob/master/converters.rkt
>
> Some more to come, but I may not be able to work on it for very long for now.
>
> Laurent
>
>
> On Sat, Oct 26, 2013 at 5:05 PM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
>
>
> Wouldn't we want something like this:
>
> #lang racket
>
> (module+ test (require rackunit))
>
> (struct distance (value) #:transparent) ;; this should be abstract
> (struct yard distance () #:transparent)
> (struct meter distance () #:transparent)
>
> ;; distance distance -> distance
>
> (module+ test
>   (check-equal? (d+ (yard 1) (yard 2)) (yard 3))
>   (check-equal? (d+ (yard 1) (meter 2)) (meter (+ .9 2)))
>   (check-equal? (d+ (meter 1.8) (yard 1)) (yard (+ 2.0 1)))
>   (check-equal? (d+ (meter 2) (meter 1)) (meter 3)))
>
> (define (d+ d1 d2)
>   (match (list d1 d2)
>     [(list (struct yard (value)) (struct yard (value2))) (yard (+ value value2))]
>     [(list (struct yard (value)) (struct meter (value2))) (meter (+ (yard->meter value) value2))]
>     [(list (struct meter (value2)) (struct yard (value))) (yard (+ (meter->yard value2) value))]
>     [(list (struct meter (value)) (struct meter (value2))) (meter (+ value value2))]))
>
> ;; distance distance-constructor -> distance
>
> (module+ test
>   (check-equal? (conversion (yard 3) meter) (meter (* 3 .9))))
>
> (define (conversion x d)
>   (match x
>     [(struct yard (y)) (if (eq? yard d) x (meter (yard->meter y)))]
>     [(struct meter (y)) (if (eq? yard d) (yard (meter->yard y)) x)]))
>
>
> ;; auxiliaries
> (define (yard->meter v) (* .9 v))
> (define (meter->yard v) (/ v .9))
>
> -- Matthias
>
>
>
> On Oct 26, 2013, at 7:20 AM, Laurent wrote:
>
>> Ok, so I just hacked together a small lib for handling numbers with unit symbols and exponents:
>>
>> Quick example:
>> > (measure->value
>>    (m* '(18 s)
>>        '(1600 km (h -1))
>>        '(1000 m (km -1))
>>        '(1/3600 h (s -1))))
>> '(8000 m)
>>
>> You can get it with:
>> \$ raco pkg install measures
>> or from the File menu in DrRacket, if you have a recent version of Racket (strictly > 5.3.6).
>>
>> Examples and details here:
>> https://github.com/Metaxal/measures
>>
>> HTH,
>> Laurent
>>
>>
>> On Fri, Oct 25, 2013 at 12:51 AM, Alvin Schatte <AlvinSchatte at skytex.net> wrote:
>> Is there a library or package that combines numbers and their operations with dimensions that may be associated with them?
>> Alvin Schatte
>>
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>>   http://lists.racket-lang.org/users
>>
>>
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>
>

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