[racket] Numbers with dimensions

The last line applies to my thoughts not yours. 

As someone else indicated, I think we should experiment with 'dimension' (distance, time) vs 'units' (meters vs yards, seconds vs hours). This separation injects a hierarchy that could be useful. 

I'd really like to see some experimentation here because people haven't explored the space much and Racket could help explore a #lang metric/racket and even #lang typed/metric/racket. 

-- Matthias





On Oct 26, 2013, at 11:36 AM, Matthias Felleisen wrote:

> 
> 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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>> 
> 
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