I can see why "meter + gram" should be forbidden.
On Sun, Apr 12, 2015 at 5:24 AM, Jan-Pieter Jacobs <
[email protected]> wrote:
> Also worth pointing out: there is a J addon helping with this:
>
> load 'math/uu'
>
> uu '1 mug' NB. string notation
>
> 1.000E-9 kg
>
> 'elephant' uu 1;'wt.human' NB. boxed notation
>
> ┌────┬────────┐
>
> │0.05│elephant│
>
> └────┴────────┘
>
> NB. Verb adding values if units correspond (Assuming boxed notation).
>
> addu =: ('Noncompatible units'"_)`((+&>&{. ; {:@])&uu) @.
> (compatible_uu_&>&{:)
>
> (1;'elephant') addu (1;'wt.human')
>
> ┌────┬──┐
>
> │3570│kg│
>
> └────┴──┘
>
> (1;'N') addu (1;'s')
>
> Noncompatible units
>
> Presumably the tabula addon, or the CAL addon can do even better, but
> documentation for CAL says you should use Tabula, and Tabula seems utterly
> broken in J803. It also does not feel it would integrate well into a
> standard J workflow ...
>
>
> 2015-04-12 1:54 GMT+02:00 Raul Miller <[email protected]>:
>
> > Ok, that makes more sense.
> >
> > I can still see problems, but at least they require other examples.
> >
> > Thanks,
> >
> > --
> > Raul
> >
> > On Sat, Apr 11, 2015 at 6:47 PM, Vijay Lulla <[email protected]>
> wrote:
> > > The statement in the article is: "We must distinguish :@ (prefixing)
> > > from :* (unit multiplication) because Kilo :@ Gram can, for example,
> > > be added to something expressed in Gram s, but Meter :* Gram cannot."
> > >
> > > I infer this as: Gram can be added to Kilogram (of course by fixing
> > > for appropriate unit conversions) but it cannot be added to "Meter :*
> > > Gram". I think that's what Bob meant.
> > >
> > > On Sat, Apr 11, 2015 at 6:10 PM, Raul Miller <[email protected]>
> > wrote:
> > >> That one strikes me as odd, also.
> > >>
> > >> Perhaps it's to prevent people from calculating center of mass?
> > >>
> > >> But why would anyone want to prevent that type of calculation?
> > >>
> > >> --
> > >> Raul
> > >>
> > >> On Sat, Apr 11, 2015 at 5:41 PM, Devon McCormick <[email protected]>
> > wrote:
> > >>> Hi Bob -
> > >>>
> > >>> this sounds interesting but why would Meter*Gram be forbidden? If
> I'm
> > >>> calculating Newtons, I want Kg * M/s^2, don't I?
> > >>>
> > >>> Regards,
> > >>>
> > >>> Devon
> > >>>
> > >>> On Sat, Apr 11, 2015 at 4:37 PM, Robert Bernecky <
> > [email protected]>
> > >>> wrote:
> > >>>
> > >>>> In the recent discussion on typing in J, I cited the Gimley Glider
> > >>>> and the Mars Climate Orbiter as events in which confusion over
> > >>>> units of measure caused expensive problems and near-disaster
> > >>>> (disaster in the case of the MCO).
> > >>>>
> > >>>> This morning, I was reading the SIGPLAN Haskell Symposium '14
> > >>>> Proceedings, and found this article:
> > >>>>
> > >>>> http://www.cis.upenn.edu/~eir/papers/2014/units/units.pdf
> > >>>>
> > >>>> By way of introduction, the paper cites the same two events, and
> also
> > >>>> cites (bottom of page 1) a paper that gives more of the same.
> > >>>> The paper is worth reading, IMO, because the authors create
> > >>>> DIMENSIONs: mass, length, density, volume, etc., that are
> > >>>> independent of units (kilogram, furlong, fortnight).
> > >>>> They also introduce two kinds of combinators (adverbs) that
> > >>>> can modify the dimensions, e.g,:
> > >>>>
> > >>>> type Velocity = Length: / Time
> > >>>> type Kilogram = Kilo :@ Gram NB. Kilo is prefix, not unit
> > >>>>
> > >>>> This lets them do things such as multiplying Kilograms times Gram
> > >>>> (and getting the right answer) , while forbidding Meter * Gram.
> > >>>>
> > >>>> I think these folks have some good ideas that could be exploited
> > >>>> in J and APL to everyone's benefit.
> > >>>>
> > >>>> Bob
> > >>>>
> > >>>> --
> > >>>> Robert Bernecky
> > >>>> Snake Island Research Inc
> > >>>> 18 Fifth Street
> > >>>> Ward's Island
> > >>>> Toronto, Ontario M5J 2B9
> > >>>>
> > >>>> [email protected]
> > >>>> tel: +1 416 203 0854
> > >>>>
> > >>>>
> ----------------------------------------------------------------------
> > >>>> For information about J forums see
> > http://www.jsoftware.com/forums.htm
> > >>>>
> > >>>
> > >>>
> > >>>
> > >>> --
> > >>> Devon McCormick, CFA
> > >>>
> ----------------------------------------------------------------------
> > >>> For information about J forums see
> http://www.jsoftware.com/forums.htm
> > >> ----------------------------------------------------------------------
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> http://www.jsoftware.com/forums.htm
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> >
> ----------------------------------------------------------------------
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>
--
Devon McCormick, CFA
----------------------------------------------------------------------
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