[kragen]

most linear algebra requires vectors of multiple unit types. think of runge-kutta for a second-order system, for example, or just about any multivariate system. see https://yosefk.com/blog/can-your-static-type-system-handle-l... for more information

if your static type system can't handle that, it can't handle unit types for basic linear algebra subroutines

[V1ndaar]

I mean that article of yours highlights the difficulties one encounters fairly well, I would say. I don't disagree that this is (generally) a tricky problem!

Nim allows you to do a lot, e.g. derivatives of a unitful expression with measurement errors [0]. But other aspects run into the reality of dealing with a static type system. For example in Measuremancer [1], the library handling measurements with uncertainties, each `Measurement` is a single generic `Measurement[T]`. Each measurement stores the derivatives for error propagation. Obviously the derivatives have different units. Now, we could make `Measurement` a two-fold generic, `Measurement[T, U]`, but that just makes things more unwieldy in practice, for not much gain.

Without rewriting a majority of existing code you will always run into trouble where your perfect unit type system will either break or you'll need to work around it anyway (e.g. calling into some C library for part of the code).

[0]: https://github.com/SciNim/astGrad#extra-fun

[1]: https://github.com/SciNim/Measuremancer/

[kragen]

just to clarify, i didn't write the article; yossi kreinin did

you seem to be saying that it's impossible to formulate a type system that handles units correctly in contexts like generic linear algebra algorithms

i think you are mistaken about that

[V1ndaar]

I nowhere said impossible! All I say it is tricky and that likely the code you write will have to be adapted in certain cases (compared to current existing implementations of numerical algorithms).

[kragen]

if you have to adapt it in certain cases because of limitations in the type system, from my point of view that amounts to the type system handling units incorrectly

in the same way that pascal's type system handled array sizes 'incorrectly' because you couldn't write a subroutine that could operate on an array of any size, just arrays of one size or another

you could say 'yes, well, the code you write will have to be adapted in certain cases (compared to current existing implementations of string algorithms)', like say if your string has more than 20 characters in it, but the reason is that you're doing something the type system can't handle