kal VS Unchained

It's obsolete now, but before async/await was part of JS proper I worked on a compile-to-JS language that handled this by compiling to callbacks: https://github.com/rzimmerman/kal

It included try/catch support and fancy stuff, like loops. The source may be interesting for anyone interested in compilers: https://github.com/rzimmerman/kal/blob/master/source/generat...

The Kal compiler is written in Kal, but it's supposed to be easy to read. Surprisingly the browser demo still works: http://rzimmerman.github.io/kal/demo.html

Anything with a finite (200 is small even) number of units misses the algebraic structure of the problem mentioned in https://news.ycombinator.com/item?id=36988497 wherein multiplying|dividing two things gives you a (potentially) new unit which implies an open ended "space" of units.

To be concrete (hah!), in C++ a template meta-type with 12 signed integer parameters (6 numerators & 6 denominators for rational exponents of SI base units) might be one way to model it.

Unlike C++ template stuff, Nim macros (like Lisp macros) makes metaprogramming more like procedural programming - just against abstract syntax trees. I think that helps to shield some of this type complexity from users, but the documentation README https://github.com/SciNim/Unchained does better job than I can in an HN comment.

Of course, for unit system conversion, the number of dimensions (6 in SI, 3 in CGS/Gaussian) changes. So, for full generality you need compile-time (if you want static type integration/CT errors) linear algebra over a rational field (at least & conventionally) to project|inverse project. That might be theoretically possible in C++. I would think it very un-fun and unlikely to ever have been done. There's probably a Mathematica package, though.

I've recently written a units library for Nim [0]. It's still WIP, but it's already proven extremely useful for me as a physicist.

Thanks to Nim's strong type system and metaprogramming features, it allows for a fully compile time design, without any runtime overhead (in form of special unit objects or such things; everything is a `distinct float`).

In addition Nim's unicode support, the code even looks nice!

A more complex use case (I can link more if desired): [1]

[0]: https://github.com/SciNim/Unchained/

[1]: https://github.com/SciNim/Unchained/tree/master/examples