Show HN: Numbat – A programming language with physical dimensions as types

• numbat

  5 836 9.8 Rust

  A statically typed programming language for scientific computations with first class support for physical dimensions and units

- Numbat might eventually be able to infer (physical dimension) function parameter types with its Hindley-Milner-style type system [1]. The only language that I know of that can do this is F#. The author of F#'s unit system wrote his PhD thesis on the subject [2], and Numbat follows the original approach in the thesis quite closely.

[1] https://github.com/sharkdp/numbat/issues/29

• Squants

  8 910 2.9 Scala

  The Scala API for Quantities, Units of Measure and Dimensional Analysis

  

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• insect

  24 3,152 4.9 PureScript

  High precision scientific calculator with support for physical units

Apparently this replaces https://github.com/sharkdp/insect

• Measuremancer

  1 20 6.7 Nim

  A library to handle measurement uncertainties & error propagation

  

Yeah, unicode characters in Nim code are supported. However, if by `x²` you'd want to square an identifier `x`, that won't work. The Nim lexer parses `x²` as a single identifier.

We do have infix unicode operators though. So `x ÷ y` (spacing required though!) could be implemented easily. I use this for `±` in Measuremancer [0] (which btw also supports Unchained units, for error propagation on unitful measurements).

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

• astGrad

  1 15 10.0 Nim

  Symbolic differentiation based on the Nim AST

  

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/

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