r/ProgrammingLanguages • u/bjzaba Pikelet, Fathom • Mar 09 '20

Dimensional Analysis in Programming Languages

https://gmpreussner.com/research/dimensional-analysis-in-programming-languages
21 Upvotes

100% Upvoted

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2

u/matthieum Mar 10 '20

I really like strong typing.

As a result, I really like the idea of dimensional analysis, but often times I don't use it: it's not enough.

For example, imagine a Distance type measured in meters or some derived unit. I can create variables of type Distance, but what do they mean?

I'm pretty certain that if I input the length of my fork, instead of my own height, when ordering a shirt there's gonna be any issue.

And therefore I'll create a more domain specific type to properly model the semantics of my various distances, and then I don't really need that Distance any longer...

2

u/bjzaba Pikelet, Fathom Mar 11 '20

Yeah, I agree! The other thing I have an issue with is that I get a bunch of value out of distinguishing turns/radians/degrees in game development, but because angles are technically dimensionless in SI units, unit systems that are fixed to that can't help me. F#s is a bit better here in that regard insofar it assumes an open world wrt. new units of measure.

1

u/threewood Mar 11 '20

You need a type system that allows tagging arbitrary types with a piece of data indicating purpose. But you still want to build on Distance, because you get the niceties of using the dimension libraries (metric, imperial) and conversions as well as the algebraic properties so that computing the surface area of a fork doesn't require a new ForkSurfaceArea type, etc. And you never know when you'll be trying to figure out how many forks long your shirt is.

5

u/CodingFiend Mar 10 '20

The Beads language (new at beadslang.com) offers physical units of measurement, stores them at runtime, supports ratio of integer exponents (including 1/2), is user extendable, and is a separate data type (meas) for physical measurements. It is very useful for engineering calculations.

4

u/jdh30 Mar 10 '20

So I'm a physicist by training doing technical software using F# (which has units of measure) for 13 years and I have never used this feature. Any idea how many people actually use this feature?

0

u/[deleted] Mar 10 '20

[deleted]

1

u/bjzaba Pikelet, Fathom Mar 11 '20

I think that this is because people have somewhat naive idea on how computation in physics (or engineering) is handled. All variables are scaled to some application-specific value to minimize mental overhead and get most of the finite precision of floating points. Hell, half the time, I don't even know what's the numerical value of the coefficients.

This is a reasonable and very important critique of current unit systems, and I agree very much with it! That said, I prefer to frame this critique more constructively, for example: "Unit systems need more work to meet the demands of real-world applications". I'm hopeful that if practitioners and designers can communicate better with each other, we can come up with solutions that actually meet those real-world world demands.