List of units

[tessus]

Is there a list of units? The documentation states fend supports many units, but it doesn't tell me which ones and/or how they are represented.

I found out by trial and error that kg and kilogram both work. But on the other side c is the unit for lightspeed, but it doesn't work in certain situations:

> 4_000_000_000 mile/s in c
Error: right-hand side of unit conversion has a numerical value
> 1c in mile/s
approx. 186282.3970512208 miles / s
> 4_000_000_000 mile/s in light
approx. 21472.7750089029 light
> 4_000_000_000 mile/s in lightspeed
Error: unknown identifier 'lightspeed'

Then I tried lightspeed instead of c when converting to c, but only light seems to represent light speed in this situation.

This is just one example, but you might understand my confusion.

I checked the source code and I could find some answers there, but I think the documentation could be more forthcoming.

[printfn]

Hi, thanks for raising these issues. I've now added light_speed and lightspeed units; they will be in the next release. As you've probably worked out all supported units are listed in https://github.com/printfn/fend/blob/main/core/src/units/builtin.rs, and built-in functions and some other constants can be found in https://github.com/printfn/fend/blob/main/core/src/ast.rs#L747.

It would definitely be good to make the list of supported units available in the documentation, perhaps by automatically generating documentation from the source code. I might take a look at implementing this soon.

The reason that converting to c doesn't work is that I've implemented c to always expand to its value in metres per second. While this makes it easy to check the value of c, it currently makes it impossible to use it as a unit by itself, rather than just as a constant. There aren't many other constants like this in fend (I can think of electron_charge and gravity), and you're right that it would be good to be able to use these as proper units.

[tessus]

Thanks for the quick reply.

I've now added light_speed and lightspeed units

Nice, thanks.

automatically generating documentation from the source code

This would make sense. It might even allow an option units to list them in fend, either by using an option fend --units, --show-units or --list-units, or to use it interactively without the --.
A help system in such a cli app could be useful. But I do understand that this is additional maintenance ovehead. But

> help [numbers|arithmetic|formats|functions|constants|...]

would be seriously awesome. ;-)

The reason that converting to c doesn't work is that I've implemented c to always expand to its value in metres per second. While this makes it easy to check the value of c, it currently makes it impossible to use it as a unit by itself, rather than just as a constant.

This is perfectly fine and I am not asking to change it. In fact I believe this particular misunderstanding was my fault, because I could have realized that trying to use c as a unit was futile, since it was defined as a constant. (It is listed as a constant in the docs.)