Looks very nice. A bit large for my taste though. Anyway, it seems they can't order their units either. That's why (|+|) :: (d1 @~ d2, Num n) => Qu d1 l n -> Qu d2 l n -> Qu d1 l n and not (|+|) :: (Num n) => Qu d l n -> Qu d l n -> Qu d l n This will always be a bit annoying. You can almost never safely write Qu (Foo :* Bar) l n but will always have to write (d @~ (Foo :* Bar)) => Qu d l n in your types. Silvio

Hi Silvio, I'm the author of the units package. Yes, the types are annoying and painfully indirect, exactly because of the problem you identify. CmpSymbol might work for you. Note that it works only on Symbols (type-level strings) and not arbitrary types. I didn't like it because I wanted it to be possible to leverage Haskell's module system to allow distinct units but with the same name, declared in different modules. (For example, "pound" can refer to a plethora of different units.) This requirement may have been a step too far, and I'd be curious to see how much the system could be simplified without it. Good luck! Richard On Aug 12, 2015, at 7:41 PM, Silvio Frischknecht wrote:

Btw I think I found a solution in

https://hackage.haskell.org/package/base-4.8.1.0/docs/GHC-TypeLits.html

there is a type level sort

type family CmpSymbol m n :: Ordering

This might work.

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