And, regarding feature toggles, this bit in the Cabal FAQ baffles me a
little:

> Question: I like to let the user enable extended functionality using a
> Cabal flag. Is this the right way?
>
> Answer: Certainly not. Since other packages can distinguish packages
> only according to their name and their version, it is not a good idea
> to allow different APIs for the same package version. Cumbersome as it
> is you have to move extra features to a separate package.

Moving the features to a separate package wouldn't really solve anything
AFAICT, because I'd still have to bring them together somehow.