The maintainer and contributors have full-time jobs. On the one hand, part of that job is keeping up Scalaz for their own professional usage. On the other hand, no part of that job is documenting it for everyone else.
Really now? As if these guys get paid to do create and fix scalaz all day right? Like Oracle yeah? This is the story about every single open source project. You can choose something else, wait it out for documentation, or contribute it. Lucky you even have the source!
Exactly. I will start considering scalaz once its authors grow up and realize that the lack of documentation is not a sign of quality.