Hello, for Grapefruit’s incremental list signal support, I needed a type class of semigroups. A semigroup is similar to a monoid. The difference is that a semigroup doesn’t need to have a neutral element. So a semigroup type class would make a perfect superclass of Monoid, by the way. Since a semigroup class could be of more general interest, I decided to not include it in Grapefruit. Since I couldn’t quickly find an implementation of semigroups in Haskell, I put my own into a new package. Now, a package only for one class with one method seems like overkill. However, it could serve as a start for a package of all kinds of algebraic structures. So I called the package “algebra” and put it on Hackage. So if someone wants to implement rings, ideals, fields or whatever, I’d be happy to receive patches. Best wishes, Wolfgang