Over the winter, I have been refining a Haskell library of functions for doing Applicative Logic. The idea is that a lot of functions involving booleans can be generalised to work on any Applicative Functor (possibly applied to Monoids), through the isomorphism Bool ≃ Maybe () – where Maybe is the applicative functor and () is the monad. There is a more complete write-up here on my website, and I have put the library on Hackage . There is also a discussion thread on r/haskell under the heading “A boolean is maybe true” . I was happy that some people got the point, and there was even a link to my write-up in Haskell Weekly .