Yesod is a Haskell web framework for productive development of type-safe, RESTful, high performance web applications. September 3, 2013By Michael SnoymanView source on Github I recently had an email thread with Greg Weber and Max Cantor about classy-prelude. We ended up focusing on classy-prelude's implementation of map. Currently, classy-prelude defines a CanMap typeclass as follows: class CanMap