funkr

https://github.com/paul-r-ml/funkr

Funkr is a functionnal toolbox for the Ruby language. In particular, it offers a simple mechanism to create Algebraic Data Types and do pattern matching on them. - It also provide modules for common categories (Monoid, Monad, Functor, Applicative ...), and extends common types to support categories they belongs to (Array, Hash ...). Categories can also be used with custom types, see provided classes. - Array and Hash classes are extended with methods providing correct behaviour with respect to categories. Enumerable module comes with a lot of useful functions for working with lists and sets. See the module documentation and the test suite for examples.