Haskell, Clean, Agda and Idris are four functional programming languages that share lots of their concepts and syntax. You usually start learning one of them and then you learn the differences with the other ones. So, why not creating a book that shows the four languages at the same time, stressing their commonalities and differences?
The flagship of purely, lazy, functional programming. Known throughout the world for its use of monads and do notation.
Offers an uniqueness typing system for resource management.
Provides dependently-typed programming along with an interesting module system, instance arguments and more.
Focused on the integration of embedded domain-specific languages.