This is a book I wrote as part of convincing myself that the purer statically typed functional languages were ready for early mainstream adoption. Instead, I convinced myself they aren't, not yet. As such, the book is orphaned but the first 400 pages may still be useful to you. Dynamically typed functional languages like Clojure and Elixir are now at the point where I'd feel comfortable basing a commercial application on them. If you use Clojure instead of Java, or Elixir and Phoenix instead of Ruby on Rails, you'll be fine. Your app might still fail, but that won't be because of the technology stack. Some statically typed languages mix functional programming and object-oriented programming. Some of them, like F# and Scala, are also safe choices. This book was conceived as an attempt to demonstrate that the purer statically typed languages – ones like Elm, Haskell, and PureScript – are suitable for adoption by the early mainstream.