★★★★

In the interest of full disclosure, I'd like to point out that I am a somewhat biased reviewer, given that bothandBjarnason worked with me at S&P Capital IQ pretty much the entire time they were writing the book.Consequently, I got to see a fair bit of how the sausage was made.On the other hand, their overall vision about the role of functional programming in the enterprise was compelling enough to me that I was willing to leave my previous job and go work with them, so I'd like to think that that indicates a level of personal trust.Both Paul and Rúnar are excellent functional programmers who really want to convey the joy of functional programming to the world. By and large I think they have succeeded in that goal with this book!It is a good mixture of theory and practical that really speaks well to the working developer who needs to shake himself out of the Enterprise Java Bean rut.In short, I find this to be a wonderful book, written with passion by two excellent developers, both of whom have a lot of good things to say.In contrast to other presentations, this book provides another viewpoint and showcases a pure approach to functional programming and they make a very compelling case for that style! Reading it can and will improve your productivity and will serve as a gateway to bigger and better things, especially if you are newer to functional programming.With that out of the way, it is with a heavy heart I only give this book 4 stars.Sadly, it has nothing to do with the book itself or the message that functional programming is a way forward for programming as a discipline that pays out easily for those who are willing to put in the time and effort to learn how to work that way.The reason, I'm hesitant to give it a fifth star is ultimately that I don't believe that Scala is a good language in which to actuallyfunctional programming.There is aof incidental complexity involved in trying to program functionally in Scala., the author of Scala, is well known for not being the biggest advocate of "pure" functional programming, favoring a hybrid "object-functional" approach. This view is shared by a number of other experts in Scala, such as my friendPersonally, I believe that if the principal language I had to think in was Scala, I'd also dislike pure functional programming! Fortunately, it is not. This speaks to me of short-comings in the language, not in functional programming per se. I don't mean to say that Scala itself is a bad language, merely that it isn't terribly good atprogramming.Consequently, my review of this wonderful book is marred by the fact that I find its premise that you should do functional programmingto be somewhat weak.On the other hand, the premise that you can teach functional programming through the use of Scala has some merit, and I can see the appeal of reaching out to an underserved demographic.But be warned, once you have let Paul and Rúnar lift the scales from your eyes, what first seemed like an end -- learning about functional programming in Scala -- may simply become a way point on a much longer journey into functional programming.The journey is worth it.I'd have given the book 4.5 stars, but alas, the rating system isn't that granular!