If you're familiar with C#, Real World Functional Programming: With Examples in F# and C# [1] is an excellent resource for learning how and when to use composition over inheritance.

[1]: http://www.amazon.com/Real-World-Functional-Programming-With...

I thought composition vs inheritance was strictly an OO, not a functional thing?

Functional programming usually leans towards composition, and OO programming towards inheritance. "Hybrid" functional languages, like F# and Scala, allow you to use both styles, mixing them in whatever way is most useful for the particular problem you're solving; "pure" functional languages, like Haskell don't offer OO-style inheritance, since composition is a better fit for combining side-effect free ("pure") functions.

tl;dr -- Composition is to functional programming as inheritance is to OO programming.

Yeesh, $40 for the ePub directly from Manning, or $33 from Amazon for the print edition with a free ePub.

There are a few chapters of the book online for free at MSDN, and if you're going to buy the book, they also have a coupon code: http://msdn.microsoft.com/en-us/library/vstudio/hh314518%28v...