I highly recommend Purely Functional Data Structures by Chris Okasaki. It really opened my mind when I was starting out in functional programming. Highly relevant to many modern problems.

Yeah that book is one of the most important book in functional world

Anyone know of an online reference with this sort of material? Not huge on book collecting these days, and freer is better.

Oksaki's thesis, the basis for the book, is available online for free:

http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf

The book itself is available on Kindle.

Awesome.

Top result in Bing/Google is a pdf. Not sure if it's a pre-print edition, looks like a PhD thesis.

IIRC, it was originally Okasaki's PhD thesis, then he converted it into a book.

edit: source: http://www.usma.edu/eecs/SitePages/Chris%20Okasaki.aspx#cup9...

The Clojure source code for its data structures.

I think its SML in the book

I am still patiently waiting for a more up-to-date of Okasaki's classic with examples written in Haskell.

The original had all examples written in Haskell, albeit in an appendix.

While reading this, did anyone else realize that this is basically formatted like a white paper, but made to be far more approachable? It reminds me a bit of this[0] presentation from Bret Victor.

[0]: http://worrydream.com/#!/MediaForThinkingTheUnthinkable

That was an awesomely formatted webpage! Which toolkit did the author use, and what were diagrams drawn with?