
Chris Okasaki's PhD thesis on purely functional data structures (pdf) - amichail
http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf
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nostrademons
Also available in extended dead-tree form: <http://www.amazon.com/Purely-
Functional-Structures-Chris-Okasaki/dp/0521663504>

I highly recommend the book if you're implementing or using a functional
programming language. There're lots of data structures that aren't mentioned
at all in traditional imperative-language textbooks. Some of them even have
decent performance.

