Hacker News Reader

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

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.

The Clojure source code for its data structures.

I think its SML in the book