

Okasaki: Purely Functional Data Structures (1996) [pdf] - tosh
https://www.cs.cmu.edu/~rwh/theses/okasaki.pdf

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Verdex
The book by the same title and author (which is heavily based off of this
paper) was actually one of the first books on functional programming I read. I
don't think I would suggest it as an introductory text to anyone, but even so
I really enjoyed reading it even though I didn't know what functional
programming was at the time.

The book is about persistent data structures and what techniques can be used
to measure their time complexity. I don't think there's much utility here for
the software engineer (although I suppose there's probably some edge cases
where it would come up), but as someone who's interested in programming
language development I plan to keep this book around for a long time.

