Programming in Haskell

It would be Graham Hutton's Programming in Haskell. That one little chapter on parser combinators was totally worth it. If I can include this functional pearl "A play on regular expression", Not a book though. These two showed how composition and simple abstraction could make the solution super beautiful.

Programming in Haskell by Graham Hutton A.I. A Modern Approach (ch 13-16) by Russell and Norvig A Tunnel In The Sky by Robert Heinlein The Revelation Space series (3 of the 5 books) by Alistair Reynolds Eon/Eternity (both by Greg Bear)