Thinking Functionally with Haskell, Richard Bird, 2015 [0] states The first edition was titled 'Introduction to Functional Programming', and was co-authored with Phil Wadler. It was published in 1988. This is the one linked and free available. The second edition was titled Introduction to 'Functional Programming using Haskell', published in 1998. The 2015 edition is also available from safaribooksonline [1].
Its also excellent, one of the best FP books I've read, and I've read quite a few. It might be the best self-study programming book I've seen as well, all the answers are included at the end of exercises at the end of each chapter, it goes from fairly simple to a theorem prover by the end. Spectacular book. I look forward to seeing how this pdf compares.
