There are many introductory Haskell books, but i was (at the time i started learning) keen of those providing also a good basis on functional programming (which was a totally new world for me at the time). ...
K. Stengel, F. Schmaus, und R. Kapitza. Proceedings of the 12th International Workshop on Adaptive and Reflective Middleware, New York, NY, USA, Association for Computing Machinery, (2013)