I have read "The Craft of Functional Programming" by Simon Thompson and a few paper on the web. "The Craft" is a good book, but it is an introduction to FP. It seems to me it there are a lot of books on OO design I can pick up at the bookstore, but in the FP world, one must worm their way through all sorts of papers. I have seen papers on Catamorphisms, Monads, Programming with Barbed Wire, folds, etc. I think these papers are hard to understand if you don't have the acadademic/mathematical background -- being papers and not textbooks these papers assume a fair bit of base knowledge. I know I can design a fold function to use in place of primitive recursion for most data structures -- I just don't know if I should. It is pretty easy to get through "The Craft of Functional Programming" without understanding what Category Theory , a Catamorphism , or a Kleisli Composition is. I can see lots of real Software Engineering oppurtunities for these various techniques if I could just put them together. Is there a good textbook on Functional Programming which starts from a base point similar to "The craft of Functional Programming" but more advanced in terms of introducing necessary topics like Category theory, catamorphisms, monads, etc? I would find such a book very useful, especially if it concentrated on lazy functional programming. Doug Ransom Systems Engineer Power Measurement Ltd. http://www.pml.com 250-652-7100 office 250-652-0411 fax mailto:doug_ransom@pml.com