Hi Luc There is a catalogue of patterns for "strategic traversal" - Ralf Lammel (umlauts on the a in Lammel) and Joost Visser - "Design Patterns for Functional Strategic Programming". Strategic traversal is a "sub-field" of generic programming. http://homepages.cwi.nl/~ralf/dp-sf.pdf This was very valuable work, at the time Strafunski had various research papers but no manual as such. Without the pattern catalogue, one had to work through the manual for Stratego - the programming language that inspired Strafunski - and transliterate to Haskell. This was very difficult - Stratego is untyped, Strafuski used cutting edge features of Haskell's type system. It is a pity that there aren't more pattern catalogues for functional programming idioms. The functionals (maps, folds unfolds) and the monads could definitely be documented as design patterns, but there is lot of further ground that merits coverage - e.g. it would be nice if something captured good uses of existential types as design patterns. A book on program *design* focused on Haskell or other functional languages is very much missing, hopefully Richard Bird's new book will go some way towards this (although I think the book aims at something rather different - developing elegant algorithms - "pearls", rather than program design per se). Best wishes Stephen