[Haskell-cafe] Newbie question: Why gfoldl has this strange type?

Hi! I am a novice in Haskell, and particularly I have interested in generic programming. This interest motivated me to read paper Scrap your boilerplate: A practical design pattern for generic programming, but I didn't understand the type of the function gfoldl, that was present in class Term (Data). Somebody could help me to understand the type of this function? Thanks... Rodrigo