Ralf Lammel has some interesting work on "generic traversals" that might be profitably viewed as monad transformers. Probably worth reading if anyone is interested in looking into this. Matthias Felleisen wrote: > > On Sep 20, 2005, at 4:29 PM, Mitchell Wand wrote: > >> ... and the interesting part is in how they interact. > > > Yes, I agree. -- Matthias >