I was trying to follow the reasoning in Don's article on using haskell for shell scripting http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10 In the source listing at the end we is newtype Shell a = Shell { runShell :: ErrorT String IO a } deriving (Functor, Monad, MonadIO) and I don't understand it what "deriving" is doing here, nor have I been able to find documentation on it. http://en.wikibooks.org/wiki/Haskell/Class_declarations claims: "You can only use deriving with a limited set of built-in classes. They are: Eq Ord Enum Bounded Show Read " But, here we are deriving classes not in that list. So, is this a recently added feature? Or something that came in from {-# OPTIONS -fglasgow-exts #-} ? I would just like to understand this, and I can't figure out how to begin. Thanks for any help! thomas.