Hi, When I look in the Haddock generated code at: http://www.haskell.org/ghc/docs/latest/html/libraries/base/ Control.Monad.html#t%3AMonadPlus, I don't seem to find any reference to the IO monad being an instance of the MonadPlus class. But when I look at the source code in libraries/mtl/Control/Monad/Error.hs it clearly is. Why is this happening? Cheers, Sean