Many kinds of visitor pattern are just fmap (better call it Functor). Here is the good explanation: http://www.haskell.org/pipermail/haskell-cafe/2009-June/062

Many kinds of visitor pattern are just fmap (better call it Functor). Here is the good explanation: http://www.haskell.org/pipermail/haskell-cafe/2009-June/062352.html http://www.haskell.org/pipermail/haskell-cafe/2009-June/0623... Haskell people are good at math