Well then, the expression problem. The guys who created scala and OCaml have opinions about this, no surprise (why not OOP and typeclasses?

http://stackoverflow.com/questions/2807629/handling-incremen...

(message 20) http://groups.google.com/group/scala-debate/browse_frm/threa...

http://lambda-the-ultimate.org/node/4400

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and "ADT" i think real world haskell is correct in reservign this for abstract data types

http://book.realworldhaskell.org/read/defining-types-streaml...