Hi (I did not received your message in my mail box and I have seen it on mailing list. I dot know why this happened (?).) /* Maybe I am misguessing why you are asking your question, but wouldn't it be better to ask how to map these Haskell concepts to CLR? If so, check out work on Mondrian. */ My intention is to employ Haskell techniques in C# where it fits. If I were going to implement Haskell on CLR the way you mentioned was proper. For something like: type Thing a b = ThisWay a | ThatWay b | NoWay actually there is no equivalents for data constructor in C# 3 (I think). I asked it if there are other ideas about this: Controlling the execution path by deciding based of structure of data with a trick other than reflecting! Thank you