[Haskell-cafe] What makes Haskell difficult as .NET?

In this presentation http://norfolk.cs.washington.edu/htbin-post/unrestricted/colloq/details.cgi?... the speaker talks about F# on .Net platform. Early on in the talk he says that they did F# because haskell would be "hard to make as a .Net language". Does anyone know what features of Haskell make it difficult as .Net language? Daryoush