[seanmcdirmid]

It is easy to do in C# and I do it often (seal your concrete subclasses if you are paranoid). F# does provide better syntax for it though...I wouldn't be surprised if under the covers they are using classes. C# still doesn't provide pattern matching to make it very useful...but someday I hope that happens.

[saosebastiao]

Yes, it does use classes under the covers. I've never consistently used an OO language before, but I've been using C# lately, and knowing how F# can be built on top of a VM that was built for C# has definitely helped me to bring some of these concepts with me. I'm probably not writing idiomatic C#, but I think I'm okay with that.