In addition to Jon's answer
- Tuples - Tuples are possible with a library but it lacks the intrinsic syntax that most functional languages have.
- Options - Pretty much the same as tuples
- Deep Type Inference Support - C# added basic type inference support in VS 2008 but it's limited to locals inside method bodies. Most functional languages, ala F#, have deep type inference support and it really makes the language more readable IMHO
Eric on why C# doesn't have deep inference: http://blogs.msdn.com/ericlippert/archive/2009/01/26/why-no-var-on-fields.aspx
- Tail recursion: C# has basic tail recursion support but it is not ingrained into the language. See my blog post on where C# tail recursion and continuations break down
http://blogs.msdn.com/jaredpar/archive/2008/11/10/comparing-continuations-in-f-and-c.aspx
