If you look at the Roslyn source, I'm not sure this would have worked too well. It looks like a lot of the C# is somewhat unidiomatic as it is (presumably to m

If you look at the Roslyn source, I'm not sure this would have worked too well. It looks like a lot of the C# is somewhat unidiomatic as it is (presumably to meet extremely aggressive performance targets), so it's not clear that F# would have provided much benefit. If you're building a compiler that doesn't need to scale to million line codebases, then F#'s a clear winner, but here I'm not so sure.