[benrjackson]

Consuming C# code from F# works fine.

Consuming F# code from C# works pretty well for the most part, although F# specific types are cumbersome to use (records, discriminated unions, computational expressions aka monads). This just means that if you want an F# DLL to be usable from C#, you need to think a little bit about the exposed API (perhaps by adding a C# specific wrapper).

Having said that, IMO the interop between the two is better than the interop between JVM languages like java, scala & clojure (Kotlin is probably different).

[tigershark]

Yes, I agree, but you need to be really careful about tail call recursion optimisation when calling f# code from c#. In F# it is always guaranteed, in c# only on 64 bit 4 and above runtime if I remember correctly, so you can't really rely on it for production code.

[MichaelGG]

Unless it's changed, F# doesn't emit "tail." prefixes for tailcall. Nor is it guaranteed. The F# compiler will, in some cases, manually turn your tailcall-OK code into a loop. But it doesn't do it in all cases (nor could it).

The F# compiler used to emit "tail." prefixes in every case that was eligible. But not only does the CLR have lots of restrictions, it was slower to request tailcalls.

Maybe that changed in the last version or two.

Edit: OK I found the email where I had asked fsbugs why tailcalls were no longer generated. But that was in 2009 so I'm more out of date than I remember.

In the release notes[1] for the May 2009 release, there's this section:

Optimizations for Tailcalls

On some implementations of the CLI, normal calls can be more efficient than tailcalls. An optimization is now applied to determine if a function is “closed” in the sense that it never takes any tailcalls outside a finite non-recursive callgraph. If so, the use of tailcalls is suppressed.

1: http://blogs.msdn.com/dsyme/archive/2009/05/20/detailed-rele...

[RaleyField]

Wouldn't C# interface only with compiled il code and not directly with F# so any tail call optimizations in F# wouldn't depend on what you later do in C# compiler?

[tigershark]

Yeah, right, the f# compiled code will be already optimised for the tail call recursion so it can be called safely from the c# code. What I remembered applies only to the c# generated IL.

[Too]

Have they fixed the intellisense yet? Last time I tried to call c# from f# it compiled but autocompletion in vs didn't work.

[bunderbunder]

Yeah, the intellisense is a lot better than it was in earlier versions.

That said, it doesn't attempt to read your mind, so the intellisense only kicks in when the type you're interacting with is unambiguous. So, for example, you'll need to explicitly state a function parameter's type before intellisense will help you figure out what methods you can call on it.

[JBReefer]

In general you should follow Demeter's law and not expose types behind value types if you can avoid it.

[Koshkin]

Regarding this 'law', Wikipedia put it quite nicely, saying quote, it is more suited as a metric for code smell as opposed to a methodology for building loosely coupled systems.