[bunderbunder]

One thing that baffles me a little bit about LINQ in .NET is that it's got a dual identity.

On one hand you've got the IEnumerable<T> interface, which supports the fluent syntax and is extremely easy to riff on with extension methods. (The "fluent syntax" itself is just a bunch of extension methods.)

On the other hand you've got the mechanisms you need to support the query syntax, which behave more like duck typing. If you implement a couple methods with certain names and signatures, not all of which are formalized by an interface, then the compiler will let you use query syntax with objects of that type. It also turns out that the stuff you need to implement are roughly the bind and return operations from a monad. . . but not exactly. In particular, the element they use in place of bind is a bit more complicated, and not in a way that adds any real expressive power. It just makes the signature a bit more irritating to support.

In other news, re: lack of higher kinded polymorphism - That's something that the maintainers of F# have forcefully resisted adding to the language. The argument, which I've yet to take the time to look into deeply, is that typeclasses interact poorly with formal interfaces so you shouldn't allow a language to have both. I'm a bit skepty on that one, though, since I'd assume there would be wailing coming from the Scala community if it were really that bad.

[platz]

Im guessing F# also may want to limit constructs which cannot interop with C# . Not sure if Scala's HKTs are usable from Java

[bunderbunder]

Maybe, but I'm inclined to guess that it could probably be made workable without much more pain than what it takes to interact with F#'s curried functions from C#.

Usually the recommended approach for making F# code usable from C# is to add an object-oriented wrapper layer to the F# library. That ends up being much, much easier in practice than trying to deal with F# code on its own terms from C#.

[MiaoYu_Goh]

"... add an object-oriented wrapper layer to the F# library."

Do you have any sample code that serves as an example? It would be immensely helpful. Thanks.