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Comment by zastrowm | Hacker News Reader

One of the primary problems with this is generics (java/JVM uses type erasure, CLR/C# keeps type information) and value types (CLR/C# has them, JVM does not); That's why you can implement the JVM on the CLR (see IKVM.NET[1]), but not the other way around.

[1]: http://en.wikipedia.org/wiki/IKVM.NET

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I'm not a vm or compiler expert by any means but Gosu and Ceylon have implemented reified generics on the JVM somehow. It seems possible, but I don't know what the performance impact would be.

Well it's obviously doable — both the JVM and CLR are equivalent to Turing machines, so it follows that they can run the same set of programs. It just, uh, might be non-trivial. :)

Fwiw, when Gavin King (Ceylon) did a AMA on Reddit a while back I asked about how they implemented reified generics on the JVM:

https://www.reddit.com/r/programming/comments/2iszra/ceylon_...

Ceylon is a great language in my opinion. I would rather programm in Ceylon than in C#.

That's good to hear! I haven't played with it yet beyond flipping through the docs.

Have you built any production ready apps or libraries in it? How was the transition from writing Java? Did anything cause you pain or surprise?

The Eclipse IDE plugin works but is pretty slow. I wouldn't use it if I wasn't so used to autocompletion + documentation in my IDE.

The module system can use the central maven repository but it doesn't accept dashes in the name like jackson-core unless you put it in quotes. (Took me a while to figure out).

Ceylon doesn't have enums but you can emulate them like this: http://ceylon-lang.org/documentation/1.1/tour/types#enumerat...

Otherwise it's fairly straightforward to translate java into ceylon.

I love immutability by default. Only 10% of my variables/fields are actually mutable. I could reduce that percentage further if the jvm had TCO.

Java is getting value types and replied generics.

Potentially. Value types seem like a lock for 10, but reified generics have only been suggested as a research topic in Project Valhalla.

Somehow F# uses type erasure. I'm not sure how it works, but I know that it does.

Taken at face value I think this is misleading - a typical F# generic type will be represented as a normal .NET generic type at the IL level. However, it is true that some types are erased, like unit-of-measure type arguments or types surfaced by type providers.

Type erasure on the CLR is exactly as it is on the JVM. Generics are needed for interop with generic libraries (which aren't used that much beyond collections anyways in core libraries).

Erasure is necessary when the type system is differently expressive from C#, which I beleive F# is.

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