My life improved considerably when I started writing servlets in Scala instead of straight Java. But Scala is a complex language. The definitive book, Programming in Scala is as dense as K&R’s classic 300-page book on C, but is 850 pages long. I’ve been programming in Scala for over a year now, and there are still “basic” features I have to look up. Plus, compiling Scala in my IDE takes 10 seconds, versus 1 second for Java. That’s the difference between being able to try out every little change, and getting distracted when it’s time to test.

Two new languages offer most of the best features of Scala, but are intended to be simpler: easier to read, write, and compile. Ceylon is developed by Red Hat as an “Enterprise” Java replacement, and version 1.0 was just released. The other is Kotlin, developed by JetBrains, makers of IDEs such as IntelliJ IDEA and WebStorm. Its primary purpose is to replace Java for developing new features of their IDEs. It’s at Milestone 6, which is to say still under initial development, but is complete enough that the latest version of WebStorm includes a major new feature written in Kotlin.

If you look at a checklist, both languages have most of the same features. If you look at code samples, they look remarkably similar. Both will compile to both Java Virtual Machine (JVM) code and JavaScript. Perhaps this is good; both are intended to be pragmatic languages, and it looks like there is some consensus on what new language features are valuable.

For myself and Vocalabs, I’ve been looking for a “glue” language that compiles to both Java and JavaScript. Last time I tried Kotlin (about 6 months ago) it looked good but was too buggy to get working. So yesterday I took another look at Ceylon. And by “look” I mean “read some documentation”, not “wrote some code.” If you want that sort of review, look here.

Instead, here are the main differences I see which will drive use of one over the other.

• Ceylon is currently more mature. It’s at 1.0, with JavaScript and JVM compilers. There will be some minor changes, but it’s ready to be used. Kotlin is maturing, but JetBrains still reserves the right to make significant changes. JavaScript is still very much an experimental feature.
• Ceylon is designed for new projects, using its tool chain. The compiler outputs packages (compressed directories) instead of JVM class files. Kotlin is designed for Java interoperability within existing Java projects, and the IDE lets you sprinkle Kotlin files willy-nilly alongside your Java files.
• Ceylon requires Java 7. This isn’t a big deal for most users (Android recently began to support Java 7), but it’s a deal killer in some cases. At Vocalabs, we use Azul Zing, a low-latency, big-memory JVM that is still on Java 6.

So for my purposes, these are two deal killers against Ceylon. But I’m still not ready to jump to Kotlin until it matures a bit more. Right now I’m actively writing code in four languages: JavaScript, Typescript, Scala, and Java. Kotlin wouldn’t let me drop any of these languages, but it might replace both Typescript and Java over time. It might even replace Scala, although that’s less likely since Scala lets me drop HTML directly into my code.