Note: information on this page refers to Ceylon 1.2, not to the current release.

Frequently Asked Questions

On this page you'll find answers to a few of the most common questions about the Ceylon project.


What is Ceylon?

Ceylon is a new programming language that's deeply influenced by Java, designed by people who are unapologetic fans of Java. It's a language designed for writing large programs in teams.

In line with this purpose, Ceylon is a language which offers disciplined static typing, built-in modularity, and excellent tooling.

It's also an extremely elegant language, and highly readable.

Where can I run Ceylon?

You can run Ceylon anywhere a Java 7 or 8 Virtual Machine is available. The Ceylon compiler uses the bytecode generator in Open JDK to produce Java bytecode. Ceylon modules even run on Vert.x or in any OSGi container.

You can also run Ceylon programs on a JavaScript virtual machine, for example, in a web browser or on Node.js.

Note that not all Ceylon modules are available for both platforms. A module might be cross-platform, it might by JVM-only, or it might be JavaScript-only. Of course, ceylon.language is completely cross-platform.

Why a new language?

Well, we've been designing and building frameworks and libraries for Java for well over a decade, and we know its limitations intimately. The most recent releases of Java go some distance to alleviating some problems, but even the newest language features strain to accommodate past mistakes and the requirement for full backward compatibility.

How is Ceylon different?

Every language has its strengths and weaknesses. Ceylon is a great language if you want to create easily understandable and maintainable code with minimum fuss, especially if you like navigating and writing code with the help of an IDE. It's also an especially great language if you care about modularity.

There are five important concerns that guide the design of the language and platform.

But there's already so many languages out there!

Well, sure, but how many of them actually meet the bare list of technical requirements we have here: cross-platform execution, modularity, great tooling? The requirement for tooling alone rules out all dynamically typed languages. And the requirement for execution on JavaScript VMs rules out essentially all the rest. In fact, I can't really name another existing language that, as of today, even arguably has the same set of technical capabilities as Ceylon. And that's without even getting started on any of our other goals and principles.

If you're not convinced, we've written a longer post on why you might want to choose Ceylon.

How about Java interoperability?

Java interoperability is a critically important feature of the language. You can use the Java SDK and other Java libraries directly from Ceylon. This gives Ceylon programs immediate access to a huge ecosystem of reusable functionality.

On the other hand, Ceylon has its own, cleaner, modular SDK, and, since code written to depend on the Java SDK can't execute on a JavaScript virtual machine, Ceylon will sometimes benefit from frameworks designed especially for Ceylon. That's reasonable, since Ceylon is a very comfortable language for development of frameworks and libraries!

You can learn more about interoperation with Java right here.

And interoperation with JavaScript?

The Ceylon language features several constructs that exist to support interoperation with languages with dynamic typing, primarily with JavaScript:

  • dynamic blocks make it possible to write and interoperate with dynamically typed code in Ceylon,
  • a dynamic instantiation expression lets you create an untyped JavaScript object in Ceylon, and
  • dynamic interfaces allow us to ascribe static types to pre-existing dynamically-typed JavaScript APIs.

You can learn more dynamic here.

Where can I read more about some of your language design choices?

Try the language design FAQ.

The project and team

Who's behind this project?

Ceylon is a community project sponsored by Red Hat. You can read more about the team here.

How is Ceylon pronounced?

There's some debate about that but the accepted pronunciation in the team is /sɨˈlɒn/. Or in less fancy schmancy phoneticsy, selón.

(On the other hand, lots of folks seem to pronounce it say-lon with the emphasis on the first syllable so if you say it like that we'll probably know what you're talking about.)

Where can I read some user's opinions of Ceylon?


How can I contribute to Ceylon?

Are you interested in joining the team and helping improve the Ceylon language, the compiler, the class libraries, or the IDE? Then contact us on our dev mailing list.

Want to get your hands on the code? Read how to access the source.

Feeling adventurous and want to help us with the compiler backend? Read about how to work on that project.

Found a problem, how can I improve the website?

The website is fully open and you can easily contribute typos, improvements, or new pages very easily.


What version of Java is required to run Ceylon?

Both Ceylon and Ceylon IDE require Java 7 or Java 8.

Can you tell me more about how it works?

You can read up on the architecture.

Can I use a profiler with Ceylon?

Yes you can, at least on the JVM, like any other Java program. If your code runs using JBoss Modules (the default for ceylon run) then you may have to use the --define jboss.modules.system.pkgs=com.yourkit runtime flag if you use YourKit.


What license is Ceylon released under?

All the code, the language specification, and even our website is open source. It's extremely important to us that the entire platform be open and unencumbered.

What is the naming convention for Ceylon platform releases?

Ceylon production releases are named after Minds from the late great Iain M. Banks' Culture series.

Am I allowed to say "ceylonish"?

No, the correct term is "ceylonic".

What is the elephant's name?

His name is "Trompon".