Ceylon 1.2.1 is now available

Three months after the last major release, Ceylon 1.2.1 is a new maintenance release, with almost 100 issues closed, including new features, improvements and bug fixes such as:

  • you can now iterate java.lang.Iterable values in for statements and use java.lang.AutoCloseable values in try statements,
  • support for Java 9 and Jigsaw modules,
  • experimental support for type functions on the JVM,
  • reduced run-time dependencies for your Ceylon program,
  • better interoperation with JavaScript arrays,
  • better compatibility with previous and future Ceylon releases.

Note that for the JVM backend, this release is backwards-compatible with the previous major release (1.2.0), which means you can use modules compiled with 1.2.0 on a 1.2.1 distribution out of the box. This is not as easy the other way around, if you want to run modules compiled for 1.2.1 on a 1.2.0 distribution, which is why we recommend you upgrade to 1.2.1.

Sadly, on the JavaScript backend, we had to break binary compatibility to fix serious interoperation issues, and so modules compiled for 1.2.1 and 1.2.0 are not compatible. We recommend you upgrade your distribution to 1.2.1 and recompile your modules.

About Ceylon

Ceylon is a modern, modular, statically typed programming language for the Java and JavaScript virtual machines. The language features a flexible and very readable syntax, a unique and uncommonly elegant static type system, a powerful module architecture, and excellent tooling, including an awesome Eclipse-based IDE.

Ceylon enables the development of cross-platform modules that execute portably in both virtual machine environments. Alternatively, a Ceylon module may target one or the other platform, in which case it may interoperate with native code written for that platform.

In the box

This release includes:

  • a complete language specification that defines the syntax and semantics of Ceylon in language accessible to the professional developer,
  • a command line toolset including compilers for Java and JavaScript, a documentation compiler, a test runner, a WAR archive packager, and support for executing modular programs on the JVM and Node.js,
  • a powerful module architecture for code organization, dependency management, and module isolation at runtime,
  • the language module, our minimal, cross-platform foundation of the Ceylon SDK, and
  • a full-featured Eclipse-based integrated development environment.


Ceylon is a highly understandable object-oriented language with static typing. The language features:

  • an emphasis upon readability and a strong bias toward omission or elimination of potentially-harmful or potentially-ambiguous constructs and toward highly disciplined use of static types,
  • an extremely powerful and uncommonly elegant type system combining subtype and parametric polymorphism with:
    • first-class union and intersection types,
    • both declaration-site and use-site variance, and
    • the use of principal types for local type inference and flow-sensitive typing,
  • a unique treatment of function and tuple types, enabling powerful abstractions, along with the most elegant approach to null of any modern language,
  • first-class constructs for defining modules and dependencies between modules,
  • a very flexible syntax including comprehensions and support for expressing tree-like structures,
  • fully-reified generic types, on both the JVM and JavaScript virtual machines, and a unique typesafe metamodel.

More information about these language features may be found in the feature list and quick introduction.


Ceylon IDE now features the following improvements, along with many bugfixes and a number of performance enhancements:

  • improved documentation hover,
  • better UI responsiveness,
  • support running on Java 9.

A number of important subsystems have been abstracted and rewritten in Ceylon, to support the ongoing development of the new IntelliJ-based IDE for Ceylon.


The platform modules, recompiled for 1.2.1, are available in the shared community repository, Ceylon Herd.

This release introduces several new platform modules:

  • ceylon.numeric is a cross-platform module containing math operations for Integer and Float. In time it will replace parts of the JVM-only ceylon.math module.
  • ceylon.decimal is a JVM-only module (but soon to be cross-platform) containing arbitrary-length decimal support. In time it will replace parts of the JVM-only ceylon.math module.
  • ceylon.whole is a cross-platform module containing arbitrary-length integer support. In time it will replace parts of the JVM-only ceylon.math module.
  • ceylon.random is a cross-platform module containing random number generators. In time it will replace parts of the JVM-only ceylon.math module.
  • ceylon.interop.browser contains JavaScript-only interoperation functions and types for the DOM, HTML and XMLHttpRequest.

Along with several API enhancements and bugfixes, including:

  • Many new features for ceylon.test, the Ceylon Test Suite.
  • Performance improvement of the ceylon.json parser.


You can try Ceylon using the Web IDE, featuring syntax highlighting, interactive error reporting, autocompletion, online documentation, and persistence and code sharing via Gist.

The Web IDE serves a dual purpose as a standard example demonstrating the use of Ceylon for web application development and deployment to the OpenShift cloud platform.


The Ceylon community site, http://ceylon-lang.org, includes documentation, and information about getting involved.

Source code

The source code for Ceylon, its specification, and its website, is freely available from GitHub.

Information about Ceylon's open source licenses is available here.


Bugs and suggestions may be reported in GitHub's issue tracker.

Migrating from Ceylon 1.2.0

Migration from Ceylon 1.2.0 is easy. To recompile a module for 1.2.1:

  • First ensure that its dependencies have also been recompiled.
  • If it imports a Ceylon SDK platform module, upgrade the version number specified by the module import statement from "1.2.0" to "1.2.1" .
  • If it was compiled against Ceylon 1.2.0 you should still be able to use it in 1.2.1 for the JVM backend, as it is backwards-compatible. Sadly, this is not the case for the JavaScript backend, and so you will need to recompile your modules with 1.2.1.


As always, we're deeply grateful to the community volunteers who contributed a substantial part of the current Ceylon codebase, working in their own spare time. The following people have contributed to Ceylon:

Gavin King, Stéphane Épardaud, Tako Schotanus, Tom Bentley, David Festal, Enrique Zamudio, Bastien Jansen, Emmanuel Bernard, Aleš Justin, Tomáš Hradec, James Cobb, Ross Tate, Max Rydahl Andersen, Mladen Turk, Lucas Werkmeister, Roland Tepp, Diego Coronel, Matej Lazar, John Vasileff, Toby Crawley, Julien Viet, Loic Rouchon, Stephane Gallès, Ivo Kasiuk, Corbin Uselton, Paco Soberón, Michael Musgrove, Daniel Rochetti, Henning Burdack, Luke deGruchy, Rohit Mohan, Griffin DeJohn, Casey Dahlin, Alexander Altman, Alexander Zolotko, Alex Szczuczko, Andrés G. Aragoneses, Anh Nhan Nguyen, Brice Dutheil, Carlos Augusto Mar, Charles Gould, Chris Gregory, klinger, Martin Voelkle, Mr. Arkansas, Paŭlo Ebermann, Vorlent, Akber Choudhry, Renato Athaydes, Flavio Oliveri, Michael Brackx, Brent Douglas, Lukas Eder, Markus Rydh, Julien Ponge, Pete Muir, Nicolas Leroux, Brett Cannon, Geoffrey De Smet, Guillaume Lours, Gunnar Morling, Jeff Parsons, Jesse Sightler, Oleg Kulikov, Raimund Klein, Sergej Koščejev, Chris Marshall, Simon Thum, Maia Kozheva, Shelby, Aslak Knutsen, Fabien Meurisse, Sjur Bakka, Xavier Coulon, Ari Kast, Dan Allen, Deniz Türkoglu, F. Meurisse, Jean-Charles Roger, Johannes Lehmann, allentc, Nikolay Tsankov, Chris Horne, Gabriel Mirea, Georg Ragaller, Harald Wellmann, klinger, Oliver Gondža, Stephen Crawley, Byron Clark, Francisco Reverbel, Jonas Berlin, Luke Hutchison, Nikita Ostroumov, Santiago Rodriguez, Sean Flanigan.