Xtend vs Rebol

Lambdas are written like Smalltalk's blocks. If it's the last argument, it can go after the parentheses like Ruby's blocks. Parentheses on method calls are optional.

It uses Java's static type system, but you don't have to declare the type of everything all the time, since the Xtend compiler can usually figure it out. This also dramatically cuts down on Java's infamous verbosity.

Because Xtend relies heavily on JDK and Android classes, it runs just as fast as native Java code.

Xtend is a low-risk option. Because it compiles to human-readable Java, if you decide you don't like it for your project, you can just switch back to Java without losing your work.

This is where it gets its name. You can open classes and add new methods, kind of like Ruby. (Of course this has to be compiled to Java, so really it lives in a kind of helper class.)

Uses functional features ,which are very concise and idiomatic. Plus it has annotations, which cuts down on the Java boilerplate.

Methods are public if you don't specify, and fields are private. Locals declared with val in Xtend are final in Java. This dramatically cuts down on Java's infamous verbosity.

Rebol's name came from "Relative Expression Based Object Language". Rebol is a functional language and everything is an expression that returns a value. Things that have to be baked into the grammar in other languages are simple function calls with block arguments in Rebol.

Code is data, and data can be code. Rebol is based on a simple block data structure, used both for data and for the code itself. Blocks can be manipulated programmatically, and then evaluated as code. This makes metaprogramming easy in Rebol.

Almost natural language, for example: write %out.html read http://google.com.

Beginners are usually stuck making command-line applications in other languages, because GUIs are too hard. Rebol GUIs are easy enough to start with.

Rebol's simple homoiconic syntax makes it easy to create "Rebol dialects"--domain-specific languages optimized for a particular purpose. The Rebol distribution includes many of these, and users are free to create more. These DSLs make tasks that would be complicated to express in other languages easy.