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Clojure is a dynamic, functional language that runs on the JVM. Although its roots are in Lisp, one of the oldest computer languages, it also embodies many modern programming concepts, including lazy evaluation and advanced concurrency abstractions. Clojure has spawned a vibrant community of programmers who are contributing a rich set of frameworks and tools. One example of these is Midje, an innovative spin on unit testing and mocking frameworks.

The functional languages F#, Clojure and Scala still reside in the assess ring of the radar. Interest in functional languages continues to grow. Two characteristics of functional languages in particular are driving this interest, immutability with its implications for parallelism and functions as first class objects. While the introduction of closures to C# brings some of the latter capability, functional languages are almost synonymous with immutability. The placement of these languages within the assess ring indicates our view of their relative maturity and appropriateness. F#, based on OCaml, is fully supported within the Visual Studio toolset. F# includes support for objects and imperative constructs in addition to functional language constructs in a natural way. Scala, like F#, combines the object and functional paradigms, although the syntax of Scala is more Java-like. Clojure began as a JVM language and is now available on the .NET CLR. Clojure does allow for mutable state although it has an extensive set of immutable persistent data structures, all supporting multi-threaded applications. There are many similarities between these three languages, but at the moment we believe F# and Clojure to be better suited to most organizations for assessing than Scala. More work clearly needs to be done to validate this assertion.

In the previous radar, we lumped functional languages together in a group. For this version, we¡¯ve exploded that group and started calling out the ones interesting to us. Of the current crop of functional languages, the one we like the most is Clojure: a simple, elegant implementation of Lisp on the JVM. The other two that we fi nd interesting are Scala (a re-thinking of Java in functional form) and F#, the OCaml derivative from Microsoft that now appears ¡°in the box¡± in Visual Studio 2010.