Scala for Scripting
Michael Dürig

Its conciseness, versatility and DSL capabilities makes Scala desirable for scripting. In this report we show how we implemented a JSR223 compliant script engine for Scala which runs inside OSGi environments.
While the Scala compiler needs a class path to load class files, OSGi only provides class loaders. To overcome this we implemented a file system abstraction on top of OSGi bundles effectively providing a class path. Furthermore, JSR223's dynamic approach for passing arguments does not play well with Scala's static types. We need to make all types of arguments visible to scripts. Our implementation generates a preamble of adequate implicit conversions which allows scripts to use statically typed variables in a manner resembling dynamic types. Finally performance constraints require caching of pre-compiled scripts.
Apache Sling, an OSGi based web application framework with a scriptable application layer, uses our implementation for type safe templating via Scala's XML support.