Meta-level Language Bridging

Scripting and composition languages offer high-level mechanisms to combine and compose services provided by a lower-level host programming language. Inter-language bridging mechanisms are therefore needed to map host language entities and services to abstractions of the scripting language, and vice versa. Many popular languages such as Python, Perl, and Ruby use a bridging approach based on wrappers that must be written or generated in the host language. Other languages like Jython and Kawa adopt a fixed bridging strategy that exploits reflective features provided by the host language. Although both of these approaches are usable, they are cumbersome and low-level. In particular, it can be very difficult to adapt host language services to cooperate seamlessly with abstractions of the scripting language. In this paper we present a lightweight bridging strategy for scripting and composition languages that simplifies the task of adapting host language services to the abstraction level of the scripting language. This strategy uses introspection facilities of the host language to automate the wrapping process, while providing a hook for programmer-defined adaptation of the generated interface. A meta-level bridging layer is responsible for wrapping and unwrapping both host and scripting language entities so they can seamlessly cooperate. The bridging strategy employs partial evaluation of wrapping and unwrapping operations to achieve acceptable performance.