Programmers combine different programming languages because it allows them to use the most suitable language for a given problem, to gradually migrate existing projects from one language to another, or to reuse existing source code. However, existing cross-language mechanisms suffer from complex interfaces, insufficient flexibility, or poor performance.

We propose a multi-language runtime that allows composing different language implementations in a seamless way. It reduces the amount of required boiler-plate code to a minimum by allowing programmers to access foreign functions or objects by using the notation of the host language. We compose language implementations that translate source code to an intermediate representation (IR), which is executed on top of a shared runtime system. Language implementations access foreign objects via language-independent messages that the runtime resolves at their first execution by transforming them to efficient foreign-language-specific operations. Our mechanism avoids conversion or marshaling of foreign objects at the language boundary and allows the dynamic compiler to perform its optimizations across language boundaries, which guarantees high performance.

This paper presents an implementation of our ideas based on the Truffle system and its guest language implementations JavaScript, Ruby, and C.