Modularity and Conventions for Maintainable Concurrent Language Implementations A Review of Our Experiences and Practices

In this paper, we review what we have learned from imple-menting languages for parallel and concurrent programming, and investigate the role of modularity. To identify the ap-proaches used to facilitate correctness and maintainability, we ask the following questions: What guides modulariza-tion? Are informal approaches used to facilitate correctness? Are concurrency concerns modularized? And, where is lan-guage support lacking most? Our subjects are AmbientTalk, SLIP, and the RoarVM. All three evolved over the years, enabling us to look back at specific experiments to understand the impact of concur-rency on modularity. We conclude from our review that concurrency concerns are one of the strongest drivers for the definition of mod-ule boundaries. It helps when languages offer sophisticated modularization constructs. However, with respect to con-currency, other language features like single-assignment are of greater importance. Furthermore, tooling that enables re-modularization taking concurrency invariants into account would be of great value