This is an idea proposed in 2024 as a Cambridge Computer Science Part II project, and is currently being worked on by Sky Batchelor. It is supervised by Patrick Ferris and Anil Madhavapeddy as part of the OCaml Labs project.

Summary

Most existing uses of effect handlers perform synchronous execution of handled effects. Xie et al proposed a traverse handler for parallelisation of independent effectful computations whose effect handlers are outside the parallel part of the program. The paper ^[1] gives a sample implementation as a Haskell library with an associated λp calculus that formalises the parallel handlers. This project aims to:

• implement the traverse handler in OCaml 5, using single-shot handlers ^[2]
• identify a selection of parallel-friendly data structures that might benefit from such parallel traversals
• investigate handlers for alternative traversal strategies beyond the folds support by traverse
• evaluate the performance of such parallel handlers, for instance using Eio's Domain_pool ^[3] on a many core machine (ranging from 8--128 cores)

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