A hyperfunction is a continuation-like construction that can be used to implement communication in the context of concurrency. Though it has been reinvented many times, it remains obscure: since its definition by Launchbury et al. , hyperfunctions have been used to implement certain algebraic effect handlers, coroutines, and breadth-first traversals; however, in each of these examples, the hyperfunction type went unrecognised. We identify the hyperfunctions hidden in all of these algorithms, and we exposit the common pattern between them, building a framework for working with and reasoning about hyperfunctions. We use this framework to solve a long-standing problem: giving a fully-abstract continuation-based semantics for a concurrent calculus, the Calculus of Communicating Systems. Finally, we use hyperfunctions to build a monadic Haskell library for efficient first-class coroutines.

@article{paperbot3931,
  title = {Hyperfunctions: Communicating Continuations},
  author = {Donnacha Oisín Kidney and Nicolas Wu},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {10},
  number = {POPL},
  year = {2026},
  doi = {10.1145/3776649}
}