Delimited Continuations, Demystified
summary
GHC gains native first-class delimited continuations in GHC 9.6, implemented as a small runtime patch completed after a three‑year proposal cycle and finished while working at Tweag. The implementation represents continuations as sequences of stack-frame memcopy to the heap and back, captures delimited regions with prompt tags, and supports control/prompt (and thus algebraic‑effects style APIs). It works and is fast in practice, with caveats: continuations live in IO, lazy code limits use, possible space‑leak patterns, and OCaml-style one‑shot optimizations trade flexibility for performance.
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chapters (10)
- 0:00Introduction
- 0:42History of delimited continuations
- 3:53First-class continuations
- 15:33Formalizing continuations
- 24:05Native delimited continuations
- 36:21Typing challenges
- 49:11Delimited continuations in Haskell
- 54:25Efficient GHC implementation
- 1:09:24Why GHC didn’t have delimited continuations earlier
- 1:14:39Summary
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