Capturing the future by replaying the past (functional pearl)
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icfp18main-p36-p.pdf
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447.15 KB
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Author(s)
Scherer, Gabriel
Koppel, James Brandon
Solar Lezama, Armando
Date Issued
July 2018
Journal
Proceedings of the ACM on Programming Languages
Publisher
Association for Computing Machinery (ACM)
Citation
Koppel, James et al. “Capturing the Future by Replaying the Past (functional Pearl).” Proceedings of the ACM on Programming Languages 2, ICFP (July 2018): 1–29 © 2018 The Authors
Version
Final published version
Abstract
Delimited continuations are the mother of all monads! So goes the slogan inspired by Filinski’s 1994 paper, which showed that delimited continuations can implement any monadic effect, letting the programmer use an effect as easily as if it was built into the language. It’s a shame that not many languages have delimited continuations.
Luckily, exceptions and state are also the mother of all monads! In this Pearl, we show how to implement delimited continuations in terms of exceptions and state, a construction we call thermometer continuations. While traditional implementations of delimited continuations require some way of ”capturing” an intermediate state of the computation, the insight of thermometer continuations is to reach this intermediate state by replaying the entire computation from the start, guiding it using a recording so that the same thing happens until the captured point.
Along the way, we explain delimited continuations and monadic reflection, show how the Filinski construction lets thermometer continuations express any monadic effect, share an elegant special-case for nondeterminism, and discuss why our construction is not prevented by theoretical results that exceptions and state cannot macro-express continuations.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Terms of Use
Creative Commons Attribution 4.0 International License
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DOI of Published Version
https://doi.org/10.1145/3236771
