| ▲ | Freer Monads, More Extensible Effects (2015) [pdf](okmij.org) |
| 74 points by todsacerdoti 10 hours ago | 14 comments |
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| ▲ | nbaksalyar 7 hours ago | parent | next [-] |
| I strongly recommend to check all other papers and articles on https://okmij.org/ftp/, every single one of them is brilliant and insightful. I love the pedagogy, the writing style and clarity. Oleg Kiselyov is one of the best technical writers I've discovered recently. |
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| ▲ | endgame 44 minutes ago | parent | prev | next [-] |
| This paper is up to Oleg's usual high standard, and is a very important step to read if you're catching up on the history of effect systems in Haskell. As a user, I think effect libraries in Haskell trade off between five main constraints: * Typelevel wizardry * Boilerplate * Performance * Ability to handle "higher-order" effects (e.g., `bracket`) * Safety (e.g., not accidentally leaking effects beyond their scope) The most compelling libraries I've seen from the industrial perspective are the "IO-wrapper" libraries like `cleff`, `effectful`, and `bluefin`. These libraries tend to give good performance, can handle higher-order effects, but trade off a little safety to get the typelevel stuff down a bit. Of these, I currently favour `effectful` but am keeping an eye on `bluefin` (which is very close to `effectful` but with explicit handle-passing). The explicit handle-passing in `bluefin` seems to get the typelevel down a bit more in exchange for asking the user to write a little more boilerplate to explicitly pass handles around. |
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| ▲ | kccqzy 5 hours ago | parent | prev | next [-] |
| If you are looking for real-world code for an effect system, not just a PDF paper, you should probably look at the eff library: https://github.com/hasura/eff The acknowledgement section on that GitHub README mentions this paper. |
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| ▲ | tome 3 hours ago | parent | next [-] | | eff has never been released to Hackage and as far as I know never used in production. I wouldn't call it "real-world code". For effect systems that people do actually use in production I suggest * Polysemy: https://hackage.haskell.org/package/polysemy * effectful: https://hackage.haskell.org/package/effectful * Bluefin: https://hackage-content.haskell.org/package/bluefin/docs/Blu... [Disclosure: Bluefin in my effect system] | |
| ▲ | solomonb 3 hours ago | parent | prev | next [-] | | `eff` is a research project that is no longer in active development and never made it to production in any sense. It would be AMAZING if `eff` were completed but I dont think that will happen at this point. `eff` is based on delimited continuations (which Alexis had to build into GHC), it is not using `Freer`. If you want to look at an effect system in Haskell that actually has been used in production AND is based on this paper then look at `freer-simple`: https://hackage.haskell.org/package/freer-simple No it is not high performance, but neither are any other Haskell effect systems and performance is relative to your problem domain. It also has the benefit of being implemented very similarly to Oleg's paper making it a lot easier to learn from then most other options. | | |
| ▲ | tome 2 hours ago | parent [-] | | > No it is not high performance, but neither are any other Haskell effect systems This is not true. IO-wrapper effect systems (in practice, effectful or Bluefin) have as good performance as Haskell's IO monad, that is to say as good as you can get in Haskell. | | |
| ▲ | solomonb 2 hours ago | parent [-] | | Yes but from what I understand at a loss of safety. You can decide if that is worth it but you aren't getting a free lunch. that said, your library is really cool. : ) |
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| ▲ | Twey 2 hours ago | parent | prev | next [-] | | As far as I know the shiniest implementations in the effect typing world at the moment are Koka and Effekt, which are both languages in their own right. They each have their own ideas about implementation to make effects (mostly) zero-cost. https://koka-lang.github.io/
https://effekt-lang.org/ Frank is pretty old now but perhaps a simpler implementation: https://github.com/frank-lang/frank | |
| ▲ | epolanski 5 hours ago | parent | prev [-] | | Also effect-ts in TypeScript world, which is by far the most popular effect system around (quite sure it has overtaken Scala's ZIO from which it is inspired). The ecosystem is massive. Cons: TypeScript is a great type system but requires some investment to get the best out of it, it's also very verbose. Pros: you have access to the entirety of the TypeScript ecosystem. https://effect.website/ | | |
| ▲ | pxeger1 3 hours ago | parent [-] | | > by far the most popular effect system around Crazy claim to make without providing any evidence | | |
| ▲ | epolanski 2 hours ago | parent [-] | | What other effect library or language has 6 millions + downloads per month (that's more than angular) and meetups popping all around the world? |
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| ▲ | wavemode 3 hours ago | parent | prev | next [-] |
| I've always loved this paper. Great reading if you're interested in implementing an effect system from scratch. Though rather overkill if you're just interested in using one. |
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| ▲ | sctb 8 hours ago | parent | prev | next [-] |
| (2015) More information here: https://okmij.org/ftp/Haskell/extensible. |
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| ▲ | EdNutting 2 hours ago | parent | prev [-] |
| See also: https://scholar.google.com/citations?hl=en&user=0E8zPucAAAAJ... Particularly (2014): https://scholar.google.com/citations?view_op=view_citation&h... |
