eff VS ghc-proposals

You can swap-out implementations for testing, avoid the crazy N^2 instances issues, etc. They're pretty cool. Currently there are many competing libraries. polysemy and eff both have good examples on their homepages.

Effect systems and Algebraic effects. ocaml has just released a stripped-down effect system. People are also working on Effect systems for Haskell (eff, fused-effects, effet). Koka is a language built with effects first and foremost and it’s rapidly gaining popularity. Unison also has effects.

There are also a few subtle issues that arise with delconts related to semantics of higher order effects (see here and here), but they might be solvable.

Details are in https://github.com/hasura/eff/issues/12 and https://www.reddit.com/r/haskell/comments/pywuqg/unresolved_challenges_of_scoped_effects_and_what/.

You'll get fearless parallel with STM in the mixture, and GHC is getting a work in progress effect system for Haskell, as Delimited continuation primops has been merged.

My last example is algebraic effects, some of which have been made possible in a both practical and efficient way thanks to extremely recent research, and that I can use to implement architectures like Ports and Adapters or Clean Architecture and have very maintainable code. (Extensible Effects — An Alternative to Monad Transformers was published in 2013, Effect Handlers in Scope was published in 2014 and they are behind Polysemy, while there is ongoing work on effects with even better performance, like Eff)

cleff's Eff monad is esentially implemented as a ReaderT IO. [...] This is first done by eff, [...]

Here is link number 1 - Previous text "eff"

Languages such as Koka only support algebraic effects, not scoping operations such as catch and listen. The Effect Handlers in Scope paper introduces scoping operations, which lead to the Haskell libraries fused-effects and polysemy, but they turned out to have some weird semantics. eff is her effort to fix that.

There are a few languages that have algebraic effect systems, most notably Haskell, but these systems are implemented as libraries, not baked into the language (which can have advantages and disadvantages).

This is really just a matter of how much syntax sugar you want to implement. Idris has this already, and there’s a proposal to add it to Haskell too [0]. But none of this changes the core properties of the system which make it monadic.

[0] https://github.com/ghc-proposals/ghc-proposals/issues/527

> I think Haskell needs a way to graduate (or retire) language extensions

https://github.com/ghc-proposals/ghc-proposals/pull/601

Additionally, while this proposal is focused on the simple implementation and so in the current proposal or patterns do not bind any variables as per #522, if we do get settled on syntax and then later wish to expand to allow binding variables as in #43, then the syntax is again clean and discoverable.

Yeah, a relatively natural thing would be to be able to opt-in to having the HasField instances be available in all contexts. The (not yet implemented, but accepted) "Modifiers" GHC proposal might be nice for that.

The local modules proposal imo is excellent as-is.

Why would you drop TypeFamilies? It seems fairly popular, given that it was just one vote short of getting added to GHC2021. Do you consider it a less-ideal compromise, that is subsumed by your second proposal (Core with GRTT)?

as syntax is contentious a topic as ever, David (the main proposal author) and I would like to invite you to give your input on https://github.com/ghc-proposals/ghc-proposals/pull/585, where we propose to change the syntax of the accepted proposal #522 introducing Or patterns. In particular, we'd like to know

This looks great, congratulations on completing it! I assume you didn’t get an opportunity to evaluate the delimited continuations based eff library? It would’ve been nice to see Cont included as one of the effects covered, though perhaps not available in all the systems you looked at? Maybe some future work.

I do hope qualified exports are available someday: https://github.com/ghc-proposals/ghc-proposals/pull/283

Right. Being able to disable "custom type warnings" at use sites was part of an earlier proposal (https://github.com/ghc-proposals/ghc-proposals/pull/454) but it ended up being shelved.