effectful VS cleff

Also a much simpler alternative in my opinion to monad transformers is effectful:

https://github.com/haskell-effectful/effectful

Here's a talk on it:

https://www.youtube.com/watch?v=BUoYKBLOOrE

effectful got rid of all issues I listed (I expanded a little on it here).

There is also a long document on Issues with the Transformer/mtl library.

cats-effects -> https://github.com/haskell-effectful/effectful

I think ReaderT over IO or an algebraic effect system that uses it under the hood like effectful is the way to go. However, you mentioned redux, so perhaps you'd be comfortable with organizing things using TEA (the elm architecture)? You would have actions that different components listen to , and your async stuff could be handled using subscriptions.

API for basic usage is very similar, but things quickly go south once you want to use higher order effects (i.e. effects that make use of the m type parameter). A lot of things then become very hard to write due to complex types or outright impossible (this issue is a good example - a reasonable thing to do that is very straightforward to write with effectful, apparently impossible to do with polysemy).

> Lets say you have a huge overly-convoluted Haskell program. Somewhere deep down a call hierachy of pure functions you need to print something to the console. That is not easy to refactor.

> Or vice-versa you have a huge convoluted program where everything happens inside an IO monad because at some point something is written to the console. Now you realize you dont need to write to the console.

These problems are essentially completely resolved these days by a modern effect system like effectful. Basically, they allow you to do arbitrary effects deep down a call stack with minimal plumbing (you still have adjust the types, as you should: that's the point of effect tracking!) and also to remove effects, so you can easily convert between pure code and "effectful code that just so happens to do no effects".

https://github.com/haskell-effectful/effectful

Also note that Polysemy has some really bad performance characteristics. Don't know how much of a problem it could be at such a small scale, but if you need to use an effect system, maybe something faster like effectful would be a better choice.

See also https://github.com/haskell-effectful/effectful/issues/99.

FYI, transformers and mtl have several subtle traps. You can read about them here.

I ended up using a different approach to guiding inference in my project, but I still thought the IP way was cool

Consider 2 Haskell projects: Cleff and Effectful. They both are extensible effect systems, built around ReaderT design pattern. At their core, they use fused ReaderT + IO monad, with extensible environment. This architecture is very similar to ZIO's. All 3 even share the same limitation - inability to express nondeterminism (not very relevant fact, but I just want to emphasize the similarity).

cleff and effectful are very similar, to the point that I offered to join forces (for the record, majority of the conversation refers to things that are no longer true for both libraries as we inspired each other to fix most quirks :). The main difference is the internal environment - in effectful it's mutable, while in cleff it's immutable. All differences pretty much grow from this. The main ones:

I'm pleased to announce cleff, a new extensible effects library for Haskell: https://github.com/re-xyr/cleff.