Damian Nadales:
I was thinking, besides the evaluation of performance, the simplicity of the approach is also important ("developer time is more expensive than CPU time" anyone?). Note that I said simple and not easy ;)
I guess this aspect is a rather subjective one, but maybe there are elements that can be intuitively quantified. Right now I'm playing with free monads and MTL, to have an idea which one seems simpler to me.
I care about simplicity too, but my interpretation might be slightly different. I also focus more on the things that a "normal" programmer cares about without going into esoteric use cases and technical properties. What I want wrt effects in haskell is: 1. easy to construct (MTL is built on top of transformers, so you get the same rat-tail there) 2. dynamic: most, of the time I don't care about the ordering of effect layers 3. no liftXY boilerplate code (freer [0] can do that to some extent with type inference) 4. being able to add and remove effects without it screwing too much with my internal API Basically, it must be declarative, intuitive and non-intrusive. For some reason, I lean more towards freer/EE here. But it's more like hope. We tried to make more complicated use of IO subtyping with freer and it turned out to be rather complicated [1]. Also, afair, edwardk wasn't particularly overwhelmed by the new EE approach [2]. [0] https://hackage.haskell.org/package/freer [1] https://gitlab.com/queertypes/freer/issues/7 [2] https://www.reddit.com/r/haskell/comments/387ex0/are_extensible_effects_a_co...