Enjoyed this wiki post by the author of Garnet on effect systems: [[PonderingEffects]]. What I liked is that it doesn't just describe the design space: it's honest about what the author finds confusing or unconvincing, including a skeptical take on algebraic effect handlers specifically. The Lobsters thread is worth reading too; someone points out that what the post calls “effects on data” is already studied under the name coeffects, which was news to me.