I was trying to write a comment making the same point but honestly, I'm not familiar enough with effects to know what exactly you can do with them. Good to know that I wasn't far off!

I'm curious about one thing though: unless you're passing a parameter that introduces an additional effect F into the function, what's the point of making it generic over the effect set? In a language with typed effects, all effects that could be performed by a function would already be known, so letting a unit function `fn get_user<F>() ->{F} T` where i.e. `F: DiagnosticData -> ()` decide which instance of an effect that takes a DiagnosticData and yields unit, as opposed to `fn get_user<F>(g: () ->{F} ()) ->{F} User` where the effect is clearly introduced by `g`, seems a bit overkill to me.