Right, it's not about what "really" happens, but more about what is ideally happening (I mean you can put IO effects in pure values through `unsafe` too). My m

Right, it's not about what "really" happens, but more about what is ideally happening (I mean you can put IO effects in pure values through `unsafe` too). My main gripe with monad transformers is that it doesn't really let you capture a "sum" of effects. Combining happens through a monad stack. The effect systems let you describe "this and that" instead of "this in that", or "this, then that". For a lot of IO, "this and that" is much more useful.