Okay... I wasn't suggesting you don't know what Reader is... you said: >Reader is like a middle-ground between dynamic-scoping and explicit passing of a contex

Okay... I wasn't suggesting you don't know what Reader is... you said: >Reader is like a middle-ground between dynamic-scoping and explicit passing of a context argument around I just wanted to point out that the-thing-which-Reader-is, is sometimes called "implicit parameters", and there are papers written about it.