A year ago, I might have opposed the proposal altogether, but diagrams has convinced me that it's quite useful.
It's almost the same for myself. I thought that I should dislike the lens library, but after being able to write code like this: grid & atCoord oldCoord . entity .~ NoEntity & atCoord newCoord . entity .~ RobotEntity rob And I think it would read even better like this: grid # atCoord oldCoord . entity .= NoEntity # atCoord newCoord . entity .= RobotEntity rob Yes, having to use '~' instead of '=' is the thing that currently bothers me the most about the lens library, because IMHO the usage in the State-Monad should be the lesser used one, should be the less encouraged one, and the "nicer" operator should be reserved for the more common case. Being able to use '.=' in the State-Monad seems mostly to be nice for writing tutorials =). Greetings, Daniel