977 B
977 B
lens 
A Racket package for creating and composing pure functional lenses.
A lens is a value that can be used to focus on a small subpiece of some larger structure. Given a lens and a value of that larger structure, two values can be dervied: a view value, which is the subpiece, and a context function, which accepts a new view value and returns a new structure with the old view replaced by the new view. Think of them as composable, pure functional getters and setters. Examples can be found in the documentation.