lens

Documentation

A Racket package for creating and composing pure functional lenses.

raco pkg install lens (require lens)

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.

Contributions

This project uses Github issues organized by a Waffle board to track what's being worked on. Check the board to see if there's any features, bugs, etc. that interest you, or create a new Github issue to inquire about something you'd like to see changed.