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Jack Firth 2015-07-08 00:07:44 -07:00
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@ -4,4 +4,8 @@ lens [![Build Status](https://travis-ci.org/jackfirth/lens.svg?branch=master)](h
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.