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Add practical applications section to readme

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Jack Firth 2015-09-27 00:46:37 -05:00
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@ -54,6 +54,22 @@ Lenses can also be extended to operate on some new data structure:
See [the documentation](http://pkg-build.racket-lang.org/doc/lens/index.html) for a full API reference See [the documentation](http://pkg-build.racket-lang.org/doc/lens/index.html) for a full API reference
#### So when would I want to use lenses?
Lenses are most effective when you're dealing with the "giant ball of state" problem. When you
have a large amount of state you need to pass around between code written in a functional
style, it's difficult to update and manage it due to the lack of mutation "magically" updating
your entire object graph when a function changes a small part of it. Lenses allow code to
break down and manipulate portions of this state, simplifying interactions and updates.
In particular, consider using lenses if you find yourself doing any of the following:
- Using a giant complex piece of state that most pieces of code only care about a small part of
- Writing `struct-copy` a lot
- Converting some hairy data structure into another one, manipulating it, then turning it back
- Wishing you could treat data X as if it were a Y, i.e. "I wish this struct was a list so I could `map` over it easily"
- Creating structs that have nested struct instances inside them.
#### Contributions #### Contributions
This project uses Github issues organized by a [Waffle board](https://waffle.io/jackfirth/lens) 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. This project uses Github issues organized by a [Waffle board](https://waffle.io/jackfirth/lens) 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.