# Neith - Javascript Zipper Library #
## About
Neith is a zipper library for Javascript. [Zippers][zippers] allow efficient
manipulation of immutable, hierarchical data structures through a formalized
interface.
Neith supports zippers for lazy, infinite data structures. The tree module
supports zippers for variations of n-ary ordered trees with labeled edges.
### Links
* [Documentation][documentation] - API documentation
### Overview
Example are written in [Khepri][khepri] but regular JS will work fine with Neith.
```
with
import 'neith::zipper' zipper,
import 'neith::tree' tree,
import 'neith::walk' walk,
import 'nu::stream' stream
in {
/// Define a new zipper type for json type objects.
var objZipper = tree.treeZipper @ (
Object.keys \> stream.from,
(.)
\_ _ children -> children());
/// Create a new zipper
var o = {'a': 1, 'b': {'c': 2, 'd': 3}};
var z = objZipper o;
/// Move around and extract info
z
|> zipper.down
|> tree.node; // 1
z
|> zipper.down
|> zipper.right
|> tree.node; // {'c': 2, 'd': 3}
z
|> zipper.down
|> zipper.right
|> zipper.down
|> tree.edge; // 'c'
/// Labeled movement for trees
z
|> tree.child @ 'b'
|> tree.child @ 'd'
|> tree.node; // 3
/// Editing
// The original object is never modified.
// Neith zippers and operations are persistent.
z
|> tree.child @ 'b'
|> tree.child @ 'd'
|> tree.modifyNode @ (+, 10)
|> tree.sibling @ 'c'
|> (tree.modifyEdge @ \e -> e + 'xyz')
|> zipper.up
|> tree.sibling @ 'a'
|> zipper.remove
|> zipper.root
|> tree.node; // {'b': {'cxyz': 2, 'd': 13}}
/// Walk in DFS order
walk.preWalk(console.log, z);
/*
Output:
Pair(null, {'a': 1, 'b': {'c': 2, 'd': 3}});
Pair('a', 1)
Pair('b', {'c': 2, 'd': 3})
Pair('c', 2)
Pair('d', 3)
*/
}
```
# Using Neith
## With node
Library code is in `dist_node` directory.
$ npm install neith
var zipper = require('neith').zipper;
var listZipper = require('neith').list;
var z = listZipper.arrayZipper([1, 2, 3]);
zipper.extract(zipper.down(z)); // 1
## With AMD
Library code is in `dist` directory.
Include any AMD style module loader and load neith:
## Code
Neith is written in Javascript / Khepri. [Khepri][khepri] is a ECMAScript subset
that, among other things, adds a shorted lambda function syntax. `dist` contains
the generated Javascript files while `lib` contains the source Khepri files.
[Zippers]: http://www.haskell.org/haskellwiki/Zipper
[khepri]: http://khepri-lang.com
[nu]: https://github.com/mattbierner/nu
[documentation]: https://github.com/mattbierner/neith/wiki