Neith NPM | npm.io

Neith - Javascript Zipper Library

About

Neith is a zipper library for Javascript. 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.

Overview

Example are written in 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:

<!DOCTYPE html>
<html>
<head></head>
<body>
    <script type="application/javascript" src="require.js"></script>
    <script type="application/javascript">
        requirejs.config({
            paths: {
                'nu-stream': 'nu/dist',
                'neith': 'neith/dist'
            }
        });
        require(['neith/zipper'], function(zipper) {
            ...
        });
    </script>
</body>

Code

Neith is written in Javascript / 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.