L3N: Flat Trees!

Construct and traverse trees with a coherent set of functions.

L3 trees can express HTML, XML, JSON or functional programs.

The Concept

Many documents can be iterated as a flat sequence of nodes, be it an XML or HTML document, a piece of JSON or even a functional program (see Raddle). The way documents are traversed is in document order, just like a SAX parser: an event is emitted for when a branch opens or closes, or when a (text) leaf is completed.

This library stores all familiar document nodes as plain JSON by using a simple convention. Traversal of documents is exposed as an Observable stream (uses RxJS 6). This ensures that there's no difference between traversing an in-memory tree or connecting to a SAX-style parser: everything is a stream.

Each node that is emitted on the stream is wrapped in a transient container that provides a reference to the parent node (see the VNode class). In addition, the VNode interface exposes more relevant properties, such as its depth relative to the root or its position relative to its parent. These enable traversal across all DOM axes. Furthermore, node names and values may be indexed to increase performance.

This library provides an immutable alternative to plain JSON (via the pnode context) and a native DOM context for the browser. The traversal context may be switched by simply binding each accessor function to another context module.

For native DOM traversal in the browser, the VNode integrates with the canonical TreeWalker API (uses ES6 WeakMap).

Note: you should not create references to VNode instances, or they can't be garbage collected. Transform them functionally instead, by using RxJS or a specialized library (see Frink).

Install / setup

npm i l3n

The easiest way to get started is with the Node.js distribution:

const l3 = require("l3n");

// Direct construction of a document-fragment, no Rx:

const frag = l3.t(
  l3.e("div",
    l3.a("class","greeting"),
    l3.e("p","Hello")
  )
)

console.log(frag.toString());

console.log(frag.toJS());

// Alternatively, you can pass a 'document implementation context' to the faux VNode directly.
// Below example will create a persistent tree
const div = l3.e("div",
  l3.a("class","greeting"),
  l3.e("p","Hello")
).node(l3.pnode);

console.log(div.toString());

console.log(div.toJS());

API documentation (WIP)

Documentation index: index

Examples (ES modules)

import { e, m, a, ensureDoc } from "l3n";

const div = e("div",
  a("class","greeting"),
  e("p","Hello")
);

const map = m(
  a("greeting","Hello")
);

HTML serialization

ensureDoc(div).subscribe(vnode => {
    console.log(vnode.toString());
});

yields

<div class="greeting"><p>Hello</p></div>

while

ensureDoc(map).subscribe(vnode => {
    console.log(vnode.toString());
});

yields

<l3-m><l3-a name="greeting">Hello</l3-a></l3-m>

JS/JSON

ensureDoc(div).subscribe(vnode => {
    console.log(vnode.toJS());
});

yields

{
  "$name":"div",
  "class":"greeting",
  "$children":[{
    "$name":"p",
    "$children":["Hello"]
  }]
}

while

ensureDoc(map).subscribe(vnode => {
    console.log(vnode.toJS());
});

yields

{
  "greeting":"Hello"
}

Serialization rules

L3N serialization rules for JSON:

Constant	VNode Type	Appearance
1	Element	{"$name":"qname","some-attr":"some-value","$children":[]}
3	teXt	"some-text"
4	Reference	{"$ref":"/some/path"}
5	List	[]
6	Map	{}
7	Processing instruction	{"$pi"":"xml-stylesheet "\"type\"=\"text/xsl\" \"href\"=\"some.xsl\""}
8	Comment	{"$comment":"some-comment"}
12	teXt	123, true or null
10	doctype	{"$doctype":"serialized-doctype"}
14	Function call	{"$name":"some-function","$args":[]}
15	Quotation (AKA lambda)	{"$args":[]}

---

L3N serialization rules for XML:

Constant	VNode Type	Appearance
1	Element	<some-element some-attr="some-value"></some-element>
3	teXt	some-text
4	Reference	<include xmlns="http://www.w3.org/2001/XInclude" href="/some/path" parse="xml"/>
5	List	<l3:l xmlns:l3="http://l3n.org"></l3:l>
6	Map	<l3:m xmlns:l3="http://l3n.org"><l3:a name="my-xml-tuple"><some-element /></l3:a></l3:m>
7	Processing instruction	<?xml-stylesheet type="text/xsl" href="some.xsl" ?>
8	Comment	<!-- some-comment -->
10	doctype
12	teXt	<l3:x xmlns:l3="http://l3n.org">123</l3:x>
14	Function call	<l3:f xmlns:l3="http://l3n.org" name="some-function"></l3:f>
15	Quotation	<l3:q xmlns:l3="http://l3n.org"></l3:q>

---

L3N serialization rules for HTML:

Constant	VNode Type	Appearance
1	Element	<some-element some-attr="some-value"></some-element>
2	Key-value pair	v
3	teXt	some-text
4	Reference	<link rel="import" href="/some/path">
5	List	<l3-l></l3-l>
6	Map	<l3-m><l3-a name="key">value</l3-a></l3-m>
7	Processing instruction	N/A
8	Comment	<!-- some-comment -->
10	doctype
12	teXt	<l3-x>123</l3-x>
14	Function call	<l3-f name="some-function"></l3-f>
15	Quotation	<l3-q></l3-q>