Occam DOM

Occam's DOM related functionality.

Contents

• Introduction
• Installation
• Example
• Usage
• Building
• Contact

Introduction

Specifically, "outer" token arrays and parse trees result from the use of Occam's lexers and parsers, respectively. These can be distilled into "inner" token arrays and parse trees for a variety of tasks.

An example is helpful. Consider the following outer parse tree that results from parsing some simple Markdown.

                                                  |                                                   
                                           markdown [0-2]                                             
                                                  |                                                   
                                           division [0-2]                                             
                                                  |                                                   
                ---------------------------------------------------------------------                 
                |                                |                                  |                 
        subDivision.. [0]               verticalSpace [0-1]                 subDivision.. [2]         
                |                                |                                  |                 
       primaryHeading [0]                 ---------------                     paragraph [2]           
                |                         |             |                           |                 
       -------------------          <END_OF_LINE> <END_OF_LINE>                 line [2]              
       |                 |                                                          |                 
"#"[hashes] [0]      line [0]                                             ---------------------       
                         |                                                |                   |       
                  plainText. [0]                                   plainText. [2]      plainText. [2] 
                         |                                                |                   |       
                "Heading"[word] [0]                             "Paragraph"[word] [2] "."[special] [2]

This contains far more information than is needed to render the Markdown as HTML. The following inner parse tree will in fact suffice:

                                                |                 
                                            division              
                                                |                 
                                       ------------------         
                                       |                |         
                                primaryHeading      paragraph     
                                       |                |         
                                     line             line        
                                       |                |         
                                   plainText       -----------    
                                                   |         |    
                                               plainText plainText

Locating the outer nodes that contribute to this inner parse tree is straightforward enough using Occam's queries. However, the arrays of nodes that result are not in the above form. This package provides the means to form such parse trees.

Installation

With npm:

npm install occam-dom

You can also clone the repository with Git...

git clone https://github.com/djalbat/occam-dom.git

...and then install the dependencies with npm from within the project's root directory:

npm install

You can also run a development server, see the section on building later on.

Example

There is a small development server that can be run from within the project's directory with the following command:

npm start

The example will then be available at the following URL:

http://localhost:8888

The source for the example can be found in the src/example.js file and corresponding src/example folder. You are encouraged to try the example whilst reading what follows. You can rebuild it on the fly with the following command:

npm run watch-debug

The development server will reload the page whenever you make changes.

One last thing to bear in mind is that this package is included by way of a relative rather than a package import. If you are importing it into your own application, however, you should use the standard package import.

Usage

Suppose that a Markdown document is being processed by way of Highmark's lexer and parser:

const markdownLexer = MarkdownLexer.fromNothing(),
      markdownParser = MarkdownParser.fromNothing();
      
...

const content = markdown, ///
      tokens = markdownLexer.tokenise(content),
      node = markdownParser.parse(tokens);

...

A number of arrays of nodes can be created from the "outer" document node using queries:

export function nodesFromNodeAndQueries(node, queries, nodes = []) {
  queries.forEach((query) => {
    const queryNodes = query.execute(node);

    push(nodes, queryNodes);
  });

  return nodes;
}

These can then be formed into an "inner" node tree using the topmostNodeFromOuterNodes() function:

import { nodeUtilities } from "occam-dom";

const { topmostNodeFromOuterNodes } = nodeUtilities;

import ClassFromOuterNode from "./classFromOuterNode";

...

const outerNodes = nodes,   ///
      topmostNode = topmostNodeFromOuterNodes(ClassFromOuterNode, outerNode);
      
...

The first argument is a callback that maps outer node classes to inner node ones:

import htmlNodeMap from "../map/node/html";
import TopmostHTMLNOde from "../node/html/topmost";

function ClassFromOuterNode(outerNode) {
  let Class;

  if (outerNode === null) {
    Class = TopmostHTMLNode;  ///
  } else {
    const nonTerminalNode = outerNode,  ///
          ruleName = nonTerminalNode.getRuleName();

    Class = htmlNodeMap[ruleName] || HTMLNode;
  }

  return Class;
}

Note that the topmost inner node has no corresponding outer node and that a default of HTMLNode has been provided. There is no need to provide a unique class for every type of outer node that the algorithm may come across, by the way.

Building

Automation is done with npm scripts, have a look at the package.json file. The pertinent commands are:

npm run build-debug
npm run watch-debug

Contact

• [email protected]