pegjs-import-loader

PEG.js import loader for webpack

A simple loader for PEG.js that supports importing multiple grammars from different PEG.js files

Install

npm install --save-dev pegjs-import-loader pegjs webpack

Setup

Apply via webpack config

webpack.config.js:

module.exports = {
  ...
  module: {
    loaders: [
      {
        test: /\.pegjs$/,
        loader: 'pegjs-import-loader',
        options: { 
            ...
        }
      }
    ]
  }
};

PEG.js options

You can pass options to PEG.js through options property in webpack config. See more about PEG.js options

Usage

Importing Syntax

parser.pegjs:

{
    const str = 'This is just an example string';
    function concat(a, b) {
        return a.concat(b);
    }
}
Expression
  = head:Term tail:(_ ("+" / "-") _ Term)* {
      return tail.reduce(function(result, element) {
        if (element[1] === "+") { return result + element[3]; }
        if (element[1] === "-") { return result - element[3]; }
      }, head);
    }
    
Factor
  = "(" _ expr:Expression _ ")" { return expr; }
  / Integer
 
@import './base-rules.pegjs'
@import './keywords.pegjs'

• Import statement must be after the initializer block of PEG.js (initializer is a piece of JavaScript code in curly braces (“{” and “}”) that precedes the first rule)
• When importing grammars from other files, all the rules in those files are accessible in the current context
• All the JS variables and functions in initializers will also be accessible from the current context
• Due to the accessibility of all the rules, variables and functions from other pegjs files in current context, users must be aware of duplication of rule, variable and function names
• Import files in one-way flow to avoid circular dependencies

Generate a parser in JS code

const parser = require('./parser.pegjs');
const result = parser.parse(content);

License

MIT (https://opensource.org/licenses/mit-license.php)