esther-medina-quintero-parser-nearley/index.js

Lab for language processors

#!/usr/bin/env node
/**
 * @description A parser for egg lang files
 * @author Esther M. Quintero <alu0101434780@ull.edu.es>
 * @since 12/03/2024
 */

 'use strict';

const fs = require('fs');
const nearley = require("nearley");
const grammar = require("./src/grammar.js");
 /**
 * A function that parses a egg file
 * @param {string} origin The name of the origin file
 * @throws Will throw if there are errors in the program or if the files
 *     can't be opened
 */
const parseFromFile = (origin) => {
  try {
    // Read the file contents
    const code = fs.readFileSync(origin, { encoding: 'utf8' });

    // Initialize Nearley parser with the grammar
    const parser = new nearley.Parser(nearley.Grammar.fromCompiled(grammar));

    // Parse the code
    parser.feed(code);
    console.log(JSON.stringify(parser.results[0], null, 2));
    
    // Check if the parsing was successful
    if (parser.results.length === 0) {
      throw new Error('No parse results. The file may be empty or not match the grammar.');
    } else if (parser.results.length > 1) {
      throw new Error('Ambiguous results. The grammar may allow multiple parses.');
    }
    /// Show the whole AST
    console.log(JSON.stringify(parser.results[0], null, 2));

    // Return the AST from the first (and should be only) parse result
    return parser.results[0];
  } catch (error) {
    // Rethrow the error with additional context if needed
    throw new Error(`\nFailed to parse file "${origin}": ${error.message}`);
  }
};

module.exports = { parseFromFile };