apg-js-examples/src/look-behind/main.js

Examples of using the suite of apg-js applications and libraries.

/*  *************************************************************************************
 *   copyright: Copyright (c) 2021 Lowell D. Thomas, all rights reserved
 *     license: BSD-2-Clause (https://opensource.org/licenses/BSD-2-Clause)
 *   ********************************************************************************* */
// This is a demonstration of the look behind operators && and !!.
module.exports = function main(args) {
  /* display the program arguments */
  console.log('look-behind args');
  console.dir(args);

  /* the help screen */
  let desc = '';
  desc += 'The "look-behind" example demonstrates the use of the look behind operators, && and !!\n';
  desc += 'Examine or run a debugger on this module, "apg-js-examples/src/look-behind/main.js" to study the example.\n';
  let help = '';
  help += 'Usage: npm run look-behind [-- arg]\n';
  help += '  arg: help       (or no arg) to display this help screen.\n';
  help += '       boundaries using look-behind to define word and line boundaries\n';
  help += '       comment    a cautionary example of using rules in look behind\n';
  help += '       negative   a simple example of using !!\n';
  help += '       positive   a simple example of using &&\n';
  if (!args[0]) {
    /* display the help screen and exit */
    console.log(desc);
    console.log(help);
    return;
  }
  switch (args[0]) {
    case 'help':
      console.log(help);
      return;
    case 'boundaries':
      console.log();
      console.log('Demonstrate: using look-behind to define word and line boundaries');
      require('./boundaries');
      break;
    case 'comment':
      console.log();
      console.log('Demonstrate: a cautionary example of using rules in look behind');
      require('./comment');
      break;
    case 'negative':
      console.log();
      console.log('Demonstrate: a simple example of using !!');
      require('./negative');
      break;
    case 'positive':
      console.log();
      console.log('Demonstrate: a simple example of using &&');
      require('./positive');
      break;
    case 'all':
      console.log();
      console.log('Demonstrate: using look-behind to define word and line boundaries');
      require('./boundaries');
      console.log();
      console.log('Demonstrate: a cautionary example of using rules in look behind');
      require('./comment');
      console.log();
      console.log('Demonstrate: a simple example of using !!');
      require('./negative');
      console.log();
      console.log('Demonstrate: a simple example of using &&');
      require('./positive');
      break;
    default:
      console.log(`unrecognized argument: ${args[0]}`);
      console.log(help);
  }
};