/* *************************************************************************************
* 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);
}
};