apg-js-examples/src/apg-exp/multiline-mode.js

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

/* eslint-disable new-cap */
/*  *************************************************************************************
 *   copyright: Copyright (c) 2021 Lowell D. Thomas, all rights reserved
 *     license: BSD-2-Clause (https://opensource.org/licenses/BSD-2-Clause)
 *   ********************************************************************************* */
// Unlike most `regex` engines, `apg-exp` has no multiline mode.
// `apg-exp` makes no assumptions about what is or isn't a line boundary.
// Nonetheless, it is very easy to create line-boundary anchors, once you have decided
// what constitutes the set of line-ending characters or character combinations.
// Line boundary anchors can be created with the look around operators.
// A line must be preceded by a line-end or the beginning of the string
// and followed by a line-end or the end of string.
// You can see how these anchors are created in the grammar below.
//
// This example will demonstrate finding defined strings but only if they constitute an entire line.
// Using the global `g` flag and user-defined line ends, we can easily mimic the multiline mode
// supported by most `regex` engines.
//
// This example will consider the carriage return (CR) and new line (LF) characters as line ends
// as well as the combination CRLF.
(function multilineMode() {
  try {
    const apgJs = require('apg-js');
    const writeHtml = require('../writeHtml');

    const { apgExp } = apgJs;
    const { apgLib } = apgJs;
    let grammar;
    let result;
    let str;
    let html;
    grammar = '';
    grammar += 'phrase-to-find = abl "The " animal " in the hat." ael\n';
    grammar += 'animal         = "cat" / "dog" / "bird" / "mouse"\n';
    grammar += 'line-end       = %d13.10 / %d10 / %d13\n';
    grammar += 'abl            = (&&line-end / %^) ; anchor begin of line\n';
    grammar += 'ael            = (&line-end / %$)  ; anchor end of line\n';
    const flags = 'g';
    const exp = new apgExp(grammar, flags);
    console.log();
    console.log('Demonstrate mimicing multi-line mode in RegExp.');
    console.log();
    console.log('SABNF grammar:');
    console.log(exp.sourceToText());
    str = '';
    str += 'The cat in the hat.\n';
    str += 'The dog in the hat.\r\n';
    str += 'The bird in the hat.\r';
    str += 'The dog is not in the hat.\n';
    str += 'The cat in the hat is black.\n';
    str += 'The mouse in the hat.';
    console.log();
    console.log('input string:');
    console.log(str);
    html = '';
    html += '<h3>grammar source</h3>\n';
    html += exp.sourceToHtml();
    html += '<h3>found lines</h3>\n';
    while (true) {
      result = exp.exec(str);
      if (result == null) {
        break;
      }
      html += `<p>${result.toHtml()}</p>`;
      console.log(result.toText());
    }
    const page = apgLib.utils.htmlToPage(html);
    const htmlName = 'multiline-mode';
    writeHtml(page, htmlName);
  } catch (e) {
    console.log(`EXCEPTION: ${e.message}`);
  }
})();