/* 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}`);
}
})();