/* *************************************************************************************
* 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 built-in notation for word boundaries.
apg-exp makes no assumptions about what is or isn’t a word boundary.
Nonetheless, it is very easy to create word-boundary anchors, once you have decided
what constitutes a word.
This example will demonstrate matching words which consist only of ASCII alphabetic characters. Once this word character set has been defined, word boundary anchors can be created with the look around operators. A word must be preceded by a non-word character or the beginning of the string and followed by a non-word character or the end of string. You can see how these anchors are created in the grammar below.
This example will show the word “cat” is matched at the beginning of a line, in the middle of the line and at the end of the line. However, the character string “cat” is not found as a word when part of a longer string, in this case in the words “Bobcat” and “caterpillar”.
(function wordBoundaries() {
try {
const { apgExp: ApgExp, apgLib } = require('apg-js');
const writeHtml = require('../writeHtml');
let grammar;
let result;
let str;
let html;
grammar = '';
grammar += 'word-to-find = abw "cat" aew\n';
grammar += 'word-char = %d65-90/%d97-122\n';
grammar += 'abw = (!!word-char / %^) ; anchor begin of word\n';
grammar += 'aew = (!word-char / %$) ; anchor end of word\n';
const flags = 'g';
const exp = new ApgExp(grammar, flags);
console.log();
console.log('Demonstrate defining and using word boundaries.');
console.log();
console.log('SABNF grammar:');
console.log(exp.sourceToText());
str = '';
str += 'Cat - a Bobcat is a cat but a caterpillar is not a cat';
console.log();
console.log('input string:');
console.log(str);
html = '';
html += '<h3>grammar source</h3>\n';
html += exp.sourceToHtml();
html += '<h3>found words</h3>\n';
const TRUE = true;
while (TRUE) {
result = exp.exec(str);
if (result == null) {
break;
}
html += `<p>${result.toHtml()}</p>`;
console.log(result.toText());
}
const page = apgLib.utils.htmlToPage(html);
const htmlName = 'word-boundaries';
writeHtml(page, htmlName);
} catch (e) {
console.log(`EXCEPTION: ${e.message}`);
}
})();