apg-js-examples/src/look-behind/boundaries.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 using `look-around` operators to define word boundaries.
// In this straight-forward grammar, parsing environment, it is a very artificial example.
// It simply wants to know if the whole word `cat` is found at the 10th character.
// However, in the context of a pattern matching engine (see `apg-exp`) it is very real use.
// You can examine the trace of each of these examples to see how the left boundary is matched,
// or not matched, using negative `look-behind` (`!!` or `BKN`) and the right boundary is determined
// with negative `look-ahead` (`!` or `NOT`).
(function boundaries() {
  let input = 'The black cat is in the window.';
  const grammar = new (require('./boundaries-grammar'))();
  const setup = require('./setup');
  setup(input, grammar, 'boundaries-cat');
  input = "Don't truncate this line.";
  setup(input, grammar, 'boundaries-truncate');
  input = "It's a Bobcat, not house cat..";
  setup(input, grammar, 'boundaries-bobcat');
  input = "You can't categorize it.";
  setup(input, grammar, 'boundaries-catagorize');
})();