/* *************************************************************************************
* copyright: Copyright (c) 2021 Lowell D. Thomas, all rights reserved
* license: BSD-2-Clause (https://opensource.org/licenses/BSD-2-Clause)
* ********************************************************************************* */apg parsers provide an optional tracing facility which is essentially the “debugger”.
When something is going wrong with either the grammar or the string being parsed,
the trace gives a step-by-step picture of how the parser is operating.
Using the debug flag, d, will make the trace also available to
apg-exp and a simple demonstration of that is given here.
This example assumes that you are already familiar with the trace object in apg parsers.
If not, check out the trace examples to get started.
We will use the floating point grammar and turn on the tracing facility to
have a look at how the parser operates.
(function trace() {
try {
const { apgExp: ApgExp, apgLib } = require('apg-js');
const writeHtml = require('../writeHtml');
const grammar = new (require('./grammars/float'))();let apgJs = require(“apg-js”); let apgExp = apgJs.apgExp; let apgLib = apgJs.apgLib;
let exp;
let result;
let str;
let html;
str = '';
str += '|||123.0e-10|||';
console.log();
console.log('Demonstrate tracing with the "d" flag.');
console.log();
console.log('input string:');
console.log(str);
const flags = 'd';
exp = new ApgExp(grammar, flags);By default, the trace will show only the rule name operators.
result = exp.exec(str);
console.log();
console.log(`result[0]: default trace: ${result[0]}`);
html = '';
html += '<h3>grammar source</h3>\n';
html += exp.sourceToHtml();
html += '<h3>input string</h3>\n';
html += `<pre>${str}</pre>\n`;
html += '<h3>the matched phrase</h3>\n';
html += `<pre>${result[0]}</pre>\n`;
html += '<h3>the default trace configuration (all rule names, no operators) </h3>\n';
html += exp.trace.toHtml();
html += '<h3> trace configured to display ALL steps taken </h3>\n';
exp = new ApgExp(grammar, flags);For anything other than the default, the trace object needs to be configured prior to calling exp.exec().
exp.trace.filter.operators['<all>'] = true;
result = exp.exec(str);
console.log();
console.log(`result[0]: configured trace: ${result[0]}`);
html += exp.trace.toHtml();
/* finally, write the HTML page */
const page = apgLib.utils.htmlToPage(html);
const htmlName = 'trace';
writeHtml(page, htmlName);
} catch (e) {
console.log(`EXCEPTION: ${e.message}`);
}
})();