/* *************************************************************************************
* copyright: Copyright (c) 2021 Lowell D. Thomas, all rights reserved
* license: BSD-2-Clause (https://opensource.org/licenses/BSD-2-Clause)
* ********************************************************************************* */This example is a stripped down version of the main apg driver function.
Note on teminology.
APG is a parser generator. However, it really only generates a “grammar object” (see below) from the defining SABNF grammar. The generated parser is incomplete at this stage. Remaining, it is the job of the user to develop the generated parser from the grammar object and the APG Library (apg-lib).
The following terminology my help clear up the confusion between the idea of a “generated parser” versus a “generated grammar object”.
module.exports = function single() {
const write = require('../writeHtml');
const apgJs = require('apg-js');
function logErrors(api, header) {
console.log('\n');
console.log(`${header}:`);
console.log(api.errorsToAscii());
console.log('\nORIGINAL GRAMMAR:');
console.log(api.linesToAscii());
}
try {
const thisFileName = `${__filename}: `;
const ApiCtor = apgJs.apgApi;
const apglib = apgJs.apgLib;
/* the SABNF grammar */
let float = '';
float += 'float = [sign] decimal [exponent]\n';
float += 'sign = "+" / "-"\n';
float += 'decimal = integer [dot [fraction]]\n';
float += ' / dot fraction\n';
float += 'integer = 1*%d48-57\n';
float += 'dot = "."\n';
float += 'fraction = 1*%d48-57\n';
float += 'exponent = "e" [esign] exp\n';
float += 'esign = "+" / "-"\n';
float += 'exp = 1*%d48-57\n';
/* test complete generation in one step */
const api = new ApiCtor(float);
api.generate();
if (api.errors.length) {
logErrors(api, 'GRAMMAR ERRORS');
console.log(api.displayAttributeErrors());
throw new Error(`${thisFileName}grammar has errors`);
}
/* make a parser from the grammar object */
const grammarObj = api.toObject();eslint-disable-next-line new-cap
const parser = new apglib.parser();
const result = parser.parse(grammarObj, 0, '123.0');
let html = apglib.utils.parserResultToHtml(result, 'generated parser');
html = apglib.utils.htmlToPage(html);
write(html, 'single-step-parser');
} catch (e) {
let msg = 'EXCEPTION THROWN: ';
if (e instanceof Error) {
msg += `${e.name}: ${e.message}`;
} else {
msg += '\n';
msg += require('node:util').inspect(e, {
showHidden: true,
depth: null,
colors: true,
});
}
console.log(msg);
}
};