/* eslint-disable func-names */
/* 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)
* ********************************************************************************* */This is a demonstration of using the parser to generate an Abstract Syntax Tree (AST). The AST is used to translate an input string. The AST can be converted to XML format.
/* Note: This function is organized embarassingly poorly. But at this point it is what it is. */
module.exports = function main(args) {
/* display the program arguments */
console.log('example ast: args');
console.dir(args);
/* the help screen */
let desc = '';
desc += 'The "ast" example is a demonstration of using the parser to generate an\n';
desc += 'Abstract Syntax Tree (AST). The AST is used to translate the input string\n';
desc += 'and it is converted to XML format.\n';
let help = '';
help += 'Usage: npm run ast [-- arg]\n';
help += ' arg: help (or no arg) to display this help screen.\n';
help += ' translate translate the input string with the AST.\n';
help += ' xml convert the AST to XML format.\n';
help += ' all run all tests.\n';
if (!args[0]) {
/* display the help screen and exit */
console.log(desc);
console.log(help);
return;
}
switch (args[0]) {
case 'help':
console.log(help);
return;
case 'translate':
case 'xml':
case 'all':
break;
default:
console.log(`unrecognized argument: ${args[0]}`);
console.log(help);
return;
}
console.log();
console.log('Demonstrate generating an AST and converting it to XML format.');
console.log();
const nodeUtil = require('node:util');const fs = require(‘node:fs’);
const inspectOptions = {
showHidden: true,
depth: null,
};
try {Acquire the required parser components.
const grammar = new (require('./phone-number'))();
const apgJs = require('apg-js');
const { apgLib } = apgJs;
const parser = new apgLib.parser();Construct an AST object and attach it to the parser.
parser.ast = new apgLib.ast();
const id = apgLib.ids;The AST translating callback functions. These are similar to the parsers syntax callback functions
in that they are each called twice, once down the tree and once up the tree, with matched phrase information.
With the AST, however, the matched phrase is known in the down direction as well as up.
SEM_PRE (down) or SEM_POST (up)SEM_OK. Can also be SEM_SKIP in the SEM_PRE
state to skip the translation of the branch below the current node. const phoneNumber = function (state, chars, phraseIndex, phraseLength, data) {
const ret = id.SEM_OK;
if (state === id.SEM_PRE) {
if (Array.isArray(data) === false) {
throw new Error("parser's user data must be an array");
}
data.length = 0;
} else if (state === id.SEM_POST) {
/* not used in this example */
}
return ret;
};
const areaCode = function (state, chars, phraseIndex, phraseLength, data) {
const ret = id.SEM_OK;
if (state === id.SEM_PRE) {
data['area-code'] = apgLib.utils.charsToString(chars, phraseIndex, phraseLength);
} else if (state === id.SEM_POST) {
/* not used in this example */
}
return ret;
};
const office = function (state, chars, phraseIndex, phraseLength, data) {
const ret = id.SEM_OK;
if (state === id.SEM_PRE) {
data.office = apgLib.utils.charsToString(chars, phraseIndex, phraseLength);
} else if (state === id.SEM_POST) {
/* not used in this example */
}
return ret;
};
const subscriber = function (state, chars, phraseIndex, phraseLength, data) {
const ret = id.SEM_OK;
if (state === id.SEM_PRE) {
data.subscriber = apgLib.utils.charsToString(chars, phraseIndex, phraseLength);
} else if (state === id.SEM_POST) {
/* not used in this example */
}
return ret;
};
parser.ast.callbacks['phone-number'] = phoneNumber;
parser.ast.callbacks['area-code'] = areaCode;
parser.ast.callbacks.office = office;
parser.ast.callbacks.subscriber = subscriber;
/* use a hard coded input string */
const inputString = 'xxxx(555)234-5678xxxx';
const inputCharacterCodes = apgLib.utils.stringToChars(inputString);
const startRule = 'phone-number';
/* parse the string here, generating an `AST` */
const result = parser.parseSubstring(grammar, startRule, inputCharacterCodes, 4, 13);
console.log();
console.log("the parser's results");
console.dir(result, inspectOptions);
if (result.success === false) {
throw new Error(`input string: '${inputString}' : parse failed`);
}Return the AST object for further processing.
const fnTranslate = function () {
const phoneParts = [];
parser.ast.translate(phoneParts);
console.log();
console.log('test: translate AST');
console.log('phone number: ');
console.log(` area-code: ${phoneParts['area-code']}`);
console.log(` office: ${phoneParts.office}`);
console.log(` subscriber: ${phoneParts.subscriber}`);
};
const fnXml = function () {
const xml = parser.ast.toXml();
console.log();
console.log('test: display AST in XML');
console.log(xml);
};
switch (args[0]) {
case 'translate':
fnTranslate();
break;
case 'xml':
fnXml();
break;
case 'all':
fnTranslate();
fnXml();
break;
default:
break;
}
if (args[0] === 'translate' || args[0] === 'all') {
fnTranslate();
} else if (args[0] === 'xml' || args[0] === 'all') {
}
} catch (e) {
let msg = '\nEXCEPTION THROWN: \n';
if (e instanceof Error) {
msg += `${e.name}: ${e.message}`;
} else if (typeof e === 'string') {
msg += e;
} else {
msg += nodeUtil.inspect(e, inspectOptions);
}
process.exitCode = 1;
console.log(msg);
throw e;
}
};