/* eslint-disable new-cap *//* eslint-disable new-cap */This module demonstrates a grammar with syntactic predicates.
These are the AND(&) and NOT(!) operators.
They have the feature of looking ahead in the input string for an
SABNF grammar-defined phrase and making parsing decisions based on what they find.
The AND operator fails if the grammar-defined phrase is not found.
The NOT operator fails if the grammar-defined phrase is found.
Neither of these operators ever returns a matched phrase.
They either return a NOMATCH state or an empty string, both having phrase length = 0.
The effect of this is that no nodes are ever retained on the AST
for any rule names (or UDT names) that appear in
the grammar-defined phrases behind the syntactic predicate operators.
even if they are explicitly defined to be kept in the AST.
In fact, the parser has an internal mechanism that suppresses AST node collection
while it is parsing syntactic predicate phrases.
This example demonstrates that the parser correctly suppresses AST node collection
within syntactic predicate phrases.
module.exports = function setup(grammar, callbacks, input) {
const nodeUtil = require('node:util');
const inspectOptions = {
showHidden: true,
depth: null,
};
try {See simple/setup.js for the basics of setting up the parser objects.
const { apgLib } = require('apg-js');
const parser = new apgLib.parser();
parser.ast = new apgLib.ast();
parser.ast.callbacks = callbacks;
const inputCharacterCodes = apgLib.utils.stringToChars(input);
const startRule = 0;
const result = parser.parse(grammar, startRule, inputCharacterCodes);
/* display parser results on the console */
console.log();
console.log("the parser's results");
console.dir(result, inspectOptions);
if (result.success === false) {
throw new Error(`input string: '${input}' : parse failed`);
}Generate and display the AST in XML format,
demonstrating that the syntactic predicate phrases are not present
even though we have requested to see them on the AST.
const xml = parser.ast.toXml();
console.log();
console.log('AST in XML format');
console.log('Note that the look-ahead phrases are not on the AST even though they have been requested.');
console.log(xml);
} catch (e) {
let msg = '\nEXCEPTION THROWN: \n';
if (e instanceof Error) {
msg += `${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;
}
};