pratt-parser

import { Parser, WhiteSpaceToken, NumberToken } from "pratt-parser"; // Helper function to create value objects for AST nodes function Value(value) { return Object.create(null, { value: { value: value } }); } // Define the grammar for arithmetic expressions const myGrammar = new Parser({ // Specify base tokens for parsing tokens: [WhiteSpaceToken, NumberToken], // Define prefix operators prefix: { "(": { nud(grammar) { // Null Denotation: parse expression inside parentheses const e = grammar.expression(0); grammar.advance(")"); // Expect closing parenthesis return e; } } }, // Define infix operators and their precedence infix: { ")": {}, // Right parenthesis acts as a terminator, no operation associated "+": { precedence: 50, combine: (left, right) => Value(left.value + right.value) // Addition operation }, "-": { precedence: 50, combine: (left, right) => Value(left.value - right.value) // Subtraction operation }, "*": { precedence: 60, // Higher precedence than + or - combine: (left, right) => Value(left.value * right.value) // Multiplication operation }, "/": { precedence: 60, // Higher precedence than + or - combine: (left, right) => Value(left.value / right.value) // Division operation } } }); // Example expression to parse and evaluate const expression = "(1 + (1 + 4 * 3)) * (2 + 1)"; const result = myGrammar.parse(expression).value; // Output the evaluated result console.log(`Parsed expression: "${expression}"`); console.log(`Evaluated result: ${result}`); // Expected output: 42