@fauton/cfg/dist/generateLR0ParsingTable.js

A package to work with context free grammars and LL1 parsers

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.generateLR0ParsingTable = exports.augmentCfg = exports.generateClosureOfLR0Item = exports.addDotToProductionRule = void 0;
const populateCfg_1 = require("./utils/populateCfg");
const dotSymbol = "$.$";
function addDotToProductionRule(productionRules, productionVariable) {
    const rulesForVariable = productionRules[productionVariable];
    // Loop through all the rules for the variable
    rulesForVariable.forEach((rule, ruleIndex) => {
        // Add the dot symbol to the left
        rulesForVariable[ruleIndex] = `${dotSymbol} ${rule}`;
    });
}
exports.addDotToProductionRule = addDotToProductionRule;
function generateClosureOfLR0Item(cfg, productionVariable) {
    const { productionRules, variables } = cfg;
    // Creating a set of variables for faster membership lookup
    const variablesSet = new Set(variables);
    const rules = productionRules[productionVariable];
    rules.forEach(rule => {
        const tokens = rule.split(" ");
        for (let tokenNumber = 0; tokenNumber < tokens.length - 1; tokenNumber += 1) {
            const token = tokens[tokenNumber];
            // We wont overflow the tokens array so its safe
            const nextToken = tokens[tokenNumber + 1];
            // Using $.$ as its a lot less common than regular .
            // Check if the next token is a variable
            if (token === dotSymbol && variablesSet.has(nextToken)) {
                // Add dotSymbol to the left of all the substitution for the variable
                addDotToProductionRule(productionRules, nextToken);
                // Generate closure of the next variable
                generateClosureOfLR0Item(cfg, nextToken);
            }
        }
    });
}
exports.generateClosureOfLR0Item = generateClosureOfLR0Item;
function augmentCfg(inputCfg) {
    const cfg = (0, populateCfg_1.populateCfg)(inputCfg);
    const { productionRules, startVariable, variables } = cfg;
    // Create the augmented grammar
    const newStartVariable = `${startVariable}'`;
    variables.unshift(newStartVariable);
    productionRules[newStartVariable] = [startVariable];
    cfg.startVariable = newStartVariable;
    return cfg;
}
exports.augmentCfg = augmentCfg;
function generateLR0ParsingTable(inputCfg) {
    augmentCfg(inputCfg);
}
exports.generateLR0ParsingTable = generateLR0ParsingTable;