@fauton/cfg/dist/generateLL1ParsingTable.js

A package to work with context free grammars and LL1 parsers

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.generateLL1ParsingTable = void 0;
const findFollow_1 = require("./findFollow");
const populateCfg_1 = require("./utils/populateCfg");
/**
 * Generate LL1 Parsing table
 * @param inputCfg Input context free grammar
 * @returns A record for LL1 Parsed table and whether the grammar is LL1 parsable
 */
function generateLL1ParsingTable(inputCfg) {
    const cfg = (0, populateCfg_1.populateCfg)(inputCfg);
    // Find the first and follow record of cfg
    const followRecord = (0, findFollow_1.findFollow)(cfg);
    let isParsable = true;
    const { variables } = cfg;
    // First key for variable, 2nd key for terminal and value is rule number or null
    const llRecord = {};
    // Populating the table
    // All variables as the row
    // All terminals as the column
    variables.forEach(variable => {
        llRecord[variable] = {};
    });
    // Loop through all the first record entries
    Object.entries(followRecord.first).forEach(([productionVariable, firstRecord]) => {
        // Substitutions is an array which contains first(substitution)
        firstRecord.substitutions.forEach((firstTokensForSubstitution, ruleNumber) => {
            // Loop through all the first token for the substitution
            firstTokensForSubstitution.forEach(firstTokenForSubstitution => {
                // If its epsilon we need to get the followed tokens of this variable
                if (firstTokenForSubstitution === "") {
                    // Loop through each followed token and assign the rule number
                    followRecord.follow[productionVariable].forEach((followedToken) => {
                        if (followedToken in llRecord[productionVariable]) {
                            isParsable = false;
                        }
                        llRecord[productionVariable][followedToken] = ruleNumber;
                    });
                }
                else {
                    // TODO: No tests reaches this path, maybe its not required?
                    // if (firstTokenForSubstitution in llRecord[productionVariable]) {
                    //   isParsable = false;
                    // }
                    llRecord[productionVariable][firstTokenForSubstitution] = ruleNumber;
                }
            });
        });
    });
    return {
        parseTable: llRecord,
        isParsable
    };
}
exports.generateLL1ParsingTable = generateLL1ParsingTable;