@fauton/cfg/dist/utils/removeProductionRules.js

A package to work with context free grammars and LL1 parsers

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.removeProductionRules = void 0;
const setOperations_1 = require("./setOperations");
function removeProductionRules(cfg) {
    const { productionRules, removedVariables, variables } = cfg;
    // Remove production variables from the production rules record
    removedVariables.forEach((removedVariable) => {
        delete productionRules[removedVariable];
    });
    const removedVariablesSet = new Set(removedVariables);
    // Now we need to remove all the production rules that references any removed production variables
    Object.entries(productionRules).forEach(([productionVariable, productionRulesSubstitutions]) => {
        productionRules[productionVariable] = productionRulesSubstitutions.filter((productionRulesSubstitution) => {
            // productionRulesSubstitution = Verb Adj Noun
            const productionRulesSubstitutionTokensSet = new Set(productionRulesSubstitution.split(' '));
            const difference = (0, setOperations_1.setDifference)(productionRulesSubstitutionTokensSet, removedVariablesSet);
            // If we dont need to remove any variables then the size before and after the set difference would be similar
            return difference.size === productionRulesSubstitutionTokensSet.size;
        });
    });
    return Array.from((0, setOperations_1.setDifference)(new Set(variables), new Set(removedVariables)));
}
exports.removeProductionRules = removeProductionRules;