kas-npm/src/compare.js

A lightweight JavaScript CAS for comparing expressions and equations. Forked from @Khan to use in NPM.

const _ = require('underscore');
const KAS = require('./parser');
(function(KAS) {
    // Assumes that both expressions have already been parsed
    // TODO(alex): be able to pass a random() function to compare()
    KAS.compare = function(expr1, expr2, options) {
        var defaults = {
            form: false, // Check that the two expressions have the same form
            simplify: false, // Check that the second expression is simplified
        };

        /* Options that could be added in the future:
         * - Allow ratios: e.g. 3/1 and 3 should both be accepted for something
         *   like slope
         * - Allow student to choose their own variable names
         */

        if (options !== undefined) {
            // eslint-disable-next-line no-undef
            options = _.extend(defaults, options);
        } else {
            options = defaults;
        }

        // TODO(CP-1614): Figure out how to make these messages translatable

        // Variable check
        var vars = expr1.sameVars(expr2);
        if (!vars.equal) {
            var message;
            if (vars.equalIgnoringCase) {
                message =
                    "Check your variables; one or more are using " +
                    "the wrong case (upper or lower).";
            } else {
                message =
                    "Check your variables; you may have used the wrong " +
                    "letter for one or more of them.";
            }
            return {
                equal: false,
                wrongVariableCase: vars.equalIgnoringCase,
                wrongVariableNames: !vars.equalIgnoringCase,
                message: message,
            };
        }

        // Semantic check
        if (!expr1.compare(expr2)) {
            return {equal: false, message: null};
        }

        // Syntactic check
        if (options.form && !expr1.sameForm(expr2)) {
            return {
                equal: false,
                message: "Your answer is not in the correct form.",
            };
        }

        // Syntactic check
        if (options.simplify && !expr1.isSimplified()) {
            return {
                equal: false,
                message: "Your answer is not fully expanded and simplified.",
            };
        }

        return {equal: true, message: null};
    };
})(KAS);