Function expect

packages/less/lib/less/parser/parser.js:89–99

(arg, msg)

    }

    function expect(arg, msg) {
        // some older browsers return typeof 'function' for RegExp
        const result = (arg instanceof Function) ? arg.call(parsers) : parserInput.$re(arg);
        if (result) {
            return result;
        }

        error(msg || (typeof arg === 'string'
            ? `expected '${arg}' got '${parserInput.currentChar()}'`
            : 'unexpected token'));
    }

    // Specialization of expect()
    function expectChar(arg, msg) {