public override Thing Eval(ProgramRunner runner)
        {
            Thing evalRight;
            if (right.IsType(typeof(Function)))
            {
                evalRight = ((Function)right).Eval(runner);
            } else
            {
                evalRight = right;
            }

            runner.SetMemory(((Things.String)left).str, evalRight);
            return new Set(left, right);
        }