This is a short Perl-script that allows you to evaluate perl expressions and statements interactively, with up-arrow recall of previous commands. It also permits function definitions, and multi-line code entry with '\'. It is even possible to 'use' external modules and interact with them.
Actually, the code is trivial, and it is Perl that provides all this power. I keep this script always running on a console as an all-purpose programmable desktop calculator.