Black box - to deduce algorithm

This is a party game idea.

One player (operator) lurks behind a Black box. In general, a black box process is one where the user cannot see its inner workings.

The operator draws one card, which contains operating instructions. Other players feed input to the Black box and the operator acts as instructions says. Finally players get some output.

Input may be two integers, two marble balls with different colors, two letters...
Output is one integer, one ball, one word...
Players try to deduce algorithm that is going on. They feed input again, get new output and make guesses.

Example: Algorithm is "If input is green ball and ball of other color, output is one blue ball. If input is two green balls, input is red ball. All other input results white ball."
Players must test various combinations and gradually figure out the procedure.

Is this idea no good? Done already?

-regzr