This puzzle just poped on my screen when I was googling http://worrydream.com/AlligatorEggs/ it’s a nice puzzle
alligator game.

This game represents the untyped lambda calculus. A hungry alligator is a lambda abstraction, an old alligator is parentheses, and eggs are variables. The eating rule corresponds to beta-reduction. The color rule corresponds to (over-cautious) alpha-conversion. The old age rule says that if a pair of parentheses contains a single term, the parentheses can be removed.
I’m sure that after 4.0 drools release I’m going to implement this game as a drools DRL.