2.3.3. Lambda Calculus
There's a model for computer programs called Lambda Calculus which proves that declaring closures and executing them is enough to perform all the operations provided by a full-fledged programming language. Perl supports Lambda-Calculus in a very straight-forward way, due to its support of lexical scoping.
Teaching Lambda-Calculus is out of the scope of this lecture, as well as pretty much off-topic. The interested reader is referred to the following links: