Programabilidade é fundamental

It is no exaggeration to regard this as the most fundamental idea in programming:

The evaluator, which determines the meaning of expressions in a programming language, is just another program.
 

To appreciate this point is to change our images of ourselves as programmers. We come to see ourselves as designers of languages, rather than only users of languages designed by others.

Structure and Interpretation of Computer Programs, Harold Abelson and Gerald Jay Sussman, The MIT Press, 2nd edition, 1996, p.297