  Object-oriented programming (OOP) is one of the most popular paradigms used
for building software systems. However, despite its industrial and academic
popularity, OOP is still missing a formal apparatus similar to
$\lambda$-calculus, which functional programming is based on. There were a
number of attempts to formalize OOP, but none of them managed to cover all the
features available in modern OO programming languages, such as C++ or Java. We
have made yet another attempt and created $\varphi$-calculus. We also created
EOLANG (also called EO), an experimental programming language based on
$\varphi$-calculus.
