Most real-world programming languages are too complex to be studied using formal methods. For this reason, academics often work with simple theoretical languages instead. The λ-calculus is a simple formal language that is often used for talking about functional languages, the π-calculus is a model of concurrent programming and there is an entire book, A Theory of Objects modelling various object-oriented systems. Animation from Financial Times article "Why the world's recycling system stopped working". Tho[...]