Lecture
This lecture focuses on the semantics of programming languages, particularly through the lens of a simple language called Add. It begins by distinguishing between syntax and semantics, emphasizing that while grammars define the structure of a language, they do not convey meaning. The instructor introduces rewriting rules as a method to express semantics, illustrating how natural number tokens can be transformed into their corresponding values. The concept of a CK machine is introduced, which serves as a formal mechanism to evaluate expressions and manage the order of operations. The lecture further explores properties of semantics, such as confluence and normalization, and discusses undefined behavior in programming languages. The instructor highlights the importance of lambda calculus as a foundational framework for expressing computation, detailing its syntax and semantics. The lecture concludes with a discussion on how these concepts apply to more complex programming languages, providing a comprehensive overview of how semantics shapes the understanding of programming languages.