The talk is about web application architecture in Haskell, focusing on the use of domain driven design (DDD) principles and Haskell's strong and expressive type system. The speaker discusses how Haskell's type system allows for the adequate representation of business domains and the tracking of side effects in a semantic way. They also talk about functional application architecture, including the concept of bounded contexts, data transfer objects, and separating commands and queries. The speaker emphasizes the importance of documentation, testing, and the use of types to guide and verify the behavior of the program. They also mention the benefits of decoupling the application from its state and discuss the use of type-directed state machines. The speaker concludes by addressing the challenges and limitations of correct by construction and the need for intellectual honesty and testing in Haskell development. Overall, the talk highlights the benefits of using Haskell and DDD principles to build resilient and well-structured web applications.