Using functional programming (FP) in enterprise software development is often quite a challenge. In this presentation, Sadek Drobi will talk about his experience of applying functional programming principles on a real-world project in relation with existing non-functional frameworks. In the year 2008 and just on the release of C# 3.0 and Linq, which is basically several FP concepts implemented on C# language, Sadek Drobi worked as a tech lead on a project where functional programming approach was used to meet performance requirements and to achieve desired response time. Facing similar issues, a mainstream architect would strive to instantiate less objects and to use mutation for optimization. Considering the big amount of data that had to be processed on each request, Sadek chose to do it otherwise: no mutation, used memoization, laziness, recursion, functions, curry, monads, list comprehensions and, then, parallelization to yield an almost purely functional core domain model. Sadek Drobi will talk more about this experience and elaborate on the good and the bad of going almost extreme through a functional programming approach from different perspectives.