This project examines the use of functional programming in gameplay programming. Two notable game development gurus, John Carmack and Tim Sweeney, claim that increased use of functional programming in game development would be beneficial. This project puts those claims to the test by comparing the use of C# and F# in the Unity game engine. We first examine experienced game developers attitude towards the claims via a usability evaluation. We found that the participants were able to write more concise and modular code in F#, but still were reluctant to use it in practise. In need of a stronger incentive we turned to a performance study, intended to measure if concurrent code in F# is more performant than concurrent code in C#. We found that F# is slightly slower than C# in most cases. Finally we put the observed benefits of F# into the context of modern game development practices to examine why those benefits are not appealing to experienced gameplay programmers