[Ironballs]

Having a team member create production code in a language nobody else on the team understands is a risky decision. That applies for anything, software, systems, infrastructure... if one developer is allowed to sit on something, what happens when the dev leaves? Or dies? And the thing he or she worked on had a non-trivial learning curve?

Choosing something like Haskell or anything else niche should be a group decision. Even when it comes to prototyping! "Guys, I'm going to prototype this .NET code in F#. Who wants to join?", instead of a developer sitting in a corner applicating his functors while others around him do something arguably simpler. It's incredibly short-sighted!

This is not aimed at you though, since I'm not sure if this was your case, I'm only guessing based on your post.