Yup, that's basically what I told him.

What's sad is that he wasn't really showing off— he's just one of those computer scientists who loves to geek out and doesn't really think how other people could interpret it; and I guess he was hoping the interviewer would just start nerding out with him, that they'd start talking about how GHC handles lazy evaluation, and that everything would be perfect.

And the interview did its function properly - the position isn't a good fit for that person. If nerding out during the interview about lazy evaluation and purity isn't happening, then its probably all for the better that the interview failed, then to have a disfunctional team with the odd language nerd.

I (and some others) once interviewed a guy who had recently started learning Lisp. He wanted to show off and use it on the whiteboard. Not a problem, theoretically - we've had a guy give us Prolog solutions beautifully explained.

He botched it. We laughed and let him retry in C. He solved it successfully - and also more people than myself could read the solution. Since he was a really junior chap, we didn't really have an issue with the botching.

I am OK with someone showing off. But you have to actually make the run successfully, IMO. Personally, if you can write FizzBuzz as a call/cc continuation, more power to you. I really want to see if you can grasp the upper reaches of computational abstraction in our field, i.e., show off. But trying and failing doesn't really win you points, at least with me.

It's only showing off if you think Haskell programmers are better than everyone else ;-).