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.
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.