I had a leader once who told us outright any mention that Haskell was a motivation for the job is a red flag. It was a Haskel codebase. Turns out we failed to hire basically anyone (most were all yes but a single no from the leader) and then the leader pushed us to move off Haskell citing difficulty hiring and that he had hired people in another office who didn't know or want to learn Haskell. Dirty tactics.