"1) Production code should be understandable by an on-call person at 4 am. If business logic is buried under layers of lenses, monad transformers and arrows, good luck troubleshooting it under stress. And real systems do break, no matter type safety."

Let's assume that your on call person is a developer. (If the person is not a developer, (s)he is not going to comprehend any language.)

1) If your application is written in Haskell, the on call developer would more than likely have been involved in the code base and reads Haskell. Your assertion about not comprehending it seems suspect.

2) You have a serious process issue if a developer is woken from a sound sleep to track down, correct, thoroughly test, and promote a fix for the bug in the middle of the night. The number of cases in which this happens should be close enough to zero to call it zero.

Your comment sounds like an attempt to cast Haskell as a purely academic language because it fails a (poorly) made up real world scenario. I'm NOT a Haskell-er so I don't feel a need to defend it. I do find the reasoning behind the criticism poorly thought out.