Why is `unescapeBytea` in IO?

[ysangkok]

This function seems pure to me, aside from the allocation that it does. But Haskell allocates in many places, and we still call those functions pure. I don't understand why unescapeBytea must be in IO? What kind of side effects can it perform?

[phadej]

But Haskell allocates in many places, and we still call those functions pure.

Sure, bytestring is littered with unsafePerformIOs.

But, there aren't a single unsafePerformIO in postgresql-libpq, so the bar of introducing the first one is extremely high.