On Fri, 29 May 2020, Zemyla wrote:
I am opposed to all the hate on Foldable ((,) a).
It's not about hate, but in _my_ code using an instance like Foldable ((,) a) or Functor ((,) a) or Traversable ((,) a) is a bug, because I would not use it by intention. That's why I want at least a warning, where there was a type error before GHC-7.10. In my code I would define a custom data type data Decorated a b = Decorated a b instead of generic pair or I would use Writer monad, if that's appropriate.
It's a failure of expectations more than anything else, and I really don't think anyone beyond beginner level is routinely running into bugs because they tried to use length or toList on a tuple.
You can also call it a beginner's problem to use tuples everywhere, where custom data types would be the better choice.