dunai: should Haskell's Prelude be imported by default?

[ivanperez-keera]

This issue is an attempt at starting a discussion about whether we should import Haskell's Prelude by default.

A lot of the issues that we've had over the years in terms of backwards compatibility have had to do with conditional imports of elements from the Prelude based on the version of base/GHC we were working with. Given how Haskell's prelude changes, I would expect similar issues in the future.

I've just ran a little experiment where I've disabled the Prelude, and use of CPP to select imports conditionally has been reduced to 1 place and could be completely eliminated. It builds correctly with all GHC versions (see build log here). Most modules do not import anything from the prelude, and the only ones I've left are those in which the imports would come otherwise from modules in the GHC.* hierarchy, which IMO is not where they should be if those entities are defined in the Haskell report:

$ grep -nHre 'Prelude' dunai/src/
dunai/src/Control/Monad/Trans/MSF/List.hs:32:import Prelude                  (seq)
dunai/src/Control/Monad/Trans/MSF/Except.hs:38:import           Prelude                    (error)
dunai/src/Data/MonadicStreamFunction/InternalCore.hs:51:import Prelude          (seq)
dunai/src/Data/MonadicStreamFunction/Util.hs:22:import Prelude          (Num, (+))
dunai/src/Data/MonadicStreamFunction/Instances/Num.hs:31:import Prelude       (Floating (..), Fractional (..), Num (..))

The branch with that experimental work will be for now at:
https://github.com/ivanperez-keera/dunai/tree/develop-no-implicit-prelude