Some time ago (before ghc 6.6 / base 2.0 release), I introduced minView and maxView in Data.Set and Data.Map (at a user's request). I agreed with Robert Dockins to implement the same functionality as in his version of the Edison library. Unfortunately, I uselessly swapped the return values of minView and maxView, introducing a difference both with the corresponding functions in the edison library and similar functions in Data.Map/Set. I propose to restore the symmetry, at the cost of incompatibility. The incompatibility is probably acceptable because the functions are still short-lived. See the trac ticket for details. http://hackage.haskell.org/trac/ghc/ticket/1134 I provide no patch nor QuickCheck properties because of the triviality of the change. Cheers, JP.