"Simon Peyton-Jones"
Christian posted a bug to Sourceforge concerning the IntMap library, function split.
Can anyone shed any light? Better still, fix it?
I consider the best approach for a bug like this is to use QuickCheck to find a small failing case, then Hat to discover the cause of the failure. The first part was easy, but unfortunately the library Data.IntMap does not yet have a traced version within Hat. So, I have a clearer formulation of the problem, but no solution yet. In the meantime,
"keys $ split 5 $ theMap" sometimes returns values greater 5.
I think you probably mean keys $ fst $ split 5 $ theMap And a failing case is the map {0:=1,1:=0,2:=0,3:=1,6:=-1,7:=0,8:=-2,9:=-2} which you can generate with e.g. theMap = (insert 0 1 . insert 1 0 . insert 2 0 . insert 3 1 . insert 6 (-1) . insert 7 0 . insert 8 (-2) . insert 8 (-2)) empty The result of split 5 myMap is ({0:=1,1:=0,2:=0,3:=1,6:=-1}, {7:=0,8:=-2}) where clearly the mapping for 6 is in the wrong half of the result. Regards, Malcolm