The
groupBy function is the non-overloaded version of
group.
When a supplied relation is not transitive, it is important to
remember that equality is checked against the first element in the
group, not against the nearest neighbour:
>>> groupBy (\a b -> b - a < 5) [0..19]
[[0,1,2,3,4],[5,6,7,8,9],[10,11,12,13,14],[15,16,17,18,19]]
It's often preferable to use
Data.List.NonEmpty.groupBy, which provides type-level
guarantees of non-emptiness of inner lists.