GitLab

Add a"same" function to Data.Eq that parallels the "comparing" function in Data.Ord. For example:

-- | 
-- > same p x y = (p x) == (p y)
--
-- Useful combinator for use in conjunction with the @xxxBy@ family
-- of functions from "Data.List", for example:
--
-- >   ... groupBy (same fst) ...
same :: (Eq a) => (b -> a) -> b -> b -> Bool
same p x y = (p x) == (p y)

For a closer parallel, I suppose "same" could return "Equality" (similar to "Ordering"), and the functions "nubBy", "deleteBy", "deleteFirstsBy", "unionBy", "intersectBy" and "groupBy" should take (a -> a -> Equality) (a -> a -> Bool). But I don't know if there's any benefit to that.