Twan van Laarhoven wrote:

Hello list,

Almost all uses of sortBy in user code use 'comparing', 'on' or a similar construction [1]. I think we should add a function that makes this common behavior more convenient:

sortOn :: Ord b => (a -> b) -> [a] -> [a]

For consistency we should also add *On for the other *By functions in Data.List:

nubOn :: Eq b => (a -> b) -> [a] -> [a] deleteOn :: Eq b => (a -> b) -> a -> [a] -> [a] deleteFirstsOn :: Eq b => (a -> b) -> [a] -> [a] -> [a] unionOn :: Eq b => (a -> b) -> [a] -> [a] -> [a] intersectOn :: Eq b => (a -> b) -> [a] -> [a] -> [a] groupOn :: Eq b => (a -> b) -> [a] -> [[a]] sortOn :: Ord b => (a -> b) -> [a] -> [a] insertOn :: Ord b => (a -> b) -> a -> [a] -> [a] maximumOn :: Ord b => (a -> b) -> [a] -> a minimumOn :: Ord b => (a -> b) -> [a] -> a (nubSortOn :: Ord b => (a -> b) -> [a] -> [a]) -- see #2629

Too many functions, and too little added functionality, IMHO.

newtype Down a = Down { getDown :: a }

I like this one. Bertram