`on` runs a binary function by first running a unary function on each argument. Prelude> import Data.Function (on) Prelude Data.Function> :t on on :: (b

`on` runs a binary function by first running a unary function on each argument. Prelude> import Data.Function (on) Prelude Data.Function> :t on on :: (b -> b -> c) -> (a -> b) -> a -> a -> c Prelude Data.Function> f = undefined :: Int -> [Int] Prelude Data.Function> g = undefined :: Int -> [Int] Prelude Data.Function> :t ((&&) `on` (not . null . ($ x))) f g ((&&) `on` (not . null . ($ x))) f g :: Bool Alternatively in Control.Arrow there's a 'fanout' operator &&&: Prelude Control.Arrow> f = undefined :: Int -> Bool Prelude Control.Arrow> g = undefined :: Int -> Bool Prelude Control.Arrow> :t uncurry (&&) . (f &&& g) uncurry (&&) . (f &&& g) :: Int -> Bool Of course it's still probably simpler to just write it out in this case.