TIL:
Link: https://github.com/thoughtbot/til/blob/main/haskell/sorting-in-reverse-order.md
📌 Sorting in reverse order
Data.Ord contains a newtype, Down, which can wrap any type that has an
Ord instance, in order to provide a reversed Ord instance for that type.
For example:
Prelude> import Data.Ord (Down(..))
Prelude Data.Ord> :info Down
newtype Down a = Down a -- Defined in ‘Data.Ord’
instance Ord a => Ord (Down a) -- Defined in ‘Data.Ord’
Prelude Data.Ord> Down 3 > Down 4
True
This can be very convenient for reversing sort order:
Prelude> import Data.Ord (Down(..), comparing)
Prelude Data.Ord> import Data.List (sortBy)
Prelude Data.Ord Data.List> sortBy (comparing Down) [1..10]
[10,9,8,7,6,5,4,3,2,1]
Link: https://github.com/thoughtbot/til/blob/main/haskell/sorting-in-reverse-order.md
📌 Sorting in reverse order
Data.Ord contains a newtype, Down, which can wrap any type that has an
Ord instance, in order to provide a reversed Ord instance for that type.
For example:
Prelude> import Data.Ord (Down(..))
Prelude Data.Ord> :info Down
newtype Down a = Down a -- Defined in ‘Data.Ord’
instance Ord a => Ord (Down a) -- Defined in ‘Data.Ord’
Prelude Data.Ord> Down 3 > Down 4
True
This can be very convenient for reversing sort order:
Prelude> import Data.Ord (Down(..), comparing)
Prelude Data.Ord> import Data.List (sortBy)
Prelude Data.Ord Data.List> sortBy (comparing Down) [1..10]
[10,9,8,7,6,5,4,3,2,1]