yihong0618 和朋友们的牛逼频道

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]

TIL:
Link: <a href="https://github.com/thoughtbot/til/blob/main/haskell/sorting-in-reverse-order.md">https://github.com/thoughtbot/til/blob/main/haskell/sorting-in-reverse-order.md</a>
<b>📌 Sorting in reverse order</b>

<code>Data.Ord</code> contains a newtype, <code>Down</code>, which can wrap any type that has an
<code>Ord</code> instance, in order to provide a reversed <code>Ord</code> instance for that type.

For example:

<pre><code>Prelude&gt; import Data.Ord (Down(..))
Prelude Data.Ord&gt; :info Down
newtype Down a = Down a         -- Defined in ‘Data.Ord’
instance Ord a =&gt; Ord (Down a)  -- Defined in ‘Data.Ord’
Prelude Data.Ord&gt; Down 3 &gt; Down 4
True
</code></pre>

This can be very convenient for reversing sort order:

<pre><code>Prelude&gt; import Data.Ord (Down(..), comparing)
Prelude Data.Ord&gt; import Data.List (sortBy)
Prelude Data.Ord Data.List&gt; sortBy (comparing Down) [1..10]
[10,9,8,7,6,5,4,3,2,1]</code></pre>