Unique.hs

module HAHP.Validation.Unique where

--import           Data.List.Unique
import           Data.List (group, sort, sortBy)

-- * Unique

-- TO REMOVE
-- https://hackage.haskell.org/package/Unique-0.4.2/docs/src/Data-List-Unique.html#repeated

sg :: Ord a => [a] -> [[a]]
sg = group . sort

filterByLength :: Ord a => (Int -> Bool) -> [a] -> [[a]]
filterByLength p = filter (p . length) . sg

-- | 'repeated' finds only the elements that are present more than once in the list. Example:
--
-- > repeated  "foo bar" == "o"

repeated :: Ord a => [a] -> [a]
repeated = repeatedBy (>1)

-- | The repeatedBy function behaves just like repeated, except it uses a user-supplied equality predicate.
--
-- > repeatedBy (>2) "This is the test line" == " eist"

repeatedBy :: Ord a => (Int -> Bool) -> [a] -> [a]
repeatedBy p = map head . filterByLength p