lib/Hcompta/Lib/NonEmpty.hs

   1 module Hcompta.Lib.NonEmpty where
   2
   3 import           Data.Function ((.))
   4 import qualified Data.List
   5 import           Data.List.NonEmpty (NonEmpty(..))
   6 import           Data.Maybe (Maybe(..))
   7 import           Data.Monoid (Monoid(..))
   8
   9 -- | Return the given 'NonEmpty' without its last section if any.
  10 parent :: NonEmpty x -> Maybe (NonEmpty x)
  11 parent (_:|[]) = Nothing
  12 parent (x:|xs) = Just (x:|Data.List.init xs)
  13
  14 -- | Return all the ancestors (i.e. prefixes)
  15 -- of the given 'NonEmpty' (including itself).
  16 ancestors_or_self :: NonEmpty x -> [NonEmpty x]
  17 ancestors_or_self (y:|ys) = go y [] ys []
  18         where
  19                 go :: x -> [x] -> [x] -> [NonEmpty x] -> [NonEmpty x]
  20                 go x0 s []     = (:) (x0:|s)
  21                 go x0 s (x:xs) = go x0 (s `mappend` [x]) xs . (:) (x0:|s)