module Hcompta.Lib.NonEmpty where

import qualified Data.List
-- import qualified Data.List.NonEmpty as NonEmpty
import           Data.List.NonEmpty (NonEmpty(..))
import           Data.Monoid ((<>))


-- | Return the given 'NonEmpty' without its last section if any.
ascending :: NonEmpty x -> Maybe (NonEmpty x)
ascending (_:|[]) = Nothing
ascending (x:|xs) = Just (x:|Data.List.init xs)
{-# INLINE ascending #-}

-- | Return all the prefixes of the given 'NonEmpty' (including itself).
prefixes :: NonEmpty x -> [NonEmpty x]
prefixes (y:|ys) = go y [] ys []
	where
		go :: x -> [x] -> [x] -> [NonEmpty x] -> [NonEmpty x]
		go x0 s []     = (:) (x0:|s)
		go x0 s (x:xs) = go x0 (s <> [x]) xs . (:) (x0:|s)