-- | Extra list functions and list-like types.
module Data.List.Extra where

import Control.DeepSeq (NFData(..))

-- * Regular lists

-- | Check if a list has more than some number of elements.
moreThan :: [a] -> Int -> Bool
moreThan [] n = n < 0
moreThan _ 0  = True
moreThan (_:xs) n = moreThan xs (n-1)

-- * Non-empty lists

-- This gets exposed to users of the library, so it has a bunch of
-- classes which aren't actually used in the rest of the code to make
-- it more friendly to further use.

-- | The type of non-empty lists.
data NonEmpty a = a :| [a] deriving (Eq, Ord, Read, Show)

instance Functor NonEmpty where
  fmap f (a :| as) = f a :| map f as

instance NFData a => NFData (NonEmpty a) where
  rnf (x:|xs) = rnf (x, xs)

-- | Convert a 'NonEmpty' to a regular non-empty list.
toList :: NonEmpty a -> [a]
toList (a :| as) = a : as