Cardinality-0.1: Data/NeverEmptyList.hs

{-
Copyright (C) 2010 Andrejs Sisojevs <andrejs.sisojevs@nextmail.ru>

All rights reserved.

For license and copyright information, see the file COPYRIGHT

-}

--------------------------------------------------------------------------
--------------------------------------------------------------------------

module Data.NeverEmptyList where

data NeverEmptyList a = NEL a [a]

-- | @neverEmptyList2List (NEL h t) = h:t@
nel2List :: NeverEmptyList a -> [a]
nel2List (NEL h t) = h:t

-- | @list2NeverEmptyList [] = Nothing@
--
--   @list2NeverEmptyList (h:t) = Just (NEL h t)@
list2nel :: [a] -> Maybe (NeverEmptyList a)
list2nel [] = Nothing
list2nel (h:t) = Just (NEL h t)

nelSingleton :: a -> NeverEmptyList a
nelSingleton a = NEL a []