Cabal/src/Distribution/Compat/SnocList.hs

   1 -----------------------------------------------------------------------------
   2
   3 -- |
   4 -- Module      :  Distribution.Compat.SnocList
   5 -- License     :  BSD3
   6 --
   7 -- Maintainer  :  cabal-dev@haskell.org
   8 -- Stability   :  experimental
   9 -- Portability :  portable
  10 --
  11 -- A very reversed list. Has efficient `snoc`
  12 module Distribution.Compat.SnocList
  13   ( SnocList
  14   , runSnocList
  15   , snoc
  16   ) where
  17
  18 import Distribution.Compat.Prelude
  19 import Prelude ()
  20
  21 newtype SnocList a = SnocList [a]
  22
  23 snoc :: SnocList a -> a -> SnocList a
  24 snoc (SnocList xs) x = SnocList (x : xs)
  25
  26 runSnocList :: SnocList a -> [a]
  27 runSnocList (SnocList xs) = reverse xs
  28
  29 instance Semigroup (SnocList a) where
  30   SnocList xs <> SnocList ys = SnocList (ys <> xs)
  31
  32 instance Monoid (SnocList a) where
  33   mempty = SnocList []
  34   mappend = (<>)