1 files changed, 143 insertions, 0 deletions
diff --git a/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Reverse.hs b/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Reverse.hs
new file mode 100644
index 0000000000..5d8c41fa15
--- /dev/null
+++ b/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Reverse.hs
@@ -0,0 +1,143 @@
+{-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__ >= 702
+{-# LANGUAGE Safe #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 706
+{-# LANGUAGE PolyKinds #-}
+#endif
+#if __GLASGOW_HASKELL__ >= 710
+{-# LANGUAGE AutoDeriveTypeable #-}
+#endif
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Data.Functor.Reverse
+-- Copyright   :  (c) Russell O'Connor 2009
+-- License     :  BSD-style (see the file LICENSE)
+--
+-- Maintainer  :  R.Paterson@city.ac.uk
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Making functors whose elements are notionally in the reverse order
+-- from the original functor.
+-----------------------------------------------------------------------------
+
+module Data.Functor.Reverse (
+    Reverse(..),
+  ) where
+
+import Control.Applicative.Backwards
+import Data.Functor.Classes
+#if MIN_VERSION_base(4,12,0)
+import Data.Functor.Contravariant
+#endif
+
+import Prelude hiding (foldr, foldr1, foldl, foldl1, null, length)
+import Control.Applicative
+import Control.Monad
+#if MIN_VERSION_base(4,9,0)
+import qualified Control.Monad.Fail as Fail
+#endif
+import Data.Foldable
+import Data.Traversable
+import Data.Monoid
+
+-- | The same functor, but with 'Foldable' and 'Traversable' instances
+-- that process the elements in the reverse order.
+newtype Reverse f a = Reverse { getReverse :: f a }
+
+instance (Eq1 f) => Eq1 (Reverse f) where
+    liftEq eq (Reverse x) (Reverse y) = liftEq eq x y
+    {-# INLINE liftEq #-}
+
+instance (Ord1 f) => Ord1 (Reverse f) where
+    liftCompare comp (Reverse x) (Reverse y) = liftCompare comp x y
+    {-# INLINE liftCompare #-}
+
+instance (Read1 f) => Read1 (Reverse f) where
+    liftReadsPrec rp rl = readsData $
+        readsUnaryWith (liftReadsPrec rp rl) "Reverse" Reverse
+
+instance (Show1 f) => Show1 (Reverse f) where
+    liftShowsPrec sp sl d (Reverse x) =
+        showsUnaryWith (liftShowsPrec sp sl) "Reverse" d x
+
+instance (Eq1 f, Eq a) => Eq (Reverse f a) where (==) = eq1
+instance (Ord1 f, Ord a) => Ord (Reverse f a) where compare = compare1
+instance (Read1 f, Read a) => Read (Reverse f a) where readsPrec = readsPrec1
+instance (Show1 f, Show a) => Show (Reverse f a) where showsPrec = showsPrec1
+
+-- | Derived instance.
+instance (Functor f) => Functor (Reverse f) where
+    fmap f (Reverse a) = Reverse (fmap f a)
+    {-# INLINE fmap #-}
+
+-- | Derived instance.
+instance (Applicative f) => Applicative (Reverse f) where
+    pure a = Reverse (pure a)
+    {-# INLINE pure #-}
+    Reverse f <*> Reverse a = Reverse (f <*> a)
+    {-# INLINE (<*>) #-}
+
+-- | Derived instance.
+instance (Alternative f) => Alternative (Reverse f) where
+    empty = Reverse empty
+    {-# INLINE empty #-}
+    Reverse x <|> Reverse y = Reverse (x <|> y)
+    {-# INLINE (<|>) #-}
+
+-- | Derived instance.
+instance (Monad m) => Monad (Reverse m) where
+#if !(MIN_VERSION_base(4,8,0))
+    return a = Reverse (return a)
+    {-# INLINE return #-}
+#endif
+    m >>= f = Reverse (getReverse m >>= getReverse . f)
+    {-# INLINE (>>=) #-}
+#if !(MIN_VERSION_base(4,13,0))
+    fail msg = Reverse (fail msg)
+    {-# INLINE fail #-}
+#endif
+
+#if MIN_VERSION_base(4,9,0)
+instance (Fail.MonadFail m) => Fail.MonadFail (Reverse m) where
+    fail msg = Reverse (Fail.fail msg)
+    {-# INLINE fail #-}
+#endif
+
+-- | Derived instance.
+instance (MonadPlus m) => MonadPlus (Reverse m) where
+    mzero = Reverse mzero
+    {-# INLINE mzero #-}
+    Reverse x `mplus` Reverse y = Reverse (x `mplus` y)
+    {-# INLINE mplus #-}
+
+-- | Fold from right to left.
+instance (Foldable f) => Foldable (Reverse f) where
+    foldMap f (Reverse t) = getDual (foldMap (Dual . f) t)
+    {-# INLINE foldMap #-}
+    foldr f z (Reverse t) = foldl (flip f) z t
+    {-# INLINE foldr #-}
+    foldl f z (Reverse t) = foldr (flip f) z t
+    {-# INLINE foldl #-}
+    foldr1 f (Reverse t) = foldl1 (flip f) t
+    {-# INLINE foldr1 #-}
+    foldl1 f (Reverse t) = foldr1 (flip f) t
+    {-# INLINE foldl1 #-}
+#if MIN_VERSION_base(4,8,0)
+    null (Reverse t) = null t
+    length (Reverse t) = length t
+#endif
+
+-- | Traverse from right to left.
+instance (Traversable f) => Traversable (Reverse f) where
+    traverse f (Reverse t) =
+        fmap Reverse . forwards $ traverse (Backwards . f) t
+    {-# INLINE traverse #-}
+
+#if MIN_VERSION_base(4,12,0)
+-- | Derived instance.
+instance Contravariant f => Contravariant (Reverse f) where
+    contramap f = Reverse . contramap f . getReverse
+    {-# INLINE contramap #-}
+#endif