1 files changed, 152 insertions, 0 deletions
diff --git a/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Constant.hs b/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Constant.hs
new file mode 100644
index 0000000000..9c0b8d42dc
--- /dev/null
+++ b/third_party/bazel/rules_haskell/examples/transformers/Data/Functor/Constant.hs
@@ -0,0 +1,152 @@
+{-# 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.Constant
+-- Copyright   :  (c) Ross Paterson 2010
+-- License     :  BSD-style (see the file LICENSE)
+--
+-- Maintainer  :  R.Paterson@city.ac.uk
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- The constant functor.
+-----------------------------------------------------------------------------
+
+module Data.Functor.Constant (
+    Constant(..),
+  ) where
+
+import Data.Functor.Classes
+#if MIN_VERSION_base(4,12,0)
+import Data.Functor.Contravariant
+#endif
+
+import Control.Applicative
+import Data.Foldable
+import Data.Monoid (Monoid(..))
+import Data.Traversable (Traversable(traverse))
+#if MIN_VERSION_base(4,8,0)
+import Data.Bifunctor (Bifunctor(..))
+#endif
+#if MIN_VERSION_base(4,9,0)
+import Data.Semigroup (Semigroup(..))
+#endif
+#if MIN_VERSION_base(4,10,0)
+import Data.Bifoldable (Bifoldable(..))
+import Data.Bitraversable (Bitraversable(..))
+#endif
+import Prelude hiding (null, length)
+
+-- | Constant functor.
+newtype Constant a b = Constant { getConstant :: a }
+    deriving (Eq, Ord)
+
+-- These instances would be equivalent to the derived instances of the
+-- newtype if the field were removed.
+
+instance (Read a) => Read (Constant a b) where
+    readsPrec = readsData $
+         readsUnaryWith readsPrec "Constant" Constant
+
+instance (Show a) => Show (Constant a b) where
+    showsPrec d (Constant x) = showsUnaryWith showsPrec "Constant" d x
+
+-- Instances of lifted Prelude classes
+
+instance Eq2 Constant where
+    liftEq2 eq _ (Constant x) (Constant y) = eq x y
+    {-# INLINE liftEq2 #-}
+
+instance Ord2 Constant where
+    liftCompare2 comp _ (Constant x) (Constant y) = comp x y
+    {-# INLINE liftCompare2 #-}
+
+instance Read2 Constant where
+    liftReadsPrec2 rp _ _ _ = readsData $
+         readsUnaryWith rp "Constant" Constant
+
+instance Show2 Constant where
+    liftShowsPrec2 sp _ _ _ d (Constant x) = showsUnaryWith sp "Constant" d x
+
+instance (Eq a) => Eq1 (Constant a) where
+    liftEq = liftEq2 (==)
+    {-# INLINE liftEq #-}
+instance (Ord a) => Ord1 (Constant a) where
+    liftCompare = liftCompare2 compare
+    {-# INLINE liftCompare #-}
+instance (Read a) => Read1 (Constant a) where
+    liftReadsPrec = liftReadsPrec2 readsPrec readList
+    {-# INLINE liftReadsPrec #-}
+instance (Show a) => Show1 (Constant a) where
+    liftShowsPrec = liftShowsPrec2 showsPrec showList
+    {-# INLINE liftShowsPrec #-}
+
+instance Functor (Constant a) where
+    fmap _ (Constant x) = Constant x
+    {-# INLINE fmap #-}
+
+instance Foldable (Constant a) where
+    foldMap _ (Constant _) = mempty
+    {-# INLINE foldMap #-}
+#if MIN_VERSION_base(4,8,0)
+    null (Constant _) = True
+    length (Constant _) = 0
+#endif
+
+instance Traversable (Constant a) where
+    traverse _ (Constant x) = pure (Constant x)
+    {-# INLINE traverse #-}
+
+#if MIN_VERSION_base(4,9,0)
+instance (Semigroup a) => Semigroup (Constant a b) where
+    Constant x <> Constant y = Constant (x <> y)
+    {-# INLINE (<>) #-}
+#endif
+
+instance (Monoid a) => Applicative (Constant a) where
+    pure _ = Constant mempty
+    {-# INLINE pure #-}
+    Constant x <*> Constant y = Constant (x `mappend` y)
+    {-# INLINE (<*>) #-}
+
+instance (Monoid a) => Monoid (Constant a b) where
+    mempty = Constant mempty
+    {-# INLINE mempty #-}
+#if !MIN_VERSION_base(4,11,0)
+    -- From base-4.11, Monoid(mappend) defaults to Semigroup((<>))
+    Constant x `mappend` Constant y = Constant (x `mappend` y)
+    {-# INLINE mappend #-}
+#endif
+
+#if MIN_VERSION_base(4,8,0)
+instance Bifunctor Constant where
+    first f (Constant x) = Constant (f x)
+    {-# INLINE first #-}
+    second _ (Constant x) = Constant x
+    {-# INLINE second #-}
+#endif
+
+#if MIN_VERSION_base(4,10,0)
+instance Bifoldable Constant where
+    bifoldMap f _ (Constant a) = f a
+    {-# INLINE bifoldMap #-}
+
+instance Bitraversable Constant where
+    bitraverse f _ (Constant a) = Constant <$> f a
+    {-# INLINE bitraverse #-}
+#endif
+
+#if MIN_VERSION_base(4,12,0)
+instance Contravariant (Constant a) where
+    contramap _ (Constant a) = Constant a
+    {-# INLINE contramap #-}
+#endif