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bundled/Basement/Compat/Identity.hs

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+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE RebindableSyntax #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+-- |
+-- Module      : Basement.Compat.Identity
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : experimental
+-- Portability : portable
+--
+-- Identity re-export, with a compat wrapper for older version of base that
+-- do not have Data.Functor.Identity
+{-# LANGUAGE CPP #-}
+module Basement.Compat.Identity
+    ( Identity(..)
+    ) where
+
+#if MIN_VERSION_base(4,8,0)
+
+import Data.Functor.Identity
+
+#else
+
+import Basement.Compat.Base
+
+newtype Identity a = Identity { runIdentity :: a }
+    deriving (Eq, Ord)
+
+instance Functor Identity where
+    fmap f (Identity a) = Identity (f a)
+
+instance Applicative Identity where
+    pure a = Identity a
+    (<*>) fab fa = Identity $ runIdentity fab (runIdentity fa)
+
+instance Monad Identity where
+    return    = pure
+    ma >>= mb = mb (runIdentity ma)
+
+#endif