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bundled/Basement/These.hs

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+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE RebindableSyntax #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+-- |
+-- Module      : Basement.These
+-- License     : BSD-style
+-- Maintainer  : Nicolas Di Prima <nicolas@primetype.co.uk>
+-- Stability   : stable
+-- Portability : portable
+--
+-- @These a b@, sum type to represent either @a@ or @b@ or both.
+--
+module Basement.These
+    ( These(..)
+    ) where
+
+import Basement.Compat.Base
+import Basement.NormalForm
+
+-- | Either a or b or both.
+data These a b
+    = This a
+    | That b
+    | These a b
+  deriving (Eq, Ord, Show, Typeable)
+
+instance (NormalForm a, NormalForm b) => NormalForm (These a b) where
+    toNormalForm (This a) = toNormalForm a
+    toNormalForm (That b) = toNormalForm b
+    toNormalForm (These a b) = toNormalForm a `seq` toNormalForm b