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