44 lines
767 B
Haskell
44 lines
767 B
Haskell
module Lets.Lens.Choice
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(
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Choice(..)
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) where
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import Lets.Data
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import Lets.Lens.Profunctor
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diswap ::
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Profunctor p =>
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p (Either a b) (Either c d)
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-> p (Either b a) (Either d c)
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diswap =
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let swap = either Right Left
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in dimap swap swap
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-- | Map on left or right of @Either@. Only one of @left@ or @right@ needs to be
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-- provided.
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class Profunctor p => Choice p where
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left ::
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p a b
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-> p (Either a c) (Either b c)
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left =
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diswap . right
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right ::
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p a b
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-> p (Either c a) (Either c b)
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right =
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diswap . left
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instance Choice (->) where
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left f =
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either (Left . f) Right
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right f =
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either Left (Right . f)
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instance Choice Tagged where
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left (Tagged x) =
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Tagged (Left x)
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right (Tagged x) =
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Tagged (Right x)
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