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21 lines
571 B
Haskell
21 lines
571 B
Haskell
module MetaBrush.Util
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( traverseMaybe
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, Exists(..)
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)
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where
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-- containers
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import Data.Sequence
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( Seq(..) )
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--------------------------------------------------------------------------------
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traverseMaybe :: Applicative f => ( a -> f ( Maybe b ) ) -> Seq a -> f ( Seq b )
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traverseMaybe _ Empty = pure Empty
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traverseMaybe f ( a :<| as ) = ( \ case { Nothing -> id; Just b -> ( b :<| ) } ) <$> f a <*> traverseMaybe f as
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--------------------------------------------------------------------------------
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data Exists c where
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Exists :: c a => a -> Exists c
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