metabrush/src/metabrushes/MetaBrush/Util.hs

module MetaBrush.Util
  ( traverseMaybe
  , Exists(..)
  )
  where

-- containers
import Data.Sequence
  ( Seq(..) )

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traverseMaybe :: Applicative f => ( a -> f ( Maybe b ) ) -> Seq a -> f ( Seq b )
traverseMaybe _ Empty        = pure Empty
traverseMaybe f ( a :<| as ) = ( \ case { Nothing -> id; Just b -> ( b :<| ) } ) <$> f a <*> traverseMaybe f as

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data Exists c where
  Exists :: c a => a -> Exists c