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TODO
Local.hs
{- This file is part of Vervis.
-
- Written in 2016, 2019 by fr33domlover <fr33domlover@riseup.net>.
-
- ♡ Copying is an act of love. Please copy, reuse and share.
-
- The author(s) have dedicated all copyright and related and neighboring
- rights to this software to the public domain worldwide. This software is
- distributed without any warranty.
-
- You should have received a copy of the CC0 Public Domain Dedication along
- with this software. If not, see
- <http://creativecommons.org/publicdomain/zero/1.0/>.
-}
module Data.Either.Local
( maybeRight
, maybeLeft
, requireEither
, requireEitherM
, requireEitherAlt
)
where
import Control.Applicative
import Control.Exception
import Control.Monad.IO.Class
maybeRight :: Either a b -> Maybe b
maybeRight (Left _) = Nothing
maybeRight (Right b) = Just b
maybeLeft :: Either a b -> Maybe a
maybeLeft (Left a) = Just a
maybeLeft (Right _) = Nothing
requireEither :: Maybe a -> Maybe b -> Either Bool (Either a b)
requireEither Nothing Nothing = Left False
requireEither (Just _) (Just _) = Left True
requireEither (Just x) Nothing = Right $ Left x
requireEither Nothing (Just y) = Right $ Right y
requireEitherM
:: MonadIO m => Maybe a -> Maybe b -> String -> String -> m (Either a b)
requireEitherM mx my f t =
case requireEither mx my of
Left b -> liftIO $ throwIO $ userError $ if b then t else f
Right exy -> return exy
requireEitherAlt
:: Applicative f
=> f (Maybe a) -> f (Maybe b) -> String -> String -> f (Either a b)
requireEitherAlt get1 get2 errNone errBoth = liftA2 mk get1 get2
where
mk Nothing Nothing = error errNone
mk (Just _) (Just _) = error errBoth
mk (Just x) Nothing = Left x
mk Nothing (Just y) = Right y
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