extensible-effects-concurrent-0.7.2: src/Control/Eff/ExceptionExtra.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE MonoLocalBinds #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
-- | Add-ons to 'Control.Eff.Exception' and 'Control.Excepion'
module Control.Eff.ExceptionExtra
  ( liftTry
  , maybeThrow
  , module X
  )
where

import qualified Control.Exception             as Exc
import           Control.Eff
import           Control.Eff.Lift
import           Control.Eff.Exception         as X
import           GHC.Stack

-- | Catch 'Exc.Exception' thrown by an effect.
liftTry
  :: forall e r a
   . (HasCallStack, Exc.Exception e, SetMember Lift (Lift IO) r)
  => Eff r a
  -> Eff r (Either e a)
liftTry m = (Right <$> m) `catchDynE` (return . Left)


-- | Very similar to 'X.liftEither' but for 'Maybe's. Unlike 'X.liftMaybe' this
-- will throw the given value (instead of using 'X.Fail').
maybeThrow :: Member (X.Exc x) e => x -> Maybe a -> Eff e a
maybeThrow x = X.liftEither . maybe (Left x) Right