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Data.Conduit.Error
-- | Conduit piping with error handling.
module Data.Conduit.Error where
import Data.Conduit.Internal
infixr 2 .|?
(.|?) :: Monad m => ConduitT a b m (Either e ()) -> ConduitT b c m (Either e r) -> ConduitT a c m (Either e r)
ConduitT left0 .|? ConduitT right0 =
ConduitT $ \rest ->
let goRight left right =
case right of
HaveOutput p o -> HaveOutput (recurse p) o
NeedInput rp rc -> goLeft rp rc left
Done r2 -> rest r2
PipeM mp -> PipeM (fmap recurse mp)
Leftover right' i -> goRight (HaveOutput left i) right'
where
recurse = goRight left
goLeft rp rc left =
case left of
HaveOutput left' o -> goRight left' (rp o)
NeedInput left' lc -> NeedInput (recurse . left') (recurse . lc)
Done r1 ->
-- Extra step add-on to normal conduit.
case r1 of
Left e -> rest (Left e)
Right r1' -> goRight (Done (pure r1')) (rc r1')
PipeM mp -> PipeM (fmap recurse mp)
Leftover left' i -> Leftover (recurse left') i
where
recurse = goLeft rp rc
in goRight (left0 Done) (right0 Done)
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