Created
January 31, 2013 12:45
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combine two Sinks
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import Data.Conduit | |
import Data.Conduit.Internal | |
import Data.Void (Void, absurd) | |
import qualified Data.Conduit.List as CL | |
import Control.Monad (zipWithM_) | |
import Control.Monad.Trans.Class (lift) | |
combine :: Monad m | |
=> Sink i1 m r1 | |
-> Sink i2 m r2 | |
-> Sink (Either i1 i2) m (r1, r2) | |
combine s1' s2' = | |
go (injectLeftovers s1') (injectLeftovers s2') | |
where | |
go :: Monad m | |
=> Pipe Void i1 Void () m r1 | |
-> Pipe Void i2 Void () m r2 | |
-> Pipe l (Either i1 i2) Void () m (r1, r2) | |
go (HaveOutput _ _ o) _ = absurd o | |
go _ (HaveOutput _ _ o) = absurd o | |
go (Leftover _ l) _ = absurd l | |
go _ (Leftover _ l) = absurd l | |
go (Done r1) s2 = do | |
r2 <- lift $ runPipe $ return () >+> s2 | |
return (r1, r2) | |
go s1 (Done r2) = do | |
r1 <- lift $ runPipe $ return () >+> s1 | |
return (r1, r2) | |
go (PipeM m1) s2 = do | |
s1 <- lift m1 | |
go s1 s2 | |
go s1 (PipeM m2) = do | |
s2 <- lift m2 | |
go s1 s2 | |
go (NeedInput p1 c1) (NeedInput p2 c2) = | |
NeedInput p c | |
where | |
p (Left i1) = go (p1 i1) (NeedInput p2 c2) | |
p (Right i2) = go (NeedInput p1 c1) (p2 i2) | |
c () = go (c1 ()) (c2 ()) | |
source :: Monad m => Source m (Either Char Int) | |
source = | |
zipWithM_ go "hello world" [1..] | |
where | |
go x y = yield (Left x) >> yield (Right y) | |
sink :: Monad m => Sink (Either Char Int) m (String, Int) | |
sink = combine CL.consume (CL.fold (+) 0) | |
main :: IO () | |
main = (source $$ sink) >>= print |
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