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Fix space leak in Shells #381

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merged 1 commit into from
Mar 29, 2020
Merged

Fix space leak in Shells #381

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17 changes: 10 additions & 7 deletions src/Turtle/Shell.hs
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}
Expand Down Expand Up @@ -101,21 +102,23 @@ data FoldShell a b = forall x . FoldShell (x -> a -> IO x) x (x -> IO b)
-- | A @(Shell a)@ is a protected stream of @a@'s with side effects
newtype Shell a = Shell { _foldShell:: forall r . FoldShell a r -> IO r }

data Maybe' a = Just' !a | Nothing'

translate :: FoldM IO a b -> FoldShell a b
translate (FoldM step begin done) = FoldShell step' Nothing done'
translate (FoldM step begin done) = FoldShell step' Nothing' done'
where
step' Nothing a = do
step' Nothing' a = do
x <- begin
x' <- step x a
return (Just x')
step' (Just x) a = do
return $! Just' x'
step' (Just' x) a = do
x' <- step x a
return (Just x')
return $! Just' x'

done' Nothing = do
done' Nothing' = do
x <- begin
done x
done' (Just x) = do
done' (Just' x) = do
done x

-- | Use a @`FoldM` `IO`@ to reduce the stream of @a@'s produced by a `Shell`
Expand Down