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Merged
merged 3 commits into from
Mar 30, 2017
Merged

stack-safe foldl #93

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8d23c17
stack-safe foldl
matthewleon Mar 27, 2017
9819cc5
name TCOd foldl fodlRec
matthewleon Mar 28, 2017
d0b3f11
add stack-safe foldl'
matthewleon Mar 28, 2017
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stack-safe foldl
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@matthewleon
matthewleon committed Mar 29, 2017
commit 8d23c1773bd3cd4a403fd00044885f03da71a08e
15 changes: 9 additions & 6 deletions src/Control/Monad/List/Trans.purs
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Expand Up @@ -39,6 +39,7 @@ import Control.Alternative (class Alternative)
import Control.Monad.Eff.Class (class MonadEff, liftEff)
import Control.Monad.Trans.Class (class MonadTrans, lift)
import Control.MonadPlus (class MonadPlus)
import Control.Monad.Rec.Class as MR
import Control.MonadZero (class MonadZero)
import Control.Plus (class Plus)

Expand Down Expand Up @@ -204,12 +205,14 @@ foldl' f = loop where
g (Just (Tuple a as)) = (f b a) >>= (flip loop as)

-- | Fold a list from the left, accumulating the result using the specified function.
foldl :: forall f a b. Monad f => (b -> a -> b) -> b -> ListT f a -> f b
foldl f = loop where
loop b l = uncons l >>= g
where
g Nothing = pure b
g (Just (Tuple a as)) = loop (f b a) as
foldl :: forall f a b. MR.MonadRec f => (b -> a -> b) -> b -> ListT f a -> f b
foldl f b l = (MR.tailRecM2 loop) b l
where
loop :: b -> ListT f a -> f (MR.Step {a :: b, b :: ListT f a} b)
loop accum l' = uncons l' >>= g
where
g Nothing = pure (MR.Done accum)
g (Just (Tuple a as)) = pure (MR.Loop {a: f accum a, b: as})

-- | Fold a list from the left, accumulating the list of results using the specified function.
scanl :: forall f a b. Monad f => (b -> a -> b) -> b -> ListT f a -> ListT f b
Expand Down