Skip to content

stack-safe foldl #93

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Mar 30, 2017
Merged

stack-safe foldl #93

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
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
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 22 additions & 0 deletions src/Control/Monad/List/Trans.purs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,9 @@ module Control.Monad.List.Trans
, dropWhile
, filter
, foldl
, foldlRec
, foldl'
, foldlRec'
, fromEffect
, head
, iterate
Expand Down Expand Up @@ -39,6 +41,7 @@ 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 @@ -203,6 +206,15 @@ foldl' f = loop where
g Nothing = pure b
g (Just (Tuple a as)) = (f b a) >>= (flip loop as)

-- | Fold a list from the left, accumulating the result (effectfully) using the specified function.
-- | Uses tail call optimization.
foldlRec' :: forall f a b. MR.MonadRec f => (b -> a -> f b) -> b -> ListT f a -> f b
foldlRec' f = MR.tailRecM2 loop where
loop b l = uncons l >>= g
where
g Nothing = pure (MR.Done b)
g (Just (Tuple a as)) = (f b a) >>= \b' -> pure (MR.Loop {a: b', b: 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
Expand All @@ -211,6 +223,16 @@ foldl f = loop where
g Nothing = pure b
g (Just (Tuple a as)) = loop (f b a) as

-- | Fold a list from the left, accumulating the result using the specified function.
-- | Uses tail call optimization.
foldlRec :: forall f a b. MR.MonadRec f => (b -> a -> b) -> b -> ListT f a -> f b
foldlRec f = MR.tailRecM2 loop
where
loop b l = uncons l >>= g
where
g Nothing = pure (MR.Done b)
g (Just (Tuple a as)) = pure (MR.Loop {a: f b 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
scanl f b l = unfold g (Tuple b l)
Expand Down