module Numeric.AD.Internal.Combinators
( zipWithT
, zipWithDefaultT
, on
) where
import Data.Traversable (Traversable, mapAccumL)
import Data.Foldable (Foldable, toList)
on :: (a -> a -> b) -> (c -> a) -> c -> c -> b
on f g a b = f (g a) (g b)
zipWithT :: (Foldable f, Traversable g) => (a -> b -> c) -> f a -> g b -> g c
zipWithT f as = snd . mapAccumL (\(a:as') b -> (as', f a b)) (toList as)
zipWithDefaultT :: (Foldable f, Traversable g) => a -> (a -> b -> c) -> f a -> g b -> g c
zipWithDefaultT z f as = zipWithT f (toList as ++ repeat z)