module Data.Fold.L
( L(..)
) where
import Control.Applicative
import Control.Comonad
import Control.Lens
import Data.Foldable
import Data.Fold.Class
import Data.Functor.Extend
import Data.Functor.Bind
import Data.Monoid
import Data.Profunctor.Unsafe
import Unsafe.Coerce
import Prelude hiding (foldl)
data L a b = forall r. L (r -> b) (r -> a -> r) r
instance Folding L where
run t (L k h z) = k (foldl h z t)
run1 t (L k h z) = k (h z t)
runOf l s (L k h z) = k (foldlOf l h z s)
prefix s = run s . duplicate
prefix1 a = run1 a . duplicate
prefixOf l s = runOf l s . duplicate
postfix t s = extend (run s) t
postfix1 t a = extend (run1 a) t
postfixOf l t s = extend (runOf l s) t
instance Profunctor L where
dimap f g (L k h z) = L (g.k) (\r -> h r . f) z
rmap g (L k h z) = L (g.k) h z
lmap f (L k h z) = L k (\r -> h r . f) z
(#.) _ = unsafeCoerce
x .# _ = unsafeCoerce x
instance Choice L where
left' (L k h z) = L (_Left %~ k) step (Left z) where
step (Left x) (Left y) = Left (h x y)
step (Right c) _ = Right c
step _ (Right c) = Right c
right' (L k h z) = L (_Right %~ k) step (Right z) where
step (Right x) (Right y) = Right (h x y)
step (Left c) _ = Left c
step _ (Left c) = Left c
instance Functor (L a) where
fmap f (L k h z) = L (f.k) h z
(<$) b = \_ -> pure b
instance Comonad (L a) where
extract (L k _ z) = k z
duplicate (L k h z) = L (L k h) h z
extend f (L k h z) = L (f . L k h) h z
data Pair a b = Pair !a !b
instance Applicative (L a) where
pure b = L (\() -> b) (\() _ -> ()) ()
L xf bxx xz <*> L ya byy yz = L
(\(Pair x y) -> xf x $ ya y)
(\(Pair x y) b -> Pair (bxx x b) (byy y b))
(Pair xz yz)
(<*) m = \_ -> m
_ *> m = m
instance Bind (L a) where
(>>-) = (>>=)
instance Monad (L a) where
return = pure
m >>= f = L (\xs a -> run xs (f a)) Snoc Nil <*> m
instance Extend (L a) where
extended = extend
duplicated = duplicate
instance Apply (L a) where
(<.>) = (<*>)
(<.) m = \_ -> m
_ .> m = m
instance ComonadApply (L a) where
(<@>) = (<*>)
(<@) m = \_ -> m
_ @> m = m
data SnocList a = Snoc (SnocList a) a | Nil
instance Foldable SnocList where
foldl f z m0 = go m0 where
go (Snoc xs x) = f (go xs) x
go Nil = z
foldMap f (Snoc xs x) = foldMap f xs `mappend` f x
foldMap _ Nil = mempty