stupid juggling

kek.hs

import Control.Applicative
import Data.Monoid
import Control.Monad
import Control.Monad.Loops

main :: IO ()
main = putStrLn =<< intersperse ':' <$> getLines

-- | The class of types that support short-circuiting on e.g. empty, false, error - almost the same as but not quite Alternative
class Circuit a where
  (<||>) :: a -> a -> a

instance Circuit [a] where
  [] <||> b = b
  a <||> _ = a

instance Circuit (Maybe a) where
  Nothing <||> b = b
  a <||> _ = a

instance Circuit (Either a b) where
  (Left _) <||> b = b
  ea@(Right a) <||> _ = ea

getLines :: IO [String]
getLines = unfoldWhileM (/= mempty) getLine

separate :: (Monoid (f a), Applicative f) => a -> f a -> f a -> f a
separate a fax fay = fax <> pure a <> fay

intersperse :: (Monoid (f a), Foldable t, Applicative f, Applicative t, Alternative t, Circuit (t (f a))) => a -> t (f a) -> f a
intersperse a as = foldl1 (separate a) (as <||> pure mempty)