import           Control.Exception
import           Data.IORef
import           System.IO.Unsafe

lastIsFalse :: [Bool]
lastIsFalse = unsafePerformIO $ do
    ref <- newIORef False
    let go = do
                b <- unsafeInterleaveIO $ readIORef ref
                bs <- unsafeInterleaveIO $ do
                    writeIORef ref True
                    _ <- evaluate b
                    writeIORef ref False
                    go
                pure $ b : bs
    go

walk :: [a] -> [a]
walk = foldr (\x r -> (:) x $! r) []

-- >>> test
-- [(1,True),(2,True),(3,True),(4,True),(5,False)]
test = walk $ take 5 $ zip [1..] lastIsFalse

lastFalse :: [a] -> [(a, Bool)]
lastFalse [] = []
lastFalse xxs@(_:xs) = go xxs xs
  where
    go (x:_) []       = [(x, False)]
    go (x:xxs) (_:xs) = (x, True) : go xxs xs
    go [] _           = error "Impossible"