module Failure where

import Prelude hiding (drop,max,seq)


--
-- * A one-dimensional airplane simulator
--

-- | The height of the airplane.
type Altitude = Int

-- | The maximum altitude of the plane.
max :: Altitude
max = 1000

-- | Go up.
rise :: Int -> Altitude -> Maybe Altitude
rise x a | a' <= max = Just a'
         | otherwise = Nothing
  where a' = a + x

-- | Go down.
drop :: Int -> Altitude -> Maybe Altitude
drop x a | a' > 0    = Just a'
         | otherwise = Nothing
  where a' = a - x

-- | Do a loopty-loop: rise 200, drop 300, rise 50.
loop :: Altitude -> Maybe Altitude
loop a = case rise 200 a of
           Nothing -> Nothing
           Just a2 -> case drop 300 a2 of
                        Nothing -> Nothing
                        Just a3 -> rise 50 a3


-- | Sequence an action after another result.
seq = undefined


-- | Do a loopty-loop using our seq function.
loopS :: Altitude -> Maybe Altitude
loopS a = undefined


-- | Do a loopty-loop in monadic style.
loopM :: Altitude -> Maybe Altitude
loopM a = undefined


-- | Do a whole stunt show starting from the ground:
--    * start at 0
--    * rise 400
--    * do two loopty-loops
--    * rise 400
--    * do two more loopty-loops
stuntM :: Maybe Altitude
stuntM = undefined