module serialize2start

/*
  Definition for assignment 2 in AFP 2017
  Pieter Koopman pieter@cs.ru.nl
  September 2017
*/

import StdEnv, StdMaybe

class serialize a where
  write :: a [String] -> [String]
  read  :: [String] -> Maybe (a,[String])

instance serialize Bool where
  write b c = [toString b:c]
  read ["True":r]  = Just (True,r)
  read ["False":r] = Just (False,r)
  read _ = Nothing

instance serialize Int where
  write i c = [toString i:c]
  read [s:r]
    # i = toInt s
    | s == toString i
      = Just (i,r)
      = Nothing
  read _ = Nothing

// ---

:: UNIT       = UNIT
:: EITHER a b = LEFT a | RIGHT b
:: PAIR   a b = PAIR a b
:: CONS   a   = CONS String a

// ---

:: ListG a :== EITHER (CONS UNIT) (CONS (PAIR a [a]))

instance serialize [a] | serialize a where  // to be imporved
  write l c = c
  read l = Nothing

:: Bin a = Leaf | Bin (Bin a) a (Bin a)
:: BinG a :== EITHER (CONS UNIT) (CONS (PAIR (Bin a) (PAIR a (Bin a))))

instance serialize (Bin a) | serialize a where // to be imporved
  write a c = c
  read l = Nothing

instance == (Bin a) | == a where // better use the generic approach
  (==) Leaf Leaf = True
  (==) (Bin l a r) (Bin k b s) = l == k && a == b && r == s
  (==) _ _ = False

// ---

Start = 
  [test True
  ,test False
  ,test 0
  ,test 123
  ,test -36
  ,test [42]
  ,test [0..4]
  ,test [[True],[]]
  ,test (Bin Leaf True Leaf)
  ,test [Bin (Bin Leaf [1] Leaf) [2] (Bin Leaf [3] (Bin Leaf [4,5] Leaf))]
  ,test [Bin (Bin Leaf [1] Leaf) [2] (Bin Leaf [3] (Bin (Bin Leaf [4,5] Leaf) [6,7] (Bin Leaf [8,9] Leaf)))]
  ]

test :: a -> ([String],[String]) | serialize, == a
test a = 
  (if (isJust r)
    (if (fst jr == a)
      (if (isEmpty (tl (snd jr)))
        ["Oke "]
        ["Fail: not all input is consumed! ":snd jr])
      ["Fail: Wrong result ":write (fst jr) []])
    ["Fail: read result is Nothing "]
  , ["write produces ": s]
  )
  where
    s = write a ["\n"]
    r = read s
    jr = fromJust r