module MyState where

type Pos s a = s -> (a, a -> s)

p2_1 :: Pos (x, y) x
p2_1 = \ (x, y) -> (x, \ x1 -> (x1, y))
xP = p2_1
p2_2 :: Pos (x, y) y
p2_2 = \ (x, y) -> (y, \ y1 -> (x, y1))
yP = p2_2

p3_1 :: Pos (x, y, z) x
p3_1 = \ (x, y, z) -> (x, \ x1 -> (x1, y, z))
xT = p3_1

p3_2 :: Pos (x, y, z) y
p3_2 = \ (x, y, z) -> (y, \ y1 -> (x, y1, z))
yT = p3_2

p3_3 :: Pos (x, y, z) z
p3_3 = \ (x, y, z) -> (z, \ z1 -> (x, y, z1))
zT = p3_3

p4_1 :: Pos (x, y, z, w) x
p4_1 = \ (x, y, z, w) -> (x, \ x1 -> (x1, y, z, w))
xQ = p4_1

p4_2 :: Pos (x, y, z, w) y
p4_2 = \ (x, y, z, w) -> (y, \ y1 -> (x, y1, z, w))
yQ = p4_2

p4_3 :: Pos (x, y, z, w) z
p4_3 = \ (x, y, z, w) -> (z, \ z1 -> (x, y, z1, w))
zQ = p4_3

p4_4 :: Pos (x, y, z, w) w
p4_4 = \ (x, y, z, w) -> (w, \ w1 -> (x, y, z, w1))
wQ = p4_3

class MyState m where
  get :: Pos s a -> m s a
  set :: Pos s a -> a -> m s ()

-- Todo: State に Dynamic を使って、cons, nil, … を実装する
--       参考: MicroKanren.hs
data MuList s a = MuNil | MuCons (Pos s a) (Pos s (MuList s a))

data MuTree s a = MuEmpty
                 | MuBranch (Pos s (MuTree s a)) (Pos s a) (Pos s (MuTree s a))

pair x y     = (x,y)
triple x y z = (x,y,z)