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{-# LANGUAGE TypeFamilies #-}
module Main (main) where
import Control.Applicative hiding (Const)
import Data.Reify
import qualified Data.Traversable as T
import Prelude
-- Notice how there is nothing Mu-ish about this datatype.
data State a b = State a [(b,State a b)]
deriving Show
s0, s1, s2 :: State Int Bool
s0 = State 0 [(True,s1),(False,s2)]
s1 = State 1 [(True,s0),(False,s1)]
s2 = State 2 [(True,s1),(False,s0)]
data StateDeRef a b r = StateDeRef a [(b,r)]
deriving Show
instance MuRef (State a b) where
type DeRef (State a b) = StateDeRef a b
mapDeRef f (State a tr) = StateDeRef a <$>
T.traverse (\ (b,s) -> ((,) b) <$> (f s)) tr
instance Functor (StateDeRef a b) where
fmap f (StateDeRef a tr) = StateDeRef a [ (b,f s) | (b,s) <- tr ]
main :: IO ()
main = do reifyGraph s0 >>= print
reifyGraphs [s0, s1] >>= print
{- Alt:
data State s i o = State s [(i,o,State s i o)]
deriving Show
state :: s -> State s i o
state s = State s []
infixl 4 %%
(%%) :: State s i o -> (i,o,State s i o) -> State s i o
(State s ts) %% (i,o,st) = State s $ (ts ++ [(i,o,st)])
s0 = state () %% (True,True,s1) %% (False,False,s0)
s1 = state () %% (True,False,s0) %% (False,True,s1)
data MuState s i o r = MuState s [(i,o,r)]
deriving Show
-}
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