Atoms.hs

{-# LANGUAGE ExistentialQuantification, ScopedTypeVariables #-}
{-
  This module is part of Chatty.
  Copyleft (c) 2014 Marvin Cohrs

  All wrongs reversed. Sharing is an act of love, not crime.
  Please share Chatty with everyone you like.

  Chatty is free software: you can redistribute it and/or modify
  it under the terms of the GNU Affero General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Chatty is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  GNU Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with Chatty. If not, see <http://www.gnu.org/licenses/>.
-}

-- | Provides a variable-storing monad and functions for access
module Data.Chatty.Atoms where

import Control.Arrow
import qualified Control.Category as C
import Control.Monad
import Control.Monad.Trans.Class
import Control.Monad.IO.Class
import Data.Dynamic
import Data.Typeable
import Data.Chatty.AVL
import Data.Chatty.Counter
import Unsafe.Coerce

-- | Phantom type for atom IDs
data Atom a = Atom Int
            | forall b. FunAtom Int (Atom b) (b -> a) (b -> a -> b)
            | forall b c. FunAtom2 Int (Atom b) (Atom c) ((b,c) -> a) ((b,c) -> a -> (b,c))

instance Eq (Atom a) where
  (Atom n) == (Atom m) = n == m
  (FunAtom i _ _ _) == (FunAtom j _ _ _) = i == j
  (FunAtom2 i _ _ _ _) == (FunAtom2 j _ _ _ _) = i == j
  _ == _ = False

instance Ord (Atom a) where
  (Atom n) `compare` (Atom m) = n `compare` m
  (FunAtom i _ _ _) `compare` (Atom m) = i `compare` m
  (FunAtom2 i _ _ _ _) `compare` (Atom m) = i `compare` m
  (Atom n) `compare` (FunAtom j _ _ _) = n `compare` j
  (FunAtom i _ _ _) `compare` (FunAtom j _ _ _) = i `compare` j
  (FunAtom2 i _ _ _ _) `compare` (FunAtom j _ _ _) = i `compare` j
  (Atom n) `compare` (FunAtom2 j _ _ _ _) = n `compare` j
  (FunAtom i _ _ _) `compare` (FunAtom2 j _ _ _ _) = i `compare` j
  (FunAtom2 i _ _ _ _) `compare` (FunAtom2 j _ _ _ _) = i `compare` j

newtype Container = Container ()

-- | The storage monad
newtype AtomStoreT m a = AtomStore { runAtomStoreT :: AVL (Int, Container) -> m (a,AVL (Int,Container)) }

instance Functor m => Functor (AtomStoreT m) where
  fmap f a = AtomStore $ \s -> fmap (first f) $ runAtomStoreT a s

instance Monad m => Monad (AtomStoreT m) where
  return a = AtomStore $ \s -> return (a,s)
  m >>= f = AtomStore $ \s -> do (a,s') <- runAtomStoreT m s; runAtomStoreT (f a) s'

instance MonadTrans AtomStoreT where
  lift m = AtomStore $ \s -> do a <- m; return (a,s)

instance MonadIO m => MonadIO (AtomStoreT m) where
  liftIO = lift . liftIO

instance ChCounter m => ChCounter (AtomStoreT m) where
  countOn = lift countOn

-- | Typeclass for all atom-storing monads.
class ChCounter m => ChAtoms m where
  -- | Reserve a new atom.
  newAtom :: m (Atom v)
  newAtom = liftM Atom countOn
  -- | Construct a new functional atom.
  funAtom :: Atom b -> (b -> a) -> (b -> a -> b) -> m (Atom a)
  funAtom b r p = do
    i <- countOn
    return $ FunAtom i b r p
  -- | Construct a new doubly-source functional atom
  funAtom2 :: Atom b -> Atom c -> ((b,c) -> a) -> ((b,c) -> a -> (b,c)) -> m (Atom a)
  funAtom2 b c r p = do
    i <- countOn
    return $ FunAtom2 i b c r p
  -- | Save a value for the given atom.
  putAtom :: Atom v -> v -> m ()
  -- | Get the value from a given atom.
  getAtom :: Atom v -> m v
  -- | Dispose the given atom.
  dispAtom :: Atom v -> m ()
  -- | Clone the given atom.
  cloneAtom :: Atom v -> m (Atom v)
  cloneAtom a = do
    b <- newAtom
    v <- getAtom a
    putAtom b v
    return b

instance ChCounter m => ChAtoms (AtomStoreT m) where
  putAtom (Atom a) v = AtomStore $ \s -> return ((),avlInsert (a,unsafeCoerce v) s)
  putAtom (FunAtom _ b _ p) v = do
    bv <- getAtom b
    putAtom b $ p bv v
  putAtom (FunAtom2 _ b c _ p) v = do
    bv <- getAtom b
    cv <- getAtom c
    let (bv',cv') = p (bv, cv) v
    putAtom b bv'
    putAtom c cv'
  getAtom (Atom a) = AtomStore $ \s -> let Just v = avlLookup a s in return (unsafeCoerce v,s)
  getAtom (FunAtom _ b g _) = liftM g $ getAtom b
  getAtom (FunAtom2 _ b c g _) = do
    bv <- getAtom b
    cv <- getAtom c
    return $ g (bv,cv)
  dispAtom (Atom a) = AtomStore $ \s -> return ((),avlRemove a s)
  dispAtom (FunAtom _ _ _ _) = return ()
  dispAtom (FunAtom2 _ _ _ _ _) = return ()

-- Stop it. This just doesn't work safely.
{-- | Arrow type operating on atoms. Works by overwriting the educt. You should really *not* use
-- this for general a->b arrows, but only for a->a, unless you are sure that all Atom a references
-- are gone! Otherwise segfaults are waiting for you!
newtype Atomar m a b = Atomar { runAtomar :: Atom a -> m (Atom b) }

instance ChAtoms m => C.Category (Atomar m) where
  id = Atomar return
  a . b = Atomar (runAtomar a <=< runAtomar b)

instance ChAtoms m => Arrow (Atomar m) where
  arr = Atomar . mapAtom
  first f = Atomar $ \a -> do
    let afst = funAtom a fst $ \(_,s) f -> (f,s)
    mapAtom afst
-}

-- | Run a pure function on atoms.
mapAtom :: ChAtoms m => (a -> a) -> Atom a -> m ()
mapAtom f a = do
  v <- getAtom a
  putAtom a $ f v

-- | Arrow type operating on atoms. Works by cloning the educt, then overwriting the clone.
-- You shouldn't use this inside long-term environments, as massive usage blows up the memory.
newtype Redundant m a b = Redundant { runRedundant :: Atom a -> m (Atom b) }

instance ChAtoms m => C.Category (Redundant m) where
  id = Redundant return
  a . b = Redundant (runRedundant a <=< runRedundant b)

instance ChAtoms m => Arrow (Redundant m) where
  arr f = Redundant $ \a -> do
    v <- getAtom a
    b <- newAtom
    putAtom b $ f v
    return b
  first f = Redundant $ \a -> do
    c <- runRedundant f =<< funAtom a fst (\(_, s) f -> (f, s))
    funAtom2 a c (\((_,s),f) -> (f,s)) $ \((e,s),f) (f',s') -> ((e,s'),f')