-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | A backtracking logic-programming monad.
--   
--   A continuation-based, backtracking, logic programming monad. An
--   adaptation of the two-continuation implementation found in the paper
--   <a>Backtracking, Interleaving, and Terminating Monad Transformers</a>
--   available here: <a>http://okmij.org/ftp/papers/LogicT.pdf</a>
@package logict
@version 0.6


-- | A backtracking, logic programming monad.
--   
--   Adapted from the paper /Backtracking, Interleaving, and Terminating
--   Monad Transformers/, by Oleg Kiselyov, Chung-chieh Shan, Daniel P.
--   Friedman, Amr Sabry
--   (<a>http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf</a>)
module Control.Monad.Logic.Class

-- | Minimal implementation: msplit
class MonadPlus m => MonadLogic m where interleave m1 m2 = msplit m1 >>= maybe m2 (\ (a, m1') -> return a `mplus` interleave m2 m1') m >>- f = do { Just (a, m') <- msplit m; interleave (f a) (m' >>- f) } ifte t th el = msplit t >>= maybe el (\ (a, m) -> th a `mplus` (m >>= th)) once m = do { Just (a, _) <- msplit m; return a }
msplit :: MonadLogic m => m a -> m (Maybe (a, m a))
interleave :: MonadLogic m => m a -> m a -> m a
(>>-) :: MonadLogic m => m a -> (a -> m b) -> m b
ifte :: MonadLogic m => m a -> (a -> m b) -> m b -> m b
once :: MonadLogic m => m a -> m a

-- | The inverse of msplit. Satisfies the following law:
--   
--   <pre>
--   msplit m &gt;&gt;= reflect == m
--   </pre>
reflect :: MonadLogic m => Maybe (a, m a) -> m a

-- | Inverts a logic computation. If <tt>m</tt> succeeds with at least one
--   value, <tt>lnot m</tt> fails. If <tt>m</tt> fails, then <tt>lnot
--   m</tt> succeeds the value <tt>()</tt>.
lnot :: MonadLogic m => m a -> m ()
instance (MonadLogic m, Monoid w) => MonadLogic (WriterT w m)
instance (MonadLogic m, Monoid w) => MonadLogic (WriterT w m)
instance MonadLogic m => MonadLogic (StateT s m)
instance MonadLogic m => MonadLogic (StateT s m)
instance MonadLogic m => MonadLogic (ReaderT e m)
instance MonadLogic []


-- | A backtracking, logic programming monad.
--   
--   Adapted from the paper /Backtracking, Interleaving, and Terminating
--   Monad Transformers/, by Oleg Kiselyov, Chung-chieh Shan, Daniel P.
--   Friedman, Amr Sabry
--   (<a>http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf</a>).
module Control.Monad.Logic

-- | The basic Logic monad, for performing backtracking computations
--   returning values of type <tt>a</tt>
type Logic = LogicT Identity

-- | A smart constructor for Logic computations.
logic :: (forall r. (a -> r -> r) -> r -> r) -> Logic a

-- | Runs a Logic computation with the specified initial success and
--   failure continuations.
runLogic :: Logic a -> (a -> r -> r) -> r -> r

-- | Extracts the first result from a Logic computation.
observe :: Logic a -> a

-- | Extracts up to a given number of results from a Logic computation.
observeMany :: Int -> Logic a -> [a]

-- | Extracts all results from a Logic computation.
observeAll :: Logic a -> [a]

-- | A monad transformer for performing backtracking computations layered
--   over another monad <tt>m</tt>
newtype LogicT m a
LogicT :: (forall r. (a -> m r -> m r) -> m r -> m r) -> LogicT m a
unLogicT :: LogicT m a -> forall r. (a -> m r -> m r) -> m r -> m r

-- | Runs a LogicT computation with the specified initial success and
--   failure continuations.
runLogicT :: LogicT m a -> (a -> m r -> m r) -> m r -> m r

-- | Extracts the first result from a LogicT computation, failing
--   otherwise.
observeT :: Monad m => LogicT m a -> m a

-- | Extracts up to a given number of results from a LogicT computation.
observeManyT :: Monad m => Int -> LogicT m a -> m [a]

-- | Extracts all results from a LogicT computation.
observeAllT :: Monad m => LogicT m a -> m [a]
instance MonadError e m => MonadError e (LogicT m)
instance MonadState s m => MonadState s (LogicT m)
instance MonadReader r m => MonadReader r (LogicT m)
instance Traversable (LogicT Identity)
instance (Monad m, Foldable m) => Foldable (LogicT m)
instance Monad m => MonadLogic (LogicT m)
instance MonadIO m => MonadIO (LogicT m)
instance MonadTrans LogicT
instance MonadPlus (LogicT m)
instance Monad (LogicT m)
instance Alternative (LogicT f)
instance Applicative (LogicT f)
instance Functor (LogicT f)