Control.Monad.Logic

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 (http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf).

Documentation

module Control.Monad.Logic.Class

The Logic monad

type Logic = LogicT Identity

The basic Logic monad, for performing backtracking computations returning values of type a

logic :: (forall r. (a -> r -> r) -> r -> r) -> Logic a

A smart constructor for Logic computations.

runLogic :: Logic a -> (a -> r -> r) -> r -> r

Runs a Logic computation with the specified initial success and failure continuations.

observe :: Logic a -> a

Extracts the first result from a Logic computation.

observeMany :: Int -> Logic a -> [a]

Extracts up to a given number of results from a Logic computation.

observeAll :: Logic a -> [a]

Extracts all results from a Logic computation.

The LogicT monad transformer

newtype LogicT m a

A monad transformer for performing backtracking computations layered over another monad m

Constructors

LogicT

Fields

unLogicT :: forall r. (a -> m r -> m r) -> m r -> m r

Instances

MonadTrans LogicT

MonadError e m => MonadError e (LogicT m)

MonadReader r m => MonadReader r (LogicT m)

MonadState s m => MonadState s (LogicT m)

Monad (LogicT m)

Functor (LogicT f)

MonadPlus (LogicT m)

Applicative (LogicT f)

(Monad m, Foldable m) => Foldable (LogicT m)

Traversable (LogicT Identity)

Alternative (LogicT f)

MonadIO m => MonadIO (LogicT m)

Monad m => MonadLogic (LogicT m)

runLogicT :: LogicT m a -> (a -> m r -> m r) -> m r -> m r

Runs a LogicT computation with the specified initial success and failure continuations.

observeT :: Monad m => LogicT m a -> m a

Extracts the first result from a LogicT computation, failing otherwise.

observeManyT :: Monad m => Int -> LogicT m a -> m [a]

Extracts up to a given number of results from a LogicT computation.

observeAllT :: Monad m => LogicT m a -> m [a]

Extracts all results from a LogicT computation.

module Control.Monad

module Control.Monad.Trans