mtl-2.2.2: Monad classes, using functional dependencies
Copyright (c) Andy Gill 2001(c) Oregon Graduate Institute of Science and Technology 2001 BSD-style (see the file LICENSE) libraries@haskell.org experimental non-portable (multi-param classes, functional dependencies) Safe Haskell2010

Description

Inspired by the paper Functional Programming with Overloading and Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.

Synopsis

# The RWS monad

type RWS r w s = RWST r w s Identity Source #

A monad containing an environment of type r, output of type w and an updatable state of type s.

rws :: (r -> s -> (a, s, w)) -> RWS r w s a Source #

Construct an RWS computation from a function. (The inverse of runRWS.)

runRWS :: RWS r w s a -> r -> s -> (a, s, w) Source #

Unwrap an RWS computation as a function. (The inverse of rws.)

Arguments

 :: RWS r w s a RWS computation to execute -> r initial environment -> s initial value -> (a, w) final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

Arguments

 :: RWS r w s a RWS computation to execute -> r initial environment -> s initial value -> (s, w) final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b Source #

Map the return value, final state and output of a computation using the given function.

• runRWS (mapRWS f m) r s = f (runRWS m r s)

withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a Source #

withRWS f m executes action m with an initial environment and state modified by applying f.

• runRWS (withRWS f m) r s = uncurry (runRWS m) (f r s)

# The RWST monad transformer

newtype RWST r w s (m :: Type -> Type) a Source #

A monad transformer adding reading an environment of type r, collecting an output of type w and updating a state of type s to an inner monad m.

Constructors

 RWST (r -> s -> m (a, s, w))

#### Instances

Instances details
 (Monoid w, Monad m) => MonadRWS r w s (RWST r w s m) Source # Instance detailsDefined in Control.Monad.RWS.Class (Monoid w, MonadError e m) => MonadError e (RWST r w s m) Source # Instance detailsDefined in Control.Monad.Error.Class MethodsthrowError :: e -> RWST r w s m a Source #catchError :: RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a Source # (Monad m, Monoid w) => MonadReader r (RWST r w s m) Source # Instance detailsDefined in Control.Monad.Reader.Class Methodsask :: RWST r w s m r Source #local :: (r -> r) -> RWST r w s m a -> RWST r w s m a Source #reader :: (r -> a) -> RWST r w s m a Source # (Monad m, Monoid w) => MonadState s (RWST r w s m) Source # Instance detailsDefined in Control.Monad.State.Class Methodsget :: RWST r w s m s Source #put :: s -> RWST r w s m () Source #state :: (s -> (a, s)) -> RWST r w s m a Source # (Monoid w, Monad m) => MonadWriter w (RWST r w s m) Source # Instance detailsDefined in Control.Monad.Writer.Class Methodswriter :: (a, w) -> RWST r w s m a Source #tell :: w -> RWST r w s m () Source #listen :: RWST r w s m a -> RWST r w s m (a, w) Source #pass :: RWST r w s m (a, w -> w) -> RWST r w s m a Source # Monoid w => MonadTrans (RWST r w s) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodslift :: Monad m => m a -> RWST r w s m a Source # (Monoid w, MonadFail m) => MonadFail (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodsfail :: String -> RWST r w s m a Source # (Monoid w, MonadFix m) => MonadFix (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodsmfix :: (a -> RWST r w s m a) -> RWST r w s m a Source # (Monoid w, MonadIO m) => MonadIO (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy MethodsliftIO :: IO a -> RWST r w s m a Source # Contravariant m => Contravariant (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodscontramap :: (a' -> a) -> RWST r w s m a -> RWST r w s m a' Source #(>$) :: b -> RWST r w s m b -> RWST r w s m a Source # (Monoid w, Functor m, MonadPlus m) => Alternative (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodsempty :: RWST r w s m a Source #(<|>) :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a Source #some :: RWST r w s m a -> RWST r w s m [a] Source #many :: RWST r w s m a -> RWST r w s m [a] Source # (Monoid w, Functor m, Monad m) => Applicative (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodspure :: a -> RWST r w s m a Source #(<*>) :: RWST r w s m (a -> b) -> RWST r w s m a -> RWST r w s m b Source #liftA2 :: (a -> b -> c) -> RWST r w s m a -> RWST r w s m b -> RWST r w s m c Source #(*>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b Source #(<*) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a Source # Functor m => Functor (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodsfmap :: (a -> b) -> RWST r w s m a -> RWST r w s m b Source #(<$) :: a -> RWST r w s m b -> RWST r w s m a Source # (Monoid w, Monad m) => Monad (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methods(>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b Source #(>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b Source #return :: a -> RWST r w s m a Source # (Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) Instance detailsDefined in Control.Monad.Trans.RWS.Lazy Methodsmzero :: RWST r w s m a Source #mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a Source # (Monoid w, MonadCont m) => MonadCont (RWST r w s m) Source # Instance detailsDefined in Control.Monad.Cont.Class MethodscallCC :: ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a Source #

runRWST :: RWST r w s m a -> r -> s -> m (a, s, w) Source #

Arguments

 :: Monad m => RWST r w s m a computation to execute -> r initial environment -> s initial value -> m (a, w) computation yielding final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

Arguments

 :: Monad m => RWST r w s m a computation to execute -> r initial environment -> s initial value -> m (s, w) computation yielding final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b Source #

Map the inner computation using the given function.

• runRWST (mapRWST f m) r s = f (runRWST m r s)

withRWST :: forall r' s r w (m :: Type -> Type) a. (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a Source #

withRWST f m executes action m with an initial environment and state modified by applying f.

• runRWST (withRWST f m) r s = uncurry (runRWST m) (f r s)