Modulemtl-2.3.1Haskell2010

Control.Monad.RWS.Lazy

Lazy RWS monad.

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.

2 types
11 values

Packagemtl-2.3.1
Exports13
LanguageHaskell2010
LicenceBSD-3-Clause
SourceLazy.hs

The RWS monad

7 declarations

typetype RWS r w s = RWST r w s Identity

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

valuerws :: (r -> s -> (a, s, w)) -> RWS r w s a

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

valuerunRWS :: RWS r w s a -> r -> s -> (a, s, w)

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

valueevalRWS

:: 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.

valueexecRWS

:: 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.

valuemapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b

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)

valuewithRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a

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

6 declarations

newtypenewtype RWST r w s (m :: Type -> Type) a

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

Instances20MonadRWS, MonadAccum, MonadError, MonadReader, MonadState, MonadWriter, …

(Monoid w, Monad m) => MonadRWS r w s (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.RWS.Class
(MonadAccum w' m, Monoid w) => MonadAccum w' (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Accum
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Error.Class
(Monad m, Monoid w) => MonadReader r (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Reader.Class
(Monad m, Monoid w) => MonadState s (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.State.Class
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(MonadSelect w' m, Monoid w) => MonadSelect w' (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Select
A combination of an 'outer' ReaderT, WriterT and StateT. In short, you get a value of type r which can influence what gets picked, but not how anything is ranked, and the 'ranking' function gets access to an s and a w, but can modify neither.
Monoid w => MonadTrans (RWST r w s)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, Monad m) => Monad (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
Functor m => Functor (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, MonadFix m) => MonadFix (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, MonadFail m) => MonadFail (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, Functor m, Monad m) => Applicative (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, Functor m, MonadPlus m) => Alternative (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, MonadIO m) => MonadIO (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
Contravariant m => Contravariant (RWST r w s m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
(Monoid w, MonadCont m) => MonadCont (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Cont.Class
Generic (RWST r w s m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy
type Rep (RWST r w s m a) = D1 ('MetaData "RWST" "Control.Monad.Trans.RWS.Lazy" "transformers-0.6.1.1-a11a" 'True) (C1 ('MetaCons "RWST" 'PrefixI 'True) (S1 ('MetaSel ('Just "runRWST") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (r -> s -> m (a, s, w)))))Defined in transformers-0.6.1.1 · Control.Monad.Trans.RWS.Lazy

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

valueevalRWST

:: 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.

valueexecRWST

:: 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.

valuemapRWST

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

Map the inner computation using the given function.

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

valuewithRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a

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)

Lazy Reader-writer-state monads

0 declarations

module Control.Monad.RWS.Class

module Control.Monad.Trans