Control.Monad.RWS.Trans

data RWSResult state result writer

Constructors

• RWSResult state result writer

newtype RWST r w s m a

The reader-writer-state monad transformer, which combines the operations of RWST, WriterT and StateT into a single monad transformer.

Constructors

• RWST (r -> s -> m (RWSResult s a w))

Instances

• Newtype (RWST r w s m a) _
• (Functor m) => Functor (RWST r w s m)
• (Bind m, Monoid w) => Apply (RWST r w s m)
• (Alt m) => Alt (RWST r w s m)
• (Monoid w, Alternative m, Monad m) => Alternative (RWST r w s m)
• (Bind m, Monoid w) => Bind (RWST r w s m)
• (Monad m, Monoid w) => Applicative (RWST r w s m)
• (Monad m, Monoid w) => Monad (RWST r w s m)
• (Monoid w) => MonadTrans (RWST r w s)
• Lazy (RWST r w s m a)
• (Monoid w, MonadEff eff m) => MonadEff eff (RWST r w s m)
• (Monad m, Monoid w) => MonadAsk r (RWST r w s m)
• (Monad m, Monoid w) => MonadReader r (RWST r w s m)
• (Monad m, Monoid w) => MonadState s (RWST r w s m)
• (Monad m, Monoid w) => MonadTell w (RWST r w s m)
• (Monad m, Monoid w) => MonadWriter w (RWST r w s m)
• (MonadThrow e m, Monoid w) => MonadThrow e (RWST r w s m)
• (MonadError e m, Monoid w) => MonadError e (RWST r w s m)
• (MonadRec m, Monoid w) => MonadRec (RWST r w s m)
• (Plus m) => Plus (RWST r w s m)

runRWST :: forall a m s w r. RWST r w s m a -> r -> s -> m (RWSResult s a w)

Run a computation in the RWST monad.

evalRWST :: forall a m s w r. Monad m => RWST r w s m a -> r -> s -> m (Tuple a w)

Run a computation in the RWST monad, discarding the final state.

execRWST :: forall a m s w r. Monad m => RWST r w s m a -> r -> s -> m (Tuple s w)

Run a computation in the RWST monad, discarding the result.

mapRWST :: forall a2 a1 m2 m1 s w2 w1 r. (m1 (RWSResult s a1 w1) -> m2 (RWSResult s a2 w2)) -> RWST r w1 s m1 a1 -> RWST r w2 s m2 a2

Change the result and accumulator types in a RWST monad action.

withRWST :: forall a m s w r2 r1. (r2 -> s -> Tuple r1 s) -> RWST r1 w s m a -> RWST r2 w s m a

Change the context type in a RWST monad action.

class MonadTrans t  where

The MonadTrans type class represents monad transformers.

A monad transformer is a type constructor of kind (* -> *) -> * -> *, which takes a Monad as its first argument, and returns another Monad.

This allows us to add additional effects to an existing monad. By iterating this process, we create monad transformer stacks, which contain all of the effects required for a particular computation.

The laws state that lift is a Monad morphism.

Laws:

• lift (pure a) = pure a
• lift (do { x <- m ; y }) = do { x <- lift m ; lift y }

Members

• lift :: forall a m. Monad m => m a -> t m a