Control.Monad.RWS

type RWS r w s = RWST r w s Identity

The RWS monad is a synonym for the RWST monad transformer, applied to the Identity monad.

rws :: forall r w s a. (r -> s -> RWSResult s a w) -> RWS r w s a

Create an action in the RWS monad from a function which uses the global context and state explicitly.

runRWS :: forall r w s a. RWS r w s a -> r -> s -> RWSResult s a w

Run a computation in the RWS monad.

evalRWS :: forall r w s a. RWS r w s a -> r -> s -> Tuple a w

Run a computation in the RWS monad, discarding the final state

execRWS :: forall r w s a. RWS r w s a -> r -> s -> Tuple s w

Run a computation in the RWS monad, discarding the result

mapRWS :: forall r w1 w2 s a1 a2. (RWSResult s a1 w1 -> RWSResult s a2 w2) -> RWS r w1 s a1 -> RWS r w2 s a2

Change the types of the result and accumulator in a RWS action

withRWS :: forall r1 r2 w s a. (r2 -> s -> Tuple r1 s) -> RWS r1 w s a -> RWS r2 w s a

Change the type of the context in a RWS action

newtype RWST r w s m a

The reader-writer-state monad transformer, which combines the operations of ReaderT, 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, MonadEffect m) => MonadEffect (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)
• (Bind m, Monoid w, Semigroup a) => Semigroup (RWST r w s m a)
• (Monad m, Monoid w, Monoid a) => Monoid (RWST r w s m a)

data RWSResult state result writer

Constructors

• RWSResult state result writer

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 m a. Monad m => m a -> t m a

withRWST :: forall r1 r2 w s m a. (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.

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

Run a computation in the RWST monad.

mapRWST :: forall r w1 w2 s m1 m2 a1 a2. (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.

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

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

evalRWST :: forall r w s m a. 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.

ask :: forall m r. MonadAsk r m => m r

local :: forall m r a. MonadReader r m => (r -> r) -> m a -> m a

asks :: forall r m a. MonadAsk r m => (r -> a) -> m a

Projects a value from the global context in a MonadAsk.

state :: forall m s a. MonadState s m => (s -> (Tuple a s)) -> m a

put :: forall m s. MonadState s m => s -> m Unit

Set the state.

modify_ :: forall s m. MonadState s m => (s -> s) -> m Unit

modify :: forall s m. MonadState s m => (s -> s) -> m s

Modify the state by applying a function to the current state. The returned value is the new state value.

gets :: forall s m a. MonadState s m => (s -> a) -> m a

Get a value which depends on the current state.

get :: forall m s. MonadState s m => m s

Get the current state.

listen :: forall m w a. MonadWriter w m => m a -> m (Tuple a w)

pass :: forall m w a. MonadWriter w m => m (Tuple a (w -> w)) -> m a

tell :: forall m w. MonadTell w m => w -> m Unit

listens :: forall w m a b. MonadWriter w m => (w -> b) -> m a -> m (Tuple a b)

Projects a value from modifications made to the accumulator during an action.

censor :: forall w m a. MonadWriter w m => (w -> w) -> m a -> m a

Modify the final accumulator value by applying a function.