Control.Monad.State.Class

class MonadState :: Type -> (Type -> Type) -> Constraintclass (Monad m) <= MonadState s m | m -> s where

The MonadState s type class represents those monads which support a single piece of mutable state of type s.

• state f updates the state using the function f.

An implementation is provided for StateT, and for other monad transformers defined in this library.

Laws:

• do { get ; get } = get
• do { put x ; put y } = put y
• do { put x ; get } = put x $> x
• do { s <- get ; put s } = pure unit

Members

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

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

Get the current state.

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

Get a value which depends on the current state.

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

Set the state.

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.

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