Control.Monad.State.Trans
- Package
- transformers
- Repository
- purescript/purescript-transformers
This module defines the state monad transformer, StateT
.
#StateT Source
newtype StateT :: Type -> (Type -> Type) -> Type -> Type
newtype StateT s m a
The state monad transformer.
This monad transformer extends the base monad with the operations get
and put
which can be used to model a single piece of mutable state.
The MonadState
type class describes the operations supported by this monad.
Constructors
Instances
Newtype (StateT s m a) _
(Functor m) => Functor (StateT s m)
(Monad m) => Apply (StateT s m)
(Monad m) => Applicative (StateT s m)
(Monad m, Alt m) => Alt (StateT s m)
(Monad m, Plus m) => Plus (StateT s m)
(Monad m, Alternative m) => Alternative (StateT s m)
(Monad m) => Bind (StateT s m)
(Monad m) => Monad (StateT s m)
(MonadRec m) => MonadRec (StateT s m)
(MonadZero m) => MonadZero (StateT s m)
(MonadPlus m) => MonadPlus (StateT s m)
MonadTrans (StateT s)
Lazy (StateT s m a)
(MonadEffect m) => MonadEffect (StateT s m)
(MonadCont m) => MonadCont (StateT s m)
(MonadThrow e m) => MonadThrow e (StateT s m)
(MonadError e m) => MonadError e (StateT s m)
(MonadAsk r m) => MonadAsk r (StateT s m)
(MonadReader r m) => MonadReader r (StateT s m)
(Monad m) => MonadState s (StateT s m)
(MonadTell w m) => MonadTell w (StateT s m)
(MonadWriter w m) => MonadWriter w (StateT s m)
(Monad m, Semigroup a) => Semigroup (StateT s m a)
(Monad m, Monoid a) => Monoid (StateT s m a)
#evalStateT Source
evalStateT :: forall s m a. Functor m => StateT s m a -> s -> m a
Run a computation in the StateT
monad, discarding the final state.
#execStateT Source
execStateT :: forall s m a. Functor m => StateT s m a -> s -> m s
Run a computation in the StateT
monad discarding the result.
#withStateT Source
withStateT :: forall s m a. (s -> s) -> StateT s m a -> StateT s m a
Modify the final state in a StateT
monad action.
Re-exports from Control.Monad.State.Class
#MonadState Source
class MonadState :: Type -> (Type -> Type) -> Constraint
class (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 functionf
.
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
#put Source
put :: forall m s. MonadState s m => s -> m Unit
Set the state.
#modify_ Source
modify_ :: forall s m. MonadState s m => (s -> s) -> m Unit
#modify Source
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 Source
gets :: forall s m a. MonadState s m => (s -> a) -> m a
Get a value which depends on the current state.
#get Source
get :: forall m s. MonadState s m => m s
Get the current state.
Re-exports from Control.Monad.Trans.Class
#MonadTrans Source
class MonadTrans :: ((Type -> Type) -> Type -> Type) -> Constraint
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
- Modules
- Control.
Comonad. Env - Control.
Comonad. Env. Class - Control.
Comonad. Env. Trans - Control.
Comonad. Store - Control.
Comonad. Store. Class - Control.
Comonad. Store. Trans - Control.
Comonad. Traced - Control.
Comonad. Traced. Class - Control.
Comonad. Traced. Trans - Control.
Comonad. Trans. Class - Control.
Monad. Cont - Control.
Monad. Cont. Class - Control.
Monad. Cont. Trans - Control.
Monad. Error. Class - Control.
Monad. Except - Control.
Monad. Except. Trans - Control.
Monad. Identity. Trans - Control.
Monad. List. Trans - Control.
Monad. Maybe. Trans - Control.
Monad. RWS - Control.
Monad. RWS. Trans - Control.
Monad. Reader - Control.
Monad. Reader. Class - Control.
Monad. Reader. Trans - Control.
Monad. State - Control.
Monad. State. Class - Control.
Monad. State. Trans - Control.
Monad. Trans. Class - Control.
Monad. Writer - Control.
Monad. Writer. Class - Control.
Monad. Writer. Trans