STMonadTrans-0.3: A monad transformer version of the ST monad

Portabilitynon-portable (GHC Extensions)
Stabilityexperimental
Maintainerjosef.svenningsson@gmail.com

Control.Monad.ST.Trans

Contents

Description

This library provides a monad transformer version of the ST monad.

Warning! This monad transformer should not be used with monads that can contain multiple answers, like the list monad. The reason is that the will be duplicated across the different answers and this cause Bad Things to happen (such as loss of referential transparency). Safe monads include the monads State, Reader, Writer, Maybe and combinations of their corresponding monad transformers.

Synopsis

The ST Monad Transformer

data STT s m a Source

STT is the monad transformer providing polymorphic updateable references

Instances

MonadError e m => MonadError e (STT s m) 
MonadReader r m => MonadReader r (STT s m) 
MonadState s m => MonadState s (STT s' m) 
MonadWriter w m => MonadWriter w (STT s m) 
MonadTrans (STT s) 
Monad m => Monad (STT s m) 
Functor m => Functor (STT s m) 
MonadFix m => MonadFix (STT s m) 
(Monad m, Functor m) => Applicative (STT s m) 

runST :: Monad m => (forall s. STT s m a) -> m aSource

Executes a computation in the STT monad transformer

Mutable references

data STRef s a Source

Mutable references

Instances

Eq (STRef s a) 

newSTRef :: Monad m => a -> STT s m (STRef s a)Source

Create a new reference

readSTRef :: Monad m => STRef s a -> STT s m aSource

Reads the value of a reference

writeSTRef :: Monad m => STRef s a -> a -> STT s m ()Source

Modifies the value of a reference

Mutable arrays

data STArray s i e Source

Mutable arrays

Instances

Eq (STArray s i e) 

newSTArray :: (Ix i, Monad m) => (i, i) -> e -> STT s m (STArray s i e)Source

Creates a new mutable array

readSTArray :: (Ix i, Monad m) => STArray s i e -> i -> STT s m eSource

Retrieves an element from the array

writeSTArray :: (Ix i, Monad m) => STArray s i e -> i -> e -> STT s m ()Source

Modifies an element in the array

boundsSTArray :: STArray s i e -> (i, i)Source

Returns the lowest and highest indices of the array

numElementsSTArray :: STArray s i e -> IntSource

Returns the number of elements in the array

freezeSTArray :: (Ix i, Monad m) => STArray s i e -> STT s m (Array i e)Source

Copy a mutable array and turn it into an immutable array

thawSTArray :: (Ix i, Monad m) => Array i e -> STT s m (STArray s i e)Source

Copy an immutable array and turn it into a mutable array

runSTArray :: (Ix i, Monad m) => (forall s. STT s m (STArray s i e)) -> m (Array i e)Source

A safe way to create and work with a mutable array before returning an immutable array for later perusal. This function avoids copying the array before returning it.

Unsafe Operations

unsafeIOToSTT :: Monad m => IO a -> STT s m aSource