Safe Haskell	Trustworthy

Control.Monad.StateVar

Contents

Description

Overloaded get and put for state variables (IORef, TVar, etc.) to make reading and writing more concise.

Synopsis

Overloaded get and put

class HasGet m v whereSource

Methods

get :: v a -> m aSource

Read the value from the variable.

Instances

HasGet IO IORef	`readIORef`
HasGet STM TVar	`readTVar`
(HasGet m v, MonadTrans t, Monad m) => HasGet (t m) v	`lift` $ `get` v
HasGet (ST s) (STRef s)	`readSTRef`
HasGet (ST s) (STRef s)	`readSTRef`

class HasPut m v whereSource

Methods

put :: v a -> a -> m ()Source

Write a new value to the variable.

Instances

HasPut IO IORef	`writeIORef`
HasPut STM TVar	`writeTVar`
(HasPut m v, MonadTrans t, Monad m) => HasPut (t m) v	`lift` $ `put` v a
HasPut (ST s) (STRef s)	`writeSTRef`
HasPut (ST s) (STRef s)	`writeSTRef`

put' :: HasPut m v => v a -> a -> m ()Source

Variant of put that forces the value before writing it.

modify :: (HasGet m v, HasPut m v, Monad m) => v a -> (a -> a) -> m ()Source

Modify the value inside the variable with the given function.

list <- newIORef [1,2,3]
modify list (0:)  -- prepend 0 to the list

modify' :: (HasGet m v, HasPut m v, Monad m) => v a -> (a -> a) -> m ()Source

Variant of modify that forces the result of the function.

tally <- newIORef (0 :: Int)
modify tally (+ 10)  -- add 10 to the tally

swap :: (HasGet m v, HasPut m v, Monad m) => v a -> a -> m aSource

Write a new value and return the old value.

Infix aliases

($=) :: HasPut m v => v a -> a -> m ()Source

Infix alias for put

($~) :: (HasGet m v, HasPut m v, Monad m) => v a -> (a -> a) -> m ()Source

Infix alias for modify

($=!) :: HasPut m v => v a -> a -> m ()Source

Infix alias for put'

($~!) :: (HasGet m v, HasPut m v, Monad m) => v a -> (a -> a) -> m ()Source

Infix alias for modify'