IORef package:breakpoint

data () => IORef a
breakpoint Debug.Breakpoint.GhcFacade
A mutable variable in the IO monad. 
>>> import Data.IORef

>>> r <- newIORef 0

>>> readIORef r
0

>>> writeIORef r 1

>>> readIORef r
1

>>> atomicWriteIORef r 2

>>> readIORef r
2

>>> modifyIORef' r (+ 1)

>>> readIORef r
3

>>> atomicModifyIORef' r (\a -> (a + 1, ()))

>>> readIORef r
4
See also STRef and MVar.