IORef package:relude

Lifted reexports from Data.IORef module.

A mutable variable in the IO monad.

>>> import GHC.Internal.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.

Lifted version of atomicModifyIORef.

>>> ref <- newIORef 42

>>> atomicModifyIORef ref (\a -> (a, a + 3))
45

>>> readIORef ref
42

• To avoid space-leaks, see atomicModifyIORef' for stricter updates
• If you are not interested in the return value, see atomicModifyIORef_

Lifted version of atomicModifyIORef'.

>>> ref <- newIORef 42

>>> atomicModifyIORef' ref (\a -> (a, a + 3))
45

>>> readIORef ref
42

• For lazier updates, see atomicModifyIORef
• If you are not interested in the return value, see atomicModifyIORef'_

Version of atomicModifyIORef' that discards return value. Useful when you want to update IORef but not interested in the returning result.

>>> ref <- newIORef 42

>>> atomicModifyIORef'_ ref (`div` 2)

>>> readIORef ref
21

Version of atomicModifyIORef that discards return value. Useful when you want to update IORef but not interested in the returning result.

>>> ref <- newIORef 42

>>> atomicModifyIORef_ ref (`div` 2)

>>> readIORef ref
21

Lifted version of atomicWriteIORef.

>>> ref <- newIORef 42

>>> atomicWriteIORef ref 45

>>> readIORef ref
45

Lifted version of modifyIORef.

>>> ref <- newIORef 42

>>> modifyIORef ref (\a -> a + 6)

>>> readIORef ref
48

• To avoid space-leaks, see modifyIORef' for stricter updates
• For atomic updates, see atomicModifyIORef

Lifted version of modifyIORef'.

>>> ref <- newIORef 42

>>> modifyIORef' ref (\a -> a + 3)

>>> readIORef ref
45

• For lazier updates, see modifyIORef
• For atomic updates, see atomicModifyIORef'

Lifted version of newIORef.

>>> ref <- newIORef False

>>> :t ref
ref :: IORef Bool

Lifted version of readIORef.

>>> ref <- newIORef 42

>>> readIORef ref
42

Lifted version of writeIORef.

>>> ref <- newIORef 42

>>> writeIORef ref 43

>>> readIORef ref
43