Data.IVar.Simple

IVars are write-once variables.

Similarily to MVars, IVars can be either empty or filled. Once filled, they keep their value indefinitely - they are immutable.

Reading from an empty IVar will block until the IVar is filled. Because the value read will never change, this is a pure computation.

Documentation

data IVar a

A write-once (immutable) Variable

new :: IO (IVar a)

Create a new, empty IVar.

newFull :: a -> IO (IVar a)

Create a new filled IVar.

This is slightly cheaper than creating a new IVar and then writing to it.

read :: IVar a -> a

Returns the value of an IVar.

The evaluation will block until a value is written to the IVar if it has no value yet.

tryRead :: IVar a -> IO (Maybe a)

Try to read an IVar. Returns Nothing if it has no value yet.

write :: IVar a -> a -> IO ()

Writes a value to an IVar. Raises a BlockedIndefinitelyOnIVar exception if the variable already has a value.

tryWrite :: IVar a -> a -> IO Bool

Writes a value to an IVar. Returns True if successful, and False otherwise.

data BlockedIndefinitelyOnIVar

The thread has attempted to write to a full IVar.

Instances

Show BlockedIndefinitelyOnIVar

Exception BlockedIndefinitelyOnIVar

Typeable * BlockedIndefinitelyOnIVar