empty -parsec +base
If the SampleVar is full, leave it empty. Otherwise, do nothing.
Returns True if the supplied Chan is empty.
Check whether a given MVar is empty.
Notice that the boolean value returned is just a snapshot of the state of the MVar. By the time you get to react on its result, the MVar may have been filled (or emptied) - so be extremely careful when using this operation. Use tryTakeMVar instead if possible.
Returns True if the SampleVar is currently empty.
Note that this function is only useful if you know that no other threads can be modifying the state of the SampleVar, because otherwise the state of the SampleVar may have changed by the time you see the result of isEmptySampleVar.
Create an MVar which is initially empty.