okeuday/pqueue — Issue #5: pqueue error on emptiness.
Author: jlouis
Created: 2011-11-11 21:18:31+00:00
State: open

The following trace constructs an error, this time in `pqueue`:

```
Shrinking .....(5 time(s))
[{set,{var,1},{call,queue_srv,in,[36,4]}},{set,{var,4},{call,queue_srv,out,[]}},{set,{var,6},{call,queue_srv,is_empty,[]}}]
History: [{{state,[]},ok},{{state,[{4,[36]}]},{value,36}},{{state,[]},false}]
State: {state,[]}
Result: {postcondition,false}
```

That is:

* Insert an element `36` with priority `4`.
* Remove that element.
* call `pqueue:is_empty` on the resulting queue.

This returns `false` - the queue is not empty. But if we try to `out` an element of the empty queue, we get told it is empty. There seem to be some problems with priorities.