Reads the next object in a mailbox.
A string or
If mailbox is empty and timeout is
mailbox-read blocks until an object is placed in mailbox. If mailbox is empty and timeout is a non-negative
mailbox-read blocks until an object is placed in mailbox or timeout seconds have passed. If the timeout occurs, then
nil as the first value and also flag is
nil. If an object is actually read from the mailbox, then flag is
The wait-reason argument defaults to
"Waiting for message in #<Mailbox...>" and will be the value returned by process-whostate while
mailbox-read is blocking.
LispWorks User Guide and Reference Manual - 20 Sep 2017