Returns a function that determines whether a process should continue to wait.
process-wait-function process => wait-function
A function designator.
process-wait-function returns the function that determines whether the Lisp process waits. The system periodically calls wait-function to decide whether to wake the process up.
wait-function is applied to wait-arguments, where both wait-function and wait-arguments were passed to process-wait.
LispWorks User Guide and Reference Manual - 20 Sep 2017