pipe-close-connection closes the connection underlying stream without closing the stream itself. This means that you cannot communicate with the child process anymore, but pipe-exit-status can still return the exit-status of the child process after a call to
pipe-close-connection. This differs from close, which prevents
pipe-exit-status from working on Microsoft Windows. You should still call
close on stream when you have finished using it.
LispWorks User Guide and Reference Manual - 20 Sep 2017