How to tell if the user pressed F3 when a command was running?

When you run, say, WRKSPLF and take option 5 against a series of spooled
files to display them, if you press Enter when viewing the spooled file, you
are shown the next one. If, however, you press F3, you are returned to the
list of spooled files.

Question: how to reproduce this behavior in a user-written application than
calls the DSPSPLF command? In other words how can a user-written calling
program (CL, RPG or whatever) "know" what key the user pressed to exit the
DSPSPLF command?

This seems such a simple question but it's got me beaten at the moment. I've
been hunting through InfoCenter but can find any way of running a command
(QCMDEXC, QCAPCMD, C-language "system" etc.) which gives any kind of
feedback or return code or message when F3 is pressed as opposed to Enter.

Any suggestions? Is there something in UIM perhaps? Does it help if you
write things as a request processor?

I've got a nasty feeling I'm missing something obvious. Or can this not be
done? I suspect WRKSPLF does not call DSPSPLF in the same way a user-written
application has to, but so far as I am aware, IBM does not provide an
API-equivalent of DSPSPLF.

Thanks