Let's now run through these. I assume that you haven't done anything
since starting the life in section 1.2, so you should
still have the initial display of figure 1 shown on your
screen. The simplest thing you can do is to stop the life and
return to Prolog. To do this, type n and then hit RETURN. It
is important that here, and other places where RETURN is needed, you do
type it. If not, the system will just sit there waiting, and you will
never get a reply.
The display should then clear. Once again, you will see Prolog's
?- prompt.
You can start another life by typing
eps( psbug2, psworld2 ).again. Remember to type the dot and the RETURN. For practice, do that now, and then exit with
n again.
You are now back in Prolog again. Start a third life as above. This
time, hit r and then RETURN. r stands for ``refresh'' or
``redraw''. The screen will flicker briefly as it is redrawn. I receive
quite a lot of Email, and when it arrives, VMS announces its
arrival by displaying a message. This may well happen when you are
running Eden: if so, use r to remove the message.
Having typed r, you are still at the start of a life, and Eden is
waiting for another control command. This time, type s, then hit
a space, then type 30, and then hit RETURN. You will see the bug
moving around in the upper part of the screen. At the same time, the
lower part will display what its ``brain'' is doing, in the form of
production-system rules. After about 20 moves, no more rules will apply,
and the life will finish, returning to Prolog.
If you want, you can try that again. It is always possible to run a bug over and over again.
You have now tried the control commands n, r and s.
The final one to try is y, which runs a bug in single-step mode.
This is where Eden pauses after each cycle and asks you whether you want
to continue. Start a new life, and then type y and RETURN. The
bug will go through one cycle, and then pause. Type y and RETURN
again. Keep doing this until the life exits.