true.

?- command_loop.
Enter command (end to exit): burp.
burp
Enter command (end to exit): eat.
eat
Enter command (end to exit): drink.
drink
Enter command (end to exit): end.
end
true ;;
Enter command (end to exit): end.
end
true e
Unknown action: e (h for help)
Action? n;
Enter command (end to exit): d.
d
Enter command (end to exit): end.
end
true ..

?- command_loop.
Enter command (end to exit): df
|: .
df
Enter command (end to exit): fd.
fd
Enter command (end to exit): df.
df
Enter command (end to exit): end.
end
true ..

?- halt.