Chapter 3: The Application Framework

Preserving programming sessions

At times it is desirable to save a snapshot of your environment for later resumption. It may be that reproducing a particular state is very time consuming, either because it involves loading many files of Lisp code, because it requires performing other lengthy computations, or perhaps because your environment has gotten into an anomalous state which you want to examine later.

MCL includes a facility for saving snapshots--also known as images--of a running Lisp session. These snapshots can be restarted at a later time. They start up just about as quickly as starting up a new Lisp system.

To save an image, just call the function save-application. This function takes one required argument and a number of keyword arguments. The required argument is a pathname. It closes any open windows (these cannot be saved), writes an image to disk at the selected pathname, and then exits to the Finder. The saved image is a stand alone application. It can be restarted by double-clicking it, just like any other stand alone application.