The Listener and the Lisp Heap

You can close the Listener at any time. This has the effect of disposing of the text in the Listener. However, it does not undo any side-effects of the interactions you've had in the Listener. Those side-effects were performed on the global state of the Lisp heap, and remain even after the Listener they were entered in is closed.

Similarly, when you save a Listener, you are simply saving text. You are not saving a snapshot of the state of your current programming session. (It is possible to save snapshots with a different technique, as described in "Preserving programming sessions" on page 47.)

To create a new Listener at any time (whether or not there is already a Listener on the screen), choose New Listener from the File menu.

The following example shows that side-effects created through a Listener interaction persist, even after the Listener is closed.

Define a variable

? (defvar new-variable 100) NEW-VARIABLE ? new-variable 100 ;a variable evaluates to its value ? (+ new-variable 50) 150

Close the Listener window and create a new one.

Use the variable in the new Listener window. It's still there. ? (* new-variable new-variable) 10000

If you want to reset the Lisp heap and start over again, you do not do this by closing the Listener, but by quitting and restarting MCL.

Gettmg Started with MCL - 19 OCT 1996

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