8.13 Summary of garbage collection symbols

8.13.7 Using special actions

In addition, users may want to perform special actions when certain types of object are garbage collected, using the functionsadd-special-free-action,flag-special-free-action,flag-not-special-free-action andremove-special-free-action.

For example, when a file stream is closed, and so garbage collected, the file descriptor must be closed also. This operation can be performed as a special action.