© Gary D. Knott 2017

Gary D. Knott, Interpreting LISP, 10.1007/978-1-4842-2707-7_28

28. Garbage Collection

Gary D. Knott

(1)Civilized Software Inc., Silver Spring, Maryland, USA

As input S-expressions are provided to the LISP interpreter to evaluate, various list structures in the list area are constructed, both from the input and during the process of evaluation. Many of these list structures have no use after they have been initially used. Such useless data objects are called garbage data objects. In the case of list area nodes, a node is garbage if it cannot be reached. This means that it is not a node in any list structure that is the value of an ordinary atom, including user-defined function and special form values, nor is it reachable from ...

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