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 {LABELS with Side Effects} Page 37

This implementation of LABELS (see Figure N6) applies the technique of {Note Driver Loop with Side Effects} to the implementation of LABELS in {Note LABELS}. This is in fact how LABELS (or its cousin LABEL) is usually implemented in "real" LISP systems.

For EVAL and EVSETQ see Figure 11. For LOOKUP1 see Figure 3 (not Figure 10, despite Figure 11!).

Figure N6 Implementation of LABELS Using Side Effects