The top level loop is the Common Lisp mechanism by which the user normally interacts with the Common Lisp system. This loop is sometimes referred to as the Lisp read-eval-print loop because it typically consists of an endless loop that reads an expression, evaluates it and prints the results.
The top level loop is not completely specified; thus the user interface is implementation-defined. The top level loop prints all values resulting from the evaluation of a form. Figure 25--1 lists variables that are maintained by the Lisp read-eval-print loop.
* + / - ** ++ // *** +++ ///
Figure 25--1: Variables maintained by the Read-Eval-Print Loop
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