#### 25.1.1 Top level loop ¶

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