a form.

implementation-dependent.

The value of - is the form that is currently being evaluated by the Lisp read-eval-print loop.

(format t "~&Evaluating ~S~%" -) 
⊳ Evaluating (FORMAT T "~&Evaluating ~S~%" -) 
→ NIL

Lisp read-eval-print loop.

+ (variable), * (variable), / (variable), Section 25.1.1 (Top level loop)