Page:AIM-453.djvu/37

 variable. If there is no such binding, then the intent is to initialize a top-level variable; EV-TOP-LEVEL-SETQ locates the top-level environment (which is always at the end of any environment) and creates a new binding by altering the environment structure.

We also modify EVAL to recognize PROGN. EVPROGN is a tail-recursive loop which evaluates each subform of the PROGN form in turn, throwing away each value but the last. {Note PROGN Wizardry}