Common Lisp the Language
2nd Edition
Each of the constructs in this section simply evaluates all the argument forms in order. They differ only in what results are returned.
[Special Form]
progn {form}*
The progn construct takes a number of forms and evaluates them sequentially in order from left to right. The values of all the forms but the last are discarded; whatever the last form returns is returned by the progn form. One says that all the forms but the last are evaluated for effect One says that all the forms but the last are evaluated for effectkes a number of forms and evaluatesA>