forms—an implicit progn.
results—the values of the forms
in the first clause whose test-form yields true,
or the primary value of the test-form
if there are no forms in that clause,
nil if no test-form yields true.
cond allows the execution of forms to be dependent
Test-forms are evaluated one at a time in the order in which they are given in the argument list until a test-form is found that evaluates to true.
If there are no forms in that clause, the primary value
of the test-form is returned by the
Otherwise, the forms associated with this test-form are
evaluated in order, left to right, as an implicit progn, and the
values returned by the last form
are returned by the
Once one test-form has yielded true,
no additional test-forms are evaluated.
If no test-form yields true,
nil is returned.
(defun select-options () (cond ((= a 1) (setq a 2)) ((= a 2) (setq a 3)) ((and (= a 3) (floor a 2))) (t (floor a 3)))) → SELECT-OPTIONS (setq a 1) → 1 (select-options) → 2 a → 2 (select-options) → 3 a → 3 (select-options) → 1 (setq a 5) → 5 (select-options) → 1, 2