cond (Macro)

Syntax:

clause::=

(test-form {form}*)

Arguments and Values:

test-form—a form.

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, or else nil if no test-form yields true.

Description:

cond allows the execution of forms to be dependent on test-form.

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 cond form. 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 cond form.

Once one test-form has yielded true, no additional test-forms are evaluated. If no test-form yields true, nil is returned.

Examples:

 (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

See Also:

if, case.