CLHS: Macro COND

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Macro COND

Syntax:

cond {clause}* => result*

    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

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

if, case.

Notes: None.

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