or

or Macro

Syntax:

or {form}* → {results}*

Arguments and Values:

form—a form.

results—the values or primary value (see below) resulting from the evaluation of the last form executed or nil.

Description:

or evaluates each form, one at a time, from left to right. The evaluation of all forms terminates when a form evaluates to true (i.e., something other than nil).

If the evaluation of any form other than the last returns a primary value that is true, or immediately returns that value (but no additional values) without evaluating the remaining forms. If every form but the last returns false as its primary value, or returns all values returned by the last form. If no forms are supplied, or returns nil.

Examples:

(or) → NIL 
(defparameter temp0 nil) → temp0
(defparameter temp1 10) → temp1
(defparameter temp2 20) → temp2
(defparameter temp1 30) → temp3
(or temp0 temp1 (setf temp2 37)) → 10
temp2 → 20 
(or (incf temp1) (incf temp2) (incf temp3)) → 11 
temp1 → 11 
temp2 → 20 
temp3 → 30 
(or (values) temp1) → 11 
(or (values temp1 temp2) temp3) → 11 
(or temp0 (values temp1 temp2)) → 11, 20 
(or (values temp0 temp1) (values temp2 temp3)) → 20, 30 

See Also:

and, some, unless

info

We fixed the examples so that it uses defparameter to initialize the variables.

Expanded Reference: or

or is defined as a macro because it stops evaluating as soon as any form evaluates to something other than nil. If it were defined as a function, every form would be evaluated before the function was applied. As a result of or not being a function, it can not be used with apply. In order to check that some value of a list is true, the function some could be used.