Don’t evaluate more than once

• A macro similar to OR

(defmacro or1 (a b)

`(if ,a ,a ,b))

• What happens for: (or1 (print 1) (print 2))

  (if (print 1) (print 1) (print 2))
  

• To avoid multiple evaluation:

(defmacro or2 (a b)

`(let ((temp ,a))

(if temp temp ,b)))

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