- set-box! box valueprocedure
Mutator. Changes box to hold value.
The behavior of boxes with the equivalence predicates eq?, eqv?, and equal? is the same as if they were implemented with records. That is, two boxes are both eq? and eqv? iff they are the product of the same call to box and not otherwise, and while they must be equal? if they are eqv?, the converse is implementation-dependent.