3.11 Boxes

A box is like a single-element vector. It can print as a quoted #& followed by the printed form of the boxed value. A #& form can also be used as an expression, but since the resulting box is constant, it has practically no use.

Examples:

> (define b (box "apple")) > b '#&"apple" > (unbox b) "apple" > (set-box! b '(banana boat)) > b '#&(banana boat)

Boxes in The Racket Reference provides more on boxes and box procedures.