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.

> (define b (box "apple"))
> b


> (unbox b)


> (set-box! b '(banana boat))
> b

'#&(banana boat)

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