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.