3.11 Boxes

A box is like a single-element vector. It prints as #& 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 Reference: PLT Scheme provides more on boxes and box procedures.