Boxes­Cowan

Boxes

This is a trivial module, providing objects with a single mutable state. Several Schemes have something like it, sometimes called cells. Boxes are a disjoint type.

Procedures

• box: constructor
• box?: predicate
• unbox: accessor
• set-box!: mutator

Existing implementations

Proposed	Racket	Gambit	SISC	Chez	Chicken	MIT	Scheme48/scsh
box	box	box	box	box	make-box	make-cell	make-cell
box?	box?	box?	box?	box?	box-mutable?	cell?	cell?
unbox	unbox	unbox	unbox	unbox	box-ref	cell-contents	cell-ref
set-box!	set-box!	set-box!	set-box!	set-box!	box-set!	set-cell-contents!	cell-set!

Lexical syntax

Racket, Gambit, SISC, Chez, and Chicken all support #& to create a box initialized with the object represented by the following datum.