Weak Boxes

A weak box is similar to a normal box (see section 4.9), but when the automatic memory manager can prove that the content value of a weak box is only reachable via weak boxes, the content of the weak box is replaced with #f.

• (make-weak-box v) returns a new weak box that initially contains v.
• (weak-box-value weak-box) returns the value contained in weak-box. If the memory manager has proven that the previous content value of weak-box was reachable only through weak boxes, then #f is returned.
• (weak-box? v) returns #t if v is a weak box, #f otherwise.