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