Return a weak vector with size elements. If the optional argument fill is given, all entries in the vector will be set to fill. The default value for fill is the empty list.
Construct a weak vector from a list:
the list of its arguments while
its only argument l (a list) to construct a weak vector
the same way
#t if obj is a weak vector.
Return the kth element of the weak vector wvect, or
#f if that element has been collected.
Set the kth element of the weak vector wvect to elt.