Weak vectors are mainly useful in Guile's implementation of weak hash tables.
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:
weak-vectoruses the list of its arguments while
list->weak-vectoruses its only argument l (a list) to construct a weak vector the same way