       lvarpop var ?indexExpr? ?string?
              The  lvarpop  command  pops (deletes) the element indexed by the
              expression indexExpr from the list  contained  in  the  variable
              var.   If  index  is  omitted, then 0 is assumed.  If string, is
              specified, then the deleted element is replaced by  string.  The
              replaced  or  deleted  element is returned.  Thus ``lvarpop argv
              0'' returns the first element of argv, setting argv  to  contain
              the remainder of the string.

              If the expression indexExpr starts with the string end, then end
              is replaced with the index of the last element in the list.   If
              the  expression  starts  with len, then len is replaced with the
              length of the list.
