& fold()
 
  Syntax: fold([<obj>/]<attr>, <list>[, <base-case>[, <delim>])
 
  This function iteratively processes a list through a function, 
  feeding the result of one step into the next step as %0, passing in 
  the next element from the list as %1. If a base case is provided, it 
  is used as the initial %0. If not, the first list element is passed 
  as %0 and the second is passed as %1, and subsequent iterations 
  proceed normally.
 
  <delimiter> may be used to specify a delimiter other than space, but 
  you must specify a base case in order to specify the delimiter.
 
  Example:
 
  > &REP_NUM object=[%0][repeat(%1,%1)]
  > say fold(object/rep_num,1 2 3 4 5,->)
  You say "->122333444455555"
  > &ADD_NUMS object=add(%0,%1)
  > say fold(object/add_nums,1 2 3 4 5)
  You say "15"
 
  See Also: u(), iter(), map(), filter()