ruby the functional way

ruby-functions.rb

def flist(list)
  clone = list.dup
  return [] if list == []
  [ clone.shift, clone ]
end

def len(list, acc = 0)
  return acc if list == []
  _, tail = flist list
  len(tail, acc + 1)
end

def sum(list, acc = 0)
  return acc if list == []
  head, tail = flist list
  sum(tail, acc + head)
end