See https://twitter.com/ftrain/status/267503513477713920

README.md

See https://twitter.com/ftrain/status/267503513477713920

ftrain.py

def ftrain(list):
  out = [ list[0] ]
  stack = [ out ]
  for i in list[1:]:
    last = stack[-1][-1]
    if i > last:
      # start a new list
      new = []
      stack[-1].append(new)
      stack.append(new)
    while i < last:
      # otherwise go back
      stack.pop()
      last = stack[-1][0]
    # add to the end...
    stack[-1].append(i)
  return out

a = [ 1, 2, 3, 3, 4, 4, 2, 1 ]
b = ftrain(a)
print b
# should be = [ 1, [ 2, [ 3, 3, [ 4, 4 ] ], 2 ], 1 ]