old_contents: # Copyright (C) 2011 by Paolo Capriotti <p.capriotti@gmail.com>
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in
  # all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  # THE SOFTWARE.
  
  import itertools
  
  
  class RuleCollection(object):
      def __init__(self):
          self.rules = { }
  
      def add_rule(self, rule, level = 0):
          self.rules.setdefault(level, [])
          self.rules[level].append(rule)
  
      def apply(self, transaction, entry):
          entries = [entry]
  
          levels = self.rules.keys()
          levels.sort()
  
          for level in levels:
              rules = self.rules[level]
              new_entries = []
              for entry in entries:
                  new_entries.append(entry)
                  for rule in rules:
                      new_entries += list(rule.apply(transaction, entry))
              entries = new_entries
  
          return entries
  
  class Generator(object):
      def __init__(self, generator):
          self.generator = generator
  
      def __call__(self, *args):
          return self.generator(*args)
  
      def __add__(self, other):
          @Generator
          def result(*args):
              return itertools.chain(self(*args), other(*args))
          return result
  Generator.null = Generator(lambda *args: [])
  
  class Rule(object):
      def __init__(self, filter, generator):
          self.filter = filter
          self.generator = generator
  
      def apply(self, transaction, entry):
          if self.filter(transaction, entry):
              return self.generator(entry)
          else:
              return []
  
  class TransactionRule(Rule):
      def apply(self, transaction):
          if self.filter(transaction, None):
              return self.generator(transaction)
          else:
              return transaction
  
new_contents: # Copyright (C) 2011 by Paolo Capriotti <p.capriotti@gmail.com>
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in
  # all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  # THE SOFTWARE.
  
  import itertools
  
  
  class RuleCollection(object):
      def __init__(self):
          self.rules = { }
  
      def add_rule(self, rule, level = 0):
          self.rules.setdefault(level, [])
          self.rules[level].append(rule)
  
      def apply(self, transaction, entry):
          entries = [entry]
  
          levels = self.rules.keys()
          levels.sort()
  
          for level in levels:
              rules = self.rules[level]
              new_entries = []
              for entry in entries:
                  new_entries.append(entry)
                  for rule in rules:
                      new_entries += list(rule.apply(transaction, entry))
              entries = new_entries
  
          return entries
  
  class Generator(object):
      def __init__(self, generator):
          self.generator = generator
  
      def __call__(self, *args):
          return self.generator(*args)
  
      def __add__(self, other):
          @Generator
          def result(*args):
              return itertools.chain(self(*args), other(*args))
          return result
  Generator.null = Generator(lambda *args: [])
  
  class Rule(object):
      def __init__(self, filter, generator):
          self.filter = filter
          self.generator = generator
  
      def apply(self, transaction, entry):
          if self.filter(transaction, entry):
              return self.generator(entry.of(transaction))
          else:
              return []
  
  class TransactionRule(Rule):
      def apply(self, transaction):
          if self.filter(transaction, None):
              return self.generator(transaction)
          else:
              return transaction
  
subject: Add transaction data to an entry before passing it to a generator.