old_contents: 
  class NIL(object):
      def __repr__(self):
          return 'NIL'
  
  def crepr(s):
      assert type(s) is str, "crepr is for strings, i.e. str() instances."
      prepr = repr(s)
      if prepr[:3] == '"""':
          # anything goes, need to manually escape everything.
          raise NotImplementedError("not implemented for this repr type.")
      elif prepr[0] == '"':
          return prepr
      else:
          assert prepr[0] == "'", "unknown repr output from python."
          return '"' + prepr[1:-1].replace("\\'", "'").replace('"', '\\"') + '"'
  
  
  def lrepr(s):
      if type(s) is str:
          return crepr(s)
      return repr(s)
  
  
  class MinimalispType(object):
      pass
  
  class Symbol(MinimalispType):
      """only stores its text representation as a python string in upper case
      - can therefore be used as a dict key."""
      def __init__(self, s, quoted=False):
          self.s = s.upper()
          self.quoted = quoted
  
      def __eq__(self, other):
          if type(other) is not Symbol:
              return False
          if self.s == other.s:
              return True
  
      def __repr__(self):
          if self.quoted:
              return "'" + self.s
          return self.s
  
      def __hash__(self):
          return hash(self.s)
  
  
  class Value(MinimalispType):
      """stored simply as the relevant python type (string, int or float)."""
      def __init__(self, v):
          self.v = eval(v)
      
      def __repr__(self):
          if isinstance(self.v, str):
              return crepr(self.v)
          else:
              return repr(self.v)
  
  class Pair(MinimalispType):
      def __init__(self, left=None, right=None, quoted=False):
          self.left = left
          self.right = right
          self.quoted = quoted
  
      @classmethod
      def pair_list_from_sexpr(cls, s, outermost_quoted = False):
          right = NIL()
          for v in reversed(s):
              right = Pair(v, right)
          if outermost_quoted:
              right.quoted = True
          return right
      
      def __repr__(self):
          q = ""
          if self.quoted:
              q = "'"
          return "%s(%s . %s)" % (q, self.left, self.right)
  
  
new_contents: 
  class NIL(object):
      def __repr__(self):
          return 'NIL'
  
  def crepr(s):
      assert type(s) is str, "crepr is for strings, i.e. str() instances."
      prepr = repr(s)
      if prepr[:3] == '"""':
          # anything goes, need to manually escape everything.
          raise NotImplementedError("not implemented for this repr type.")
      elif prepr[0] == '"':
          return prepr
      else:
          assert prepr[0] == "'", "unknown repr output from python."
          return '"' + prepr[1:-1].replace("\\'", "'").replace('"', '\\"') + '"'
  
  
  def lrepr(s):
      if type(s) is str:
          return crepr(s)
      return repr(s)
  
  
  class MinimalispType(object):
      pass
  
  class Symbol(MinimalispType):
      """only stores its text representation as a python string in upper case
      - can therefore be used as a dict key."""
      def __init__(self, s, quoted=False):
          self.s = s.upper()
          self.quoted = quoted
  
      def __eq__(self, other):
          if type(other) is not Symbol:
              return False
          if self.s == other.s:
              return True
  
      def __repr__(self):
          if self.quoted:
              return "'" + self.s
          return self.s
  
      def __hash__(self):
          return hash(self.s)
  
  
  class Value(MinimalispType):
      """stored simply as the relevant python type (string, int or float)."""
      def __init__(self, v, actual=False):
          if actual:
              self.v = v
          else:
              self.v = eval(v)
      
      def __repr__(self):
          if isinstance(self.v, str):
              return crepr(self.v)
          else:
              return repr(self.v)
  
  class Pair(MinimalispType):
      def __init__(self, left=None, right=None, quoted=False):
          self.left = left
          self.right = right
          self.quoted = quoted
  
      @classmethod
      def pair_list_from_sexpr(cls, s, outermost_quoted = False):
          right = NIL()
          for v in reversed(s):
              right = Pair(v, right)
          if outermost_quoted:
              right.quoted = True
          return right
      
      def __repr__(self):
          q = ""
          if self.quoted:
              q = "'"
          return "%s(%s . %s)" % (q, self.left, self.right)
  
  
subject: support for actual values via python-implemented library functions