def compile_to_python(exp, env, done=None): 
  '''assemble steps from dao expression to python code'''
  original_exp = exp
  compiler = Compiler()
  if done is None:
    done = il.Done(compiler.new_var(il.ConstLocalVar('v')))
  compiler.exit_block_cont_map = {}
  compiler.continue_block_cont_map = {}
  compiler.protect_cont = done
  if env is None: env = Environment()
  exp = element(exp)
  exp = exp.alpha(env, compiler)
  exp = exp.cps(compiler, done)
  exp.analyse(compiler)
  env = Environment()
  exp = exp.optimize(env, compiler)
  #exp = exp.tail_recursive_convert()
  function = compiler.new_var(il.ConstLocalVar('compiled_dao_function'))
  exp = il.Function(function, (), exp)
  exp = il.begin(*exp.pythonize(env, compiler)[0])
  if isinstance(exp, il.Begin):
    exp = exp.statements[0]
  exp.body = exp.body.replace_return_with_yield()
  compiler = Compiler()
  result = exp.to_code(compiler)
  return prelude + result
assemble steps from dao expression to python code