How to use the expression.gen_E_id function in Expression

@takes(AST)
@returns(Clazz)
def parse_enum(node):
  _kind = node.getText()
  cls = Clazz(kind=_kind)
  cls.name = node.getChild(0).getChild(0).getText()
  _nodes = node.getChildren()[1:] # exclude name
  constants = util.implode_id(util.mk_v_node_w_children(_nodes)).split(',')
  for c in constants:
    # define representative field
    fld = field.Field(clazz=cls, mods=C.PBST, typ=cls.name, name=c)
    cls.add_fld(fld)
    # initialize it in 
    f = exp.gen_E_id(cls.name)
    init_e = exp.gen_E_new(exp.gen_E_call(f, []))
    init_s = st.gen_S_assign(exp.gen_E_id(c), init_e)
    cls.clinit_fld(fld, [init_s])
  return cls

  @staticmethod
  def call_init(tname, params=[]):
    args = []
    try:
      cls = class_lookup(tname)
      inits = cls.mtd_by_name(tname) # AttributeError if cls is NoneType
      for init in inits:
        _args = method.sig_match(init.params, params)
        # try to find best matched one
        if len(args) <= len(_args): args = _args
    except (AttributeError, IndexError): pass
    f = exp.gen_E_id(tname)
    args = map(exp.to_expression, args)
    return exp.gen_E_new(exp.gen_E_call(f, args)), args

@takes(AST)
@returns(Clazz)
def parse_enum(node):
  _kind = node.getText()
  cls = Clazz(kind=_kind)
  cls.name = node.getChild(0).getChild(0).getText()
  _nodes = node.getChildren()[1:] # exclude name
  constants = util.implode_id(util.mk_v_node_w_children(_nodes)).split(',')
  for c in constants:
    # define representative field
    fld = field.Field(clazz=cls, mods=C.PBST, typ=cls.name, name=c)
    cls.add_fld(fld)
    # initialize it in 
    f = exp.gen_E_id(cls.name)
    init_e = exp.gen_E_new(exp.gen_E_call(f, []))
    init_s = st.gen_S_assign(exp.gen_E_id(c), init_e)
    cls.clinit_fld(fld, [init_s])
  return cls

  @takes("Clazz", "Field", list_of("Statement"))
  @returns(nothing)
  def init_fld(self, fld, init_ss=[]):
    # declare  if not exists
    inits = self.mtd_by_name(self._name)
    if not inits: inits = [self.add_default_init()]

    # make initializing statements
    if not init_ss and not fld.is_final:
      call = Clazz.call_init_if_instantiable(fld.typ)
      if call: init_ss = [st.gen_S_assign(exp.gen_E_id(fld.name), call)]

    # update the method body
    if init_ss:
      for init in inits: init.body.extend(init_ss[:])

cs = map(curried_s, rm_braces(__node.getChildren()[1:]))
        catches.append( (e, cs) )
      elif __kind == '}': break
      idx = idx - 1

    b = map(curried_s, rm_braces(_nodes[1:idx+1]))
    s = gen_S_try(b, catches, fs)

  # (S... typ var (= (E... )) ';')
  elif _nodes[-2].getText() == '=':
    var = _nodes[-3].getText()
    # type can be a list of nodes, e.g., List < T >
    ty_node = util.mk_v_node_w_children(_nodes[:-3])
    ty = util.implode_id(ty_node)
    mtd.locals[var] = ty
    le = gen_E_id(var, ty)
    re = curried_e(_nodes[-2].getChild(0))
    s = gen_S_assign(le, re)

  # (DECL typ var ';') # local variable declaration
  elif node.getText() == C.T.DECL:
    # type can be a list of nodes, e.g., Class < ? extends Activity >
    ty_node = util.mk_v_node_w_children(_nodes[:-2])
    ty = util.implode_id(ty_node)
    var = _nodes[-2].getText()
    mtd.locals[var] = ty
    e_decl = gen_E_id(var, ty)
    s = gen_S_e(e_decl)

  else: raise Exception("unhandled statement", node.toStringTree())

  return s

# type can be a list of nodes, e.g., List < T >
    ty_node = util.mk_v_node_w_children(_nodes[:-3])
    ty = util.implode_id(ty_node)
    mtd.locals[var] = ty
    le = gen_E_id(var, ty)
    re = curried_e(_nodes[-2].getChild(0))
    s = gen_S_assign(le, re)

  # (DECL typ var ';') # local variable declaration
  elif node.getText() == C.T.DECL:
    # type can be a list of nodes, e.g., Class < ? extends Activity >
    ty_node = util.mk_v_node_w_children(_nodes[:-2])
    ty = util.implode_id(ty_node)
    var = _nodes[-2].getText()
    mtd.locals[var] = ty
    e_decl = gen_E_id(var, ty)
    s = gen_S_e(e_decl)

  else: raise Exception("unhandled statement", node.toStringTree())

  return s