(p)
opt_expression_list : expression_list
                        |    expression_list commas
                        |    empty
opt_expression_list : expression_list
                        |    expression_list commas
                        |    empty
opt_expression_list : expression_list | expression_list commas | empty
def p_opt_expression_list(p):
    '''opt_expression_list : expression_list
                        |    expression_list commas
                        |    empty'''
def p_opt_expression_list ( p ) :