def p_if_stmt(p):
    """
    if_stmt : IF expr sep stmt_list_opt elseif_stmt END_STMT
            | IF LPAREN expr RPAREN stmt_list_opt elseif_stmt END_STMT
    """
    if len(p) == 7:
        p[0] = node.if_stmt(cond_expr=p[2], then_stmt=p[4], else_stmt=p[5])
    elif len(p) == 8:
        p[0] = node.if_stmt(cond_expr=p[3], then_stmt=p[5], else_stmt=p[6])
    else:
        assert 0