LR语法分析算法

LR语法分析器

组成：一个输入，一个输出，状态栈，驱动程序，语法分析表

注意：规约后需要寻找新的符号在栈顶状态上的转换

例如：

状态栈   符号栈       输入

0 5        $id              *id$           此时需要按F -> id规约

0 3        $F               *id$           3是规约的新符号F在栈顶状态0上的转换

代码实现

/**
     * P159 算法4.44 LR语法分析算法
     */
    public boolean parse(Grammar grammar, List<Symbol> inputs, ParsingTable table) {
        LinkedList<Symbol> inputQueue = new LinkedList<>(inputs);
        inputQueue.addLast(Terminal.dollar);

        // 符号栈 （方便打印）
        Stack<Symbol> symbolStack = new Stack<>();
        int state = 0;// 当前状态
        // 状态栈
        Stack<Integer> stateStack = new Stack<>();
        stateStack.push(state);

        while (true) {
            state = stateStack.peek();
            printStack(state, symbolStack, inputQueue);

            Symbol symbol = inputQueue.getFirst();
            Action action = table.getAction(state, symbol);
            if (action instanceof ShiftAction) {// 移入
                inputQueue.removeFirst();

                ShiftAction shiftAction = (ShiftAction) action;
                stateStack.push(shiftAction.getToId());
                symbolStack.push(symbol);

                LogUtil.print("移入:" + shiftAction.getToId());
                LogUtil.newline();
            } else if (action instanceof ReduceAction) {// 规约
                ReduceAction reduceAction = (ReduceAction) action;
                Production production = reduceAction.getProduction();

                for (Symbol bo : production.getBody()) {
                    if (bo.equals(Terminal.epsilon)) {
                        continue;
                    }
                    stateStack.pop();
                    symbolStack.pop();
                }
                symbolStack.push(production.getHead());

                state = stateStack.peek();
                Integer gotoState = table.gotoSet(state, production.getHead());
                stateStack.push(gotoState);

                LogUtil.print("规约:" + production + " GOTO:" + gotoState);
                LogUtil.newline();

            } else if (action instanceof AcceptAction) {
                LogUtil.print("接受");
                return true;
            } else {
                LogUtil.print("错误");
                return false;
            }
        }
    }