构造SLR语法分析表

构造SLR语法分析表

方法：

1）构造G‘的规范LR(0)项集族

2）根据规则生成动作

3）生成转换

4）设置报错

/**
     * P157 规范LR(0)项集族
     * @param grammar
     */
    public List<SetOfItems> items(Grammar grammar) {

        int setId = 0;

        List<SetOfItems> result = new ArrayList<>();
        Map<Symbol, SetOfItems> gotoMap = new HashMap<>();

        List<Production> production = grammar.getProduction(grammar.start);

        // 开始状态
        SetOfItems startSet = new SetOfItems();
        startSet.add(Item.of(production.get(0), 0));
        startSet = closure(startSet, grammar);
        startSet.setId(setId++);
        result.add(startSet);

        boolean hasNew;// 是否产生新的项集
        do {
            hasNew = false;
            List<SetOfItems> allSet = new ArrayList<>(result);
            for (SetOfItems setOfItems : allSet) {
                for (Symbol symbol : grammar.allSymbols) {

                    SetOfItems gotoTarget = gotoSet(grammar, setOfItems, symbol);
                    // 在符号symbol上没有GOTO集合
                    if (gotoTarget == null) {
                        continue;
                    }

                    // 判断项集是否已经存在
                    SetOfItems pre = CollectionUtil.find(result, gotoTarget);
                    if (pre != null) {// 已经存在只记录GOTO
                        setOfItems.addGoto(symbol, pre);
                        continue;
                    }

                    gotoTarget.setId(setId++);
                    setOfItems.addGoto(symbol, gotoTarget);
                    result.add(gotoTarget);
                    hasNew = true;
                }
            }
        } while (hasNew);

        return result;
    }

语法分析表的结构

1.动作函数ACTION，移入，规约，接受，报错

2.转换函数GOTO

/**
 * 语法分析表
 */
public class ParsingTable {

    private Map<Integer, Map<Symbol, Action>> set_symbol_action = new HashMap<>();
    private Map<Integer, Map<Symbol, Integer>> set_symbol_set = new HashMap<>();

    public void addAction(int fromId, Symbol symbol, Action action) {
        Map<Symbol, Action> actionMap = set_symbol_action.computeIfAbsent(fromId, k -> new HashMap<>());
        actionMap.put(symbol, action);
    }

    public void addGoto(int fromId, Symbol symbol, int toId) {
        Map<Symbol, Integer> actionMap = set_symbol_set.computeIfAbsent(fromId, k -> new HashMap<>());
        actionMap.put(symbol, toId);
    }

    public Action getAction(int setId, Symbol symbol) {
        Map<Symbol, Action> actionMap = set_symbol_action.get(setId);
        if (actionMap == null) {
            return null;
        }
        return actionMap.get(symbol);
    }

    public Integer gotoSet(int setId, Symbol symbol) {
        Map<Symbol, Integer> setMap = set_symbol_set.get(setId);
        if (setMap == null) {
            return null;
        }
        return setMap.get(symbol);
    }
}

构建语法分析表

/**
     * P161 算法4.46 构造一个SLR语法分析表
     * @param grammar
     * @param setList
     * @return
     */
    public ParsingTable buildParsingTable(Grammar grammar, List<SetOfItems> setList) {
        ParsingTable result = new ParsingTable();

        for (SetOfItems from : setList) {

            for (Item item : from.getItems()) {

                if (item.pos != item.getProduction().getBody().size()) {
                    continue;
                }

                Nonterminal head = item.getProduction().getHead();
                if (head.equals(grammar.start)) {
                    // 如果[S' -> S·]在I中，那么将ACTION[i $]设置为接受
                    Set<Terminal> follows = grammar.follow(head);
                    for (Terminal symbol : follows) {
                        result.addAction(from.getId(), symbol, AcceptAction.of());
                    }
                } else {
                    // 如果[A -> α·]在I中，那么对于所有FOLLOW(A)中的所有a，将ACTION[i a]设置为规约
                    Set<Terminal> follows = grammar.follow(head);
                    for (Terminal symbol : follows) {
                        result.addAction(from.getId(), symbol, ReduceAction.of(item.getProduction()));
                    }
                }
            }

            for (Map.Entry<Symbol, SetOfItems> entry : from.getGotoMap().entrySet()) {
                Symbol symbol = entry.getKey();
                SetOfItems to = entry.getValue();

                // 如果[A -> α·aβ]在from中并且GOTO(from, a) = to，那么将Action[from,a]设置为移入to，a必须为一个终结符
                if (symbol instanceof Terminal) {
                    result.addAction(from.getId(), symbol, ShiftAction.of(to.getId()));
                } else {
                    result.addGoto(from.getId(), symbol, to.getId());
                }

            }
        }

        return result;
    }