compile-work/parser/grammar/AnalysisTableBuilder.cpp

//
// Created by lenfrex on 2023/5/8.
//

#include "Grammar.h"

using namespace std;

// 求是否有交集
bool hasUnion(const set<char> &a, const set<char> &b) {
  for (const auto &selectChars: b) {
    if (a.contains(selectChars)) {
      return true;
    }
  }

  return false;
}

// 检查是否为LL1文法
bool Grammar::isLL1Grammar() {
  // 逐个非终止符检查
  for (const auto &nonTerminal: nonTerminals) {
    SelectSet select = selectSet[nonTerminal];

    // 取一行
    for (auto current = select.begin(); current != select.end();) {
      const auto &productionSelectSet = current->second;
      // 取剩下的行进行比较，注意这里已经++current了，外层for就不要++了
      for (auto innerCurrent = ++current; innerCurrent != select.end(); innerCurrent++) {
        if (hasUnion(productionSelectSet, innerCurrent->second)) {
          return false;
        }
      }
    }
  }

  return true;
}

void Grammar::buildAnalysisTable() {
  if (!isLL1Grammar()) {
    throw NotSupportedGrammarException("文法定义不符合LL1文法");
  }

  for (const auto &nonTerminal: nonTerminals) {
    SelectSet select = selectSet[nonTerminal];
    for (const auto &selectPair: select) {
      const auto &prod = selectPair.first;
      const auto &selectChars = selectPair.second;

      // 填充预测分析表
      for (const auto &selectableTerminal: selectChars) {
        analysisTable[nonTerminal][selectableTerminal] = prod;
      }
    }
  }
}