SLR(1) 分析表构建详解：LR1 项目集族构建及代码实现
class SLR1 : LR
{
//LR1项目
public class LR1Node
{
public string Left;
public string Right;
public string LookAhead;
public LR1Node(string Left, string Right, string LookAhead)
{
this.Left = Left;
this.Right = Right;
this.LookAhead = LookAhead;
}
}
public List<LR1Node> LR1objNum = new List<LR1Node>(50);//LR1项目列表
public List<char> Vchar = new List<char>(50);//所有符号集合
//构造LR1项目
public void BuildLR1prod(string str)
{
LRNode Lr;
int i = 0;
string left = "";
string right = "";
left += "S'";
right += str[0];
Lr = new LRNode(left, right);//拓广文法开始
LRproNum.Add(Lr);
while (i < str.Length)
{
left = right = "";//还原
int j = i;
while (i < str.Length && str[i] != '\r' && str[i] != '\n')//换行符‘\r\n’
{
if (str[i] == ' ')
{
i++;
continue;
}
if (str[i] == '|') // 遇到'|'可构造一条产生式
{
Lr = new LRNode(left, right);
LRproNum.Add(Lr);
right = ""; //产生式左边相同 右边重新积累
i++; //跳过'|'
continue;
}
if ((i - j) == 0)
{
if (!exist(Nchar, str[i]))//如果非终结符集合中不存在str[i],加入Nchar 产生式左边 只有非终结符 不必判断终结符
Nchar.Add(str[i]);
left += str[i++];
}
else if (i - j <= 2)
i++;
else
{
if (isFinalsymbol(str[i]) && !exist(Nchar, str[i]))//如果非终结符集合中不存在str[i],加入Nchar isfinalsymbol 非终结符返回T 终结符返回F
Nchar.Add(str[i]);
else if (!isFinalsymbol(str[i]) && !exist(Echar, str[i]))//产生式右边 需要判断终结符
Echar.Add(str[i]);
right += str[i++];
}
}//while
i++;//跳过换行符
if (left != "" && right != "")
{
Lr = new LRNode(left, right);//构造每一行最后一个产生式，不存在'|'时就是该行产生式本身
LRproNum.Add(Lr);
}
}//while
Echar.Add('#');
//构造LR1项目
LR1Node LR1obj;
for (i = 0; i < LRproNum.Count; i++)
{
left = LRproNum[i].Left;
right = CreObj(LRproNum[i].Right, 0);//在第0个位置插入'.'
LR1obj = new LR1Node(left, right, "#");//初始展望符为#
LR1objNum.Add(LR1obj);
for (int j = 1; j <= LRproNum[i].Right.Length; j++)//j可以等于length 项目共
{
left = LRproNum[i].Left;
right = CreObj(LRproNum[i].Right, j);
LR1obj = new LR1Node(left, right, "#");
LR1objNum.Add(LR1obj);
}
}
//将终结符和非终结符添加到Vchar
for (i = 0; i < Echar.Count; i++)
{
if (!exist(Vchar, Echar[i]))
{
Vchar.Add(Echar[i]);
}
}
for (i = 0; i < Nchar.Count; i++)
{
if (!exist(Vchar, Nchar[i]))
{
Vchar.Add(Nchar[i]);
}
}
}
//求LR1项目的闭包
public List<int> ClosureLR1(List<int> lr_item)
{
List<int> new_item = new List<int>();
List<int> temp_item = new List<int>(lr_item);
while (temp_item.Count != 0)
{
for (int i = 0; i < temp_item.Count; i++)
{
int index = temp_item[i];
if (!exist(new_item, index))
{
new_item.Add(index);
int pos = LR1objNum[index].Right.IndexOf('.');
if (pos < LR1objNum[index].Right.Length - 1)
{
char symbol = LR1objNum[index].Right[pos + 1];
string LA = LR1objNum[index].LookAhead;
if (!isFinalsymbol(symbol)) //如果当前符号为非终结符
{
for (int j = 0; j < LRproNum.Count; j++)
{
if (LRproNum[j].Left == symbol.ToString())
{
for (int k = 0; k < LRproNum[j].Right.Length + 1; k++)
{
string right = CreObj(LRproNum[j].Right, k);
string lookAhead = GetLookAhead(LR1objNum[index].LookAhead, LRproNum[j].Right, k);//计算展望符
LR1Node LR1obj = new LR1Node(LRproNum[j].Left, right, lookAhead);
int itemindex = LR1objNum.IndexOf(LR1obj);
if (itemindex == -1)
{
LR1objNum.Add(LR1obj);
itemindex = LR1objNum.Count - 1;
}
if (!exist(new_item, itemindex))
{
temp_item.Add(itemindex);
}
}
}
}
}
}
}
}
temp_item.Clear();
temp_item = new List<int>(new_item);
}
return new_item;
}
//计算展望符
public string GetLookAhead(string LA, string right, int k)
{
if (k == right.Length)
{
return LA;
}
else
{
string lookahead = "";
for (int i = k; i < right.Length; i++)
{
lookahead += right[i];
}
return lookahead;
}
}
//构建LR1项目集族
public void CreteLR1itemsets()
{
List<int> lr_item = new List<int>(100);//记录项目的序号
lr_item.Add(0);
lr_item = ClosureLR1(lr_item);//构造初始项目集 求闭包
LRitemsets LR_C = new LRitemsets();
LR_C.Container = lr_item;//集合----项目集序号的集合
proitemset.Add(LR_C);//集合的集合----存放项目集序号集合 的集合
for (int i = 0; i < proitemset.Count; i++)//整体集合中 第i个项目集
{
proitemset[i].Container.Sort();//排序由小到大 后面用于判断是否存在的比较
int[] flag = new int[proitemset[i].Container.Count];
for (int fi = 0; fi < proitemset[i].Container.Count; fi++)//标志位，用来判断该序号是否已经构造
{
flag[fi] = 0;
}
for (int j = 0; j < proitemset[i].Container.Count; j++)//第i个项目集的第j个项目
{
if (flag[j] == 1)//如果已经访问过 就不再构造 找下一个项目
continue;
int index = proitemset[i].Container[j];
for (int pi = 0; pi < LR1objNum[index].Right.Length - 1; pi++)//length-1是避免匹配到.在最后的规约项目
{
if (LR1objNum[index].Right[pi] == '.')
{
List<int> lr2_club = new List<int>(100);//记录项目的序号
char symbol = LR1objNum[index].Right[pi + 1];//记录.a转移状态a.的符号a
lr2_club.Add((index + 1));//如果遇到.a形式的项目序号为index 那么项目a.的序号为index+1
for (int m1 = j + 1; m1 < proitemset[i].Container.Count; m1++)
{//在第i个项目集中找到了可以移动的.：.a 重新遍历第i个项目集j项目之后的 找到同样可以移动a的项目集
int index2 = proitemset[i].Container[m1];
for (int m2 = 0; m2 < LR1objNum[index2].Right.Length - 1; m2++)
{
if (LR1objNum[index2].Right[m2] == '.' && LR1objNum[index2].Right[m2 + 1] == symbol)
{
flag[m1] = 1;//标记位置为1 已经访问 之后不再访问
lr2_club.Add(index2 + 1);
}
}
}
lr2_club = ClosureLR1(lr2_club);//求闭包
int value = isexist(lr2_club);
if (value == -1)//-1表示不存在相同的
{
LRitemsets LR_C2 = new LRitemsets();
dfa[Pindex++] = new DFA(i, symbol, proitemset.Count);//count不用加1 本身从0开始
LR_C2.Container = lr2_club;
proitemset.Add(LR_C2);
}
else
{
dfa[Pindex++] = new DFA(i, symbol, value);
}
break;
}
}
}//end-forj
}//end-fori
}//end-Cre_club
//SLR1分析表构建
public void SLR1Analy()
{
CreteLR1itemsets();
Table tnode = new Table();
LRAna = new Table[proitemset.Count][];
for (int i = 0; i < proitemset.Count; i++)
LRAna[i] = new Table[Vchar.Count];
for (int i = 0; i < proitemset.Count; i++)//初始化 赋予ERROR属性
for (int j = 0; j < Vchar.Count; j++)//为终结符加r状态
LRAna[i][j] = tnode;
tnode = new Table('A', 0);
LRAna[1][FindID(Vchar, '#')] = tnode;//项目集1必定是接受项目 构建[1][#]:acc的情况 先直接赋值好 dfa里没有
for (int i = 0; i < Gy_itemset.Count; i++)
{
tnode = new Table('r', Find_pro(LR1objNum[proitemset[Gy_itemset[i]].Container[0]]));//归约项目 找到原产生式序号 添加状态r
for (int j = 0; j < Echar.Count; j++)
{
LRAna[Gy_itemset[i]][j] = tnode;
}
}
for (int i = 0; i < Pindex; i++)
{
if (isFinalsymbol(dfa[i].symbol))//symbol为非终结符 添加状态N
{
int CID = FindID(Vchar, dfa[i].symbol);
tnode = new Table('N', dfa[i].to);
LRAna[dfa[i].from][CID] = tnode;
}
else //不是归约项目 添加状态S
{
int CID = FindID(Vchar, dfa[i].symbol);
tnode = new Table('S', dfa[i].to);
LRAna[dfa[i].from][CID] = tnode;
}
}
}
public Table[][] GET_SLR1_ANA()
{
SLR1Analy();
RStr_ANA += "\r\nSLR1分析表:\r\n ";
int i;
for (i = 0; i < Vchar.Count; i++)
{
RStr_ANA += Vchar[i].ToString() + " ";
}
RStr_ANA += "\r\n";
for (i = 0; i < proitemset.Count; i++)
{
RStr_ANA += i.ToString() + " ";
for (int j = 0; j < Vchar.Count; j++)
{
if (LRAna[i][j].error)
{
RStr_ANA += " " + " ";
}
else if (i == 1 && j == Vchar.Count - 1)
{
RStr_ANA += "AC" + " ";
}
else if (LRAna[i][j].type != 'N')
{
RStr_ANA += LRAna[i][j].type.ToString() + LRAna[i][j].id.ToString() + " ";
}
else
RStr_ANA += LRAna[i][j].id.ToString() + " ";
}
RStr_ANA += "\r\n";
}
return LRAna;
}
//判断字符是否为终结符
public bool isFinalsymbol(char symbol)
{
if (Nchar.Contains(symbol))
{
return false;
}
else
{
return true;
}
}
//查找字符在集合中的序号
public int FindID(List<char> charlist, char symbol)
{
int index = charlist.IndexOf(symbol);
if (index == -1)
{
return -1;
}
return index;
}
//查找项目在项目集族中的序号
public int isexist(List<int> lr_item)
{
for (int i = 0; i < proitemset.Count; i++)
{
if (proitemset[i].Container.Count == lr_item.Count)
{
int count = 0;
for (int j = 0; j < lr_item.Count; j++)
{
if (proitemset[i].Container[j] == lr_item[j])
{
count++;
}
}
if (count == lr_item.Count)
{
return i;
}
}
}
return -1;
}
//判断项目是否存在于项目集族中
public bool isnexist(List<int> lr_item, int item)
{
for (int i = 0; i < lr_item.Count; i++)
{
if (lr_item[i] == item)
{
return true;
}
}
return false;
}
//查找产生式在产生式集合中的序号
public int Find_pro(LR1Node Lr_item)
{
for (int i = 0; i < LRproNum.Count; i++)
{
if (LRproNum[i].Left == Lr_item.Left && LRproNum[i].Right == Lr_item.Right.Replace(".", ""))
{
return i;
}
}
return -1;
}
//在字符串的指定位置插入'.'
public string CreObj(string str, int k)
{
string s = "";
if (k < str.Length)
{
for (int i = 0; i < k; i++)
{
s += str[i];
}
s += ".";
for (int i = k; i < str.Length; i++)
{
s += str[i];
}
}
else
{
s = str + ".";
}
return s;
}
//判断字符是否在集合中
public bool exist(List<char> charlist, char symbol)
{
if (charlist.Contains(symbol))
return true;
return false;
}
}
原文地址: https://www.cveoy.top/t/topic/f0LX 著作权归作者所有。请勿转载和采集!