LL(1) 文法预测分析表构造 - C# 代码实现
using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.IO; using System.Linq; using System.Text; using System.Text.RegularExpressions; using System.Threading.Tasks; using System.Windows.Forms; using static System.Windows.Forms.VisualStyles.VisualStyleElement;
namespace byyljxfzxt { public partial class Form4 : Form { public Form4() { InitializeComponent(); }
//--------------------预处理
Dictionary<string, List<string>> production;
Dictionary<string, List<string>> firsts;
Dictionary<string, List<string>> follows;
Dictionary<string, List<string>> selects;
List<string> terminals;
List<string> nonterminals;
private void button4_Click(object sender, EventArgs e)
{
string text = richTextBox1.Text;
production = new Dictionary<string, List<string>>();
string[] pro = text.Split('
'); foreach (string s in pro) { if (s == "") continue;
Regex.Replace(s, " ", "");
string[] ga = Regex.Split(s, "->");
if (ga.Length != 2) return;
if (ga[0].Length == 0 || ga[1].Length == 0)
return;
if (ga[0].Length != 1 || !char.IsUpper(ga[0][0])) return;
string[] ga2 = Regex.Split(ga[1], "|");
if (!production.ContainsKey(ga[0]))
production.Add(ga[0], new List<string>());
foreach (string s1 in ga2)
production[ga[0]].Add(s1);
}
firsts = new Dictionary<string, List<string>>();
foreach (var item in production.Keys)
GetFirst(item, production, firsts);
follows = new Dictionary<string, List<string>>();
foreach (var item in production.Keys)
GetFollow(item, production, firsts, follows);
if (JudgeLL1(production, firsts, follows))
{
MessageBox.Show("该文法是LL(1)文法\n");
}
else
{
MessageBox.Show("该文法不是LL(1)文法，存在左递归或者存在FIRST集合有交集的情况！\n");
}
button1.Enabled = true;
button2.Enabled = true;
button3.Enabled = true;
}
private void button6_Click(object sender, EventArgs e)
{
// 获取所有终结符和非终结符
terminals = new List<string>();
nonterminals = new List<string>();
foreach (var item in production)
{
if (!nonterminals.Contains(item.Key))
nonterminals.Add(item.Key);
foreach (var prod in item.Value)
{
foreach (var s in prod)
{
if (IsTerminal(s) && !terminals.Contains(s.ToString()))
terminals.Add(s.ToString());
else if (!IsTerminal(s) && !nonterminals.Contains(s.ToString()))
nonterminals.Add(s.ToString());
}
}
}
terminals.Add("#");
// 初始化预测分析表
Dictionary<string, Dictionary<string, string>> table = new Dictionary<string, Dictionary<string, string>>();
foreach (var nonterm in nonterminals)
{
table.Add(nonterm, new Dictionary<string, string>());
foreach (var term in terminals)
{
table[nonterm].Add(term, "");
}
}
// 填充预测分析表
Dictionary<string, List<string>> selects = GetSelect(production, firsts, follows);
foreach (var nonterm in nonterminals)
{
foreach (var prod in production[nonterm])
{
List<string> select = selects[nonterm][production[nonterm].IndexOf(prod)].Split(new char[] { ' ', '\t' }, StringSplitOptions.RemoveEmptyEntries).ToList();
foreach (var term in select)
{
if (term.Equals("#"))
{
foreach (var f in follows[nonterm])
table[nonterm][f] = prod;
}
else
table[nonterm][term] = prod;
}
}
}
// 输出预测分析表到 listView3 中
listView3.Columns.Clear();
listView3.Items.Clear();
listView3.Columns.Add("非终结符");
foreach (var term in terminals)
{
listView3.Columns.Add(term);
}
foreach (var nonterm in nonterminals)
{
ListViewItem item = new ListViewItem(nonterm);
foreach (var term in terminals)
{
item.SubItems.Add(table[nonterm][term]);
}
listView3.Items.Add(item);
}
}
private void GetFirst(string symbol, Dictionary<string, List<string>> production1, Dictionary<string, List<string>> firsts1)
{
// 如果该非终结符的 FIRST 集已经被计算出，则直接返回
if (firsts1.ContainsKey(symbol))
{
return;
}
firsts1.Add(symbol, new List<string>());
// 遍历产生式，计算 FIRST 集
foreach (var prod in production1[symbol])
{
// 如果产生式首字符为终结符，则直接将其加入 FIRST 集中
if (prod.Length > 0 && IsTerminal(prod[0]))
{
if (!firsts1[symbol].Contains(prod[0].ToString()))
firsts1[symbol].Add(prod[0].ToString());
continue;
}
// 如果产生式首字符为非终结符，则计算该非终结符的 FIRST 集，并将结果加入首字符的 FIRST 集中
else if (prod.Length > 0 && !IsTerminal(prod[0]))
{
GetFirst(prod[0].ToString(), production1, firsts1);
foreach (var f in firsts1[prod[0].ToString()])
{
if (!firsts1[symbol].Contains(f) && !f.Equals('#'))
firsts1[symbol].Add(f);
}
}
//如果第一个非终结符能推出#
if (IsReachEmpty(prod[0].ToString(), production1))
{
// 递归计算第二个和后面的字符的 FIRST 集，并将结果加入该非终结符的 FIRST 集中
for (int j = 1; j < prod.Length; j++)
{
if (IsTerminal(prod[j]))
{
if (!firsts1[symbol].Contains(prod[j].ToString()))
firsts1[symbol].Add(prod[j].ToString());
break;
}
GetFirst(prod[j].ToString(), production1, firsts1);
foreach (var f in firsts1[prod[j].ToString()])
{
if (!firsts1[symbol].Contains(f) && !f.Equals('#'))
firsts1[symbol].Add(f);
}
// 如果该非终结符的 FIRST 集没有包含空串，则可以结束循环
if (!IsReachEmpty(prod[j].ToString(), production1))
{
break;
}
// 如果是最后一个字符且所有非终结符的 FIRST 集都含有空串，则将空串加入该非终结符的 FIRST 集中
if (j == prod.Length - 1)
{
if (!firsts1[symbol].Contains("#"))
firsts1[symbol].Add("#");
}
}
}
}
}
// 判断一个字符是否为终结符
private bool IsTerminal(char c)
{
if (char.IsUpper(c))
return false;
return true;
}
// 判断一个非终结符是否能推出空串
private bool IsReachEmpty(string symbol, Dictionary<string, List<string>> production1)
{
if (!production1.ContainsKey(symbol))
return false;
foreach (var prod in production1[symbol])
{
if (prod.Equals("#"))
return true;
bool flag = true;
for (int i = 0; i < prod.Length; i++)
{
if (!IsReachEmpty(prod[i].ToString(), production1))
{
flag = false;
break;
}
}
if (flag)
return true;
}
return false;
}
// 计算 FOLLOW 集
private void GetFollow(string symbol, Dictionary<string, List<string>> production1, Dictionary<string, List<string>> firsts1, Dictionary<string, List<string>> follows1)
{
// 如果该非终结符的 FOLLOW 集已经被计算出，则直接返回
if (follows1.ContainsKey(symbol))
{
return;
}
follows1.Add(symbol, new List<string>());
// 如果是起始符号，则将 # 加入 FOLLOW 集中
if (symbol.Equals(production1.Keys.First()))
{
if (!follows1[symbol].Contains("#"))
follows1[symbol].Add("#");
}
// 遍历产生式，计算 FOLLOW 集
foreach (var item in production1)
{
foreach (var prod in item.Value)
{
int index = prod.IndexOf(symbol);
if (index == -1)
continue;
// 如果该非终结符位于产生式末尾，则将产生式左部的 FOLLOW 集加入该非终结符的 FOLLOW 集中
if (index == prod.Length - 1)
{
GetFollow(item.Key, production1, firsts1, follows1);
foreach (var f in follows1[item.Key])
{
if (!follows1[symbol].Contains(f))
follows1[symbol].Add(f);
}
}
else
{
// 如果该非终结符后面是终结符，则将该终结符加入该非终结符的 FOLLOW 集中
if (IsTerminal(prod[index + 1]))
{
if (!follows1[symbol].Contains(prod[index + 1].ToString()))
follows1[symbol].Add(prod[index + 1].ToString());
}
// 如果该非终结符后面是非终结符，则将该非终结符的 FIRST 集加入该非终结符的 FOLLOW 集中
else
{
GetFirst(prod[index + 1].ToString(), production1, firsts1);
foreach (var f in firsts1[prod[index + 1].ToString()])
{
if (!f.Equals("#") && !follows1[symbol].Contains(f))
follows1[symbol].Add(f);
}
// 如果该非终结符后面的所有符号都能推出空串，则将产生式左部的 FOLLOW 集加入该非终结符的 FOLLOW 集中
if (IsReachEmpty(prod[index + 1].ToString(), production1))
{
GetFollow(item.Key, production1, firsts1, follows1);
foreach (var f in follows1[item.Key])
{
if (!follows1[symbol].Contains(f))
follows1[symbol].Add(f);
}
}
}
}
}
}
}
private Dictionary<string, List
// 遍历每个产生式，计算对应的 SELECT 集
foreach (var nonterm in production1.Keys)
{
foreach (var prod in production1[nonterm])
{
List<string> select = new List<string>();
bool flag = true;
// 对于产生式中的每个符号，计算其 FIRST 集
foreach (var s in prod)
{
if (IsTerminal(s))
{
select.Add(s.ToString());
flag = false;
break;
}
else
{
GetFirst(s.ToString(), production1, firsts1);
foreach (var f in firsts1[s.ToString()])
{
if (!f.Equals("#") && !select.Contains(f))
select.Add(f);
}
if (!IsReachEmpty(s.ToString(), production1))
{
flag = false;
break;
}
}
}
// 如果产生式中所有符号的 FIRST 集都包含空串，则将 FOLLOW 集加入 SELECT 集中
if (flag)
{
GetFollow(nonterm, production1, firsts1, follows1);
foreach (var f in follows1[nonterm])
{
if (!select.Contains(f))
select.Add(f);
}
}
selects1[nonterm].Add(string.Join("", select.ToArray()));
}
}
return selects1;
}
// 判断一个文法是否是 LL(1) 文法
private bool JudgeLL1(Dictionary<string, List<string>> production1, Dictionary<string, List<string>> firsts1, Dictionary<string, List<string>> follows1)
{
foreach (var item in production1)
{
Dictionary<string, List<string>> map = new Dictionary<string, List<string>>();
foreach (var prod in item.Value)
{
List<string> list = new List<string>();
foreach (var c in prod)
{
if (IsTerminal(c))
{
list.Add(c.ToString());
break;
}
else
{
GetFirst(c.ToString(), production1, firsts1);
foreach (var f in firsts1[c.ToString()])
{
if (!f.Equals("#") && !list.Contains(f))
list.Add(f);
}
if (!IsReachEmpty(c.ToString(), production1))
break;
}
}
if (list.Contains("#"))
{
GetFollow(item.Key, production1, firsts1, follows1);
foreach (var f in follows1[item.Key])
{
if (!list.Contains(f))
list.Add(f);
}
}
string key = string.Join("", list.ToArray());
if (map.ContainsKey(key))
return false;
map.Add(key, list);
}
}
return true;
}
}
原文地址: https://www.cveoy.top/t/topic/ox3C 著作权归作者所有。请勿转载和采集!