如何使用C#语言实现LR0文法分析器请给出示例的生成项目集信息的代码要求生成的结果分成状态和项目族信息两列显示在datagridview1中
首先需要定义文法的产生式和终结符、非终结符等信息，可以使用以下类来表示：
public class Production
{
public string Left { get; set; }
public List<string> Right { get; set; }
}
public class Grammar
{
public List<string> Terminals { get; set; }
public List<string> NonTerminals { get; set; }
public string StartSymbol { get; set; }
public List<Production> Productions { get; set; }
}
接下来，需要实现生成LR0项目集的算法。LR0项目集是指在LR0分析过程中的状态，包含了当前扫描到的符号、已经处理的符号、以及可能的移进或规约操作。可以使用以下类来表示：
public class LR0Item
{
public Production Production { get; set; }
public int DotPosition { get; set; }
public HashSet<string> LookAhead { get; set; }
}
public class LR0State
{
public int StateNumber { get; set; }
public List<LR0Item> Items { get; set; }
}
生成LR0项目集的算法可以使用以下伪代码实现：
- 初始化初始状态为包含S'->.S和$的LR0项目集I0。
- 对于每个LR0项目集I：
- 对于每个文法符号X：
- 计算I中所有项目的闭包，得到新的LR0项目集J。
- 如果J不为空且不在已有的项目集中，则将J加入项目集族中，并将I到J的转移加入转移表中。
- 对于每个终结符a和非终结符A：
- 计算I中所有项目的移进操作，得到新的LR0项目集J。
- 如果J不为空且不在已有的项目集中，则将J加入项目集族中，并将I到J的转移加入转移表中。
- 如果J不为空，则将移进操作加入转移表中。
- 对于每个规约项目A->α.，将规约操作加入转移表中。
- 对于每个文法符号X：
- 根据转移表生成LR0分析表。
以下是一个示例的LR0文法分析器的实现，包含了生成LR0项目集的代码和将结果显示在DataGridView中的代码：
public partial class Form1 : Form
{
private Grammar grammar;
private List<LR0State> states;
private Dictionary<LR0State, int> stateMap;
private Dictionary<int, Dictionary<string, int>> actionTable;
private Dictionary<int, Dictionary<string, int>> gotoTable;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
// 初始化文法
grammar = new Grammar
{
Terminals = new List<string> { "+", "*", "(", ")", "id" },
NonTerminals = new List<string> { "E", "T", "F" },
StartSymbol = "E",
Productions = new List<Production>
{
new Production { Left = "E", Right = new List<string> { "E", "+", "T" } },
new Production { Left = "E", Right = new List<string> { "T" } },
new Production { Left = "T", Right = new List<string> { "T", "*", "F" } },
new Production { Left = "T", Right = new List<string> { "F" } },
new Production { Left = "F", Right = new List<string> { "(", "E", ")" } },
new Production { Left = "F", Right = new List<string> { "id" } },
}
};
// 生成LR0项目集
states = GenerateLR0States(grammar);
// 生成LR0分析表
actionTable = GenerateActionTable(states, grammar);
gotoTable = GenerateGotoTable(states, grammar);
// 显示LR0项目集
ShowLR0States(states);
}
private List<LR0State> GenerateLR0States(Grammar grammar)
{
// 初始化初始状态为包含S'->.S和$的LR0项目集I0
var startProduction = grammar.Productions.First(p => p.Left == grammar.StartSymbol);
var startItem = new LR0Item { Production = startProduction, DotPosition = 0, LookAhead = new HashSet<string> { "$" } };
var i0 = new LR0State { StateNumber = 0, Items = new List<LR0Item> { startItem } };
var states = new List<LR0State> { i0 };
stateMap = new Dictionary<LR0State, int> { { i0, 0 } };
// 初始化转移表
var transitionTable = new Dictionary<LR0State, Dictionary<string, LR0State>>();
foreach (var symbol in grammar.Terminals.Concat(grammar.NonTerminals))
{
transitionTable[i0] = new Dictionary<string, LR0State>();
}
// 计算所有LR0项目集
var queue = new Queue<LR0State>();
queue.Enqueue(i0);
while (queue.Count > 0)
{
var i = queue.Dequeue();
// 计算I中所有项目的闭包，得到新的LR0项目集J
var j = Closure(i, grammar);
// 如果J不为空且不在已有的项目集中，则将J加入项目集族中，并将I到J的转移加入转移表中
if (j.Items.Count > 0 && !stateMap.ContainsKey(j))
{
j.StateNumber = states.Count;
states.Add(j);
stateMap[j] = j.StateNumber;
queue.Enqueue(j);
transitionTable[j] = new Dictionary<string, LR0State>();
}
// 对于每个终结符a和非终结符A，计算I中所有项目的移进操作，得到新的LR0项目集J
foreach (var symbol in grammar.Terminals.Concat(grammar.NonTerminals))
{
var k = Goto(i, symbol, grammar);
// 如果J不为空且不在已有的项目集中，则将J加入项目集族中，并将I到J的转移加入转移表中
if (k.Items.Count > 0 && !stateMap.ContainsKey(k))
{
k.StateNumber = states.Count;
states.Add(k);
stateMap[k] = k.StateNumber;
queue.Enqueue(k);
transitionTable[k] = new Dictionary<string, LR0State>();
}
// 如果J不为空，则将移进操作加入转移表中
if (k.Items.Count > 0)
{
transitionTable[i][symbol] = k;
}
}
// 对于每个规约项目A->α.，将规约操作加入转移表中
foreach (var item in i.Items.Where(item => item.DotPosition == item.Production.Right.Count))
{
foreach (var lookahead in item.LookAhead)
{
if (item.Production.Left == grammar.StartSymbol && lookahead == "$")
{
// 接受状态
actionTable[i.StateNumber][lookahead] = -1;
}
else
{
// 规约操作
var productionNumber = grammar.Productions.IndexOf(item.Production);
actionTable[i.StateNumber][lookahead] = -productionNumber - 1;
}
}
}
}
// 将转移表转换为goto表
var gotoTable = new Dictionary<int, Dictionary<string, int>>();
foreach (var state in states)
{
gotoTable[state.StateNumber] = new Dictionary<string, int>();
foreach (var symbol in grammar.NonTerminals)
{
if (transitionTable[state].ContainsKey(symbol))
{
gotoTable[state.StateNumber][symbol] = transitionTable[state][symbol].StateNumber;
}
}
}
return states;
}
private LR0State Closure(LR0State state, Grammar grammar)
{
var closure = new LR0State { StateNumber = -1, Items = new List<LR0Item>() };
var processedItems = new HashSet<LR0Item>();
foreach (var item in state.Items)
{
closure.Items.Add(item);
processedItems.Add(item);
}
var added = true;
while (added)
{
added = false;
foreach (var item in closure.Items.ToList())
{
if (item.DotPosition < item.Production.Right.Count &&
grammar.NonTerminals.Contains(item.Production.Right[item.DotPosition]))
{
var b = item.Production.Right[item.DotPosition];
var beta = item.Production.Right.Skip(item.DotPosition + 1).ToList();
var firstBeta = First(beta, state.Items.Where(i => i.LookAhead.Contains(item.LookAhead)));
foreach (var production in grammar.Productions.Where(p => p.Left == b))
{
foreach (var a in firstBeta)
{
var newItem = new LR0Item { Production = production, DotPosition = 0, LookAhead = new HashSet<string> { a } };
if (!processedItems.Contains(newItem))
{
closure.Items.Add(newItem);
processedItems.Add(newItem);
added = true;
}
}
}
}
}
}
return closure;
}
private LR0State Goto(LR0State state, string symbol, Grammar grammar)
{
var gotoState = new LR0State { StateNumber = -1, Items = new List<LR0Item>() };
foreach (var item in state.Items.Where(item => item.DotPosition < item.Production.Right.Count && item.Production.Right[item.DotPosition] == symbol))
{
gotoState.Items.Add(new LR0Item { Production = item.Production, DotPosition = item.DotPosition + 1, LookAhead = item.LookAhead });
}
return Closure(gotoState, grammar);
}
private HashSet<string> First(List<string> symbols, IEnumerable<LR0Item> items)
{
var firstSet = new HashSet<string>();
foreach (var symbol in symbols)
{
if (!symbol.StartsWith("'"))
{
var nonTerminal = symbol;
var firstNonTerminal = items.Where(item => item.Production.Left == nonTerminal).SelectMany(item => First(item.Production.Right, items));
firstSet.UnionWith(firstNonTerminal);
if (!firstNonTerminal.Contains(""))
{
return firstSet;
}
}
firstSet.Add(symbol);
}
return firstSet;
}
private Dictionary<int, Dictionary<string, int>> GenerateActionTable(List<LR0State> states, Grammar grammar)
{
var actionTable = new Dictionary<int, Dictionary<string, int>>();
foreach (var state in states)
{
actionTable[state.StateNumber] = new Dictionary<string, int>();
foreach (var item in state.Items.Where(item => item.DotPosition == item.Production.Right.Count))
{
foreach (var lookahead in item.LookAhead)
{
if (item.Production.Left == grammar.StartSymbol && lookahead == "$")
{
// 接受状态
actionTable[state.StateNumber][lookahead] = -1;
}
else
{
// 规约操作
var productionNumber = grammar.Productions.IndexOf(item.Production);
actionTable[state.StateNumber][lookahead] = -productionNumber - 1;
}
}
}
}
return actionTable;
}
private Dictionary<int, Dictionary<string, int>> GenerateGotoTable(List<LR0State> states, Grammar grammar)
{
var gotoTable = new Dictionary<int, Dictionary<string, int>>();
foreach (var state in states)
{
gotoTable[state.StateNumber] = new Dictionary<string, int>();
foreach (var symbol in grammar.NonTerminals)
{
var nextState = GetNextState(state, symbol);
if (nextState != null)
{
gotoTable[state.StateNumber][symbol] = nextState.StateNumber;
}
}
}
return gotoTable;
}
private LR0State GetNextState(LR0State state, string symbol)
{
foreach (var item in state.Items.Where(item => item.DotPosition < item.Production.Right.Count && item.Production.Right[item.DotPosition] == symbol))
{
var nextState = new LR0State { StateNumber = -1, Items = new List<LR0Item>() };
nextState.Items.Add(new LR0Item { Production = item.Production, DotPosition = item.DotPosition + 1, LookAhead = item.LookAhead });
return Closure(nextState, grammar);
}
return null;
}
private void ShowLR0States(List<LR0State> states)
{
dataGridView1.Columns.Clear();
dataGridView1.Columns.Add("StateNumber", "状态编号");
dataGridView1.Columns.Add("Items", "项目");
foreach (var state in states)
{
var itemStrings = state.Items.Select(item => $"{item.Production.Left} -> {string.Join(" ", item.Production.Right.Take(item.DotPosition))}·{string.Join(" ", item.Production.Right.Skip(item.DotPosition))}, {string.Join("/", item.LookAhead)}");
dataGridView1.Rows.Add(state.StateNumber, string.Join("\n", itemStrings));
}
}
}
``
原文地址: https://www.cveoy.top/t/topic/hdHw 著作权归作者所有。请勿转载和采集!