CanonSharp/CanonSharp.Common/LexicalAnalyzer/RegularExpression.cs
2024-07-27 14:56:28 +08:00

110 lines
3.6 KiB
C#

namespace CanonSharp.Common.LexicalAnalyzer;
public abstract class RegularExpression
{
public abstract NondeterministicFiniteAutomation Convert2Nfa();
public static RegularExpression Empty => new EmptyExpression();
public static RegularExpression Single(char c) => new SymbolExpression(c);
public static RegularExpression Alternate(RegularExpression left, RegularExpression right) =>
new AlternationExpression(left, right);
public static RegularExpression Concatenate(RegularExpression first, RegularExpression second) =>
new ConcatenationExpression(first, second);
public static RegularExpression Kleene(RegularExpression inner) => new KleeneExpression(inner);
}
public class EmptyExpression : RegularExpression
{
public override NondeterministicFiniteAutomation Convert2Nfa()
{
NondeterministicState final = new();
NondeterministicState start = new();
start.AddTransaction(EmptyChar.Empty, final);
return new NondeterministicFiniteAutomation(start, [final]);
}
}
public class SymbolExpression(char symbol) : RegularExpression
{
public char Symbol { get; } = symbol;
public override NondeterministicFiniteAutomation Convert2Nfa()
{
NondeterministicState final = new();
NondeterministicState start = new();
start.AddTransaction(new EmptyChar(Symbol), final);
return new NondeterministicFiniteAutomation(start, [final]);
}
}
public class AlternationExpression(RegularExpression left, RegularExpression right) : RegularExpression
{
public RegularExpression Left { get; } = left;
public RegularExpression Right { get; } = right;
public override NondeterministicFiniteAutomation Convert2Nfa()
{
NondeterministicFiniteAutomation left = Left.Convert2Nfa();
NondeterministicFiniteAutomation right = Right.Convert2Nfa();
NondeterministicState final = new();
foreach (NondeterministicState state in left.FinalStates.Concat(right.FinalStates))
{
state.AddTransaction(EmptyChar.Empty, final);
}
NondeterministicState start = new();
start.AddTransaction(EmptyChar.Empty, left.Start);
start.AddTransaction(EmptyChar.Empty, right.Start);
return new NondeterministicFiniteAutomation(start, [final]);
}
}
public class ConcatenationExpression(RegularExpression first, RegularExpression second) : RegularExpression
{
public RegularExpression First { get; } = first;
public RegularExpression Second { get; } = second;
public override NondeterministicFiniteAutomation Convert2Nfa()
{
NondeterministicFiniteAutomation first = First.Convert2Nfa();
NondeterministicFiniteAutomation second = Second.Convert2Nfa();
foreach (NondeterministicState state in first.FinalStates)
{
state.AddTransaction(EmptyChar.Empty, second.Start);
}
return new NondeterministicFiniteAutomation(first.Start, second.FinalStates);
}
}
public class KleeneExpression(RegularExpression inner) : RegularExpression
{
public RegularExpression Inner { get; } = inner;
public override NondeterministicFiniteAutomation Convert2Nfa()
{
NondeterministicFiniteAutomation inner = Inner.Convert2Nfa();
NondeterministicState final = new();
final.AddTransaction(EmptyChar.Empty, inner.Start);
foreach (NondeterministicState state in inner.FinalStates)
{
state.AddTransaction(EmptyChar.Empty, final);
}
return new NondeterministicFiniteAutomation(final, [final]);
}
}