C# Abstract Syntax Tree Example: Simple Pascal Compiler, C#

Language: Layout:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
using System.Text;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string input = string.Empty;
            Console.WriteLine("Input an expression, for example:"
                + Environment.NewLine
                + Environment.NewLine
                + "    begin x := 5; y := 6.5; begin z := 7; z := (2.11*-z*(5+7.18+9.23))+---x+++(-+-+--(y+2))*(-+-3+x)*(5+y)+3*(2+1);end; t := z*2 end.");
            
            input = "    begin x := 5; y := 6.5; begin z := 7; z := (2.11*-z*(5+7.18+9.23))+---x+++(-+-+--(y+2))*(-+-3+x)*(5+y)+3*(2+1);end; t := z*2 end.";

//while (true)
            {
                //Console.WriteLine();
                //Console.Write("Input (q = quit): ");
                //Console.WriteLine();
                //FlushConsole();
                //input = Console.ReadLine();

//if (input == "q")
                //{
                //    break;
                //}

try
                {
                    Parser interpreter = new Parser(input);
                    Node node = interpreter.Parse();

Console.WriteLine();
                    Console.WriteLine(string.Format("Tree graph:{0}{1}", Environment.NewLine + Environment.NewLine, node.Accept(new GraphBuilder(), GraphBuilder.InitialData)));
                    Console.WriteLine();
                    Console.WriteLine();
                    Console.WriteLine(string.Format("Value:{0}{1}", Environment.NewLine + Environment.NewLine, node.Accept(new ValueBuilder(), null)));
                    Console.WriteLine();
                    Console.WriteLine();
                    Console.WriteLine(string.Format("Lisp form:{0}{1}", Environment.NewLine + Environment.NewLine, node.Accept(new LispFormBuilder(), null)));
                    Console.WriteLine();
                }
                catch (InvalidSyntaxException ex)
                {
                    Console.WriteLine(ex.Message);
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex);
                }
            }
        }

static void FlushConsole()
        {
            while (Console.KeyAvailable)
            {
                Console.ReadKey(false);
            }
        }
    }

internal class Parser
    {
        private Token curToken;
        private int curPos;
        private int charCount;
        private char curChar;
        public string Text { get; private set; }

public Parser(string text)
        {
            this.Text = string.IsNullOrEmpty(text) ? string.Empty : text;
            this.charCount = this.Text.Length;
            this.curToken = Token.None();

this.curPos = -1;
            this.Advance();
        }

internal Node Parse()
        {
            this.NextToken();
            Node node = this.GrabCompoundStatement();
            this.ExpectToken(TokenType.Dot);

return node;
        }

private Node GrabCompoundStatement()
        {
            this.EatToken(TokenType.Begin);
            List<Node> statementList = this.GrabStatementList();
            this.EatToken(TokenType.End);

return new CompoundStatement(statementList);
        }

private List<Node> GrabStatementList()
        {
            List<Node> statementList = new List<Node>();
            Node statement = this.GrabStatement();
            statementList.Add(statement);

while (this.curToken.Type == TokenType.Semi)
            {
                this.EatToken(TokenType.Semi);
                statement = this.GrabStatement();
                statementList.Add(statement);
            }

return statementList;
        }

private Node GrabStatement()
        {
            Node statement;

if (this.curToken.Type == TokenType.Begin)
            {
                statement = this.GrabCompoundStatement();
            }
            else if (this.curToken.Type == TokenType.Variable)
            {
                statement = this.GrabAssignStatement();
            }
            else
            {
                statement = new NoOp();
            }

return statement;
        }

private Node GrabAssignStatement()
        {
            Token varToken = this.EatToken(TokenType.Variable);
            Token assignToken = this.EatToken(TokenType.Assignment);
            Node expr = this.GrabExpr();

return new AssignStatement(new Variable(varToken), assignToken, expr);
        }

private Token ExpectToken(TokenType tokenType)
        {
            if (this.curToken.Type == tokenType)
            {
                return this.curToken;
            }
            else
            {
                throw new InvalidSyntaxException(string.Format("Invalid syntax at position {0}. Expected {1} but {2} is given.", this.curPos, tokenType, this.curToken.Type.ToString()));
            }
        }

private Token EatToken(TokenType tokenType)
        {
            if (this.curToken.Type == tokenType)
            {
                Token token = this.curToken;
                this.NextToken();
                return token;
            }
            else
            {
                throw new InvalidSyntaxException(string.Format("Invalid syntax at position {0}. Expected {1} but {2} is given.", this.curPos, tokenType, this.curToken.Type.ToString()));
            }
        }

private Node GrabExpr()
        {
            Node left = this.GrabTerm();

while (this.curToken.Type == TokenType.Plus
                || this.curToken.Type == TokenType.Minus)
            {
                Token op = this.curToken;
                this.NextToken();
                Node right = this.GrabTerm();
                left = new BinOp(op, left, right);
            }

return left;
        }

private Node GrabTerm()
        {
            Node left = this.GrabFactor();

while (this.curToken.Type == TokenType.Multiply
                || this.curToken.Type == TokenType.Divide)
            {
                Token op = this.curToken;
                this.NextToken();
                Node right = this.GrabFactor();
                left = new BinOp(op, left, right);
            }

return left;
        }

private Node GrabFactor()
        {
            if (this.curToken.Type == TokenType.Plus
                || this.curToken.Type == TokenType.Minus)
            {
                Node node = this.GrabUnaryExpr();
                return node;
            }
            else if (this.curToken.Type == TokenType.LeftParenthesis)
            {
                Node node = this.GrabBracketExpr();
                return node;
            }
            else if (this.curToken.Type == TokenType.Variable)
            {
                Node node = this.GrabVariable();
                return node;
            }
            else
            {
                Token token = this.ExpectToken(TokenType.Number);
                this.NextToken();
                return new Num(token);
            }
        }

private Node GrabVariable()
        {
            Token token = this.ExpectToken(TokenType.Variable);
            this.NextToken();

return new Variable(token);
        }

private Node GrabUnaryExpr()
        {
            Token op;

if (this.curToken.Type == TokenType.Plus)
            {
                op = this.ExpectToken(TokenType.Plus);
            }
            else
            {
                op = this.ExpectToken(TokenType.Minus);
            }

this.NextToken();

if (this.curToken.Type == TokenType.Plus
                || this.curToken.Type == TokenType.Minus)
            {
                Node expr = this.GrabUnaryExpr();
                return new UnaryOp(op, expr);
            }
            else
            {
                Node expr = this.GrabFactor();
                return new UnaryOp(op, expr);
            }
        }

private Node GrabBracketExpr()
        {
            this.ExpectToken(TokenType.LeftParenthesis);
            this.NextToken();
            Node node = this.GrabExpr();
            this.ExpectToken(TokenType.RightParenthesis);
            this.NextToken();
            return node;
        }

private void NextToken()
        {
            if (this.curChar == char.MinValue)
            {
                this.curToken = Token.None();
                return;
            }

if (this.curChar == ' ')
            {
                while (this.curChar != char.MinValue && this.curChar == ' ')
                {
                    this.Advance();
                }

if (this.curChar == char.MinValue)
                {
                    this.curToken = Token.None();
                    return;
                }
            }

if (this.curChar == '+')
            {
                this.curToken = new Token(TokenType.Plus, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar == '-')
            {
                this.curToken = new Token(TokenType.Minus, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar == '*')
            {
                this.curToken = new Token(TokenType.Multiply, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar == '/')
            {
                this.curToken = new Token(TokenType.Divide, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar == '(')
            {
                this.curToken = new Token(TokenType.LeftParenthesis, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar == ')')
            {
                this.curToken = new Token(TokenType.RightParenthesis, this.curChar.ToString());
                this.Advance();
                return;
            }

if (this.curChar >= '0' && this.curChar <= '9')
            {
                string num = string.Empty;
                while (this.curChar >= '0' && this.curChar <= '9')
                {
                    num += this.curChar.ToString();
                    this.Advance();
                }

if (this.curChar == '.')
                {
                    num += this.curChar.ToString();
                    this.Advance();

if (this.curChar >= '0' && this.curChar <= '9')
                    {
                        while (this.curChar >= '0' && this.curChar <= '9')
                        {
                            num += this.curChar.ToString();
                            this.Advance();
                        }
                    }
                    else
                    {
                        throw new InvalidSyntaxException(string.Format("Invalid syntax at position {0}. Unexpected symbol {1}", this.curPos + 1, this.curChar));
                    }
                }

this.curToken = new Token(TokenType.Number, num);
                return;
            }

if ((this.curChar >= 'a' && this.curChar <= 'z')
                || this.curChar >= 'A' && this.curChar <= 'Z')
            {
                string word = string.Empty;
                word += this.curChar;
                this.Advance();

if ((this.curChar >= 'a' && this.curChar <= 'z')
                    || (this.curChar >= 'A' && this.curChar <= 'Z')
                    || this.curChar == '_'
                    || (this.curChar >= '0' && this.curChar <= '9'))
                {
                    while ((this.curChar >= 'a' && this.curChar <= 'z')
                        || (this.curChar >= 'A' && this.curChar <= 'Z')
                        || this.curChar == '_'
                        || (this.curChar >= '0' && this.curChar <= '9'))
                    {
                        word += this.curChar.ToString();
                        this.Advance();
                    }
                }

if (string.Compare(word, "BEGIN", true) == 0)
                {
                    this.curToken = new Token(TokenType.Begin, word);
                }
                else if (string.Compare(word, "END", true) == 0)
                {
                    this.curToken = new Token(TokenType.End, word);
                }
                else
                {
                    this.curToken = new Token(TokenType.Variable, word);
                }

return;
            }

if (this.curChar == ';')
            {
                this.curToken = new Token(TokenType.Semi, ";");
                this.Advance();
                return;
            }

if (this.curChar == '.')
            {
                this.curToken = new Token(TokenType.Dot, ".");
                this.Advance();
                return;
            }

if (this.curChar == ':')
            {
                if (this.Peek() == '=')
                {
                    this.Advance();
                    this.curToken = new Token(TokenType.Assignment, ":=");
                    this.Advance();
                    return;
                }
            }

throw new InvalidSyntaxException(string.Format("Invalid syntax at position {0}. Unexpected symbol {1}", this.curPos + 1, this.curChar));
        }

private void Advance()
        {
            this.curPos += 1;

if (this.curPos < this.charCount)
            {
                this.curChar = this.Text[this.curPos];
            }
            else
            {
                this.curChar = char.MinValue;
            }
        }

private Char Peek()
        {
            if (this.curPos + 1 < this.charCount)
            {
                return this.Text[this.curPos + 1];
            }
            else
            {
                return char.MinValue;
            }
        }
    }

internal class AssignStatement : Node
    {
        private Variable variable;
        private Node expr;
        private Token assignToken;

public AssignStatement(Variable variable, Token assignToken, Node expr)
        {
            this.variable = variable;
            this.expr = expr;
            this.assignToken = assignToken;
        }

public override object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitAssignStatement(variable, assignToken, expr, options);
        }
    }

internal class NoOp : Node
    {
        public override object Accept(INodeVisitor visitor, object options)
        {
            throw new NotImplementedException();
        }
    }

internal class CompoundStatement : Node
    {
        private List<Node> statementList;

public CompoundStatement(List<Node> statementList)
        {
            this.statementList = new List<Node>();

foreach (Node node in statementList)
            {
                if (node is NoOp)
                    continue;

this.statementList.Add(node);
            }
        }

public override object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitCompoundStatement(this.statementList, options);
        }
    }

[Serializable]
    internal class InvalidSyntaxException : Exception
    {
        public InvalidSyntaxException()
        {
        }

public InvalidSyntaxException(string message) : base(message)
        {
        }

public InvalidSyntaxException(string message, Exception innerException) : base(message, innerException)
        {
        }

protected InvalidSyntaxException(SerializationInfo info, StreamingContext context) : base(info, context)
        {
        }
    }

internal class GraphBuilder : INodeVisitor
    {
        private static string ReplaceLastChar(string str, char rep = ' ')
        {
            if (!string.IsNullOrEmpty(str))
            {
                return str.Substring(0, str.Length - 1) + rep.ToString();
            }
            else
            {
                return "";
            }
        }

const Char SPACE = ' ';
        const Char L_TURN = '┌';
        const Char M_TURN = '├';
        const Char R_TURN = '└';
        const Char V_PIPE = '│';
        const string TAB = "    ";
        const string H_PIPE = "──";

internal static readonly LegacyData InitialData = new LegacyData { LegacyIndent = TAB, LegacyOrientation = BranchOrientation.Right };

private StringBuilder sb;

public GraphBuilder()
        {
            this.sb = new StringBuilder();
            this.sb.AppendLine("(Root)");
        }

public object VisitBinOp(Token op, INode left, INode right, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Left)
            {
                left.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, SPACE) + TAB + L_TURN,
                    LegacyOrientation = BranchOrientation.Left
                });
            }
            else
            {
                left.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, V_PIPE) + TAB + V_PIPE,
                    LegacyOrientation = BranchOrientation.Left
                });
            }

if (legacyOrientation == BranchOrientation.Left)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, L_TURN) + H_PIPE + " (" + op.ToString() + ")");
            }
            else
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, R_TURN) + H_PIPE + " (" + op.ToString() + ")");
            }

if (legacyOrientation == BranchOrientation.Right)
            {
                right.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, SPACE) + TAB + R_TURN,
                    LegacyOrientation = BranchOrientation.Right
                });
            }
            else
            {
                right.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, V_PIPE) + TAB + V_PIPE,
                    LegacyOrientation = BranchOrientation.Right
                });
            }

return this.sb.ToString();
        }

public object VisitNum(Token num, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Left)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, L_TURN) + H_PIPE + "  " + num.ToString());
            }
            else
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, R_TURN) + H_PIPE + "  " + num.ToString());
            }

return this.sb.ToString();
        }

public object VisitUnaryOp(Token op, INode node, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Right)
            {
                node.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, SPACE) + TAB + R_TURN,
                    LegacyOrientation = BranchOrientation.Right
                });
            }
            else
            {
                node.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, V_PIPE) + TAB + R_TURN,
                    LegacyOrientation = BranchOrientation.Right
                });
            }

return this.sb.ToString();
        }

public object VisitAssignStatement(Variable variable, Token op, Node expr, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Left)
            {
                variable.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, SPACE) + TAB + L_TURN,
                    LegacyOrientation = BranchOrientation.Left
                });
            }
            else
            {
                variable.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, V_PIPE) + TAB + V_PIPE,
                    LegacyOrientation = BranchOrientation.Left
                });
            }

if (legacyOrientation == BranchOrientation.Left)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, L_TURN) + H_PIPE + " (" + op.ToString() + ")");
            }
            else if (legacyOrientation == BranchOrientation.Mid)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, M_TURN) + H_PIPE + " (" + op.ToString() + ")");
            }
            else
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, R_TURN) + H_PIPE + " (" + op.ToString() + ")");
            }

if (legacyOrientation == BranchOrientation.Right)
            {
                expr.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, SPACE) + TAB + R_TURN,
                    LegacyOrientation = BranchOrientation.Right
                });
            }
            else
            {
                expr.Accept(this, new LegacyData
                {
                    LegacyIndent = ReplaceLastChar(legacyIndent, V_PIPE) + TAB + V_PIPE,
                    LegacyOrientation = BranchOrientation.Right
                });
            }

return this.sb.ToString();
        }

public object VisitCompoundStatement(List<Node> statements, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Left)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, L_TURN) + H_PIPE + " (Compound)");
            }
            else if (legacyOrientation == BranchOrientation.Mid)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, M_TURN) + H_PIPE + " (Compound)");
            }
            else
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, R_TURN) + H_PIPE + " (Compound)");
            }

string childIndent = legacyIndent;
            if (legacyOrientation == BranchOrientation.Right)
            {
                childIndent = ReplaceLastChar(childIndent, SPACE) + TAB;
            }
            else
            {
                childIndent = ReplaceLastChar(childIndent, V_PIPE) + TAB;
            }

for (int i = 0; i < statements.Count; i++)
            {
                Node statement = statements[i];

if (i < statements.Count - 1)
                {
                    statement.Accept(this, new LegacyData
                    {
                        LegacyIndent = childIndent,
                        LegacyOrientation = BranchOrientation.Mid
                    });
                }
                else
                {
                    statement.Accept(this, new LegacyData
                    {
                        LegacyIndent = childIndent,
                        LegacyOrientation = BranchOrientation.Right
                    });
                }
            }

return this.sb.ToString();
        }

public object VisitVariable(Token variable, object options)
        {
            LegacyData legacyData = (LegacyData)options;

BranchOrientation legacyOrientation = legacyData.LegacyOrientation;
            string legacyIndent = legacyData.LegacyIndent;

if (legacyOrientation == BranchOrientation.Left)
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, L_TURN) + H_PIPE + "  " + variable.ToString());
            }
            else
            {
                sb.AppendLine(ReplaceLastChar(legacyIndent, R_TURN) + H_PIPE + "  " + variable.ToString());
            }

return this.sb.ToString();
        }

internal enum BranchOrientation
        {
            Mid,
            Left,
            Right
        }

internal class LegacyData
        {
            public BranchOrientation LegacyOrientation { get; internal set; }
            public string LegacyIndent { get; internal set; }
        }
    }

internal class ValueBuilder : INodeVisitor
    {
        Dictionary<string, decimal> varLookup = new Dictionary<string, decimal>();

public object VisitBinOp(Token op, INode left, INode right, object options)
        {
            switch (op.Type)
            {
                case TokenType.Plus:
                    return (decimal)left.Accept(this, options) + (decimal)right.Accept(this, options);
                case TokenType.Minus:
                    return (decimal)left.Accept(this, options) - (decimal)right.Accept(this, options);
                case TokenType.Multiply:
                    return (decimal)left.Accept(this, options) * (decimal)right.Accept(this, options);
                case TokenType.Divide:
                    return (decimal)left.Accept(this, options) / (decimal)right.Accept(this, options);
                default:
                    throw new Exception(string.Format("Token of type {0} cannot be evaluated.", op.Type.ToString()));
            }
        }

public object VisitNum(Token num, object options)
        {
            return decimal.Parse(num.Value);
        }

public object VisitAssignStatement(Variable variable, Token op, Node expr, object options)
        {
            string varName = variable.ToString();
            decimal value = (decimal)expr.Accept(this, options);
            this.varLookup[varName] = value;

return value;
        }

public object VisitCompoundStatement(List<Node> statements, object options)
        {
            foreach (Node statement in statements)
            {
                statement.Accept(this, options);
            }

StringBuilder sb = new StringBuilder();

foreach (String key in this.varLookup.Keys)
            {
                sb.AppendLine(string.Format("{0} = {1}", key, this.varLookup[key]));
            }

return sb.ToString(0, sb.Length - 1);
        }

public object VisitUnaryOp(Token op, INode node, object options)
        {
            switch (op.Type)
            {
                case TokenType.Plus:
                    return (decimal)node.Accept(this, options);
                case TokenType.Minus:
                    return -(decimal)node.Accept(this, options);
                default:
                    throw new Exception(string.Format("Token of type {0} cannot be evaluated.", op.Type.ToString()));
            }
        }

public object VisitVariable(Token variable, object options)
        {
            string varName = variable.Value;

if (this.varLookup.ContainsKey(varName))
            {
                return this.varLookup[varName];
            }
            else
            {
                throw new Exception(string.Format("Variable {0} is not existed.", varName));
            }
        }
    }

internal class LispFormBuilder : INodeVisitor
    {
        public object VisitBinOp(Token op, INode left, INode right, object options)
        {
            return "(" + op.ToString() + " " + left.Accept(this, options) + " " + right.Accept(this, options) + ")";
        }

public object VisitNum(Token num, object options)
        {
            return num.ToString();
        }

public object VisitAssignStatement(Variable variable, Token op, Node expr, object options)
        {
            return "(" + op.ToString() + " " + variable.Accept(this, options) + " " + expr.Accept(this, options) + ")";
        }

public object VisitCompoundStatement(List<Node> statements, object options)
        {
            StringBuilder sb = new StringBuilder();

foreach (Node expr in statements)
            {
                sb.AppendLine(expr.Accept(this, options).ToString());
            }

return sb.ToString(0, sb.Length - 1);
        }

public object VisitUnaryOp(Token op, INode node, object options)
        {
            return "(" + op.ToString() + " " + node.Accept(this, options) + ")";
        }

public object VisitVariable(Token variable, object options)
        {
            return variable.ToString();
        }
    }

internal interface INode
    {
        object Accept(INodeVisitor visitor, object options);
    }

internal interface INodeVisitor
    {
        object VisitNum(Token num, object options);
        object VisitUnaryOp(Token op, INode node, object options);
        object VisitBinOp(Token op, INode left, INode right, object options);
        object VisitAssignStatement(Variable variable, Token op, Node expr, object options);
        object VisitCompoundStatement(List<Node> statements, object options);
        object VisitVariable(Token variable, object options);
    }

internal abstract class Node : INode
    {
        abstract public object Accept(INodeVisitor visitor, object options);
    }

internal class Num : Node
    {
        internal Token Token { get; private set; }

public Num(Token token)
        {
            this.Token = token;
        }

override public object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitNum(this.Token, options);
        }
    }

internal class Variable : Node
    {
        internal Token Token { get; private set; }

public Variable(Token token)
        {
            this.Token = token;
        }

override public object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitVariable(this.Token, options);
        }

public override string ToString()
        {
            return this.Token.ToString();
        }
    }

internal class UnaryOp : Node
    {
        internal Token Op { get; private set; }
        internal Node Node { get; private set; }

public UnaryOp(Token op, Node node)
        {
            this.Op = op;
            this.Node = node;
        }

override public object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitUnaryOp(this.Op, this.Node, options);
        }
    }

internal class BinOp : Node
    {
        internal Token Op { get; private set; }
        internal Node Left { get; private set; }
        internal Node Right { get; private set; }

public BinOp(Token op, Node left, Node right)
        {
            this.Op = op;
            this.Left = left;
            this.Right = right;
        }

override public object Accept(INodeVisitor visitor, object options)
        {
            return visitor.VisitBinOp(this.Op, this.Left, this.Right, options);
        }
    }

internal class Token
    {
        public TokenType Type { get; private set; }
        public string Value { get; private set; }

public Token(TokenType type, string value)
        {
            this.Type = type;
            this.Value = value;
        }

internal static Token None()
        {
            return new Token(TokenType.None, "");
        }

public override string ToString()
        {
            return this.Value;
        }
    }

internal enum TokenType
    {
        None,
        Plus,
        Minus,
        Multiply,
        Divide,
        Number,
        LeftParenthesis,
        RightParenthesis,
        Variable,
        Assignment,
        End,
        Begin,
        Dot,
        Semi
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,13 sec, cpu time: 0,12 sec, average memory usage: 16 Mb, average nr of threads: 3