grammar MyGrammar;/** Parser Rules*/program: expression
;expression : '(' expression ')'    #Parenthesis| expression operate = ('*' | '/') expression  #MultiplyDivide| expression operate = ('+' | '-') expression  #AddSubtraction     | INT   #Number
;/** Lexer Rules*/ADD : '+' ;
SUB : '-' ;
MUL : '*' ;
DIV : '/' ;INT : '0'..'9'+ ;WS : [ \t\r\n]+ -> skip ;

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Antlr4.Runtime;namespace ConsoleApplication1
{public class MyGrammarVisitor : MyGrammarBaseVisitor<object>{Dictionary<string, object> memory = new Dictionary<string, object>();public override object VisitParenthesis(MyGrammarParser.ParenthesisContext context){object obj = Visit(context.expression());return obj;}public override object VisitMultiplyDivide(MyGrammarParser.MultiplyDivideContext context){double left = Convert.ToDouble(Visit(context.expression(0)));double right = Convert.ToDouble(Visit(context.expression(1)));object obj = new object(); if (context.operate.Type == MyGrammarParser.MUL) {obj = left * right;} else if (context.operate.Type == MyGrammarParser.DIV) {if (right == 0) {throw new Exception("Cannot divide by zero.");}obj = left / right;}return obj;}public override object VisitAddSubtraction(MyGrammarParser.AddSubtractionContext context){double left = Convert.ToDouble(Visit(context.expression(0)));double right = Convert.ToDouble(Visit(context.expression(1)));object obj = new object(); if (context.operate.Type == MyGrammarParser.ADD) {obj = left + right;}else if (context.operate.Type == MyGrammarParser.SUB) {obj = left - right;}return obj;}public override object VisitNumber(MyGrammarParser.NumberContext context){object obj = context.GetText();return obj;}}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Antlr4.Runtime;namespace ConsoleApplication1
{class Program{static void Main(string[] args){string input = @"1 + (2 - 3) * 4";var stream = new AntlrInputStream(input);var lexer = new MyGrammarLexer(stream);var tokens = new CommonTokenStream(lexer);var parser = new MyGrammarParser(tokens);var tree = parser.program();var visitor = new MyGrammarVisitor();var result = visitor.Visit(tree);Console.WriteLine(tree.ToStringTree(parser));Console.WriteLine(result);Console.ReadKey();}}
}