diff --git a/examples/HelloWorld.juk b/examples/HelloWorld.juk
index f10e6993..2dd600f0 100644
--- a/examples/HelloWorld.juk
+++ b/examples/HelloWorld.juk
@@ -1,4 +1,4 @@
-func main() = {
+sub main() = {
     // Print Hello World
     printLine("Hello World");
 }
diff --git a/examples/classtest.juk b/examples/classtest.juk
index e2c9da69..677e37f5 100644
--- a/examples/classtest.juk
+++ b/examples/classtest.juk
@@ -1,12 +1,12 @@
 class x(var initializer) = {
    var z = initializer;
 
-   func m() = {
+   sub m() = {
       return z;
    }
 }
 
-func y() = {
+sub y() = {
    var d = new x(32);
    printLine(d.m());
 }
diff --git a/examples/dontest.juk b/examples/dontest.juk
index 11fcdc6c..53017771 100644
--- a/examples/dontest.juk
+++ b/examples/dontest.juk
@@ -1,23 +1,23 @@
-func main() = {
+sub main() = {
 	foo();
 	printLine("main");
 	var bb = testClass();
 }
 
-func process() = {
+sub process() = {
 	printLine("process");
 }
 
-func foo() = {
+sub foo() = {
 	process();
 	printLine("foo");
 }
 
 
 class testClass = {
-	func one() = {
+	sub one() = {
 	}
 
-	func two() = {
+	sub two() = {
 	}
 }
\ No newline at end of file
diff --git a/examples/scanner.juk b/examples/scanner.juk
index ca8d41f8..490a1860 100644
--- a/examples/scanner.juk
+++ b/examples/scanner.juk
@@ -1,4 +1,4 @@
-func main()={
+sub main()={
     if ( 2<3 ) 
     {
         printLine("foo");
@@ -9,7 +9,7 @@ func main()={
     }
 }
 
-func foo() = {
+sub foo() = {
     var x = 3;
     while (x<=4)
     {
@@ -18,7 +18,7 @@ func foo() = {
     }
 }
 
-func three()={
+sub three()={
     3+3
     x=function(3+3);
     x=1++==4
diff --git a/examples/test.juk b/examples/test.juk
index e61ffb4c..691da385 100644
--- a/examples/test.juk
+++ b/examples/test.juk
@@ -1,10 +1,10 @@
-func process() = 
+sub process() = 
 {
 	printLine("process");
 }
 
 
-func main() = 
+sub main() = 
 {
 	printLine("main");
 	process();
diff --git a/examples/test2.juk b/examples/test2.juk
index 0c65c6e3..3cf33c22 100644
--- a/examples/test2.juk
+++ b/examples/test2.juk
@@ -1,7 +1,7 @@
-func testC_sharp() = {
+sub testC_sharp() = {
   printLine("AsdfA");
 }
 
-func main() = {
+sub main() = {
    testC_sharp();
 }
\ No newline at end of file
diff --git a/src/Juka/REPL.cs b/src/Juka/REPL.cs
index 7a8d8012..ea6987b9 100644
--- a/src/Juka/REPL.cs
+++ b/src/Juka/REPL.cs
@@ -8,10 +8,11 @@ namespace Juka
     public class Repl
     {
         private static Compiler? compiler;
-        private static Stack<string> funcData = new();
+        private static Stack<string> subData = new();
+        private static readonly Stack<string> redoStack = new();
         private static string? dataStart;
         private static string? dataEnd;
-        private static bool isFuncOrClass;
+        private static bool isSubOrClass;
 
         public static async Task RunRepl()
         {
@@ -46,11 +47,11 @@ private static async Task InitializeRepl()
 
             await SelfUpdate.Check();
 
-            isFuncOrClass = false;
-            dataStart = "func main() = {";
+            isSubOrClass = false;
+            dataStart = "sub main() = {";
             dataEnd = "}";
 
-            funcData = new Stack<string>();
+            subData = new Stack<string>();
 
             AnsiConsole.Write(new FigletText("Juka").Color(Color.Purple));
             AnsiConsole.MarkupLine("[bold yellow]Hello[/] and [bold red]Welcome to 🍲 Juka Programming Language![/] For info visit [link blue]https://jukalang.com[/]. Type [bold palegreen1]!menu[/] to see options");
@@ -90,6 +91,9 @@ private static async Task HandleCommandAsync(string command)
                 case "!undo":
                     UndoLastCommand();
                     break;
+                case "!redo":
+                    RedoLastCommand();
+                    break;
                 case "!update":
                     await UpdateJuka();
                     break;
@@ -107,25 +111,25 @@ private static async Task HandleCommandAsync(string command)
 
         private static void HandleCode(string code)
         {
-            if (code.StartsWith("func") || code.StartsWith("class"))
+            if (code.StartsWith("sub") || code.StartsWith("class"))
             {
-                isFuncOrClass = true;
-                funcData.Push(code);
-                Trace.WriteLine("Starting Func: " + code);
+                isSubOrClass = true;
+                subData.Push(code);
+                Trace.WriteLine("Starting Subroutine: " + code);
             }
-            else if (isFuncOrClass)
+            else if (isSubOrClass)
             {
                 if (code.StartsWith("}", StringComparison.OrdinalIgnoreCase))
                 {
-                    funcData.Push(code);
-                    Trace.WriteLine("Ending Func: " + code);
-                    ExecuteFunction();
-                    isFuncOrClass = false;
+                    subData.Push(code);
+                    Trace.WriteLine("Ending Subroutine: " + code);
+                    ExecuteSub();
+                    isSubOrClass = false;
                 }
                 else
                 {
-                    Trace.WriteLine("Reading Func: " + code);
-                    funcData.Push(code);
+                    Trace.WriteLine("Reading Subroutine: " + code);
+                    subData.Push(code);
                 }
             }
             else
@@ -136,7 +140,7 @@ private static void HandleCode(string code)
                     code = "";
                 }
 
-                funcData.Push(code);
+                subData.Push(code);
                 ExecuteLine();
             }
         }
@@ -150,13 +154,16 @@ private static void DisplayMenu()
             table.AddColumn(new TableColumn("Description"));
 
             // Add some rows
+            table.AddRow("!menu", "[yellow]Displays this menu[/]");
+            table.AddRow("!clear", "[green]Clears the REPL[/]");
             table.AddRow("!list", "[red]Lists the current code[/]");
-            table.AddRow("!clear", "[green]Clears The REPL[/]");
+            table.AddRow("!get", "[aqua]Get list of libraries for Juka[/]");
             table.AddRow("!undo", "[blue]Undoes last entered command[/]");
+            table.AddRow("!redo", "[red]Redoes the undone command[/]");
             table.AddRow("!update", "[yellow]Update Juka to latest version[/]");
-            table.AddRow("!restart", "[fuchsia]Restart Application[/]");
-            table.AddRow("!get", "[aqua]Get List of Libraries for Juka[/]");
-            table.AddRow("!exit", "[darkred_1]Exits REPL[/]");
+            table.AddRow("!restart", "[fuchsia]Restart application[/]");
+            
+            table.AddRow("!exit", "[yellow]Exits REPL[/]");
             AnsiConsole.Write(table);
             DisplayPrompt();
         }
@@ -165,16 +172,16 @@ private static void ClearConsole()
         {
             Console.Clear();
             compiler = new Compiler();
-            isFuncOrClass = false;
-            funcData.Clear();
-            dataStart = "func main() = {";
+            isSubOrClass = false;
+            subData.Clear();
+            dataStart = "sub main() = {";
             dataEnd = "}";
             DisplayPrompt();
         }
 
         private static void ListCode()
         {
-            foreach (var data in funcData.Reverse())
+            foreach (var data in subData.Reverse())
             {
                 Console.WriteLine(data);
             }
@@ -190,11 +197,20 @@ private static void GetLibraries()
 
         private static void UndoLastCommand()
         {
-            var templine = funcData.Pop();
+            var templine = subData.Pop();
+            redoStack.Push(templine);
             AnsiConsole.MarkupLine("[bold red]Removed: [/]" + templine);
             DisplayPrompt();
         }
 
+        private static void RedoLastCommand()
+        {
+            var templine = redoStack.Pop();
+            subData.Push(templine);
+            AnsiConsole.MarkupLine("[bold green]Added: [/]" + templine);
+            DisplayPrompt();
+        }
+
         private static async Task UpdateJuka()
         {
             await SelfUpdate.Update();
@@ -213,15 +229,15 @@ private static void ExitRepl()
             Environment.Exit(0);
         }
 
-        private static void ExecuteFunction()
+        private static void ExecuteSub()
         {
             StringBuilder userDataToExecute = new();
-            foreach (string item in funcData.Reverse())
+            foreach (string item in subData.Reverse())
             {
                 userDataToExecute.Append(item);
             }
 
-            funcData = new Stack<string>();
+            subData = new Stack<string>();
 
             dataEnd += userDataToExecute.ToString();
             DisplayPrompt();
@@ -229,7 +245,7 @@ private static void ExecuteFunction()
 
         private static void ExecuteLine()
         {
-            string codeToExecute = dataStart + funcData.Peek() + dataEnd;
+            string codeToExecute = dataStart + subData.Peek() + dataEnd;
 
             Trace.WriteLine(codeToExecute);
             string output = "Something went wrong! Please restart the application";
diff --git a/src/JukaApi/Program.cs b/src/JukaApi/Program.cs
index 4a7612f4..6759abfa 100644
--- a/src/JukaApi/Program.cs
+++ b/src/JukaApi/Program.cs
@@ -79,10 +79,10 @@ static IResult ExecuteCode(string code)
     if (compiler.HasErrors())
     {
         string errors = string.Join(Environment.NewLine, compiler.ListErrors());
-        return Results.Json(new { errors, original = decoded });
+        return Results.Ok(new { errors, original = decoded });
     }
 
-    return Results.Json(new { output = outputValue, original = decoded });
+    return Results.Ok(new { output = outputValue, original = decoded });
 }
 
 static async Task<IResult> ExecuteCodeFromBody(HttpRequest request)
diff --git a/src/JukaAzureFunction/JukaAzureFunction.cs b/src/JukaAzureFunction/JukaAzureFunction.cs
index e5c83668..a0a777a1 100644
--- a/src/JukaAzureFunction/JukaAzureFunction.cs
+++ b/src/JukaAzureFunction/JukaAzureFunction.cs
@@ -10,18 +10,12 @@
 
 namespace JukaAzureFunction;
 
-public class JukaAzureFunction
+public class JukaAzureFunction(ILogger<JukaAzureFunction> log)
 {
-    private readonly ILogger<JukaAzureFunction> logger;
+    private readonly ILogger<JukaAzureFunction> logger = log;
 
-    public JukaAzureFunction(ILogger<JukaAzureFunction> log)
-    {
-        logger = log;
-    }
-
-        
     [Function("JukaAzureFunction")]
-    [OpenApiOperation(operationId: "Run", tags: new[] { "name" })]
+    [OpenApiOperation(operationId: "Run", tags: "name" )]
     [OpenApiSecurity("function_key", SecuritySchemeType.ApiKey, Name = "Pass Code as Get or Post", In = OpenApiSecurityLocationType.Query)]
     [OpenApiParameter(name: "code", In = ParameterLocation.Query, Required = true, Type = typeof(string), Description = "Enter the **Code**")]
     [OpenApiResponseWithBody(statusCode: HttpStatusCode.OK, contentType: "text/plain", bodyType: typeof(string), Description = "The OK response")]
diff --git a/src/JukaCompiler/Compiler.cs b/src/JukaCompiler/Compiler.cs
index b93f397f..f3fc8de0 100644
--- a/src/JukaCompiler/Compiler.cs
+++ b/src/JukaCompiler/Compiler.cs
@@ -8,26 +8,18 @@
 using JukaCompiler.Expressions;
 using JukaCompiler.SystemCalls;
 using JukaCompiler.Lexer;
-using System.Linq;
 
 namespace JukaCompiler
 {
-    /*
-     * Main entry point into the compiler responsible for setting up DI container 
-     * and calling parser and compiler (currently interpreter).
-     */
     public class Compiler
     {
-        private ServiceProvider? serviceProvider = null;
+        private ServiceProvider serviceProvider;
+        private readonly HostBuilder hostBuilder;
 
-        public Compiler()
-        {
-            Initialize();
-        }
 
-        internal void Initialize()
+        public Compiler()
         {
-            var hostBuilder = new HostBuilder();
+            hostBuilder = new HostBuilder();
             hostBuilder.ConfigureServices(services =>
             {
                 services.AddSingleton<ICompilerError, CompilerError>();
@@ -41,13 +33,10 @@ internal void Initialize()
             hostBuilder.Build();
         }
 
-        // Run the Compiler (Step: 3)
+
         public string Go(string data, bool isFile = true)
         {
-            if (serviceProvider == null)
-            {
-                throw new JRuntimeException("Service provider is not created");
-            }
+            CheckServiceProvider();
 
             try
             {
@@ -96,25 +85,35 @@ private static void SetupMainMethodRuntimeHook(List<Stmt> statements, Resolver r
             var mainFunction = statements.OfType<Stmt.Function>().FirstOrDefault(f => f.StmtLexemeName.Equals("main")) ?? throw new Exception("No main function is defined");
             Lexeme lexeme = new(LexemeType.Types.IDENTIFIER, 0, 0);
             lexeme.AddToken("main");
-            Expr.Variable functionName = new(lexeme);
-            Expr.Call call = new(functionName, false, []);
+            Expr.Variable subroutineName = new(lexeme);
+            Expr.Call call = new(subroutineName, false, []);
             Stmt.Expression expression = new(call);
             resolver.Resolve([expression]);
         }
 
         public bool HasErrors()
         {
-            return serviceProvider != null && serviceProvider.GetRequiredService<ICompilerError>().HasErrors();
+            CheckServiceProvider();
+            return serviceProvider.GetRequiredService<ICompilerError>().HasErrors();
         }
 
         public List<string> ListErrors()
+        {
+            CheckServiceProvider();
+            return serviceProvider.GetRequiredService<ICompilerError>().ListErrors();
+        }
+
+        private void CheckServiceProvider()
         {
             if (serviceProvider == null)
             {
-                throw new JRuntimeException("Unable to initialize provider for errors");
+                throw new JRuntimeException("Service provider is not created");
             }
-
-            return serviceProvider.GetRequiredService<ICompilerError>().ListErrors();
         }
     }
+    public class CompilerException(string message, Exception innerException) : Exception(message, innerException)
+    {
+    }
 }
+
+
diff --git a/src/JukaCompiler/Exceptions/CompilerError.cs b/src/JukaCompiler/Exceptions/CompilerError.cs
index b16a58da..8e833f3c 100644
--- a/src/JukaCompiler/Exceptions/CompilerError.cs
+++ b/src/JukaCompiler/Exceptions/CompilerError.cs
@@ -2,7 +2,7 @@
 {
     internal class CompilerError : ICompilerError
     {
-        internal List<String> Errors = new List<String>();
+        internal List<string> Errors = [];
         internal string sourceFileName = string.Empty;
 
         public CompilerError()
diff --git a/src/JukaCompiler/Exceptions/ParserException.cs b/src/JukaCompiler/Exceptions/ParserException.cs
index c3a34e06..ebb5e15c 100644
--- a/src/JukaCompiler/Exceptions/ParserException.cs
+++ b/src/JukaCompiler/Exceptions/ParserException.cs
@@ -4,7 +4,7 @@ namespace JukaCompiler.Exceptions
 {
     internal class ParserException : Exception
     {
-        internal ParserException(string? message, LexemeType lexemeType) 
+        internal ParserException(string? message) 
             : base(message)
         {
         }
diff --git a/src/JukaCompiler/Expressions/Expr.cs b/src/JukaCompiler/Expressions/Expr.cs
index 431e45cf..4637c3b3 100644
--- a/src/JukaCompiler/Expressions/Expr.cs
+++ b/src/JukaCompiler/Expressions/Expr.cs
@@ -25,7 +25,7 @@ internal interface IVisitor<R>
             R VisitDeleteExpr(DeleteDeclarationExpr expr);
         }
 
-        internal abstract R Accept<R>(Expr.IVisitor<R> visitor);
+        internal abstract R Accept<R>(IVisitor<R> visitor);
 
         private Lexeme? expressionLexeme;
         internal Lexeme? initializerContextVariableName;
@@ -223,7 +223,7 @@ internal override R Accept<R>(IVisitor<R> visitor)
         }
         internal class Unary : Expr
         {
-            private LexemeType.Types lexemeType;
+            private readonly LexemeType.Types lexemeType;
             internal Unary(Lexeme lex, LexemeType.Types lexemeType)
             {
                 expressionLexeme = lex;
diff --git a/src/JukaCompiler/Interpreter/JukaClass.cs b/src/JukaCompiler/Interpreter/JukaClass.cs
index 07ef3208..65ef6d66 100644
--- a/src/JukaCompiler/Interpreter/JukaClass.cs
+++ b/src/JukaCompiler/Interpreter/JukaClass.cs
@@ -2,9 +2,9 @@
 {
     internal class JukaClass : IJukaCallable
     {
-        private string name;
-        private JukaClass superClass;
-        private Dictionary<string, JukaFunction> methods;
+        private readonly string name;
+        private readonly JukaClass superClass;
+        private readonly Dictionary<string, JukaFunction> methods;
 
         internal JukaClass(string name, JukaClass superClass, Dictionary<string, JukaFunction> methods)
         {
@@ -28,12 +28,9 @@ public int Arity()
         {
             // FIND METHOD is broken
             // Declaration is never set correctly.
-            JukaInstance? instance = new JukaInstance(this);
+            JukaInstance? instance = new(this);
             JukaFunction? initializer = FindMethod("main");
-            if (initializer != null)
-            {
-                initializer.Bind(instance).Call(methodName, interpreter, arguments);
-            }
+            initializer?.Bind(instance).Call(methodName, interpreter, arguments);
 
             return instance;
         }
diff --git a/src/JukaCompiler/Interpreter/JukaEnvironment.cs b/src/JukaCompiler/Interpreter/JukaEnvironment.cs
index b8387ef9..535ec1df 100644
--- a/src/JukaCompiler/Interpreter/JukaEnvironment.cs
+++ b/src/JukaCompiler/Interpreter/JukaEnvironment.cs
@@ -6,7 +6,7 @@ namespace JukaCompiler.Interpreter
     internal class JukaEnvironment
     {
         private JukaEnvironment? enclosing;
-        private Dictionary<string, object?> values = new Dictionary<string, object?>();
+        private readonly Dictionary<string, object?> values = [];
         
         internal JukaEnvironment()
         {
@@ -40,7 +40,7 @@ internal JukaEnvironment(JukaEnvironment enclosing)
 
         internal void Assign(Lexeme? name, object? value)
         {
-            var nameAsString = name?.ToString() ?? throw new JRuntimeException("unable to get variable name");
+            var nameAsString = name?.ToString() ?? throw new JRuntimeException("unable to get variable name: "+name);
 
             if (values.ContainsKey(nameAsString))
             {
diff --git a/src/JukaCompiler/Interpreter/JukaFunction.cs b/src/JukaCompiler/Interpreter/JukaFunction.cs
index be56a8cc..b98dd499 100644
--- a/src/JukaCompiler/Interpreter/JukaFunction.cs
+++ b/src/JukaCompiler/Interpreter/JukaFunction.cs
@@ -1,14 +1,13 @@
 using JukaCompiler.Exceptions;
 using JukaCompiler.Statements;
-using System.Reflection;
 
 namespace JukaCompiler.Interpreter
 {
     internal class JukaFunction : IJukaCallable
     {
-        private Stmt.Function? declaration;
-        private JukaEnvironment? closure;
-        private bool isInitializer;
+        private readonly Stmt.Function declaration;
+        private readonly JukaEnvironment closure;
+        private readonly bool isInitializer;
 
         internal JukaFunction(Stmt.Function declaration, JukaEnvironment closure, bool isInitializer)
         {
@@ -61,10 +60,10 @@ public int Arity()
                         var parameterNameExpressionLexeme = declaration.Params[i].parameterName.ExpressionLexeme;
                         if (parameterNameExpressionLexeme != null)
                         {
-                            string? name = parameterNameExpressionLexeme.ToString();
+                            string name = parameterNameExpressionLexeme.ToString();
                             if (string.IsNullOrEmpty(name))
                             {
-                                throw new ArgumentException("Unable to call function");
+                                throw new ArgumentException("Unable to call function: "+methodName);
                             }
 
                             object? value = arguments[i];
diff --git a/src/JukaCompiler/Interpreter/JukaInstance.cs b/src/JukaCompiler/Interpreter/JukaInstance.cs
index 434d64dc..afed4800 100644
--- a/src/JukaCompiler/Interpreter/JukaInstance.cs
+++ b/src/JukaCompiler/Interpreter/JukaInstance.cs
@@ -4,8 +4,8 @@ namespace JukaCompiler.Interpreter
 {
     internal class JukaInstance
     {
-        private JukaClass Class;
-        private Dictionary<string,object> fields = new Dictionary<string,object>();
+        private readonly JukaClass Class;
+        private readonly Dictionary<string, object> fields = [];
 
         internal JukaInstance(JukaClass Class)
         {
diff --git a/src/JukaCompiler/Interpreter/JukaInterpreter.cs b/src/JukaCompiler/Interpreter/JukaInterpreter.cs
index fe848638..51f23eb1 100644
--- a/src/JukaCompiler/Interpreter/JukaInterpreter.cs
+++ b/src/JukaCompiler/Interpreter/JukaInterpreter.cs
@@ -87,7 +87,7 @@ internal void ExecuteBlock(List<Stmt> statements, JukaEnvironment env)
         }
         Stmt Stmt.IVisitor<Stmt>.VisitBlockStmt(Stmt.Block stmt)
         {
-            ExecuteBlock(stmt.statements, new(this.environment));
+            ExecuteBlock(stmt.statements, new(environment));
             return new Stmt.DefaultStatement();
         }
 
@@ -220,10 +220,7 @@ private void PrintLiteralExpr(Expr expr, Action<object> printAction)
             }
         }
 
-        private void PrintLiteral(Expr.Literal expr, Action<object> printAction)
-        {
-            printAction(expr.ExpressionLexemeName);
-        }
+        private void PrintLiteral(Expr.Literal expr, Action<object> printAction) => printAction(expr.ExpressionLexemeName);
 
         private void PrintLiteral(Expr.LexemeTypeLiteral expr, Action<object> printAction)
         {
@@ -642,7 +639,7 @@ private static bool IsEqual(object a, object b)
             switch (argumentsMap.Count)
             {
                 case > 0:
-                    currentStackFrame.AddVariables(argumentsMap, this);
+                    currentStackFrame.AddVariables(argumentsMap);
                     break;
             }
 
diff --git a/src/JukaCompiler/Interpreter/Resolver.cs b/src/JukaCompiler/Interpreter/Resolver.cs
index c5ace576..96380cdb 100644
--- a/src/JukaCompiler/Interpreter/Resolver.cs
+++ b/src/JukaCompiler/Interpreter/Resolver.cs
@@ -9,15 +9,15 @@ namespace JukaCompiler.Interpreter
 {
     internal class Resolver : Stmt.IVisitor<object>, Expr.IVisitor<object>
     {
-        private JukaInterpreter interpreter;
+        private readonly JukaInterpreter interpreter;
         private FunctionType currentFunction = FunctionType.NONE;
         private ClassType currentClass = ClassType.NONE;
-        private ServiceProvider? ServiceProvider;
-        private Stack<Dictionary<string, bool>> scopes = new();
-        Dictionary<string, BlockScope?> processScope = new();
-        private Stack<string> blockScope = new();
-        private ICompilerError? compilerError;
-        private string errorMessage = "Resolver error - message:{0}";
+        private readonly ServiceProvider? ServiceProvider;
+        private readonly Stack<Dictionary<string, bool>> scopes = new();
+        private readonly Dictionary<string, BlockScope?> processScope = [];
+        private readonly Stack<string> blockScope = new();
+        private readonly ICompilerError? compilerError;
+        private readonly string errorMessage = "Resolver error - message:{0}";
 
         private enum FunctionType
         {
@@ -65,13 +65,8 @@ private void Resolve(Expr expr)
 
         public object VisitAssignExpr(Expr.Assign expr)
         {
-            var frame = blockScope.Peek();
-            if (frame == null)
-            {
-                throw new Exception(string.Format(errorMessage,"No stack frames"));
-            }
-
-            if(processScope.TryGetValue(frame, out BlockScope? value))
+            var frame = blockScope.Peek() ?? throw new Exception(string.Format(errorMessage,"No stack frames"));
+            if (processScope.TryGetValue(frame, out BlockScope? value))
             {
                 if (value != null && value.lexemeScope.TryGetValue(expr.ExpressionLexeme?.ToString()!, out var lexeme))
                 {
@@ -100,11 +95,11 @@ public object VisitBlockStmt(Stmt.Block stmt)
             return new Stmt.DefaultStatement();
         }
 
-        public object VisitCallExpr(Expr.Call expr)
+        public object VisitCallExpr(Call expr)
         {
-            if (expr is Expr.Call)
+            if (expr is not null)
             {
-                var call = (Expr.Call)expr;
+                Call call = expr;
                 BeginScope(expr.callee.ExpressionLexeme?.ToString()!);
                 if (expr.callee.ExpressionLexeme != null)
                 {
@@ -125,7 +120,7 @@ public object VisitClassStmt(Stmt.Class stmt)
         {
             ClassType enclosingClass = currentClass;
             currentClass = ClassType.CLASS;
-            BlockScope? blockScope = new BlockScope();
+            BlockScope blockScope = new();
 
             Declare(stmt.name);
             Define(stmt.name);
@@ -153,8 +148,9 @@ public object VisitClassStmt(Stmt.Class stmt)
             scopes.Peek().Add("this", true);
             processScope.Add("this", blockScope);
 
-            foreach (Stmt.Function method in stmt.methods)
+            for (int i = 0; i < stmt.methods.Count; i++)
             {
+                Stmt.Function method = stmt.methods[i];
                 //FunctionType decl = FunctionType.METHOD;
                 //implement ctor
                 // if(method.ExpressionLexeme.ToString
@@ -206,7 +202,7 @@ public object VisitGroupingExpr(Expr.Grouping expr)
         {
             if (expr == null || expr.expression == null)
             {
-                throw new ArgumentNullException("grouping has some null stuff");
+                throw new ArgumentNullException("Grouping has some null stuff");
             }
 
             Resolve(expr.expression);
@@ -280,7 +276,7 @@ public object VisitReturnStmt(Stmt.Return stmt)
 
         public object VisitBreakStmt(Stmt.Break stmt)
         {
-            Stmt.Return returnStatement = new Stmt.Return();
+            Stmt.Return returnStatement = new();
             return VisitReturnStmt(returnStatement);
         }
 
@@ -358,16 +354,16 @@ private void ResolveLocal(Expr expr, Lexeme name)
             {
                 if (scopes.Peek().ContainsKey(name.ToString()))
                 {
-                    this.interpreter.Resolve(expr, scopes.Count() - 1 - i);
+                    this.interpreter.Resolve(expr, scopes.Count - 1 - i);
                 }
             }
         }
 
         public object VisitVarStmt(Stmt.Var stmt)
         {
-            if (stmt==null || stmt.name == null)
+            if (stmt == null || stmt.name == null)
             {
-                throw new ArgumentNullException("new vist stmt == null");
+                throw new ArgumentNullException("new vist stmt == null"+stmt);
             }
 
             Declare(stmt.name);
@@ -406,7 +402,7 @@ private void Declare(Lexeme name)
                     return;
                 }
 
-                BlockScope? bsObject = new BlockScope();
+                BlockScope bsObject = new();
                 if (bsObject.lexemeScope.ContainsKey(name.ToString()))
                 {
                     throw new Exception("variable already exist");
@@ -419,7 +415,7 @@ private void Declare(Lexeme name)
 
         private void Define(Lexeme name)
         {
-            if (!scopes.Any() || (scopes.Peek().Count == 0))
+            if (scopes.Count == 0 || (scopes.Peek().Count == 0))
             {
                 return;
             }
@@ -441,12 +437,7 @@ private void ResolveFunction(Stmt.Function function, FunctionType type)
 
             foreach (var param in function.typeParameterMaps)
             {
-                var literalName = param.parameterName as Expr.Variable;
-                if (literalName == null)
-                {
-                    throw new Exception("Something went wrong when resolving the function");
-                }
-
+                Variable literalName = param.parameterName as Expr.Variable ?? throw new Exception("Something went wrong when resolving the function");
                 if (literalName.ExpressionLexeme != null)
                 {
                     Declare(literalName.ExpressionLexeme);
@@ -458,13 +449,16 @@ private void ResolveFunction(Stmt.Function function, FunctionType type)
                 }
             }
 
-            Resolve(function.body);
+            if (function != null && function.body != null)
+            {
+                Resolve(function.body);
+            }
             currentFunction = enclosingFunction;
         }
 
         private void BeginScope(string scopeName)
         {
-            scopes.Push(new Dictionary<string, bool>());
+            scopes.Push([]);
             blockScope.Push(scopeName);
         }
 
@@ -477,7 +471,7 @@ private void EndScope()
 
     internal class BlockScope
     {
-        internal Dictionary<string, Dictionary<string, Expr>> processScope = new();
-        internal Dictionary<string, Lexeme> lexemeScope = new();
+        internal Dictionary<string, Dictionary<string, Expr>> processScope = [];
+        internal Dictionary<string, Lexeme> lexemeScope = [];
     }
 }
diff --git a/src/JukaCompiler/Interpreter/StackFrame.cs b/src/JukaCompiler/Interpreter/StackFrame.cs
index 0f095409..9a800466 100644
--- a/src/JukaCompiler/Interpreter/StackFrame.cs
+++ b/src/JukaCompiler/Interpreter/StackFrame.cs
@@ -7,34 +7,33 @@ namespace JukaCompiler.Interpreter
 {
     internal class StackFrame
     {
-        private Dictionary<string, Lexeme> frameVariables = new();
-        private string frameName;
-        private Dictionary<string, object?> variables = new();
-        private Dictionary<string, StackVariableState> variableAndKind = new();
+        private readonly Dictionary<string, Lexeme> frameVariables = [];
+        private readonly string frameName;
+        private readonly Dictionary<string, object?> variables = [];
+        private readonly Dictionary<string, StackVariableState> variableAndKind = [];
 
         internal StackFrame(string name)
         {
             this.frameName = name;
         }
 
-        internal void AddVariables(Dictionary<string, object?> variables, JukaInterpreter interpreter)
+        internal void AddVariables(Dictionary<string, object?> variables)
         {
             foreach (var variable in variables)
             {
                 string name = variable.Key;
 
-                object? value = null;
+                object? value;
                 if (variable.Value is Expr.Literal)
                 {
                     value = variable.Value;
+                    AddVariable(name, value, variable.Value.GetType(), null);
                 }
-                else
+                else if(variable.Value != null)
                 {
                     value = ((Expr.LexemeTypeLiteral)variable.Value).literal;
+                    AddVariable(name, value, variable.Value.GetType(), null);
                 }
-
-                //
-                AddVariable(name, value, variable.Value.GetType(), null);
             }
         }
 
@@ -42,14 +41,8 @@ internal void AddVariables(Dictionary<string, object?> variables, JukaInterprete
         {
             if (variable.exprInitializer != null)
             {
-                object? variableValue = interpreter.Evaluate(variable.exprInitializer);
-
-                if (variableValue == null)
-                {
-                    throw new JRuntimeException("the value of the variable is null");
-                }
-
-                if (!(variable.exprInitializer is Expr.Call))
+                object? variableValue = interpreter.Evaluate(variable.exprInitializer) ?? throw new JRuntimeException("The value of the variable is null");
+                if (variable.exprInitializer is not Expr.Call)
                 {
                     string variableName = variable.name?.ToString() ?? throw new JRuntimeException("variable name is missing");
                     AddVariable(variableName, variableValue, variableValue.GetType(),variable.exprInitializer);
@@ -58,7 +51,7 @@ internal void AddVariables(Dictionary<string, object?> variables, JukaInterprete
                 return variableValue;
             }
 
-            throw new JRuntimeException("unable to add variable");
+            throw new JRuntimeException("Unable to add variable to StackFrame");
         }
 
         internal void AddVariable(string name, object? variableValue, Type? variableKind, Expr? expressionContext)
@@ -94,13 +87,7 @@ internal bool UpdateVariable(string name, object? value)
 
         internal bool DeleteVariable(string name)
         {
-            if (variables.ContainsKey(name))
-            {
-                variables.Remove(name);
-                return true;
-            }
-
-            return false;
+            return variables.Remove(name);
         }
 
         internal bool TryGetStackVariableByName(string name, out StackVariableState? variable)
@@ -122,7 +109,7 @@ internal class StackVariableState
             internal object? Value;
             internal Type? type;
             internal Expr? expressionContext;
-            internal object[] arrayValues;
+            internal object[] arrayValues = [];
         }
     }
 }
diff --git a/src/JukaCompiler/Lexer/Keywords.cs b/src/JukaCompiler/Lexer/Keywords.cs
index 4bde6af0..db2ff6ea 100644
--- a/src/JukaCompiler/Lexer/Keywords.cs
+++ b/src/JukaCompiler/Lexer/Keywords.cs
@@ -21,6 +21,7 @@ public enum KeyWordsEnum
         While,
         Debugger,
         Func,
+        Sub,
         This,
         With,
         Default,
@@ -60,6 +61,7 @@ public class KeyWords
         public const string WHILE = "while";
         public const string DEBUGGER = "debugger";
         public const string FUNC = "func";
+        public const string SUB = "sub";
         public const string THIS = "this";
         public const string WITH = "with";
         public const string DEFAULT = "default";
@@ -80,10 +82,7 @@ public class KeyWords
 
         public const string LPAREN = "(";
         public const string RPAREN = ")";
-
-    
-
-        public static List<string> keyWordNames = new List<string>()
+        private static readonly List<string> list = new()
         {
             {"array"},
             {"break"},
@@ -104,6 +103,7 @@ public class KeyWords
             {"while"},
             {"debugger"},
             {"function"},
+            {"subroutine"},
             {"this"},
             {"with"},
             {"default"},
@@ -122,8 +122,9 @@ public class KeyWords
             {"class"},
             {"main"},
         };
+        public static List<string> keyWordNames = list;
 
-        public static Dictionary<string, KeyWordsEnum> keyValuePairs = new Dictionary<string, KeyWordsEnum>()
+        public static Dictionary<string, KeyWordsEnum> keyValuePairs = new()
         {
             { "array",      KeyWordsEnum.Array },
             { "break",      KeyWordsEnum.Break },
@@ -143,7 +144,8 @@ public class KeyWords
             { "switch",     KeyWordsEnum.Switch },       
             { "while",      KeyWordsEnum.While },        
             { "debugger",   KeyWordsEnum.Debugger },     
-            { "func",       KeyWordsEnum.Func },     
+            { "func",       KeyWordsEnum.Func },
+            { "sub",       KeyWordsEnum.Sub },
             { "this",       KeyWordsEnum.This },         
             { "with",       KeyWordsEnum.With },         
             { "default",    KeyWordsEnum.Default },      
diff --git a/src/JukaCompiler/Lexer/Lexeme.cs b/src/JukaCompiler/Lexer/Lexeme.cs
index 106cb9ac..dea2fc9f 100644
--- a/src/JukaCompiler/Lexer/Lexeme.cs
+++ b/src/JukaCompiler/Lexer/Lexeme.cs
@@ -39,6 +39,7 @@ internal enum Types
             ELSE,
             FALSE,
             FUNC,
+            SUB,
             FOR,
             IF,
             NULL,
@@ -66,11 +67,11 @@ internal enum Types
     }
     internal class Lexeme
     {
-        private StringBuilder tokenBuilder = new StringBuilder();
+        private readonly StringBuilder tokenBuilder = new();
         private bool isKeyWord = false;
         private Int64 typeOfKeyWord;
-        private int lineNumber;
-        private int columnNumber;
+        private readonly int lineNumber;
+        private readonly int columnNumber;
 
         internal LexemeType.Types LexemeType { get; set; }
 
diff --git a/src/JukaCompiler/Parse/Parser.cs b/src/JukaCompiler/Parse/Parser.cs
index c3153801..c7ac6dde 100644
--- a/src/JukaCompiler/Parse/Parser.cs
+++ b/src/JukaCompiler/Parse/Parser.cs
@@ -10,11 +10,11 @@ namespace JukaCompiler.Parse
 {
     public class Parser
     {
-        private List<Lexeme> tokens = new();
+        private List<Lexeme> tokens = [];
         private int current = 0;
         private Scanner? scanner;
         public ServiceProvider Services { get; }
-        private ICompilerError compilerError;
+        private readonly ICompilerError compilerError;
 
         internal Parser(Scanner scanner, ServiceProvider services)
         {
@@ -32,7 +32,7 @@ internal List<Stmt> Parse()
             }
 
             tokens = scanner.Scan()!;
-            List<Stmt> statements = new();
+            List<Stmt> statements = [];
             while(!IsAtEnd())
             {
                 statements.Add(Declaration());
@@ -89,9 +89,9 @@ private Stmt Declaration()
             }
 
 
-            if (Match(LexemeType.Types.FUNC))
+            if (Match(LexemeType.Types.SUB))
             {
-                return Function("func");
+                return Function("sub");
             }
 
             if (MatchKeyWord())
@@ -147,7 +147,7 @@ private Stmt Statement()
             return ExpressionStatement();
         }
 
-        private Stmt IfStatement()
+        private Stmt.If IfStatement()
         {
             Consume(LexemeType.Types.LEFT_PAREN, Previous());
 
@@ -176,7 +176,7 @@ private Stmt IfStatement()
             throw new JRuntimeException("If statement failure");
         }
 
-        private Stmt WhileStatement()
+        private Stmt.While WhileStatement()
         {
             Consume(LexemeType.Types.LEFT_PAREN, Previous());
 
@@ -189,7 +189,7 @@ private Stmt WhileStatement()
             return new Stmt.While(condition, whileBlock);
         }
 
-        private Stmt ForStatement()
+        private Stmt.For ForStatement()
         {
             Consume(LexemeType.Types.LEFT_PAREN, Previous());
             if (MatchKeyWord())
@@ -217,7 +217,7 @@ private Stmt ForStatement()
             throw new JRuntimeException("no valid variable");
         }
 
-        private Stmt BreakStatement()
+        private Stmt.Break BreakStatement()
         {
             Consume(LexemeType.Types.SEMICOLON, Previous());
             var expr = Expr();
@@ -225,7 +225,7 @@ private Stmt BreakStatement()
         }
 
 
-        private Stmt ReturnStatement()
+        private Stmt.Return ReturnStatement()
         {
             var keyword = Previous();
             Expr value = null!;
@@ -244,14 +244,14 @@ private Stmt ReturnStatement()
             return new Stmt.Return(keyword, value);
         }
 
-        private Stmt ExpressionStatement()
+        private Stmt.Expression ExpressionStatement()
         {
             Expr expr = Expr();
             Consume(LexemeType.Types.SEMICOLON, Peek());
             return new Stmt.Expression(expr);
         }
 
-        private Stmt PrintLine()
+        private Stmt.PrintLine PrintLine()
         {
             Lexeme keyword = Previous();
             Consume(LexemeType.Types.LEFT_PAREN, Peek());
@@ -264,7 +264,7 @@ private Stmt PrintLine()
             return new Stmt.PrintLine(value);
         }
 
-        private Stmt Print()
+        private Stmt.Print Print()
         {
             Lexeme keyword = Previous();
             Consume(LexemeType.Types.LEFT_PAREN, Peek());
@@ -371,7 +371,7 @@ private bool CheckKeyWord()
             return false;
         }
 
-        private Stmt Function(string kind)
+        private Stmt.Function Function(string kind)
         {
             Lexeme name = Consume(LexemeType.Types.IDENTIFIER, Peek());
             Consume(LexemeType.Types.LEFT_PAREN, Peek());
@@ -401,13 +401,13 @@ private Stmt Function(string kind)
             return stmt;
         }
 
-        private Stmt ClassDeclaration(string kind)
+        private Stmt.Class ClassDeclaration(string kind)
         {
             Lexeme name = Consume(LexemeType.Types.IDENTIFIER, Peek());
             Consume(LexemeType.Types.EQUAL, Peek());
             Consume(LexemeType.Types.LEFT_BRACE, Peek());
-            List<Stmt.Function> functions = new();
-            List<Stmt> variableDeclarations = new();
+            List<Stmt.Function> functions = [];
+            List<Stmt> variableDeclarations = [];
 
             if(!Check(LexemeType.Types.RIGHT_BRACE))
             {
@@ -419,7 +419,7 @@ private Stmt ClassDeclaration(string kind)
                         break;
                     }
 
-                    if (isFunc.LexemeType == LexemeType.Types.FUNC)
+                    if (isFunc.LexemeType == LexemeType.Types.SUB)
                     {
                         functions.Add((Stmt.Function)Declaration());
                     }
@@ -480,11 +480,11 @@ private Expr Assignment()
 
                 //expr.ExpressionLexemeName =
 
-                if (expr is Expr.Variable && 
-                    ((Expr.Variable)expr) != null && 
-                    ((Expr.Variable)expr).ExpressionLexeme != null)
+                if (expr is Expr.Variable exprVariables &&
+                    exprVariables != null &&
+                    exprVariables.ExpressionLexeme != null)
                 {
-                    Expr.Variable variable = (Expr.Variable)expr;
+                    Expr.Variable variable = exprVariables;
                     //expr.ExpressionLexemeName = variable.ExpressionLexeme.
                     if (variable != null && variable.ExpressionLexeme != null) 
                     {
@@ -493,11 +493,11 @@ private Expr Assignment()
                     //> Classes assign-set
                 }
 
-                if (expr is Expr.Get &&
-                    ((Expr.Get)expr) != null &&
-                    ((Expr.Get)expr).ExpressionLexeme != null) 
+                if (expr is Expr.Get exprGet &&
+                    exprGet != null &&
+                    exprGet.ExpressionLexeme != null) 
                 {
-                    Expr.Get get = (Expr.Get)expr;
+                    Expr.Get get = exprGet;
                     if (get != null && get.ExpressionLexeme != null)
                     {
                         return new Expr.Set(get, get.ExpressionLexeme, value);
@@ -615,9 +615,9 @@ private Expr Unary()
 
             if (Match(LexemeType.Types.BANG))
             {
-                Lexeme op = Previous();
-                Expr right = Unary();
-                //******* return new Expr.Unary(op, right);
+                //Lexeme op = Previous();
+                //Expr right = Unary();
+                //return new Expr.Unary(op, right);
             }
 
             Lexeme idLexeme = Peek();
@@ -745,9 +745,9 @@ private Expr Primary()
             throw new Exception(Peek() + "Expect expr");
         }
 
-        private Expr FinishCall(Expr callee)
+        private Expr.Call FinishCall(Expr callee)
         {
-            List<Expr> arguments = new();
+            List<Expr> arguments = [];
             if (!Check(LexemeType.Types.RIGHT_PAREN))
             {
                 do
diff --git a/src/JukaCompiler/Scan/Scanner.cs b/src/JukaCompiler/Scan/Scanner.cs
index f74eb689..e1d10668 100644
--- a/src/JukaCompiler/Scan/Scanner.cs
+++ b/src/JukaCompiler/Scan/Scanner.cs
@@ -12,9 +12,9 @@ internal class Scanner
         private int current = 0;
         private int line = 1;
         private int column = 0;
-        private byte[] fileData;
-        private readonly List<Lexeme?> lexemes = new();
-        private ICompilerError compilerError;
+        private readonly byte[] fileData;
+        private readonly List<Lexeme?> lexemes = [];
+        //private readonly ICompilerError compilerError;
 
         private static readonly Dictionary<string, LexemeType.Types> keywordsDictionary = new()
         {
@@ -22,6 +22,7 @@ internal class Scanner
             { "class",  LexemeType.Types.CLASS },
             { "else",   LexemeType.Types.ELSE },
             { "func",   LexemeType.Types.FUNC },
+            { "sub",   LexemeType.Types.SUB },
             { "for",    LexemeType.Types.FOR },
             { "if",     LexemeType.Types.IF },
             { "null",   LexemeType.Types.NULL },
@@ -50,12 +51,12 @@ internal class Scanner
 
         internal Scanner(string data, IServiceProvider serviceProvider, bool isFile = true)
         {
-            this.compilerError = serviceProvider.GetRequiredService<ICompilerError>();
+            //this.compilerError = serviceProvider.GetRequiredService<ICompilerError>();
             if (isFile)
             {
                 if (string.IsNullOrEmpty(data))
                 {
-                    throw new ArgumentNullException("The path is null");
+                    throw new ArgumentNullException("The path is null"+data);
                 }
 
                 if (!File.Exists(data))
@@ -255,7 +256,7 @@ internal void AddSymbol(char symbol, LexemeType.Types type)
             this.lexemes.Add(lex);
         }
 
-        internal bool TryGetKeyWord(Lexeme? lex)
+        internal static bool TryGetKeyWord(Lexeme? lex)
         {
             bool isKeyword = false;
 
@@ -308,7 +309,7 @@ internal void Identifier()
                 Advance();
             }
 
-            var svalue = Encoding.Default.GetString(Memcopy(fileData, start, current));
+            var svalue = Encoding.Default.GetString(Memcopy(fileData, start));
             Lexeme? identifier = new(LexemeType.Types.IDENTIFIER, this.line, this.column);
             
             identifier.AddToken(svalue);
@@ -326,7 +327,7 @@ internal void Number()
                 temp = Peek();
             }
 
-            var svalue = System.Text.Encoding.Default.GetString(Memcopy(fileData, start, current));
+            var svalue = System.Text.Encoding.Default.GetString(Memcopy(fileData, start));
             Lexeme? number = new(LexemeType.Types.NUMBER, this.line, this.column);
 
             number.AddToken(svalue);
@@ -352,14 +353,14 @@ private void String()
                 return;
             }
 
-            var svalue = System.Text.Encoding.Default.GetString(Memcopy(fileData, start + 1, current - 1));
+            var svalue = Encoding.Default.GetString(Memcopy(fileData, start + 1));
             Lexeme? s = new(LexemeType.Types.STRING, this.line, this.column);
             s.AddToken(svalue.ToString());
             this.lexemes.Add(s);
             Advance();
         }
 
-        private byte[] Memcopy(byte[] from, int start, int size)
+        private byte[] Memcopy(byte[] from, int start)
         {
             byte [] to = new byte[current - start];
             for(int toIndex = 0, i = start; i < current; i++, toIndex++)
diff --git a/src/JukaCompiler/Statements/Statement.cs b/src/JukaCompiler/Statements/Statement.cs
index 0dbe1aa5..91b1fa65 100644
--- a/src/JukaCompiler/Statements/Statement.cs
+++ b/src/JukaCompiler/Statements/Statement.cs
@@ -23,7 +23,7 @@ internal interface IVisitor<R>
             R VisitForStmt(For stmt);
             object VisitArrayExpr(Expr.ArrayDeclarationExpr expr);
         }
-        internal abstract R Accept<R>(Stmt.IVisitor<R> vistor);
+        internal abstract R Accept<R>(IVisitor<R> vistor);
         private Lexeme stmtLexeme = new();
 
         internal Lexeme StmtLexeme
@@ -39,29 +39,20 @@ internal string StmtLexemeName
 
         internal class Block : Stmt
         {
-            internal Block(List<Stmt> statements)
-            {
-                this.statements = statements;
-            }
+            internal Block(List<Stmt> statements) => this.statements = statements;
 
-            internal List<Stmt>? statements;
-            internal override R Accept<R>(IVisitor<R> vistor)
-            {
-               return vistor.VisitBlockStmt(this);
-            }
+            internal List<Stmt> statements;
+            internal override R Accept<R>(IVisitor<R> vistor) => vistor.VisitBlockStmt(this);
         }
         internal class Function : Stmt
         {
             internal List<Stmt>? body = [];
             internal List<TypeParameterMap> typeParameterMaps;
 
-            public override bool Equals(object? obj)
-            {
-                return this.StmtLexemeName.Equals(obj);
-            }
+            public override bool Equals(object? obj) => StmtLexemeName.Equals(obj);
             internal Function(Lexeme stmtLexeme, List<TypeParameterMap> parametersMap, List<Stmt> body)
             {
-                if (!(stmtLexeme.ToString().All(c => char.IsLetterOrDigit(c) || c == '_')))
+                if (!stmtLexeme.ToString().All(c => char.IsLetterOrDigit(c) || c == '_'))
                 {
                     throw new Exception("Function {ExpressionLexeme.ToString()} has an invalid ExpressionLexeme");
                 }
@@ -70,29 +61,20 @@ internal Function(Lexeme stmtLexeme, List<TypeParameterMap> parametersMap, List<
                 this.body = body;
             }
 
-            internal override R Accept<R>(IVisitor<R> vistor)
-            {
-                return vistor.VisitFunctionStmt(this);
-            }
+            internal override R Accept<R>(IVisitor<R> vistor) => vistor.VisitFunctionStmt(this);
 
-            internal List<TypeParameterMap> Params
-            {
-                get { return this.typeParameterMaps; }
-            }
+            internal List<TypeParameterMap> Params => typeParameterMaps;
 
-            public override int GetHashCode()
-            {
-                return base.GetHashCode();
-            }
+            public override int GetHashCode() => base.GetHashCode();
         }
         internal class Class : Stmt
         {
-            internal Lexeme? name;
-            internal List<Stmt.Function>? methods;
-            internal List<Stmt>? variableDeclarations;
+            internal Lexeme name;
+            internal List<Function> methods;
+            internal List<Stmt> variableDeclarations;
             internal Expr.Variable? superClass;
 
-            internal Class(Lexeme name, List<Stmt.Function> methods, List<Stmt> variableDeclarations)
+            internal Class(Lexeme name, List<Function> methods, List<Stmt> variableDeclarations)
             {
                 this.name = name;
                 this.methods = methods;
@@ -107,11 +89,11 @@ internal override R Accept<R>(IVisitor<R> vistor)
         }
         internal class Expression : Stmt
          {
-            internal Expr? Expr;
+            internal Expr Expr;
 
             internal Expression(Expr expr)
             {
-                this.Expr = expr;
+                Expr = expr;
             }
 
              internal override R Accept<R>(IVisitor<R> vistor)
@@ -121,9 +103,9 @@ internal override R Accept<R>(IVisitor<R> vistor)
         }
         internal class If : Stmt
         {
-            internal Expr? condition;
-            internal Stmt? thenBranch;
-            internal Stmt? elseBranch;
+            internal Expr condition;
+            internal Stmt thenBranch;
+            internal Stmt elseBranch;
 
             internal If(Expr condition, Stmt thenBranch, Stmt elseBranch)
             {
@@ -149,6 +131,7 @@ internal PrintLine(Expr expr)
 
             internal PrintLine()
             {
+                this.expr = null;
             }
 
             internal override R Accept<R>(IVisitor<R> vistor)
@@ -167,6 +150,7 @@ internal Print(Expr expr)
 
             internal Print()
             {
+                this.expr = null;
             }
 
             internal override R Accept<R>(IVisitor<R> vistor)
@@ -178,7 +162,7 @@ internal class Var : Stmt
         {
             internal Lexeme? name;
             internal Expr? exprInitializer;
-            internal bool? isInitalizedVar = false;
+            internal bool isInitalizedVar = false;
 
             internal Var(Lexeme name, Expr expr)
             {
@@ -215,8 +199,8 @@ internal override R Accept<R>(IVisitor<R> vistor)
 
         internal class While : Stmt
         {
-            internal Expr? condition;
-            internal Stmt? whileBlock;
+            internal Expr condition;
+            internal Stmt whileBlock;
 
             internal While(Expr condition, Stmt whileBlock)
             {
@@ -232,10 +216,10 @@ internal override R Accept<R>(IVisitor<R> vistor)
 
         internal class For : Stmt
         {
-            private Stmt.Var init;
-            private Expr breakExpr;
-            private Expr incExpr;
-            private Stmt forBody;
+            private readonly Var init;
+            private readonly Expr breakExpr;
+            private readonly Expr incExpr;
+            private readonly Stmt forBody;
 
             internal For(Stmt.Var init, Expr breakExpr, Expr incExpr, Stmt forBody)
             {
@@ -267,6 +251,8 @@ internal Return(Lexeme keyword, Expr expr)
 
             internal Return()
             {
+                this.expr = null;
+                this.keyword = null;
             }
 
             internal override R Accept<R>(IVisitor<R> vistor)
@@ -276,7 +262,7 @@ internal override R Accept<R>(IVisitor<R> vistor)
         }
         internal class Break : Stmt
         {
-            internal Expr? expr;
+            internal Expr expr;
 
             internal Break(Expr expr)
             {
@@ -299,7 +285,7 @@ internal override R Accept<R>(IVisitor<R> vistor)
 
         internal class LiteralLexemeExpression : Stmt
         {
-            internal Expr.LexemeTypeLiteral? ltl;
+            internal Expr.LexemeTypeLiteral ltl;
 
             internal LiteralLexemeExpression(Expr.LexemeTypeLiteral lexemeTypeLiteral)
             {
diff --git a/src/JukaUnitTest/ArithmeticUnitTest.cs b/src/JukaUnitTest/ArithmeticUnitTest.cs
index c1e8e763..e9180417 100644
--- a/src/JukaUnitTest/ArithmeticUnitTest.cs
+++ b/src/JukaUnitTest/ArithmeticUnitTest.cs
@@ -11,7 +11,7 @@ public class ArithmeticUnitTest : UnitTestStructure
     public void Add(dynamic a, dynamic b, string expected)
     {
         SourceAsString += @"
-                func test_func() = {
+                sub test_func() = {
                     var x=" + a + @";
                     var y=" + b + @";
                     var z=x+y;
@@ -26,7 +26,7 @@ func test_func() = {
     [DataRow(-5, -5, "0")]
     public void Subtract(dynamic a, dynamic b, string expected)
     {
-        SourceAsString += @"func test_func() = {
+        SourceAsString += @"sub test_func() = {
                 var x=" + a + @"; var y=" + b + @"; var z=x-y;
                 print(z);
             }";
@@ -38,7 +38,7 @@ public void Subtract(dynamic a, dynamic b, string expected)
     [DataRow(-5, -5, "1")] // Expected result should be "1.0" for division
     public void Divide(dynamic a, dynamic b, string expected)
     {
-        SourceAsString += @"func test_func() =
+        SourceAsString += @"sub test_func() =
             {
                 var x=" + a + @";
                 var y=" + b + @";
@@ -54,7 +54,7 @@ public void Divide(dynamic a, dynamic b, string expected)
     [DataRow(-5, -5, "25")]
     public void Multiply(dynamic a, dynamic b, string expected)
     {
-        SourceAsString += @"func test_func() = 
+        SourceAsString += @"sub test_func() = 
             {
                 var x=" + a + @";
                 var y=" + b + @";
diff --git a/src/JukaUnitTest/CommentsUnitTest.cs b/src/JukaUnitTest/CommentsUnitTest.cs
index 6e501347..1c4d1523 100644
--- a/src/JukaUnitTest/CommentsUnitTest.cs
+++ b/src/JukaUnitTest/CommentsUnitTest.cs
@@ -11,7 +11,7 @@ public class CommentsUnitTest : UnitTestStructure
     [DataRow(0, "0")]
     public void EmptyComment(dynamic value, string expected)
     {
-        SourceAsString += @"func test_func() =
+        SourceAsString += @"sub test_func() =
                 {
                     var y = " + value + @";
                     print(y); // Uncommented this line
diff --git a/src/JukaUnitTest/CompilerUnitTest.cs b/src/JukaUnitTest/CompilerUnitTest.cs
index 41a4bd2d..9effd5de 100644
--- a/src/JukaUnitTest/CompilerUnitTest.cs
+++ b/src/JukaUnitTest/CompilerUnitTest.cs
@@ -10,7 +10,7 @@ public class CompilerUnitTest : UnitTestStructure
     public void StackBasedArray()
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = array[3];
                     x[1] = ""test"";
@@ -27,7 +27,7 @@ public void StackBasedArray()
     public void HeapBasedArray()
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var y = ""te"";
                     print(y);
@@ -47,7 +47,7 @@ public void HeapBasedArray()
     public void PrintLiteral(dynamic value, string expected)
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     printLine("+value+@"); 
                 }";
@@ -61,7 +61,7 @@ public void PrintLiteral(dynamic value, string expected)
     public void PrintVariable(dynamic value, string expected)
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = "+value+@";
                     print(x); 
@@ -77,13 +77,13 @@ public void PrintVariable(dynamic value, string expected)
     public void PassVariable(dynamic value, string expected)
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = "+value+@";
                     varpass(x);
                 }
                 
-                func varpass(var x) = 
+                sub varpass(var x) = 
                 {
                     print(x); 
                 }";
@@ -98,18 +98,18 @@ func varpass(var x) =
     public void PrintThreeLevelsNesting(dynamic value, string expected)
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var y = "+value+@";
                     nest1(y);
                 }
                 
-                func nest1(var y) = 
+                sub nest1(var y) = 
                 {
                     nest2(y);
                 }
 
-                func nest2(var z) = 
+                sub nest2(var z) = 
                 {
                     print(z);
                 }";
@@ -126,7 +126,7 @@ func nest2(var z) =
     public void MultipleVariables(dynamic value, string expected)
     {
         SourceAsString += @"
-                func test_func() = 
+                sub test_func() = 
                 {
                     var z = 3;
                     var x="+value+@"; 
diff --git a/src/JukaUnitTest/IfWhileUnitTest.cs b/src/JukaUnitTest/IfWhileUnitTest.cs
index 83c0f484..93220dad 100644
--- a/src/JukaUnitTest/IfWhileUnitTest.cs
+++ b/src/JukaUnitTest/IfWhileUnitTest.cs
@@ -9,7 +9,7 @@ public class IfWhileUnitTest : UnitTestStructure
     public void IfBoolean()
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = true;
                     if ( x == true)
@@ -29,7 +29,7 @@ public void IfBoolean()
     public void IfBooleanElseBranch()
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = false;
                     if ( x == true)
@@ -49,7 +49,7 @@ public void IfBooleanElseBranch()
     public void WhileBoolean()
     {
         SourceAsString +=
-            @"func test_func() = 
+            @"sub test_func() = 
                 {
                     var x = true;
                     while(x == true)
@@ -71,7 +71,7 @@ public void WhileBoolean()
     public void ForLoop(dynamic loops, string expected)
     {
         SourceAsString += @"
-                func test_func() = 
+                sub test_func() = 
                 {
                     for(var i = 0; i<" + loops + @"; i++;)
                     {
diff --git a/src/JukaUnitTest/StructureUnitTest.cs b/src/JukaUnitTest/StructureUnitTest.cs
index fa97a10e..422034a2 100644
--- a/src/JukaUnitTest/StructureUnitTest.cs
+++ b/src/JukaUnitTest/StructureUnitTest.cs
@@ -11,18 +11,18 @@ public void Class()
         SourceAsString += @"
                 class x = 
                 {
-                    func xmethod() = 
+                    sub xmethod() = 
                     {
                         print(""foo"");
                     }
 
-                    func zmethod() = 
+                    sub zmethod() = 
                     {
                         print(""bar"");
                     }
                 }
 
-                func test_func() = 
+                sub test_func() = 
                 {
                     var v = x();
                     v.xmethod();
diff --git a/src/JukaUnitTest/SystemCallsUnitTest.cs b/src/JukaUnitTest/SystemCallsUnitTest.cs
index d0403c68..a2551666 100644
--- a/src/JukaUnitTest/SystemCallsUnitTest.cs
+++ b/src/JukaUnitTest/SystemCallsUnitTest.cs
@@ -10,12 +10,12 @@ public class SystemCallsUnitTest : UnitTestStructure
     public void Primitives(string primitive)
     {
         SourceAsString += @"
-                func test_func() = 
+                sub test_func() = 
                 {
                     testme();
                 }
 
-                func testme() = 
+                sub testme() = 
                 {
                     var v = " + primitive + @";
                     print(v);
diff --git a/src/JukaUnitTest/UnitTestStructure.cs b/src/JukaUnitTest/UnitTestStructure.cs
index 8cc6fdde..3d0c52d6 100644
--- a/src/JukaUnitTest/UnitTestStructure.cs
+++ b/src/JukaUnitTest/UnitTestStructure.cs
@@ -9,7 +9,7 @@ public abstract class UnitTestStructure
     /// The source code string to be tested. The default main function calls a test function.
     /// </summary>
     public string SourceAsString { get; set; } =
-        @"func main() = 
+        @"sub main() = 
                 {
                     test_func();
                 }";