From 5daf4f9aa2308004dc7bc7ba977a4de20df44351 Mon Sep 17 00:00:00 2001
From: Sky Johnson <skylearj@gmail.com>
Date: Tue, 6 May 2025 17:49:04 -0500
Subject: [PATCH] add nil literal

---
 compiler/compiler.go | 4 ++++
 lexer/lexer.go       | 3 +++
 parser/ast.go        | 7 +++++++
 parser/parser.go     | 5 +++++
 vm/vm.go             | 4 ++--
 5 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/compiler/compiler.go b/compiler/compiler.go
index 37f8a1e..edb7e09 100644
--- a/compiler/compiler.go
+++ b/compiler/compiler.go
@@ -136,6 +136,10 @@ func (c *compiler) compileExpression(expr parser.Expression) {
 		constIndex := c.addConstant(e.Value)
 		c.emit(types.OpConstant, constIndex)
 
+	case *parser.NilLiteral:
+		constIndex := c.addConstant(nil)
+		c.emit(types.OpConstant, constIndex)
+
 	case *parser.Identifier:
 		nameIndex := c.addConstant(e.Value)
 
diff --git a/lexer/lexer.go b/lexer/lexer.go
index aa6b4f7..ccf8001 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -37,6 +37,7 @@ const (
 	TokenOr
 	TokenNot
 	TokenElseIf
+	TokenNil
 )
 
 type Token struct {
@@ -166,6 +167,8 @@ func (l *Lexer) NextToken() Token {
 				tok.Type = TokenOr
 			case "not":
 				tok.Type = TokenNot
+			case "nil":
+				tok.Type = TokenNil
 			default:
 				tok.Type = TokenIdentifier
 			}
diff --git a/parser/ast.go b/parser/ast.go
index 0c82620..2311ff4 100644
--- a/parser/ast.go
+++ b/parser/ast.go
@@ -156,3 +156,10 @@ type BooleanLiteral struct {
 
 func (bl *BooleanLiteral) expressionNode()      {}
 func (bl *BooleanLiteral) TokenLiteral() string { return bl.Token.Value }
+
+type NilLiteral struct {
+	Token lexer.Token
+}
+
+func (nl *NilLiteral) expressionNode()      {}
+func (nl *NilLiteral) TokenLiteral() string { return nl.Token.Value }
diff --git a/parser/parser.go b/parser/parser.go
index 8f04bbd..a3917fa 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -74,6 +74,7 @@ func New(l *lexer.Lexer) *Parser {
 	p.registerPrefix(lexer.TokenTrue, p.parseBooleanLiteral)
 	p.registerPrefix(lexer.TokenFalse, p.parseBooleanLiteral)
 	p.registerPrefix(lexer.TokenNot, p.parsePrefixExpression)
+	p.registerPrefix(lexer.TokenNil, p.parseNilLiteral)
 
 	// Initialize infix parse functions
 	p.infixParseFns = make(map[lexer.TokenType]infixParseFn)
@@ -573,3 +574,7 @@ func (p *Parser) parseUnexpectedToken() Expression {
 		p.curToken.Line, p.curToken.Value))
 	return nil
 }
+
+func (p *Parser) parseNilLiteral() Expression {
+	return &NilLiteral{Token: p.curToken}
+}
diff --git a/vm/vm.go b/vm/vm.go
index cb9e17a..9fb5ca6 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -190,7 +190,7 @@ func (vm *VM) Run(bytecode *types.Bytecode) {
 			case types.TypeBoolean:
 				fmt.Println(value.Data.(bool))
 			case types.TypeNull:
-				fmt.Println("null")
+				fmt.Println("nil")
 			case types.TypeTable:
 				fmt.Println(vm.formatTable(value.Data.(*types.Table)))
 			}
@@ -465,7 +465,7 @@ func (vm *VM) formatValue(value types.Value) string {
 	case types.TypeBoolean:
 		return fmt.Sprintf("%v", value.Data.(bool))
 	case types.TypeNull:
-		return "null"
+		return "nil"
 	case types.TypeTable:
 		return vm.formatTable(value.Data.(*types.Table))
 	default: