diff --git a/.task/checksum/astgen b/.task/checksum/astgen
index 8582cb7..bbd454f 100644
--- a/.task/checksum/astgen
+++ b/.task/checksum/astgen
@@ -1 +1 @@
-5f28a0838ca9382a947da5bd52756cf3
+f630c7b1cf9f3b55f1467ac4c8704152
diff --git a/Taskfile.yml b/Taskfile.yml
index 65f86b1..dd130a2 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -31,11 +31,11 @@ tasks:
   astgen:
     desc: "Generate AST nodes"
     cmds:
-      - go run cmd/astgen/main.go "./parser"
+      - go run cmd/astgen/main.go "./ast"
     sources:
       - cmd/astgen/main.go
     generates:
-      - parser/expr.go
+      - ast/expr.go
 
   clean:
     desc: "Clean up"
diff --git a/parser/expr.go b/ast/expr.go
similarity index 98%
rename from parser/expr.go
rename to ast/expr.go
index c6ba2f0..cd6fc3d 100644
--- a/parser/expr.go
+++ b/ast/expr.go
@@ -1,4 +1,4 @@
-package parser
+package ast
 
 import "golox/token"
 
diff --git a/ast/printer.go b/ast/printer.go
index fdd6ca9..343d6df 100644
--- a/ast/printer.go
+++ b/ast/printer.go
@@ -2,44 +2,43 @@ package ast
 
 import (
 	"fmt"
-	"golox/parser"
 )
 
 type Printer struct {
 }
 
-func New() *Printer {
+func NewPrinter() *Printer {
 	return &Printer{}
 }
 
-func (ap *Printer) Print(expr parser.Expr) string {
+func (ap *Printer) Print(expr Expr) string {
 	return expr.Accept(ap).(string)
 }
 
-func (ap *Printer) VisitBinaryExpr(expr *parser.BinaryExpr) any {
+func (ap *Printer) VisitBinaryExpr(expr *BinaryExpr) any {
 	return ap.parenthesize(expr.Operator.Lexeme, expr.Left, expr.Right)
 }
 
-func (ap *Printer) VisitGroupingExpr(expr *parser.GroupingExpr) any {
+func (ap *Printer) VisitGroupingExpr(expr *GroupingExpr) any {
 	return ap.parenthesize("group", expr.Expression)
 }
 
-func (ap *Printer) VisitLiteralExpr(expr *parser.LiteralExpr) any {
+func (ap *Printer) VisitLiteralExpr(expr *LiteralExpr) any {
 	if expr.Value == nil {
 		return "nil"
 	}
 	return fmt.Sprint(expr.Value)
 }
 
-func (ap *Printer) VisitUnaryExpr(expr *parser.UnaryExpr) any {
+func (ap *Printer) VisitUnaryExpr(expr *UnaryExpr) any {
 	return ap.parenthesize(expr.Operator.Lexeme, expr.Right)
 }
 
-func (ap *Printer) VisitErrorExpr(expr *parser.ErrorExpr) any {
+func (ap *Printer) VisitErrorExpr(expr *ErrorExpr) any {
 	return expr.Value
 }
 
-func (ap *Printer) parenthesize(name string, exprs ...parser.Expr) string {
+func (ap *Printer) parenthesize(name string, exprs ...Expr) string {
 	str := "(" + name
 
 	for _, expr := range exprs {
diff --git a/ast/printer_test.go b/ast/printer_test.go
new file mode 100644
index 0000000..ec2c8ce
--- /dev/null
+++ b/ast/printer_test.go
@@ -0,0 +1,64 @@
+package ast
+
+import (
+	"golox/token"
+	"testing"
+)
+
+func TestPrinter(t *testing.T) {
+	tests := []struct {
+		name     string
+		expr     Expr
+		expected string
+	}{
+		{
+			name: "Binary expression",
+			expr: &BinaryExpr{
+				Left:     &LiteralExpr{Value: 1},
+				Operator: token.Token{Type: token.PLUS, Lexeme: "+"},
+				Right:    &LiteralExpr{Value: 2},
+			},
+			expected: "(+ 1 2)",
+		},
+		{
+			name: "Grouping expression",
+			expr: &GroupingExpr{
+				Expression: &LiteralExpr{Value: 1},
+			},
+			expected: "(group 1)",
+		},
+		{
+			name:     "Literal expression",
+			expr:     &LiteralExpr{Value: 123},
+			expected: "123",
+		},
+		{
+			name: "Unary expression",
+			expr: &UnaryExpr{
+				Operator: token.Token{Type: token.MINUS, Lexeme: "-"},
+				Right:    &LiteralExpr{Value: 123},
+			},
+			expected: "(- 123)",
+		},
+		{
+			name:     "Nil literal expression",
+			expr:     &LiteralExpr{Value: nil},
+			expected: "nil",
+		},
+		{
+			name:     "Error expression",
+			expr:     &ErrorExpr{Value: "error"},
+			expected: "error",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			printer := NewPrinter()
+			result := printer.Print(tt.expr)
+			if result != tt.expected {
+				t.Errorf("expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
diff --git a/cmd/astgen/main.go b/cmd/astgen/main.go
index d7ee37d..982f3cd 100644
--- a/cmd/astgen/main.go
+++ b/cmd/astgen/main.go
@@ -40,7 +40,7 @@ func defineAst(outputDir, baseName string, types []string) {
 	}
 	defer file.Close()
 
-	file.WriteString("package parser\n\n")
+	file.WriteString("package ast\n\n")
 	file.WriteString("import \"golox/token\"\n\n")
 	defineVisitor(file, baseName, types)
 
diff --git a/lox/lox.go b/lox/lox.go
index 99b632f..0fb1158 100644
--- a/lox/lox.go
+++ b/lox/lox.go
@@ -80,6 +80,6 @@ func (l *Lox) run(source string) {
 		return
 	}
 
-	p := ast.New()
+	p := ast.NewPrinter()
 	fmt.Println(p.Print(expr))
 }
diff --git a/lox/lox_test.go b/lox/lox_test.go
index c6ff114..9e23514 100644
--- a/lox/lox_test.go
+++ b/lox/lox_test.go
@@ -24,7 +24,7 @@ func TestRun(t *testing.T) {
 		outC <- buf.String()
 	}()
 
-	source := "print('Hello, World!');"
+	source := "1+4/2"
 	l := New()
 	l.run(source)
 
@@ -34,7 +34,7 @@ func TestRun(t *testing.T) {
 	out := <-outC
 
 	// reading our temp stdout
-	expected := source + "\n"
+	expected := "(+ 1 (/ 4 2))\n"
 	if out != expected {
 		t.Errorf("run() = %v; want %v", out, expected)
 	}
@@ -63,7 +63,7 @@ func TestRunFile(t *testing.T) {
 	}
 	defer os.Remove(tmpfile.Name())
 
-	content := "print('Hello, World!');"
+	content := "1+4/2"
 	if _, err := tmpfile.Write([]byte(content)); err != nil {
 		t.Fatal(err)
 	}
@@ -79,7 +79,7 @@ func TestRunFile(t *testing.T) {
 	out := <-outC
 
 	// reading our temp stdout
-	expected := "print('Hello, World!');\n"
+	expected := "(+ 1 (/ 4 2))\n"
 	if out != expected {
 		t.Errorf("RunFile() = %v; want %v", out, expected)
 	}
@@ -166,7 +166,7 @@ func TestRunPrompt(t *testing.T) {
 		outC <- buf.String()
 	}()
 
-	input := "print('Hello, World!');\n\n"
+	input := "1+4/2\n\n"
 	wIn.Write([]byte(input))
 	wIn.Close()
 
@@ -178,7 +178,7 @@ func TestRunPrompt(t *testing.T) {
 	os.Stdout = oldStdout
 	out := <-outC
 
-	expected := "> print('Hello, World!');\n\n> "
+	expected := "> (+ 1 (/ 4 2))\n> "
 	if out != expected {
 		t.Errorf("RunPrompt() = %v; want %v", out, expected)
 	}
diff --git a/parser/parser.go b/parser/parser.go
index b85fb23..bacb271 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -15,6 +15,7 @@
 package parser
 
 import (
+	"golox/ast"
 	"golox/errors"
 	"golox/token"
 )
@@ -32,96 +33,96 @@ func New(tokens []token.Token, el errors.Logger) *Parser {
 }
 
 // Parse parses the tokens and returns the AST.
-func (p *Parser) Parse() Expr {
+func (p *Parser) Parse() ast.Expr {
 	return p.expression()
 }
 
 // expression → equality ;
-func (p *Parser) expression() Expr {
+func (p *Parser) expression() ast.Expr {
 	return p.equality()
 }
 
 // equality → comparison ( ( "!=" | "==" ) comparison )* ;
-func (p *Parser) equality() Expr {
+func (p *Parser) equality() ast.Expr {
 	expr := p.comparison()
 
 	for p.match(token.BANG_EQUAL, token.EQUAL_EQUAL) {
 		operator := p.previous()
 		right := p.comparison()
-		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+		expr = &ast.BinaryExpr{Left: expr, Operator: operator, Right: right}
 	}
 
 	return expr
 }
 
 // comparison → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
-func (p *Parser) comparison() Expr {
+func (p *Parser) comparison() ast.Expr {
 	expr := p.term()
 
 	for p.match(token.GREATER, token.GREATER_EQUAL, token.LESS, token.LESS_EQUAL) {
 		operator := p.previous()
 		right := p.term()
-		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+		expr = &ast.BinaryExpr{Left: expr, Operator: operator, Right: right}
 	}
 
 	return expr
 }
 
 // term → factor ( ( "-" | "+" ) factor )* ;
-func (p *Parser) term() Expr {
+func (p *Parser) term() ast.Expr {
 	expr := p.factor()
 
 	for p.match(token.MINUS, token.PLUS) {
 		operator := p.previous()
 		right := p.factor()
-		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+		expr = &ast.BinaryExpr{Left: expr, Operator: operator, Right: right}
 	}
 
 	return expr
 }
 
 // factor → unary ( ( "/" | "*" ) unary )* ;
-func (p *Parser) factor() Expr {
+func (p *Parser) factor() ast.Expr {
 	expr := p.unary()
 
 	for p.match(token.SLASH, token.STAR) {
 		operator := p.previous()
 		right := p.unary()
-		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+		expr = &ast.BinaryExpr{Left: expr, Operator: operator, Right: right}
 	}
 
 	return expr
 }
 
 // unary → ( "!" | "-" ) unary | primary ;
-func (p *Parser) unary() Expr {
+func (p *Parser) unary() ast.Expr {
 	if p.match(token.BANG, token.MINUS) {
 		operator := p.previous()
 		right := p.unary()
-		return &UnaryExpr{Operator: operator, Right: right}
+		return &ast.UnaryExpr{Operator: operator, Right: right}
 	}
 
 	return p.primary()
 }
 
 // primary → NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" ;
-func (p *Parser) primary() Expr {
+func (p *Parser) primary() ast.Expr {
 	switch {
 	case p.match(token.FALSE):
-		return &LiteralExpr{Value: false}
+		return &ast.LiteralExpr{Value: false}
 	case p.match(token.TRUE):
-		return &LiteralExpr{Value: true}
+		return &ast.LiteralExpr{Value: true}
 	case p.match(token.NIL):
-		return &LiteralExpr{Value: nil}
+		return &ast.LiteralExpr{Value: nil}
 	case p.match(token.NUMBER, token.STRING):
-		return &LiteralExpr{Value: p.previous().Literal}
+		return &ast.LiteralExpr{Value: p.previous().Literal}
 	case p.match(token.LEFT_PAREN):
 		expr := p.expression()
 		err := p.consume(token.RIGHT_PAREN, "Expect ')' after expression.")
 		if err != nil {
 			return err
 		}
-		return &GroupingExpr{Expression: expr}
+		return &ast.GroupingExpr{Expression: expr}
 	}
 
 	return p.newErrorExpr(p.peek(), "Expect expression.")
@@ -140,7 +141,7 @@ func (p *Parser) match(types ...token.TokenType) bool {
 }
 
 // consume consumes the current token if it is of the given type.
-func (p *Parser) consume(tt token.TokenType, message string) *ErrorExpr {
+func (p *Parser) consume(tt token.TokenType, message string) *ast.ErrorExpr {
 	if p.check(tt) {
 		p.advance()
 		return nil
@@ -183,9 +184,9 @@ func (p *Parser) previous() token.Token {
 }
 
 // newErrorExpr creates a new ErrorExpr and reports the error.
-func (p *Parser) newErrorExpr(t token.Token, message string) *ErrorExpr {
+func (p *Parser) newErrorExpr(t token.Token, message string) *ast.ErrorExpr {
 	p.errLogger.ErrorAtToken(t, message)
-	return &ErrorExpr{Value: message}
+	return &ast.ErrorExpr{Value: message}
 }
 
 // synchronize synchronizes the parser after an error.
diff --git a/parser/parser_test.go b/parser/parser_test.go
new file mode 100644
index 0000000..9974b0e
--- /dev/null
+++ b/parser/parser_test.go
@@ -0,0 +1,91 @@
+package parser
+
+import (
+	"golox/ast"
+	"golox/token"
+	"testing"
+)
+
+type mockErrorLogger struct{}
+
+func (el *mockErrorLogger) Error(line int, message string) {
+}
+
+func (el *mockErrorLogger) ErrorAtToken(t token.Token, message string) {
+}
+
+func newMockErrorLogger() *mockErrorLogger {
+	return &mockErrorLogger{}
+}
+
+func TestParser(t *testing.T) {
+	tests := []struct {
+		name     string
+		tokens   []token.Token
+		expected string
+	}{
+		{
+			name: "Simple expression",
+			tokens: []token.Token{
+				{Type: token.NUMBER, Literal: 1},
+				{Type: token.PLUS, Lexeme: "+"},
+				{Type: token.NUMBER, Literal: 2},
+				{Type: token.EOF},
+			},
+			expected: "(+ 1 2)",
+		},
+		{
+			name: "Unary expression",
+			tokens: []token.Token{
+				{Type: token.MINUS, Lexeme: "-"},
+				{Type: token.NUMBER, Literal: 123},
+				{Type: token.EOF},
+			},
+			expected: "(- 123)",
+		},
+		{
+			name: "Grouping expression",
+			tokens: []token.Token{
+				{Type: token.LEFT_PAREN, Lexeme: "("},
+				{Type: token.NUMBER, Literal: 1},
+				{Type: token.PLUS, Lexeme: "+"},
+				{Type: token.NUMBER, Literal: 2},
+				{Type: token.RIGHT_PAREN, Lexeme: ")"},
+				{Type: token.EOF},
+			},
+			expected: "(group (+ 1 2))",
+		},
+		{
+			name: "Comparison expression",
+			tokens: []token.Token{
+				{Type: token.NUMBER, Literal: 1},
+				{Type: token.GREATER, Lexeme: ">"},
+				{Type: token.NUMBER, Literal: 2},
+				{Type: token.EOF},
+			},
+			expected: "(> 1 2)",
+		},
+		{
+			name: "Equality expression",
+			tokens: []token.Token{
+				{Type: token.NUMBER, Literal: 1},
+				{Type: token.EQUAL_EQUAL, Lexeme: "=="},
+				{Type: token.NUMBER, Literal: 2},
+				{Type: token.EOF},
+			},
+			expected: "(== 1 2)",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			parser := New(tt.tokens, newMockErrorLogger())
+			expr := parser.Parse()
+			ap := ast.NewPrinter()
+			s := ap.Print(expr)
+			if s != tt.expected {
+				t.Errorf("expected %v, got %v", tt.expected, s)
+			}
+		})
+	}
+}
diff --git a/scanner/scanner_test.go b/scanner/scanner_test.go
index 004baae..824866e 100644
--- a/scanner/scanner_test.go
+++ b/scanner/scanner_test.go
@@ -310,32 +310,33 @@ func TestScanToken(t *testing.T) {
 		name     string
 		source   string
 		expected token.TokenType
+		lexeme   string
 	}{
-		{"Left paren", "(", token.LEFT_PAREN},
-		{"Right paren", ")", token.RIGHT_PAREN},
-		{"Left brace", "{", token.LEFT_BRACE},
-		{"Right brace", "}", token.RIGHT_BRACE},
-		{"Comma", ",", token.COMMA},
-		{"Dot", ".", token.DOT},
-		{"Minus", "-", token.MINUS},
-		{"Plus", "+", token.PLUS},
-		{"Semicolon", ";", token.SEMICOLON},
-		{"Star", "*", token.STAR},
-		{"Bang", "!", token.BANG},
-		{"Bang equal", "!=", token.BANG_EQUAL},
-		{"Equal", "=", token.EQUAL},
-		{"Equal equal", "==", token.EQUAL_EQUAL},
-		{"Less", "<", token.LESS},
-		{"Less equal", "<=", token.LESS_EQUAL},
-		{"Greater", ">", token.GREATER},
-		{"Greater equal", ">=", token.GREATER_EQUAL},
-		{"Slash", "/", token.SLASH},
-		{"Comment", "// comment\n", token.EOF},
-		{"Whitespace", " \r\t\n", token.EOF},
-		{"String", `"hello"`, token.STRING},
-		{"Number", "123", token.NUMBER},
-		{"Identifier", "var", token.VAR},
-		{"Unexpected character", "@", token.EOF},
+		{"Left paren", "(", token.LEFT_PAREN, "("},
+		{"Right paren", ")", token.RIGHT_PAREN, ")"},
+		{"Left brace", "{", token.LEFT_BRACE, "{"},
+		{"Right brace", "}", token.RIGHT_BRACE, "}"},
+		{"Comma", ",", token.COMMA, ","},
+		{"Dot", ".", token.DOT, "."},
+		{"Minus", "-", token.MINUS, "-"},
+		{"Plus", "+", token.PLUS, "+"},
+		{"Semicolon", ";", token.SEMICOLON, ";"},
+		{"Star", "*", token.STAR, "*"},
+		{"Bang", "!", token.BANG, "!"},
+		{"Bang equal", "!=", token.BANG_EQUAL, "!="},
+		{"Equal", "=", token.EQUAL, "="},
+		{"Equal equal", "==", token.EQUAL_EQUAL, "=="},
+		{"Less", "<", token.LESS, "<"},
+		{"Less equal", "<=", token.LESS_EQUAL, "<="},
+		{"Greater", ">", token.GREATER, ">"},
+		{"Greater equal", ">=", token.GREATER_EQUAL, ">="},
+		{"Slash", "/", token.SLASH, "/"},
+		{"Comment", "// comment\n", token.EOF, ""},
+		{"Whitespace", " \r\t\n", token.EOF, ""},
+		{"String", `"hello"`, token.STRING, `"hello"`},
+		{"Number", "123", token.NUMBER, "123"},
+		{"Identifier", "var", token.VAR, "var"},
+		{"Unexpected character", "@", token.EOF, ""},
 	}
 
 	for _, tt := range tests {
@@ -346,6 +347,9 @@ func TestScanToken(t *testing.T) {
 				if scanner.tokens[0].Type != tt.expected {
 					t.Errorf("expected %v, got %v", tt.expected, scanner.tokens[0].Type)
 				}
+				if scanner.tokens[0].Lexeme != tt.lexeme {
+					t.Errorf("expected %v, got %v", tt.lexeme, scanner.tokens[0].Lexeme)
+				}
 			} else if tt.expected != token.EOF {
 				t.Errorf("expected %v, got no tokens", tt.expected)
 			}