diff --git a/run.sh b/run.sh
index 7e8ed4b..cf90732 100755
--- a/run.sh
+++ b/run.sh
@@ -1,9 +1,12 @@
 #!/bin/bash
 
-# Compile
+# Compile Lox
 javac -d out src/com/lox/*.java
-
-# Run 
-
+# Compile Lox tool
+javac -d out src/com/tool/*.java
+# Run Lox interpreter
 java -cp out com.lox.Lox
-
+# Run Lox ast print printer
+java -cp out com.lox.AstPrinter
+# Run Lox tool
+java -cp out com.tool.GenerateAst
\ No newline at end of file
diff --git a/src/com/lox/AstPrinter.java b/src/com/lox/AstPrinter.java
new file mode 100644
index 0000000..594f847
--- /dev/null
+++ b/src/com/lox/AstPrinter.java
@@ -0,0 +1,52 @@
+package com.lox;
+// import com.
+class AstPrinter implements Expr.Visitor<String> {
+  String print(Expr expr) {
+    return expr.accept(this);
+  }
+  @Override
+  public String visitBinaryExpr(Expr.Binary expr) {
+    return parenthesize(expr.operator.lexeme,
+                        expr.left, expr.right);
+  }
+
+  @Override
+  public String visitGroupingExpr(Expr.Grouping expr) {
+    return parenthesize("group", expr.expression);
+  }
+
+  @Override
+  public String visitLiteralExpr(Expr.Literal expr) {
+    if (expr.value == null) return "nil";
+    return expr.value.toString();
+  }
+
+  @Override
+  public String visitUnaryExpr(Expr.Unary expr) {
+    return parenthesize(expr.operator.lexeme, expr.right);
+  }
+  private String parenthesize(String name, Expr... exprs) {
+    StringBuilder builder = new StringBuilder();
+
+    builder.append("(").append(name);
+    for (Expr expr : exprs) {
+      builder.append(" ");
+      builder.append(expr.accept(this));
+    }
+    builder.append(")");
+
+    return builder.toString();
+  }
+  public static void main(String[] args) {
+    Expr expression = new Expr.Binary(
+        new Expr.Unary(
+            new Token(TokenType.MINUS, "-", null, 1),
+            new Expr.Literal(123)),
+        new Token(TokenType.STAR, "*", null, 1),
+        new Expr.Grouping(
+            new Expr.Literal(45.67)));
+
+    System.out.println(new AstPrinter().print(expression));
+  }
+
+}
\ No newline at end of file
diff --git a/src/com/lox/Expr.java b/src/com/lox/Expr.java
new file mode 100644
index 0000000..4220dc3
--- /dev/null
+++ b/src/com/lox/Expr.java
@@ -0,0 +1,68 @@
+package com.lox;
+
+import java.util.List;
+
+abstract class Expr {
+  interface Visitor<R> {
+    R visitBinaryExpr(Binary expr);
+    R visitGroupingExpr(Grouping expr);
+    R visitLiteralExpr(Literal expr);
+    R visitUnaryExpr(Unary expr);
+  }
+  static class Binary extends Expr {
+    Binary(Expr left, Token operator, Expr right) {
+      this.left = left;
+      this.operator = operator;
+      this.right = right;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitBinaryExpr(this);
+    }
+
+    final Expr left;
+    final Token operator;
+    final Expr right;
+  }
+  static class Grouping extends Expr {
+    Grouping(Expr expression) {
+      this.expression = expression;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitGroupingExpr(this);
+    }
+
+    final Expr expression;
+  }
+  static class Literal extends Expr {
+    Literal(Object value) {
+      this.value = value;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitLiteralExpr(this);
+    }
+
+    final Object value;
+  }
+  static class Unary extends Expr {
+    Unary(Token operator, Expr right) {
+      this.operator = operator;
+      this.right = right;
+    }
+
+    @Override
+    <R> R accept(Visitor<R> visitor) {
+      return visitor.visitUnaryExpr(this);
+    }
+
+    final Token operator;
+    final Expr right;
+  }
+
+  abstract <R> R accept(Visitor<R> visitor);
+}
\ No newline at end of file
diff --git a/src/com/tool/GenerateAst.java b/src/com/tool/GenerateAst.java
new file mode 100644
index 0000000..0d8f0d8
--- /dev/null
+++ b/src/com/tool/GenerateAst.java
@@ -0,0 +1,98 @@
+package com.tool;
+
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.util.Arrays;
+import java.util.List;
+
+public class GenerateAst {
+  public static void main(String[] args) throws IOException {
+    if (args.length != 1) {
+        System.err.println("Usage: generate_ast <output directory>");        
+        System.exit(64);
+    }    
+    String outputDir = args[0];
+    defineAst(outputDir, "Expr", Arrays.asList(
+        "Binary   : Expr left, Token operator, Expr right",
+        "Grouping : Expr expression",
+        "Literal  : Object value",
+        "Unary    : Token operator, Expr right"
+        ));    
+  }
+  private static void defineAst(
+      String outputDir, String baseName, List<String> types)
+      throws IOException {
+    String path = outputDir + "/" + baseName + ".java";
+    PrintWriter writer = new PrintWriter(path, "UTF-8");
+
+    writer.println("package com.craftinginterpreters.lox;");
+    writer.println();
+    writer.println("import java.util.List;");
+    writer.println();
+    writer.println("abstract class " + baseName + " {");
+    
+    defineVisitor(writer, baseName, types);
+
+    // The AST classes.
+    for (String type : types) {
+      String className = type.split(":")[0].trim();
+      String fields = type.split(":")[1].trim(); 
+      defineType(writer, baseName, className, fields);
+    }
+    
+    // The base accept() method.
+    writer.println();
+    writer.println("  abstract <R> R accept(Visitor<R> visitor);");
+
+    writer.println("}");
+    writer.close();
+  }
+  private static void defineType(
+      PrintWriter writer, String baseName,
+      String className, String fieldList) {
+    writer.println("  static class " + className + " extends " +
+        baseName + " {");
+
+    // Constructor.
+    writer.println("    " + className + "(" + fieldList + ") {");
+
+    // Store parameters in fields.
+    String[] fields = fieldList.split(", ");
+    for (String field : fields) {
+      String name = field.split(" ")[1];
+      writer.println("      this." + name + " = " + name + ";");
+    }
+
+    writer.println("    }");
+    
+    // Visitor pattern.
+    writer.println();
+    writer.println("    @Override");
+    writer.println("    <R> R accept(Visitor<R> visitor) {");
+    writer.println("      return visitor.visit" +
+        className + baseName + "(this);");
+    writer.println("    }");
+    
+    // Fields.
+    writer.println();
+    for (String field : fields) {
+      writer.println("    final " + field + ";");
+    }
+
+    writer.println("  }");
+
+    
+  }
+  private static void defineVisitor(
+      PrintWriter writer, String baseName, List<String> types) {
+    writer.println("  interface Visitor<R> {");
+
+    for (String type : types) {
+      String typeName = type.split(":")[0].trim();
+      writer.println("    R visit" + typeName + baseName + "(" +
+          typeName + " " + baseName.toLowerCase() + ");");
+    }
+
+    writer.println("  }");
+  }
+}
\ No newline at end of file