12.5 This

src/com/craftinginterpreters/lox/Interpreter.java

@@ -62,6 +62,11 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return value;
     }
 
+    @Override
+    public Object visitThisExpr(Expr.This expr) {
+        return lookUpVariable(expr.keyword, expr);
+    }
+
     @Override
     public Object visitUnaryExpr(Expr.Unary expr) {
         Object right = evaluate(expr.right);

src/com/craftinginterpreters/lox/LoxFunction.java

@@ -11,6 +11,12 @@ class LoxFunction implements LoxCallable {
         this.declaration = declaration;
     }
 
+    LoxFunction bind(LoxInstance instance) {
+        Environment environment = new Environment(closure);
+        environment.define("this", instance);
+        return new LoxFunction(declaration, environment);
+    }
+
     @Override
     public int arity() {
         return declaration.params.size();

src/com/craftinginterpreters/lox/LoxInstance.java

@@ -18,7 +18,7 @@ class LoxInstance {
 
         LoxFunction method = klass.findMethod(name.lexeme);
         if (method != null)
-            return method;
+            return method.bind(this);
 
         throw new RuntimeError(name, "Undefined proprety '" + name.lexeme + "'.");
     }

src/com/craftinginterpreters/lox/Parser.java

@@ -355,6 +355,8 @@ class Parser {
             return new Expr.Literal(previous().literal);
         }
 
+        if (match(THIS)) return new Expr.This(previous());
+
         if (match(IDENTIFIER)) {
             return new Expr.Variable(previous());
         }

src/com/craftinginterpreters/lox/Resolver.java

@@ -37,11 +37,16 @@ class Resolver implements Expr.Visitor<Void>, Stmt.Visitor<Void> {
         declare(stmt.name);
         define(stmt.name);
 
+        beginScope();
+        scopes.peek().put("this", true);
+
         for (Stmt.Function method : stmt.methods) {
             FunctionType declaration = FunctionType.METHOD;
             resolveFunction(method, declaration);
         }
 
+        endScope();
+
         return null;
     }
 
@@ -154,6 +159,12 @@ class Resolver implements Expr.Visitor<Void>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitThisExpr(Expr.This expr) {
+        resolveLocal(expr, expr.keyword);
+        return null;
+    }
+
     @Override
     public Void visitLogicalExpr(Expr.Logical expr) {
         resolve(expr.left);

src/com/craftinginterpreters/tool/GenerateAst.java

@@ -19,7 +19,7 @@ public class GenerateAst {
                         "Call : Expr callee, Token paren, List<Expr> arguments", "Get : Expr object, Token name",
                         "Grouping : Expr expression", "Literal : Object value",
                         "Logical : Expr left, Token operator, Expr right", "Set : Expr object, Token name, Expr value",
-                        "Unary : Token operator, Expr right", "Variable : Token name"));
+                        "This : Token keyword", "Unary : Token operator, Expr right", "Variable : Token name"));
         defineAst(outputDir, "Stmt",
                 Arrays.asList("Block : List<Stmt> statements", "Class : Token name, List<Stmt.Function> methods",
                         "Expression : Expr expression", "Function : Token name, List<Token> params, List<Stmt> body",