12.6

ruby/lib/lox/expr.rb

@@ -18,6 +18,7 @@ module Lox
     expr :Literal, :value
     expr :Logical, :left, :op, :right
     expr :Set, :object, :name, :value
+    expr :This, :keyword
     expr :Unary, :op, :right
     expr :Variable, :name
   end

ruby/lib/lox/function.rb

@@ -6,6 +6,12 @@ module Lox
       @decl, @closure = decl, closure
     end
 
+    def bind(instance)
+      env = Environment.new(@closure)
+      env.define("this", instance)
+      Function.new(@decl, env)
+    end
+
     def arity = @decl.params.size
 
     def call(interpreter, args)

ruby/lib/lox/instance.rb

@@ -13,7 +13,7 @@ module Lox
       return @fields.fetch(name.lexeme) if @fields.has_key?(name.lexeme)
 
       method = @klass.find_method(name.lexeme)
-      return method unless method.nil?
+      return method.bind(self) unless method.nil?
 
       raise RuntimeError.new(name, "Undefined property '#{name.lexeme}'.")
     end

ruby/lib/lox/interpreter.rb

@@ -136,6 +136,8 @@ module Lox
       value
     end
 
+    def visit_this(expr) = lookup_var(expr.keyword, expr)
+
     def visit_unary(expr)
       right = evaluate(expr.right)
 

ruby/lib/lox/parser.rb

@@ -308,6 +308,7 @@ module Lox
       return Expr::Literal.new(true) if match?(:TRUE)
       return Expr::Literal.new(nil) if match?(:NIL)
       return Expr::Literal.new(prev.literal) if match?(:NUMBER, :STRING)
+      return Expr::This.new(prev) if match?(:THIS)
       return Expr::Variable.new(prev) if match?(:IDENTIFIER)
 
       if match?(:LEFT_PAREN)

ruby/lib/lox/resolver.rb

@@ -27,11 +27,16 @@ module Lox
     def visit_class(stmt)
       declare(stmt.name)
 
+      with_scope do
+        @scopes.last["this"] = true
+
         stmt.methods.each do |method|
           resolve_function(method, :METHOD)
         end
 
         define(stmt.name)
+      end
+
       nil
     end
 
@@ -98,6 +103,11 @@ module Lox
       nil
     end
 
+    def visit_this(expr)
+      resolve_local(expr, expr.keyword)
+      nil
+    end
+
     def visit_unary(expr) = resolve(expr.right)
 
     private

ruby/test/lox/test_interpreter.rb

@@ -356,22 +356,50 @@ class TestInterpreter < Lox::Test
       Bacon().eat(); // Prints "Crunch crunch crunch!".
     SRC
 
-    # assert_interpreted "", <<~SRC
+    assert_interpreted "The German chocolate cake is delicious!", <<~SRC
-    #   class Person {
+      class Cake {
-    #     sayName() {
+        taste() {
-    #       print this.name;
+          var adjective = "delicious";
-    #     }
+          print "The " + this.flavor + " cake is " + adjective + "!";
-    #   }
+        }
-
+      }
-    #   var jane = Person();
+
-    #   jane.name = "Jane";
+      var cake = Cake();
-
+      cake.flavor = "German chocolate";
-    #   var bill = Person();
+      cake.taste(); // Prints "The German chocolate cake is delicious!".
-    #   bill.name = "Bill";
+    SRC
-
+
-    #   bill.sayName = jane.sayName;
+    assert_interpreted "Thing instance", <<~SRC
-    #   bill.sayName(); // "Jane"
+      class Thing {
-    # SRC
+        getCallback() {
+          fun localFunction() {
+            print this;
+          }
+
+          return localFunction;
+        }
+      }
+
+      var callback = Thing().getCallback();
+      callback();
+    SRC
+
+    assert_interpreted "Jane", <<~SRC
+      class Person {
+        sayName() {
+          print this.name;
+        }
+      }
+
+      var jane = Person();
+      jane.name = "Jane";
+
+      var bill = Person();
+      bill.name = "Bill";
+
+      bill.sayName = jane.sayName;
+      bill.sayName(); // "Jane"
+    SRC
   end
 
   private