Chapter 12, Sections 1, 2, and 3

src/com/craftinginterpreters/lox/CMakeLists.txt

@@ -23,4 +23,6 @@ add_jar(Lox
   LoxFunction.java
   Return.java
   Resolver.java
+  LoxClass.java
+  LoxInstance.java
   ENTRY_POINT com/craftinginterpreters/lox/Lox)

src/com/craftinginterpreters/lox/Interpreter.java

@@ -49,6 +49,19 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return evaluate(expr.right);
     }
 
+    @Override
+    public Object visitSetExpr(Expr.Set expr) {
+        Object object = evaluate(expr.object);
+
+        if (!(object instanceof LoxInstance)) {
+            throw new RuntimeError(expr.name, "Only instances have fields.");
+        }
+
+        Object value = evaluate(expr.value);
+        ((LoxInstance) object).set(expr.name, value);
+        return value;
+    }
+
     @Override
     public Object visitUnaryExpr(Expr.Unary expr) {
         Object right = evaluate(expr.right);
@@ -161,6 +174,14 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitClassStmt(Stmt.Class stmt) {
+        environment.define(stmt.name.lexeme, null);
+        LoxClass klass = new LoxClass(stmt.name.lexeme);
+        environment.assign(stmt.name, klass);
+        return null;
+    }
+
     @Override
     public Void visitExpressionStmt(Stmt.Expression stmt) {
         evaluate(stmt.expression);
@@ -304,6 +325,16 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
         return function.call(this, arguments);
     }
 
+    @Override
+    public Object visitGetExpr(Expr.Get expr) {
+        Object object = evaluate(expr.object);
+        if (object instanceof LoxInstance) {
+            return ((LoxInstance) object).get(expr.name);
+        }
+
+        throw new RuntimeError(expr.name, "Only instances have properties.");
+    }
+
     public void interpret(List<Stmt> statements) {
         try {
             for (Stmt statement : statements) {

src/com/craftinginterpreters/lox/LoxClass.java

@@ -0,0 +1,27 @@
+package com.craftinginterpreters.lox;
+
+import java.util.List;
+
+class LoxClass implements LoxCallable {
+    final String name;
+
+    LoxClass(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+
+    @Override
+    public Object call(Interpreter interpreter, List<Object> arguments) {
+        LoxInstance instance = new LoxInstance(this);
+        return instance;
+    }
+
+    @Override
+    public int arity() {
+        return 0;
+    }
+}

src/com/craftinginterpreters/lox/LoxInstance.java

@@ -0,0 +1,30 @@
+package com.craftinginterpreters.lox;
+
+import java.util.HashMap;
+import java.util.Map;
+
+class LoxInstance {
+    private LoxClass klass;
+    private final Map<String, Object> fields = new HashMap<>();
+
+    LoxInstance(LoxClass klass) {
+        this.klass = klass;
+    }
+
+    Object get(Token name) {
+        if (fields.containsKey(name.lexeme)) {
+            return fields.get(name.lexeme);
+        }
+
+        throw new RuntimeError(name, "Undefined proprety '" + name.lexeme + "'.");
+    }
+
+    void set(Token name, Object value) {
+        fields.put(name.lexeme, value);
+    }
+
+    @Override
+    public String toString() {
+        return klass.name + " instance";
+    }
+}

src/com/craftinginterpreters/lox/Parser.java

@@ -33,6 +33,8 @@ class Parser {
 
     private Stmt declaration() {
         try {
+            if (match(CLASS))
+                return classDeclaration();
             if (match(FUN))
                 return function("function");
             if (match(VAR))
@@ -45,6 +47,20 @@ class Parser {
         }
     }
 
+    private Stmt classDeclaration() {
+        Token name = consume(IDENTIFIER, "Expect class name.");
+        consume(LEFT_BRACE, "Expect '{' before class body.");
+
+        List<Stmt.Function> methods = new ArrayList<>();
+        while (!check(RIGHT_BRACE) && !isAtEnd()) {
+            methods.add(function("method"));
+        }
+
+        consume(RIGHT_BRACE, "Expect '}' after class body.");
+
+        return new Stmt.Class(name, methods);
+    }
+
     private Stmt statement() {
         if (match(FOR))
             return forStatement();
@@ -201,6 +217,9 @@ class Parser {
             if (expr instanceof Expr.Variable) {
                 Token name = ((Expr.Variable) expr).name;
                 return new Expr.Assign(name, value);
+            } else if (expr instanceof Expr.Get) {
+                Expr.Get get = (Expr.Get)expr;
+                return new Expr.Set(get.object, get.name, value);
             }
 
             error(equals, "Invalid assignment target.");
@@ -313,6 +332,9 @@ class Parser {
         while (true) {
             if (match(LEFT_PAREN)) {
                 expr = finishCall(expr);
+            } else if (match(DOT)) {
+                Token name = consume(IDENTIFIER, "Expect property name after '.'");
+                expr = new Expr.Get(expr, name);
             } else {
                 break;
             }

src/com/craftinginterpreters/lox/Resolver.java

@@ -32,6 +32,13 @@ class Resolver implements Expr.Visitor<Void>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitClassStmt(Stmt.Class stmt) {
+        declare(stmt.name);
+        define(stmt.name);
+        return null;
+    }
+
     @Override
     public Void visitExpressionStmt(Stmt.Expression stmt) {
         resolve(stmt.expression);
@@ -117,6 +124,12 @@ class Resolver implements Expr.Visitor<Void>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitGetExpr(Expr.Get expr) {
+        resolve(expr.object);
+        return null;
+    }
+
     @Override
     public Void visitGroupingExpr(Expr.Grouping expr) {
         resolve(expr.expression);
@@ -128,6 +141,13 @@ class Resolver implements Expr.Visitor<Void>, Stmt.Visitor<Void> {
         return null;
     }
 
+    @Override
+    public Void visitSetExpr(Expr.Set expr) {
+        resolve(expr.value);
+        resolve(expr.object);
+        return null;
+    }
+
     @Override
     public Void visitLogicalExpr(Expr.Logical expr) {
         resolve(expr.left);

src/com/craftinginterpreters/tool/GenerateAst.java

@@ -16,12 +16,13 @@ public class GenerateAst {
 
         defineAst(outputDir, "Expr",
                 Arrays.asList("Assign : Token name, Expr value", "Binary : Expr left, Token operator, Expr right",
-                        "Call : Expr callee, Token paren, List<Expr> arguments", "Grouping : Expr expression",
+                        "Call : Expr callee, Token paren, List<Expr> arguments", "Get : Expr object, Token name",
-                        "Literal : Object value", "Logical : Expr left, Token operator, Expr right",
+                        "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"));
         defineAst(outputDir, "Stmt",
-                Arrays.asList("Block : List<Stmt> statements", "Expression : Expr expression",
+                Arrays.asList("Block : List<Stmt> statements", "Class : Token name, List<Stmt.Function> methods",
-                        "Function : Token name, List<Token> params, List<Stmt> body",
+                        "Expression : Expr expression", "Function : Token name, List<Token> params, List<Stmt> body",
                         "If : Expr condition, Stmt thenBranch, Stmt elseBranch", "Print : Expr expression",
                         "Return : Token keyword, Expr value", "Var : Token name, Expr initializer",
                         "While : Expr condition, Stmt body"));