chapter 12

examples/simple_class.lox

@@ -0,0 +1,8 @@
+class DevonshireCream {
+  fn serveOn() {
+    return "Scones";
+  }
+}
+
+print(DevonshireCream);
+print(DevonshireCream());

main.rb

@@ -8,8 +8,8 @@ case ARGV.length
   when 1 then
     begin
       file ARGV[0]
-    rescue StandardError => e
-      STDERR.puts e
+    #rescue StandardError => e
+    #  STDERR.puts e
     end
   else
     puts "Usage: rlox [script]"

rlox/call.rb

@@ -1,12 +1,14 @@
 class Callable
-  def initialize(name, arity, &block)
+  def initialize(name, params, body, env, &block)
+    @env = env
     @name = name
-    @arity = arity
+    @params = params
+    @body = body
     @call = block
   end
 
   def to_s()
-    "#{@name}:#{@arity}"
+    "#{@name}:#{arity}"
   end
 
   def name()
@@ -14,7 +16,7 @@ class Callable
   end
 
   def arity()
-    @arity
+    @params.length
   end
 
   def call(args)
@@ -24,4 +26,17 @@ class Callable
       e.value
     end
   end
+
+  def bind(instance)
+    env = @env.child
+    env.vars.define("self", instance)
+    Callable.new(@name, @params, @env, @body) { | args |
+      nenv = env.child
+      for i in 0..@params.length-1
+        nenv.vars.define(@params[i].lexeme, args[i])
+      end
+
+      @body.eval(env)
+    }
+  end
 end

rlox/classes.rb

@@ -0,0 +1,82 @@
+class LoxInstance
+  def initialize(klass)
+    @klass = klass
+    @fields = {}
+  end
+
+  def fieldnames()
+    "(#{@fields.keys.join(", ")})"
+  end
+
+  def get(name)
+    if @fields.has_key? name.lexeme
+      return @fields[name.lexeme]
+    end
+
+    method = @klass.find_method(self, name)
+    if method
+      return method
+    end
+
+    raise ExecError.new(
+      name.line,
+      "Undefined property '#{name.lexeme}' on #{self}, has #{fieldnames}."
+    )
+  end
+
+  def set(name, val)
+    @fields[name.lexeme] = val
+  end
+
+  def to_s()
+    "<instance of '#{@klass}'>"
+  end
+end
+
+class LoxClass
+  def initialize(name, methods)
+    @name = name
+    @methods = methods
+  end
+
+  def to_s()
+    if @name
+      @name.to_s
+    else
+      "<anonymous class>"
+    end
+  end
+
+  def arity()
+    init = @methods["init"]
+    if init
+      init.arity
+    else
+      0
+    end
+  end
+
+  def name()
+    @name
+  end
+
+  def call(args)
+    ins = LoxInstance.new(self)
+    init = @methods["init"]
+    if init
+      init.bind(ins).call(args)
+    end
+
+    ins
+  end
+
+  def find_method(instance, name)
+    if name.lexeme == "init"
+      raise ExecError.new(name.line, "Cannot re-initialize class.")
+    end
+
+    if @methods.has_key? name.lexeme
+      return @methods[name.lexeme].bind(instance)
+    end
+  end
+end

rlox/environment.rb

@@ -4,8 +4,14 @@ class Environment
   def self.global()
     env = self.new()
 
-    env.define("print", Callable.new("print", 1) { | args | puts args[0] })
-    env.define("clock", Callable.new("clock", 0) { | args | Time.now.to_i })
+    env.define("print", Callable.new("print", ["obj"], nil, env) {
+      | args |
+      puts args[0]
+    })
+    env.define("clock", Callable.new("clock", [], nil, env) {
+      | args |
+      Time.now.to_i
+    })
     env
   end
 

rlox/executor.rb

@@ -2,7 +2,7 @@ require './rlox/environment'
 require './rlox/parse'
 require './rlox/scan'
 
-Env = Struct.new(:map, :scopes, :vars, :fn) do
+Env = Struct.new(:map, :scopes, :vars, :fn, :cls) do
   def child()
     Env.new(map, scopes, Environment.new(vars), fn)
   end
@@ -19,7 +19,7 @@ end
 
 class Executor
   def initialize()
-    @env = Env.new({}, [], Environment.global, nil)
+    @env = Env.new({}, [], Environment.global, nil, nil)
     @scanner = Scanner.new
     @parser = Parser.new
   end
@@ -42,7 +42,7 @@ class Executor
       return
     end
 
-    ast.each { | stmt |
+    ast.map { | stmt |
       stmt.eval(@env)
     }
   end

rlox/expression.rb

@@ -1,3 +1,5 @@
+require './rlox/classes'
+
 def truthy?(obj)
   if [nil, false, "", 0].include? obj
     false
@@ -215,7 +217,8 @@ Unary = Struct.new(:operator, :right) do
 end
 Var = Struct.new(:name) do
   def resolve(env)
-    if env.scopes.length > 0 and env.scopes[-1][name.lexeme][:assigned] == false
+    if (env.scopes.length > 0 and env.scopes[-1][name.lexeme] and
+      env.scopes[-1][name.lexeme][:assigned] == false)
       raise VarError.new(
         name.line,
         "Cannot read local variable #{name.lexeme} in its own initializer."
@@ -266,7 +269,7 @@ Fn = Struct.new(:params, :body) do
   end
 
   def eval(env)
-    Callable.new("fn", params.length) { | args |
+    Callable.new("fn", params, body, env) { | args |
       nenv = env.child
       for i in 0..params.length-1
         nenv.vars.define(params[i].lexeme, args[i])
@@ -275,6 +278,106 @@ Fn = Struct.new(:params, :body) do
     }
   end
 end
+Get = Struct.new(:object, :name) do
+  def resolve(env)
+    object.resolve(env)
+  end
+
+  def eval(env)
+    obj = object.eval(env)
+
+    if obj.is_a? LoxInstance
+      return obj.get(name)
+    end
+
+    raise ExecError.new(
+      expr.name.line,
+      "Only instances have properties, #{object.lexeme} is a #{obj.class}."
+    )
+  end
+end
+Set = Struct.new(:object, :name, :value) do
+  def resolve(env)
+    value.resolve(env)
+    object.resolve(env)
+  end
+
+  def eval(env)
+    obj = object.eval(env)
+
+    if not obj.is_a? LoxInstance
+      raise ExecError.new(
+        name.line,
+        "Only instances have fields, #{obj} is a #{obj.class}."
+      )
+    end
+
+    val = value.eval(env)
+
+    obj.set(name, val)
+
+    val
+  end
+end
+Klass = Struct.new(:name, :methods) do
+  def resolve(env)
+    enclosing = env.cls
+    env.cls = :class
+    declare(env.scopes, name)
+    define(env.scopes, name)
+
+    begin_scope(env.scopes)
+    dummy = Token.new(:id, "self", nil, 0)
+    declare(env.scopes, dummy)
+    define(env.scopes, dummy)
+
+    methods.each { | method |
+      method.resolve(env, method.name.lexeme == "init" ? :init : :method)
+    }
+
+    end_scope(env.scopes)
+    env.cls = enclosing
+  end
+
+  def eval(env)
+    if name
+      env.vars.define(name.lexeme, nil)
+    end
+
+    methods_dict = {}
+    methods.each { | method |
+      fn = Callable.new(method.name.lexeme, method.params, method.body, env) {
+        | args |
+        nenv = env.child
+        for i in 0..method.params.length-1
+          nenv.vars.define(method.params[i].lexeme, args[i])
+        end
+        method.body.eval(nenv)
+      }
+      methods_dict[method.name.lexeme] = fn
+    }
+
+    klass = LoxClass.new(name ? name.lexeme : nil, methods_dict)
+
+    if name
+      env.vars.assign(name, klass)
+    end
+    klass
+  end
+end
+Self = Struct.new(:keyword) do
+  def resolve(env)
+    if env.cls != :class
+      raise VarError.new(keyword.line, "Cannot use 'self' outside of a class.")
+    end
+
+    resolve_local(env, self, keyword)
+  end
+
+  def eval(env)
+    env.lookup(self, keyword)
+  end
+end
 
 Expression = Struct.new(:expression) do
   def resolve(env)
@@ -353,12 +456,12 @@ While = Struct.new(:cond, :body) do
   end
 end
 FnDef = Struct.new(:name, :params, :body) do
-  def resolve(env)
+  def resolve(env, fn=:fn)
     declare(env.scopes, name)
     define(env.scopes, name)
 
     enclosing = env.fn
-    env.fn = :fn
+    env.fn = fn
     begin_scope(env.scopes)
 
     params.each{ | param |
@@ -372,7 +475,7 @@ FnDef = Struct.new(:name, :params, :body) do
   end
 
   def eval(env)
-    env.vars.define(name.lexeme, Callable.new(name.lexeme, params.length) {
+    env.vars.define(name.lexeme, Callable.new(name.lexeme, params, body, env) {
       | args |
       nenv = env.child
       for i in 0..params.length-1
@@ -389,6 +492,9 @@ Return = Struct.new(:keyword, :value) do
     end
 
     if value
+      if env.fn == :init
+        raise VarError.new(keyword.line, "Cannot return a value from 'init()'.")
+      end
       value.resolve(env)
     end
   end

rlox/parse.rb

@@ -88,6 +88,8 @@ class Parser
       if expr.is_a? Var
         name = expr.name
         return Assign.new(name, value)
+      elsif expr.is_a? Get
+        return Set.new(expr.object, expr.name, value)
       end
 
       error(equals, "Invalid assignment target: '#{expr.dbg}'.")
@@ -160,6 +162,9 @@ class Parser
     while true
       if match(:left_paren)
         expr = finish_call(expr)
+      elsif match(:dot)
+        name = consume(:id, "Expect property name after '.'.")
+        expr = Get.new(expr, name)
       else
         break
       end
@@ -198,6 +203,20 @@ class Parser
     Fn.new(params, body)
   end
 
+  def anon_class()
+    consume(:left_brace, "Expect '{' before body of anonymous class.")
+
+    methods = []
+
+    while not check(:right_brace) and not is_at_end
+      methods << function("method")
+    end
+
+    consume(:right_brace, "Expect '}' after class body.")
+
+    Klass.new(nil, methods)
+  end
+
   def primary()
     if match(:false)
       Literal.new(false)
@@ -205,6 +224,8 @@ class Parser
       Literal.new(true)
     elsif match(:nil)
       Literal.new(nil)
+    elsif match(:self)
+      Self.new(previous)
     elsif match(:number, :string)
       Literal.new(previous.literal)
     elsif match(:left_paren)
@@ -215,6 +236,8 @@ class Parser
       Var.new(previous)
     elsif match(:fn)
       anon_fn
+    elsif match(:class)
+      anon_class
     else
       error(peek, "Expect expression.")
     end
@@ -399,9 +422,28 @@ class Parser
     FnDef.new(name, params, body)
   end
 
+  def class_declaration()
+    consume(:class, "Expect 'class' keyword.")
+    name = consume(:id, "Expect class name.")
+
+    consume(:left_brace, "Expect '{' before body of class '#{name.lexeme}.'")
+
+    methods = []
+
+    while not check(:right_brace) and not is_at_end
+      methods << function("method")
+    end
+
+    consume(:right_brace, "Expect '}' after class body.")
+
+    Klass.new(name, methods)
+  end
+
   def declaration()
     begin
-      if check(:fn) and check_next(:id)
+      if check(:class) and check_next(:id)
+        class_declaration
+      elsif check(:fn) and check_next(:id)
         function("fn")
       elsif match(:let)
         var_declaration

rlox/prompt.rb

@@ -19,7 +19,12 @@ def prompt()
       end
 
       begin
-        puts exec.run(buf).to_s
+        res = exec.run(buf)
+        if res
+          res.each { | res |
+            puts res.to_s
+          }
+        end
       rescue LoxError => err
         STDERR.puts err
       ensure

rlox/scan.rb

@@ -14,7 +14,7 @@ KEYWORDS = [
   "or",
   "return",
   "super",
-  "this",
+  "self",
   "true",
   "let",
   "while",