done with 11

README.md

@@ -7,4 +7,7 @@ because I want to learn it.
 It deviates a little from the “canonical” version of Lox. I don’t use code
 generation for the expressions, and I don’t use the visitor pattern. `var` and
 `fun` are `let` and `fn`, respectively. And we don’t need parentheses around
-branching conditions, instead we require the bodies to be blocks.
+branching conditions, instead we require the bodies to be blocks. We also have
+closures and anonymous functions (and literals for them), and implicit returns.
+
+If you wonder what that looks like, you can look at the [examples](/examples).

examples/counter.lox

@@ -0,0 +1,10 @@
+fn makeCounter() {
+  let i = 0;
+  fn count() {
+    i = i + 1;
+  }
+}
+
+let counter = makeCounter();
+print(counter()); // "1".
+print(counter()); // "2".

examples/fib.lox

@@ -0,0 +1,8 @@
+fn fibonacci(n) {
+  if n <= 1 { return n; }
+  return fibonacci(n - 2) + fibonacci(n - 1);
+}
+
+for let i = 0; i < 25; i = i + 1 {
+  print(fibonacci(i));
+}

examples/thrice.lox

@@ -0,0 +1,9 @@
+fn thrice(f) {
+  for let i = 1; i <= 3; i = i + 1 {
+    f(i);
+  }
+}
+
+thrice(fn (a) {
+  print(a);
+});

rlox/call.rb

@@ -0,0 +1,27 @@
+class Callable
+  def initialize(name, arity, &block)
+    @name = name
+    @arity = arity
+    @call = block
+  end
+
+  def to_s()
+    "#{@name}:#{@arity}"
+  end
+
+  def name()
+    @name
+  end
+
+  def arity()
+    @arity
+  end
+
+  def call(args)
+    begin
+      @call.call(args)
+    rescue ReturnError => e
+      e.value
+    end
+  end
+end

rlox/environment.rb

@@ -1,4 +1,14 @@
+require './rlox/call'
+
 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
+  end
+
   def initialize(parent=nil)
     @values = {}
     @parent = parent

rlox/error.rb

@@ -20,3 +20,13 @@ end
 
 class ExecError < LoxError
 end
+
+class ReturnError < StandardError
+  def initialize(value)
+    @value = value
+  end
+
+  def value()
+    @value
+  end
+end

rlox/executor.rb

@@ -4,7 +4,7 @@ require './rlox/scan'
 
 class Executor
   def initialize()
-    @env = Environment.new
+    @env = Environment.global
     @scanner = Scanner.new
     @parser = Parser.new
   end
@@ -14,7 +14,7 @@ class Executor
     ast = @parser.parse_on(tokens)
 
     ast.each { | stmt |
-      @env = stmt.eval(@env)
+      stmt.eval(@env)
     }
   end
 

rlox/expression.rb

@@ -24,6 +24,30 @@ def check_same_type_op(operator, *operands)
     end
   }
 end
+Call = Struct.new(:callee, :paren, :arguments) do
+  def eval(env)
+    to_call = callee.eval(env)
+    al = arguments.length
+
+    if not to_call.class.method_defined? :call
+      raise ExecError.new(paren.line, "Can only call functions and classes.")
+    end
+
+    if al != to_call.arity
+      raise ExecError.new(
+        paren.line,
+        "#{to_call.name} expected #{to_call.arity} arguments but got #{al}."
+      )
+    end
+
+    args = []
+    arguments.each{ | arg |
+      args << arg.eval(env)
+    }
+
+    to_call.call(args)
+  end
+end
 
 Assign = Struct.new(:name, :value) do
   def eval(env)
@@ -115,17 +139,21 @@ Logical = Struct.new(:left, :operator, :right) do
     right.eval(env)
   end
 end
+Fn = Struct.new(:params, :body) do
+  def eval(env)
+    Callable.new("fn", params.length) { | args |
+      nenv = Environment.new(env)
+      for i in 0..params.length-1
+        nenv.define(params[i].lexeme, args[i])
+      end
+      body.eval(nenv)
+    }
+  end
+end
 
 Expression = Struct.new(:expression) do
   def eval(env)
     expression.eval(env)
-    env
-  end
-end
-Print = Struct.new(:print) do
-  def eval(env)
-    puts print.eval(env)
-    env
   end
 end
 Variable = Struct.new(:name, :initializer) do
@@ -136,16 +164,16 @@ Variable = Struct.new(:name, :initializer) do
     end
 
     env.define(name.lexeme, value)
-    env
   end
 end
 Block = Struct.new(:stmts) do
   def eval(env)
     child = Environment.new(env)
+    ret = nil
     stmts.each{ | stmt |
-      stmt.eval(child)
+      ret = stmt.eval(child)
     }
-    env
+    ret
   end
 end
 If = Struct.new(:cond, :thn, :els) do
@@ -155,14 +183,31 @@ If = Struct.new(:cond, :thn, :els) do
     elsif els != nil
       els.eval(env)
     end
-    env
   end
 end
 While = Struct.new(:cond, :body) do
   def eval(env)
+    ret = nil
     while truthy? cond.eval(env)
-      body.eval(env)
+      ret = body.eval(env)
     end
-    env
+    ret
+  end
+end
+FnDef = Struct.new(:name, :params, :body) do
+  def eval(env)
+    env.define(name.lexeme, Callable.new(name.lexeme, params.length) {
+      | args |
+      nenv = Environment.new(env)
+      for i in 0..params.length-1
+        nenv.define(params[i].lexeme, args[i])
+      end
+      body.eval(nenv)
+    })
+  end
+end
+Return = Struct.new(:value) do
+  def eval(env)
+    raise ReturnError.new(value == nil ? nil : value.eval(env))
   end
 end

rlox/parse.rb

@@ -23,6 +23,15 @@ class Parser
     end
   end
 
+
+  def check_next(type)
+    if is_at_end or peek_next.type == :eof
+      false
+    else
+      peek_next.type == type
+    end
+  end
+
   def advance()
     if !is_at_end
       @current += 1
@@ -38,20 +47,12 @@ class Parser
     @tokens[@current]
   end
 
-  def previous()
+  def peek_next()
-    @tokens[@current-1]
+    @tokens[@current+1]
   end
 
-  def comma()
+  def previous()
-    expr = assignment
+    @tokens[@current-1]
-
-    while match(:comma)
-      operator = previous
-      right = comparison
-      expr = Binary.new(expr, operator, right)
-    end
-
-    expr
   end
 
   def and_expr()
@@ -134,7 +135,7 @@ class Parser
   def comparison()
     expr = addition
 
-    while match(:gt, :geq, :lt, :geq)
+    while match(:gt, :geq, :lt, :leq)
       operator = previous
       right = addition
       expr = Binary.new(expr, operator, right)
@@ -150,7 +151,51 @@ class Parser
       return Unary.new(operator, right)
     end
 
-    primary
+    call
+  end
+
+  def call()
+    expr = primary
+
+    while true
+      if match(:left_paren)
+        expr = finish_call(expr)
+      else
+        break
+      end
+    end
+
+    expr
+  end
+
+  def finish_call(callee)
+    args = []
+
+    if not check(:right_paren)
+      begin
+        args << expression
+      end while match(:comma)
+    end
+
+    paren = consume(:right_paren, "Expect ')' after arguments.")
+
+    return Call.new(callee, paren, args)
+  end
+
+  def anon_fn()
+    consume(:left_paren, "Expect '(' after 'fn' keyword'.")
+
+    params = []
+    if not check(:right_paren)
+      begin
+        params << consume(:id, "Expect parameter name")
+      end while match(:comma)
+    end
+    consume(:right_paren, "Expect ')' after parameters.")
+
+    consume(:left_brace, "Expect '{' before fn body.")
+    body = Block.new(block)
+    Fn.new(params, body)
   end
 
   def primary()
@@ -168,6 +213,8 @@ class Parser
       Grouping.new(expr)
     elsif match(:id)
       Var.new(previous)
+    elsif match(:fn)
+      anon_fn
     else
       error(peek, "Expect expression.")
     end
@@ -190,7 +237,7 @@ class Parser
   end
 
   def expression()
-    comma
+    assignment
   end
 
   def synchronize()
@@ -202,7 +249,7 @@ class Parser
       end
 
       case peek.type
-        when :class, :fun, :let, :for, :if, :while, :print, :return then
+        when :class, :fun, :let, :for, :if, :while, :return then
           return
       end
 
@@ -210,12 +257,6 @@ class Parser
     end
   end
 
-  def print_statement()
-    value = expression
-    consume(:semicolon, "Expect ';' after value.")
-    Print.new(value)
-  end
-
   def expression_statement()
     expr = expression
     consume(:semicolon, "Expect ';' after expression.")
@@ -261,7 +302,7 @@ class Parser
   def for_statement()
     init = if match(:semicolon)
       nil
-    elsif match(:var)
+    elsif match(:let)
       var_declaration
     else
       expression_statement
@@ -284,30 +325,41 @@ class Parser
     consume(:left_brace, "Expect '{' after 'if' condition.")
     body = Block.new(block)
 
-    if inc
+    if inc != nil
-      body = Block.new([body, Expr.new(inc)])
+      body = Block.new([body, Expression.new(inc)])
     end
 
-    if not cond
+    if cond == nil
       cond = Literal.new(true)
     end
 
-    if init
-      body = Block.new([init, body])
-    end
-
     body = While.new(cond, body)
 
+    if init != nil
+      body = Block.new([init, body])
+    end
+
     body
   end
 
+  def return_statement()
+    value = nil
+
+    if !check(:semicolon)
+      value = expression
+    end
+
+    consume(:semicolon, "Expect ';' after return value.")
+    Return.new(value)
+  end
+
   def statement()
     if match(:if)
       if_statement
     elsif match(:for)
       for_statement
-    elsif match(:print)
+    elsif match(:return)
-      print_statement
+      return_statement
     elsif match(:while)
       while_statement
     elsif match(:left_brace)
@@ -328,12 +380,33 @@ class Parser
     Variable.new(name, initializer)
   end
 
+  def function(kind)
+    consume(:fn, "Expect 'fn' keyword.")
+    name = consume(:id, "Expect #{kind} name.")
+    consume(:left_paren, "Expect '(' after #{kind} name.")
+
+    params = []
+    if not check(:right_paren)
+      begin
+        params << consume(:id, "Expect paramenter name")
+      end while match(:comma)
+    end
+    consume(:right_paren, "Expect ')' after parameters.")
+
+    consume(:left_brace, "Expect '{' before #{kind} body.")
+    body = Block.new(block)
+    FnDef.new(name, params, body)
+  end
+
   def declaration()
     begin
-      if match(:let)
+      if check(:fn) and check_next(:id)
-        return var_declaration
+        function("fn")
+      elsif match(:let)
+        var_declaration
+      else
+        statement
       end
-      return statement
     rescue ParseError => e
       synchronize
       raise e
@@ -344,6 +417,7 @@ class Parser
     statements = []
     while not is_at_end
       statements << declaration
+      match(:semicolon)
     end
 
     statements

rlox/prompt.rb

@@ -14,8 +14,12 @@ def prompt()
     while buf = Readline.readline("> ", true)
       Readline::HISTORY.pop if /^\s*$/ =~ buf
 
+      if buf[-1] != ';'
+        buf << ';'
+      end
+
       begin
-        exec.run buf
+        puts exec.run(buf).to_s
       rescue LoxError => err
         STDERR.puts err
       ensure

rlox/scan.rb

@@ -12,7 +12,6 @@ KEYWORDS = [
   "if",
   "nil",
   "or",
-  "print",
   "return",
   "super",
   "this",