done with 9

README.md

@@ -3,3 +3,8 @@
 `rlox` is an unpronouncable variant of the tree-walk interpreter laid out in
 [Crafting Interpreters](http://craftinginterpreters.com/), written in Ruby,
 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.

rlox/environment.rb

@@ -24,11 +24,13 @@ class Environment
 
   def assign(name, value)
     if @values.has_key? name.lexeme
-      @values.put(name.lexeme, value)
+      @values[name.lexeme] = value
+      return
     end
     if @parent != nil
       return @parent.assign(name, value)
     end
-    raise ExecError.new(name.line, "Undefined variable '#{name.lexeme}'.")
+    raise ExecError.new(name.line,
+                        "Can’t assign undefined variable '#{name.lexeme}'.")
   end
 end

rlox/expression.rb

@@ -1,20 +1,6 @@
-def parenthesize(name, *exprs)
-  res = "(#{name}"
-
-  exprs.each { | expr |
-    res << " "
-    res << expr.dbg
-  }
-  res << ")"
-
-  res
-end
-
-def truthy(obj)
-  if obj == nil
+def truthy?(obj)
+  if [nil, false, "", 0].include? obj
     false
-  elsif obj.is_a? Boolean
-    obj
   else
     true
   end
@@ -47,10 +33,6 @@ Assign = Struct.new(:name, :value) do
   end
 end
 Binary = Struct.new(:left, :operator, :right) do
-  def dbg()
-    parenthesize(operator.lexeme, left, right)
-  end
-
   def eval(env)
     l = left.eval(env)
     r = right.eval(env)
@@ -82,38 +64,27 @@ Binary = Struct.new(:left, :operator, :right) do
         l <= r
       when :bang_eq then l != r
       when :eq_eq then l == r
+      when :comma then r
       else nil
     end
   end
 end
 Grouping = Struct.new(:expression) do
-  def dbg()
-    parenthesize("group", expression)
-  end
-
   def eval(env)
     expression.eval(env)
   end
 end
 Literal = Struct.new(:value) do
-  def dbg()
-    value.to_s
-  end
-
   def eval(env)
     value
   end
 end
 Unary = Struct.new(:operator, :right) do
-  def dbg()
-    parenthesize(operator.lexeme, right)
-  end
-
   def eval(env)
     r = right.eval(env)
 
     case operator.type
-      when :bang then is_truthy(r)
+      when :bang then truthy?(r)
       when :minus then
         check_number_op(operator, r)
         -r
@@ -126,6 +97,25 @@ Var = Struct.new(:name) do
     env.get(name)
   end
 end
+Logical = Struct.new(:left, :operator, :right) do
+  def eval(env)
+    l = left.eval(env)
+
+    case operator.type
+      when :or then
+        if truthy?(l)
+          return l
+        end
+      when :and then
+        if not truthy?(l)
+          return l
+        end
+    end
+
+    right.eval(env)
+  end
+end
+
 Expression = Struct.new(:expression) do
   def eval(env)
     expression.eval(env)
@@ -158,3 +148,21 @@ Block = Struct.new(:stmts) do
     env
   end
 end
+If = Struct.new(:cond, :thn, :els) do
+  def eval(env)
+    if truthy? cond.eval(env)
+      thn.eval(env)
+    elsif els != nil
+      els.eval(env)
+    end
+    env
+  end
+end
+While = Struct.new(:cond, :body) do
+  def eval(env)
+    while truthy? cond.eval(env)
+      body.eval(env)
+    end
+    env
+  end
+end

rlox/parse.rb

@@ -24,7 +24,7 @@ class Parser
   end
 
   def advance()
-    if !is_at_end()
+    if !is_at_end
       @current += 1
     end
     return previous
@@ -54,9 +54,33 @@ class Parser
     expr
   end
 
-  def assignment()
+  def and_expr()
     expr = equality
 
+    if match(:and)
+      operator = previous
+      right = equality
+      expr = Logical.new(expr, operator, right)
+    end
+
+    expr
+  end
+
+  def or_expr()
+    expr = and_expr
+
+    if match(:or)
+      operator = previous
+      right = and_expr
+      expr = Logical.new(expr, operator, right)
+    end
+
+    expr
+  end
+
+  def assignment()
+    expr = or_expr
+
     if match(:eq)
       equals = previous
       value = assignment
@@ -126,7 +150,7 @@ class Parser
       return Unary.new(operator, right)
     end
 
-    primary()
+    primary
   end
 
   def primary()
@@ -166,7 +190,7 @@ class Parser
   end
 
   def expression()
-    comma()
+    comma
   end
 
   def synchronize()
@@ -210,9 +234,82 @@ class Parser
     return stmts
   end
 
+  def if_statement()
+    cond = expression
+
+    consume(:left_brace, "Expect '{' after 'if' condition.")
+    thn = Block.new(block)
+    els = nil
+
+    if match(:else)
+      consume(:left_brace, "Expect '{' after 'else'.")
+      els = Block.new(block)
+    end
+
+    If.new(cond, thn, els)
+  end
+
+  def while_statement()
+    cond = expression
+
+    consume(:left_brace, "Expect '{' after 'if' condition.")
+    body = Block.new(block)
+
+    While.new(cond, body)
+  end
+
+  def for_statement()
+    init = if match(:semicolon)
+      nil
+    elsif match(:var)
+      var_declaration
+    else
+      expression_statement
+    end
+
+    cond = nil
+
+    if !check(:semicolon)
+      cond = expression
+    end
+
+    consume(:semicolon, "Expect ';' after loop condition.")
+
+    inc = nil
+
+    if !check(:semicolon)
+      inc = expression
+    end
+
+    consume(:left_brace, "Expect '{' after 'if' condition.")
+    body = Block.new(block)
+
+    if inc
+      body = Block.new([body, Expr.new(inc)])
+    end
+
+    if not cond
+      cond = Literal.new(true)
+    end
+
+    if init
+      body = Block.new([init, body])
+    end
+
+    body = While.new(cond, body)
+
+    body
+  end
+
   def statement()
-    if match(:print)
+    if match(:if)
+      if_statement
+    elsif match(:for)
+      for_statement
+    elsif match(:print)
       print_statement
+    elsif match(:while)
+      while_statement
     elsif match(:left_brace)
       Block.new(block)
     else

rlox/prompt.rb

@@ -5,9 +5,9 @@ require './rlox/executor'
 def prompt()
   exec = Executor.new
 
-  f = File.new("#{Dir.home}/.rlox", File::CREAT|File::RDWR)
+  f = File.new("#{Dir.home}/.rlox", "a+")
   File.readlines("#{Dir.home}/.rlox").each { | line |
-    Readline::HISTORY.push line
+    Readline::HISTORY.push line.rstrip
   }
 
   begin
@@ -16,9 +16,10 @@ def prompt()
 
       begin
         exec.run buf
-        f.write("#{buf}\n")
       rescue LoxError => err
         STDERR.puts err
+      ensure
+        f.write("#{buf}\n")
       end
       exec.inc_line
     end