diff --git a/main.rb b/main.rb
index b9d0042..ee5884a 100644
--- a/main.rb
+++ b/main.rb
@@ -8,7 +8,7 @@ case ARGV.length
   when 1 then
     begin
       file ARGV[0]
-    rescue Error => e
+    rescue StandardError => e
       STDERR.puts e
     end
   else
diff --git a/rlox/environment.rb b/rlox/environment.rb
new file mode 100644
index 0000000..4b7dcd3
--- /dev/null
+++ b/rlox/environment.rb
@@ -0,0 +1,34 @@
+class Environment
+  def initialize(parent=nil)
+    @values = {}
+    @parent = parent
+  end
+
+  def to_s()
+    @values.to_s
+  end
+
+  def define(name, value)
+    @values[name] = value
+  end
+
+  def get(name)
+    if @values.has_key? name.lexeme
+      return @values[name.lexeme]
+    end
+    if @parent != nil
+      return @parent.get(name)
+    end
+    raise ExecError.new(name.line, "Undefined variable '#{name.lexeme}'.")
+  end
+
+  def assign(name, value)
+    if @values.has_key? name.lexeme
+      @values.put(name.lexeme, value)
+    end
+    if @parent != nil
+      return @parent.assign(name, value)
+    end
+    raise ExecError.new(name.line, "Undefined variable '#{name.lexeme}'.")
+  end
+end
diff --git a/rlox/executor.rb b/rlox/executor.rb
index b426735..c5b53f9 100644
--- a/rlox/executor.rb
+++ b/rlox/executor.rb
@@ -1,13 +1,24 @@
-require './rlox/scan'
+require './rlox/environment'
 require './rlox/parse'
+require './rlox/scan'
 
 class Executor
-  def run(source)
-    scanner = Scanner.new source
-    tokens = scanner.scan
-    parser = Parser.new tokens
-    ast = parser.parse
+  def initialize()
+    @env = Environment.new
+    @scanner = Scanner.new
+    @parser = Parser.new
+  end
 
-    puts ast.eval
+  def run(source)
+    tokens = @scanner.scan_on(source)
+    ast = @parser.parse_on(tokens)
+
+    ast.each { | stmt |
+      @env = stmt.eval(@env)
+    }
+  end
+
+  def inc_line()
+    @scanner.inc_line
   end
 end
diff --git a/rlox/expression.rb b/rlox/expression.rb
index 3f1cb22..355a577 100644
--- a/rlox/expression.rb
+++ b/rlox/expression.rb
@@ -39,14 +39,21 @@ def check_same_type_op(operator, *operands)
   }
 end
 
+Assign = Struct.new(:name, :value) do
+  def eval(env)
+    val = value.eval(env)
+    env.assign(name, val)
+    val
+  end
+end
 Binary = Struct.new(:left, :operator, :right) do
   def dbg()
     parenthesize(operator.lexeme, left, right)
   end
 
-  def eval()
-    l = left.eval
-    r = right.eval
+  def eval(env)
+    l = left.eval(env)
+    r = right.eval(env)
 
     case operator.type
       when :minus then
@@ -84,8 +91,8 @@ Grouping = Struct.new(:expression) do
     parenthesize("group", expression)
   end
 
-  def eval(fn)
-    expression.eval
+  def eval(env)
+    expression.eval(env)
   end
 end
 Literal = Struct.new(:value) do
@@ -93,7 +100,7 @@ Literal = Struct.new(:value) do
     value.to_s
   end
 
-  def eval()
+  def eval(env)
     value
   end
 end
@@ -102,8 +109,8 @@ Unary = Struct.new(:operator, :right) do
     parenthesize(operator.lexeme, right)
   end
 
-  def eval()
-    r = right.eval
+  def eval(env)
+    r = right.eval(env)
 
     case operator.type
       when :bang then is_truthy(r)
@@ -114,3 +121,40 @@ Unary = Struct.new(:operator, :right) do
     end
   end
 end
+Var = Struct.new(:name) do
+  def eval(env)
+    env.get(name)
+  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
+  def eval(env)
+    value = nil
+    if initializer != nil
+      value = initializer.eval(env)
+    end
+
+    env.define(name.lexeme, value)
+    env
+  end
+end
+Block = Struct.new(:stmts) do
+  def eval(env)
+    child = Environment.new(env)
+    stmts.each{ | stmt |
+      stmt.eval(child)
+    }
+    env
+  end
+end
diff --git a/rlox/parse.rb b/rlox/parse.rb
index 77443be..fee246c 100644
--- a/rlox/parse.rb
+++ b/rlox/parse.rb
@@ -1,8 +1,7 @@
 require './rlox/expression'
 
 class Parser
-  def initialize(tokens)
-    @tokens = tokens
+  def initialize()
     @current = 0
   end
 
@@ -44,7 +43,7 @@ class Parser
   end
 
   def comma()
-    expr = equality
+    expr = assignment
 
     while match(:comma)
       operator = previous
@@ -55,6 +54,23 @@ class Parser
     expr
   end
 
+  def assignment()
+    expr = equality
+
+    if match(:eq)
+      equals = previous
+      value = assignment
+      if expr.is_a? Var
+        name = expr.name
+        return Assign.new(name, value)
+      end
+
+      error(equals, "Invalid assignment target: '#{expr.dbg}'.")
+    end
+
+    expr
+  end
+
   def equality()
     expr = comparison
 
@@ -126,6 +142,8 @@ class Parser
       expr = expression
       consume(:right_paren, "Expect ')' after expression.")
       Grouping.new(expr)
+    elsif match(:id)
+      Var.new(previous)
     else
       error(peek, "Expect expression.")
     end
@@ -160,7 +178,7 @@ class Parser
       end
 
       case peek.type
-        when :class, :fun, :var, :for, :if, :while, :print, :return then
+        when :class, :fun, :let, :for, :if, :while, :print, :return then
           return
       end
 
@@ -168,7 +186,76 @@ 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.")
+    Expression.new(expr)
+  end
+
+  def block()
+    stmts = []
+
+    while not check(:right_brace) and not is_at_end
+      stmts << declaration
+    end
+
+    consume(:right_brace, "Expect '}' after block.")
+
+    return stmts
+  end
+
+  def statement()
+    if match(:print)
+      print_statement
+    elsif match(:left_brace)
+      Block.new(block)
+    else
+      expression_statement
+    end
+  end
+
+  def var_declaration()
+    name = consume(:id, "Expect variable name.")
+
+    initializer = nil
+    if match(:eq)
+      initializer = expression
+    end
+    consume(:semicolon, "Expect ';' after variable declaration.")
+    Variable.new(name, initializer)
+  end
+
+  def declaration()
+    begin
+      if match(:let)
+        return var_declaration
+      end
+      return statement
+    rescue ParseError => e
+      synchronize
+      raise e
+    end
+  end
+
   def parse()
-    expression
+    statements = []
+    while not is_at_end
+      statements << declaration
+    end
+
+    statements
+  end
+
+  def parse_on(tokens)
+    @current = 0
+    @tokens = tokens
+
+    parse
   end
 end
diff --git a/rlox/prompt.rb b/rlox/prompt.rb
index 6ac3655..840f1e4 100644
--- a/rlox/prompt.rb
+++ b/rlox/prompt.rb
@@ -4,20 +4,26 @@ require './rlox/executor'
 
 def prompt()
   exec = Executor.new
-  while buf = Readline.readline("> ", true)
-    Readline::HISTORY.pop if /^\s*$/ =~ buf
 
-    begin
-      if Readline::HISTORY[Readline::HISTORY.length-2] == buf
-        Readline::HISTORY.pop
+  f = File.new("#{Dir.home}/.rlox", File::CREAT|File::RDWR)
+  File.readlines("#{Dir.home}/.rlox").each { | line |
+    Readline::HISTORY.push line
+  }
+
+  begin
+    while buf = Readline.readline("> ", true)
+      Readline::HISTORY.pop if /^\s*$/ =~ buf
+
+      begin
+        exec.run buf
+        f.write("#{buf}\n")
+      rescue LoxError => err
+        STDERR.puts err
       end
-    rescue IndexError
-    end
-
-    begin
-      exec.run buf
-    rescue LoxError => err
-      STDERR.puts err
+      exec.inc_line
     end
+  rescue Interrupt
+  ensure
+    f.close
   end
 end
diff --git a/rlox/scan.rb b/rlox/scan.rb
index ea0c3dc..292fa76 100644
--- a/rlox/scan.rb
+++ b/rlox/scan.rb
@@ -22,8 +22,7 @@ KEYWORDS = [
 ]
 
 class Scanner
-  def initialize(source)
-    @source = source
+  def initialize()
     @start = 0
     @current = 0
     @line = 1
@@ -53,7 +52,7 @@ class Scanner
 
   def peek()
     if is_at_end
-      '\0'
+      "\0"
     else
       @source[@current]
     end
@@ -61,7 +60,7 @@ class Scanner
 
   def peek_next()
     if @current + 1 >= @source.length
-      '\0'
+      "\0"
     else
       @source[@current+1]
     end
@@ -69,7 +68,7 @@ class Scanner
 
   def string()
     while peek != '"' and not is_at_end
-      if peek == '\n'
+      if peek == "\n"
         @line += 1
       end
       advance
@@ -148,7 +147,7 @@ class Scanner
       when '>' then add_token(match('=') ? :geq : :gt)
       when '/' then
         if match('/')
-          while peek != '\n' and not is_at_end
+          while peek != "\n" and not is_at_end
             advance
           end
         elsif match('*')
@@ -165,8 +164,8 @@ class Scanner
         else
           add_token(:slash)
         end
-      when ' ', '\r', '\t' then nil
-      when '\n' then
+      when ' ', "\r", "\t" then nil
+      when "\n" then
         @line += 1
         nil
       when '"' then string
@@ -176,7 +175,9 @@ class Scanner
         elsif is_alpha(c)
           identifier
         else
-          raise ParseError.new(@line, "Unexpected character: #{c}.")
+          raise ParseError.new(
+            @line,
+            "Unexpected character: #{c} (char code: #{c.ord}).")
         end
     end
   end
@@ -205,4 +206,16 @@ class Scanner
 
     tokens
   end
+
+  def scan_on(source)
+    @start = 0
+    @current = 0
+    @source = source
+
+    scan
+  end
+
+  def inc_line()
+    @line += 1
+  end
 end