diff --git a/crisp.cr b/crisp.cr
new file mode 100644
index 0000000..503f6aa
--- /dev/null
+++ b/crisp.cr
@@ -0,0 +1,12 @@
+require "./src/crisp/interpreter"
+
+if ARGV.empty?
+  begin
+    Crisp::Interpreter.new.run
+  rescue e
+    STDERR.puts e
+    exit 1
+  end
+else
+  Crisp::Interpreter.new(ARGV[1..-1]).run(ARGV.first)
+end
diff --git a/src/crisp.cr b/src/crisp.cr
index 80f8103..81bc19b 100644
--- a/src/crisp.cr
+++ b/src/crisp.cr
@@ -1,303 +1 @@
-require "colorize"
-require "readline"
-
-require "./reader"
-require "./printer"
-require "./types"
-require "./env"
-require "./core"
-require "./error"
-
-# Note:
-# Employed downcase names because Crystal prohibits uppercase names for methods
-
-module Crisp
-  extend self
-
-  def func_of(env, binds, body)
-    -> (args : Array(Crisp::Type)) {
-      new_env = Crisp::Env.new(env, binds, args)
-      eval(body, new_env)
-    } as Crisp::Func
-  end
-
-  def eval_ast(ast, env)
-    return ast.map{|n| eval(n, env) as Crisp::Type} if ast.is_a? Array
-
-    val = ast.unwrap
-
-    Crisp::Type.new case val
-    when Crisp::Symbol
-      if e = env.get(val.str)
-        e
-      else
-        eval_error "'#{val.str}' not found"
-      end
-    when Crisp::List
-      val.each_with_object(Crisp::List.new){|n, l| l << eval(n, env)}
-    when Crisp::Vector
-      val.each_with_object(Crisp::Vector.new){|n, l| l << eval(n, env)}
-    when Crisp::HashMap
-      new_map = Crisp::HashMap.new
-      val.each{|k, v| new_map[k] = eval(v, env)}
-      new_map
-    else
-      val
-    end
-  end
-
-  def read(str)
-    read_str str
-  end
-
-  macro pair?(list)
-    {{list}}.is_a?(Array) && !{{list}}.empty?
-  end
-
-  def quasiquote(ast)
-    list = ast.unwrap
-
-    unless pair?(list)
-      return Crisp::Type.new(
-        Crisp::List.new << gen_type(Crisp::Symbol, "quote") << ast
-      )
-    end
-
-    head = list.first.unwrap
-
-    case
-    # ("unquote" ...)
-    when head.is_a?(Crisp::Symbol) && head.str == "unquote"
-      list[1]
-    # (("splice-unquote" ...) ...)
-    when pair?(head) && (arg0 = head.first.unwrap).is_a?(Crisp::Symbol) && arg0.str == "splice-unquote"
-      tail = Crisp::Type.new list[1..-1].to_crisp_value
-      Crisp::Type.new(
-        Crisp::List.new << gen_type(Crisp::Symbol, "concat") << head[1] << quasiquote(tail)
-      )
-    else
-      tail = Crisp::Type.new list[1..-1].to_crisp_value
-      Crisp::Type.new(
-        Crisp::List.new << gen_type(Crisp::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
-      )
-    end
-  end
-
-  def macro_call?(ast, env)
-    list = ast.unwrap
-    return false unless list.is_a? Crisp::List
-    return false if list.empty?
-
-    sym = list.first.unwrap
-    return false unless sym.is_a? Crisp::Symbol
-
-    func = env.find(sym.str).try(&.data[sym.str])
-    return false unless func && func.macro?
-
-    true
-  end
-
-  def macroexpand(ast, env)
-    while macro_call?(ast, env)
-
-      # Already checked in macro_call?
-      list = ast.unwrap as Crisp::List
-      func_sym = list[0].unwrap as Crisp::Symbol
-      func = env.get(func_sym.str).unwrap
-
-      case func
-      when Crisp::Func
-        ast = func.call(list[1..-1])
-      when Crisp::Closure
-        ast = func.fn.call(list[1..-1])
-      else
-        eval_error "macro '#{func_sym.str}' must be function: #{ast}"
-      end
-    end
-
-    ast
-  end
-
-  macro invoke_list(l, env)
-    f = eval({{l}}.first, {{env}}).unwrap
-    args = eval_ast({{l}}[1..-1], {{env}}) as Array
-
-    case f
-    when Crisp::Closure
-      ast = f.ast
-      {{env}} = Crisp::Env.new(f.env, f.params, args)
-      next # TCO
-    when Crisp::Func
-      return f.call args
-    else
-      eval_error "expected function as the first argument: #{f}"
-    end
-  end
-
-  def debug(ast)
-    puts print(ast).colorize.red
-  end
-
-  def eval(ast, env)
-    # 'next' in 'do...end' has a bug in crystal 0.7.1
-    # https://github.com/manastech/crystal/issues/659
-    while true
-      return eval_ast(ast, env) unless ast.unwrap.is_a? Crisp::List
-
-      ast = macroexpand(ast, env)
-
-      list = ast.unwrap
-
-      return ast unless list.is_a? Crisp::List
-      return ast if list.empty?
-
-      head = list.first.unwrap
-
-      return invoke_list(list, env) unless head.is_a? Crisp::Symbol
-
-      return Crisp::Type.new case head.str
-        when "def!"
-          eval_error "wrong number of argument for 'def!'" unless list.size == 3
-          a1 = list[1].unwrap
-          eval_error "1st argument of 'def!' must be symbol: #{a1}" unless a1.is_a? Crisp::Symbol
-          env.set(a1.str, eval(list[2], env))
-        when "let*"
-          eval_error "wrong number of argument for 'def!'" unless list.size == 3
-
-          bindings = list[1].unwrap
-          eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
-          eval_error "size of binding list must be even" unless bindings.size.even?
-
-          new_env = Crisp::Env.new env
-          bindings.each_slice(2) do |binding|
-            key, value = binding
-            name = key.unwrap
-            eval_error "name of binding must be specified as symbol #{name}" unless name.is_a? Crisp::Symbol
-            new_env.set(name.str, eval(value, new_env))
-          end
-
-          ast, env = list[2], new_env
-          next # TCO
-        when "do"
-          if list.empty?
-            ast = Crisp::Type.new nil
-            next
-          end
-
-          eval_ast(list[1..-2].to_crisp_value, env)
-          ast = list.last
-          next # TCO
-        when "if"
-          ast = unless eval(list[1], env).unwrap
-            list.size >= 4 ? list[3] : Crisp::Type.new(nil)
-          else
-            list[2]
-          end
-          next # TCO
-        when "fn*"
-          params = list[1].unwrap
-          unless params.is_a? Array
-            eval_error "'fn*' parameters must be list or vector: #{params}"
-          end
-          Crisp::Closure.new(list[2], params, env, func_of(env, params, list[2]))
-        when "quote"
-          list[1]
-        when "quasiquote"
-          ast = quasiquote list[1]
-          next # TCO
-        when "defmacro!"
-          eval_error "wrong number of argument for 'defmacro!'" unless list.size == 3
-          a1 = list[1].unwrap
-          eval_error "1st argument of 'defmacro!' must be symbol: #{a1}" unless a1.is_a? Crisp::Symbol
-          env.set(a1.str, eval(list[2], env).tap{|n| n.is_macro = true})
-        when "macroexpand"
-          macroexpand(list[1], env)
-        when "try*"
-          catch_list = list[2].unwrap
-          return eval(list[1], env) unless catch_list.is_a? Crisp::List
-
-          catch_head = catch_list.first.unwrap
-          return eval(list[1], env) unless catch_head.is_a? Crisp::Symbol
-          return eval(list[1], env) unless catch_head.str == "catch*"
-
-          begin
-            eval(list[1], env)
-          rescue e : Crisp::RuntimeException
-            new_env = Crisp::Env.new(env, [catch_list[1]], [e.thrown])
-            eval(catch_list[2], new_env)
-          rescue e
-            new_env = Crisp::Env.new(env, [catch_list[1]], [Crisp::Type.new e.message])
-            eval(catch_list[2], new_env)
-          end
-        else
-          invoke_list(list, env)
-        end
-    end
-  end
-
-  def print(result)
-    pr_str(result, true)
-  end
-
-  def rep(str)
-    print(eval(read(str), $repl_env))
-  end
-
-  class ProgramState
-    def rep(str)
-      print(eval(read(str), @env))
-    end
-
-    def initialize(args)
-      @env = Crisp::Env.new nil
-
-      Crisp::NameSpace.each{|k,v| @curent_env.set(k, Crisp::Type.new(v))}
-
-      @env.set("eval", Crisp::Type.new -> (args: Array(Crisp::Type)){ Crisp.eval(args[0], @env) })
-
-      rep "(def! not (fn* (a) (if a false true)))"
-      rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
-      rep "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"
-      rep "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
-      rep "(def! *host-language* \"crystal\")"
-
-      argv = Crisp::List.new
-
-      if args
-        args.each do |a|
-          argv << Crisp::Type.new a
-        end
-      end
-
-      @env.set("*ARGV*", Crisp::Type.new argv)
-    end
-  end
-
-  class Interpreter
-    def initialize(args)
-      @state = ProgramState.new args
-    end
-
-    def run(filename = nil)
-      if filename
-        begin
-          Crisp.rep "(load-file \"#{filename}\")"
-        rescue e
-          STDERR.puts e
-          exit 1
-        end
-
-        exit
-      end
-
-      while line = Readline.readline("Crisp> ", true)
-        begin
-          puts @state.rep(line)
-        rescue e
-          STDERR.puts e
-        end
-      end
-    end
-  end
-end
-
+require "./**"
diff --git a/src/core.cr b/src/crisp/core.cr
similarity index 100%
rename from src/core.cr
rename to src/crisp/core.cr
diff --git a/src/env.cr b/src/crisp/env.cr
similarity index 100%
rename from src/env.cr
rename to src/crisp/env.cr
diff --git a/src/error.cr b/src/crisp/error.cr
similarity index 100%
rename from src/error.cr
rename to src/crisp/error.cr
diff --git a/src/crisp/interpreter.cr b/src/crisp/interpreter.cr
new file mode 100644
index 0000000..1df9418
--- /dev/null
+++ b/src/crisp/interpreter.cr
@@ -0,0 +1,285 @@
+require "colorize"
+require "readline"
+
+require "./reader"
+require "./printer"
+require "./types"
+require "./env"
+require "./core"
+require "./error"
+
+# Note:
+# Employed downcase names because Crystal prohibits uppercase names for methods
+
+module Crisp
+
+  class Interpreter
+    def initialize(args)
+      @env = Crisp::Env.new nil
+
+      Crisp::NameSpace.each{|k,v| @curent_env.set(k, Crisp::Type.new(v))}
+      @env.set("eval", Crisp::Type.new -> (args: Array(Crisp::Type)){ eval(args[0], @env) })
+
+      rep "(def! not (fn* (a) (if a false true)))"
+      rep "(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))"
+      rep "(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))"
+      rep "(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))"
+      rep "(def! *host-language* \"crystal\")"
+
+      argv = Crisp::List.new
+
+      if args
+        args.each do |a|
+          argv << Crisp::Type.new a
+        end
+      end
+
+      @env.set("*ARGV*", Crisp::Type.new argv)
+    end
+
+    def func_of(env, binds, body)
+        -> (args : Array(Crisp::Type)) {
+        new_env = Crisp::Env.new(env, binds, args)
+        eval(body, new_env)
+        } as Crisp::Func
+    end
+
+    def eval_ast(ast, env)
+        return ast.map{|n| eval(n, env) as Crisp::Type} if ast.is_a? Array
+
+        val = ast.unwrap
+
+        Crisp::Type.new case val
+        when Crisp::Symbol
+        if e = env.get(val.str)
+            e
+        else
+            eval_error "'#{val.str}' not found"
+        end
+        when Crisp::List
+        val.each_with_object(Crisp::List.new){|n, l| l << eval(n, env)}
+        when Crisp::Vector
+        val.each_with_object(Crisp::Vector.new){|n, l| l << eval(n, env)}
+        when Crisp::HashMap
+        new_map = Crisp::HashMap.new
+        val.each{|k, v| new_map[k] = eval(v, env)}
+        new_map
+        else
+        val
+        end
+    end
+
+    def read(str)
+        read_str str
+    end
+
+    macro pair?(list)
+        {{list}}.is_a?(Array) && !{{list}}.empty?
+    end
+
+    def quasiquote(ast)
+        list = ast.unwrap
+
+        unless pair?(list)
+        return Crisp::Type.new(
+            Crisp::List.new << gen_type(Crisp::Symbol, "quote") << ast
+        )
+        end
+
+        head = list.first.unwrap
+
+        case
+        # ("unquote" ...)
+        when head.is_a?(Crisp::Symbol) && head.str == "unquote"
+        list[1]
+        # (("splice-unquote" ...) ...)
+        when pair?(head) && (arg0 = head.first.unwrap).is_a?(Crisp::Symbol) && arg0.str == "splice-unquote"
+        tail = Crisp::Type.new list[1..-1].to_crisp_value
+        Crisp::Type.new(
+            Crisp::List.new << gen_type(Crisp::Symbol, "concat") << head[1] << quasiquote(tail)
+        )
+        else
+        tail = Crisp::Type.new list[1..-1].to_crisp_value
+        Crisp::Type.new(
+            Crisp::List.new << gen_type(Crisp::Symbol, "cons") << quasiquote(list.first) << quasiquote(tail)
+        )
+        end
+    end
+
+    def macro_call?(ast, env)
+        list = ast.unwrap
+        return false unless list.is_a? Crisp::List
+        return false if list.empty?
+
+        sym = list.first.unwrap
+        return false unless sym.is_a? Crisp::Symbol
+
+        func = env.find(sym.str).try(&.data[sym.str])
+        return false unless func && func.macro?
+
+        true
+    end
+
+    def macroexpand(ast, env)
+        while macro_call?(ast, env)
+
+        # Already checked in macro_call?
+        list = ast.unwrap as Crisp::List
+        func_sym = list[0].unwrap as Crisp::Symbol
+        func = env.get(func_sym.str).unwrap
+
+        case func
+        when Crisp::Func
+            ast = func.call(list[1..-1])
+        when Crisp::Closure
+            ast = func.fn.call(list[1..-1])
+        else
+            eval_error "macro '#{func_sym.str}' must be function: #{ast}"
+        end
+        end
+
+        ast
+    end
+
+    macro invoke_list(l, env)
+        f = eval({{l}}.first, {{env}}).unwrap
+        args = eval_ast({{l}}[1..-1], {{env}}) as Array
+
+        case f
+        when Crisp::Closure
+        ast = f.ast
+        {{env}} = Crisp::Env.new(f.env, f.params, args)
+        next # TCO
+        when Crisp::Func
+        return f.call args
+        else
+        eval_error "expected function as the first argument: #{f}"
+        end
+    end
+
+    def debug(ast)
+        puts print(ast).colorize.red
+    end
+
+    def eval(ast, env)
+        # 'next' in 'do...end' has a bug in crystal 0.7.1
+        # https://github.com/manastech/crystal/issues/659
+        while true
+        return eval_ast(ast, env) unless ast.unwrap.is_a? Crisp::List
+
+        ast = macroexpand(ast, env)
+
+        list = ast.unwrap
+
+        return ast unless list.is_a? Crisp::List
+        return ast if list.empty?
+
+        head = list.first.unwrap
+
+        return invoke_list(list, env) unless head.is_a? Crisp::Symbol
+
+        return Crisp::Type.new case head.str
+            when "def!"
+            eval_error "wrong number of argument for 'def!'" unless list.size == 3
+            a1 = list[1].unwrap
+            eval_error "1st argument of 'def!' must be symbol: #{a1}" unless a1.is_a? Crisp::Symbol
+            env.set(a1.str, eval(list[2], env))
+            when "let*"
+            eval_error "wrong number of argument for 'def!'" unless list.size == 3
+
+            bindings = list[1].unwrap
+            eval_error "1st argument of 'let*' must be list or vector" unless bindings.is_a? Array
+            eval_error "size of binding list must be even" unless bindings.size.even?
+
+            new_env = Crisp::Env.new env
+            bindings.each_slice(2) do |binding|
+                key, value = binding
+                name = key.unwrap
+                eval_error "name of binding must be specified as symbol #{name}" unless name.is_a? Crisp::Symbol
+                new_env.set(name.str, eval(value, new_env))
+            end
+
+            ast, env = list[2], new_env
+            next # TCO
+            when "do"
+            if list.empty?
+                ast = Crisp::Type.new nil
+                next
+            end
+
+            eval_ast(list[1..-2].to_crisp_value, env)
+            ast = list.last
+            next # TCO
+            when "if"
+            ast = unless eval(list[1], env).unwrap
+                list.size >= 4 ? list[3] : Crisp::Type.new(nil)
+            else
+                list[2]
+            end
+            next # TCO
+            when "fn*"
+            params = list[1].unwrap
+            unless params.is_a? Array
+                eval_error "'fn*' parameters must be list or vector: #{params}"
+            end
+            Crisp::Closure.new(list[2], params, env, func_of(env, params, list[2]))
+            when "quote"
+            list[1]
+            when "quasiquote"
+            ast = quasiquote list[1]
+            next # TCO
+            when "defmacro!"
+            eval_error "wrong number of argument for 'defmacro!'" unless list.size == 3
+            a1 = list[1].unwrap
+            eval_error "1st argument of 'defmacro!' must be symbol: #{a1}" unless a1.is_a? Crisp::Symbol
+            env.set(a1.str, eval(list[2], env).tap{|n| n.is_macro = true})
+            when "macroexpand"
+            macroexpand(list[1], env)
+            when "try*"
+            catch_list = list[2].unwrap
+            return eval(list[1], env) unless catch_list.is_a? Crisp::List
+
+            catch_head = catch_list.first.unwrap
+            return eval(list[1], env) unless catch_head.is_a? Crisp::Symbol
+            return eval(list[1], env) unless catch_head.str == "catch*"
+
+            begin
+                eval(list[1], env)
+            rescue e : Crisp::RuntimeException
+                new_env = Crisp::Env.new(env, [catch_list[1]], [e.thrown])
+                eval(catch_list[2], new_env)
+            rescue e
+                new_env = Crisp::Env.new(env, [catch_list[1]], [Crisp::Type.new e.message])
+                eval(catch_list[2], new_env)
+            end
+            else
+            invoke_list(list, env)
+            end
+        end
+    end
+
+    def print(result)
+        pr_str(result, true)
+    end
+
+    private def rep(str)
+      print(eval(read(str), @env))
+    end
+
+    def run(filename = nil)
+      if filename
+        rep "(load-file \"#{filename}\")"
+        return
+      end
+
+      while line = Readline.readline("Crisp> ", true)
+        begin
+          puts rep(line)
+        rescue e
+          STDERR.puts e
+        end
+      end
+    end
+  end
+end
+
diff --git a/src/printer.cr b/src/crisp/printer.cr
similarity index 100%
rename from src/printer.cr
rename to src/crisp/printer.cr
diff --git a/src/reader.cr b/src/crisp/reader.cr
similarity index 100%
rename from src/reader.cr
rename to src/crisp/reader.cr
diff --git a/src/types.cr b/src/crisp/types.cr
similarity index 100%
rename from src/types.cr
rename to src/crisp/types.cr
diff --git a/src/main.cr b/src/main.cr
deleted file mode 100644
index 5f1dba7..0000000
--- a/src/main.cr
+++ /dev/null
@@ -1,7 +0,0 @@
-require "./crisp"
-
-if ARGV.empty?
-  Crisp::Interpreter.new.run
-else
-  Crisp::Interpreter.new(ARGV[1..-1]).run(ARGV.first)
-end