diff --git a/language.rb b/language.rb
new file mode 100644
index 0000000..6072b85
--- /dev/null
+++ b/language.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+require './lib/core'
+require './lib/dictionary'
+require './lib/parser'
+require './lib/runner'
+
+module Rpl
+  class Language
+    attr_reader :stack
+
+    def initialize( stack = [] )
+      @stack = stack
+      @dictionary = Rpl::Lang::Dictionary.new
+      @parser = Rpl::Lang::Parser.new
+      @runner = Rpl::Lang::Runner.new
+    end
+
+    def run( input )
+      @stack, @dictionary = @runner.run_input( @parser.parse_input( input ),
+                                               @stack, @dictionary )
+    end
+  end
+end
diff --git a/lib/core.rb b/lib/core.rb
index 0fdf6e0..a22b1ee 100644
--- a/lib/core.rb
+++ b/lib/core.rb
@@ -1,14 +1,15 @@
 require 'bigdecimal/math'
 
-require_relative './language/branch'
-require_relative './language/general'
-require_relative './language/mode'
-require_relative './language/operations'
-require_relative './language/program'
-require_relative './language/stack'
-require_relative './language/string'
-require_relative './language/test'
-require_relative './language/time-date'
+require_relative './core/branch'
+require_relative './core/general'
+require_relative './core/mode'
+require_relative './core/operations'
+require_relative './core/program'
+require_relative './core/stack'
+require_relative './core/store'
+require_relative './core/string'
+require_relative './core/test'
+require_relative './core/time-date'
 
 module Rpl
   module Lang
diff --git a/lib/language/branch.rb b/lib/core/branch.rb
similarity index 100%
rename from lib/language/branch.rb
rename to lib/core/branch.rb
diff --git a/lib/language/general.rb b/lib/core/general.rb
similarity index 100%
rename from lib/language/general.rb
rename to lib/core/general.rb
diff --git a/lib/language/mode.rb b/lib/core/mode.rb
similarity index 100%
rename from lib/language/mode.rb
rename to lib/core/mode.rb
diff --git a/lib/language/operations.rb b/lib/core/operations.rb
similarity index 100%
rename from lib/language/operations.rb
rename to lib/core/operations.rb
diff --git a/lib/language/program.rb b/lib/core/program.rb
similarity index 78%
rename from lib/language/program.rb
rename to lib/core/program.rb
index 1aeeed9..7233f90 100644
--- a/lib/language/program.rb
+++ b/lib/core/program.rb
@@ -11,7 +11,8 @@ module Rpl
         preparsed_input = args[0][:type] == :word ? args[0][:value] : args[0][:value][1..-2]
         parsed_input = Rpl::Lang::Parser.new.parse_input( preparsed_input )
 
-        stack, _dictionary = Rpl::Lang::Runner.new.run_input( stack, dictionary, parsed_input )
+        stack, _dictionary = Rpl::Lang::Runner.new.run_input( parsed_input,
+                                                              stack, dictionary )
         # TODO: check that STO actually updates dictionary
 
         stack
diff --git a/lib/language/stack.rb b/lib/core/stack.rb
similarity index 100%
rename from lib/language/stack.rb
rename to lib/core/stack.rb
diff --git a/lib/language/string.rb b/lib/core/string.rb
similarity index 100%
rename from lib/language/string.rb
rename to lib/core/string.rb
diff --git a/lib/language/test.rb b/lib/core/test.rb
similarity index 100%
rename from lib/language/test.rb
rename to lib/core/test.rb
diff --git a/lib/language/time-date.rb b/lib/core/time-date.rb
similarity index 100%
rename from lib/language/time-date.rb
rename to lib/core/time-date.rb
diff --git a/lib/runner.rb b/lib/runner.rb
index 775931d..e083108 100644
--- a/lib/runner.rb
+++ b/lib/runner.rb
@@ -1,11 +1,11 @@
-# coding: utf-8
+# frozen_string_literal: true
 
 module Rpl
   module Lang
     class Runner
       def initialize; end
 
-      def run_input( stack, dictionary, input )
+      def run_input( input, stack, dictionary )
         input.each do |elt|
           case elt[:type]
           when :word
diff --git a/repl.rb b/repl.rb
index 81a35ea..02ebb47 100644
--- a/repl.rb
+++ b/repl.rb
@@ -3,28 +3,9 @@
 
 require 'readline'
 
-require './lib/core'
-require './lib/dictionary'
-require './lib/parser'
-require './lib/runner'
+require './language'
 
 module Rpl
-  class Language
-    attr_reader :stack
-
-    def initialize
-      @stack = []
-      @dictionary = Dictionary.new
-      @parser = Parser.new
-      @runner = Runner.new
-    end
-
-    def run( input )
-      @stack, @dictionary = @runner.run_input( @stack, @dictionary,
-                                               @parser.parse_input( input ) )
-    end
-  end
-
   class Repl
     def initialize
       @lang = Rpl::Language.new
@@ -47,8 +28,7 @@ module Rpl
         # Remove blank lines from history
         Readline::HISTORY.pop if input.empty?
 
-        @stack, @dictionary = @runner.run_input( @stack, @dictionary,
-                                                 @parser.parse_input( input ) )
+        @lang.run( input )
 
         print_stack
       end
@@ -73,9 +53,9 @@ module Rpl
     end
 
     def print_stack
-      stack_size = @stack.size
+      stack_size = @lang.stack.size
 
-      @stack.each_with_index do |elt, i|
+      @lang.stack.each_with_index do |elt, i|
         puts "#{stack_size - i}: #{format_element( elt )}"
       end
     end