diff --git a/exe/referator b/exe/referator
index de270cd..3553108 100755
--- a/exe/referator
+++ b/exe/referator
@@ -31,70 +31,13 @@ workdir = ARGV.first
 workdir = Dir.pwd if String(workdir).strip.empty?
 workdir = File.expand_path(workdir).freeze
 
-config = Referator::Config.new workdir
-footnotes = Referator::Footnotes.new config
+machine = Referator::Machine.new workdir
 
 while (line = $stdin.gets)
   begin
     command = Referator::Command.parse line
-    case command.name
-    ##################
-    # Administrative #
-    ##################
-    when :exit
-      success
-      exit
-    when :ping
-      success :pong
-    ##########
-    # Config #
-    ##########
-    when :register_script
-      config.scripts.register(**command.data.transform_keys(&:to_sym))
-      success
-    when :register_category
-      config.categories.register command.data
-      success
-    when :register_format
-      config.formats.register(**command.data.transform_keys(&:to_sym))
-      success
-    when :register_ref
-      config.repo.register_ref(**command.data.transform_keys(&:to_sym))
-      success
-    ########
-    # Info #
-    ########
-    when :ref
-      config.freeze
-      success config.repo[command.data['category'],
-                          command.data['id']].to_h
-    ############
-    # Creation #
-    ############
-    when :make_ref
-      config.freeze
-      success footnotes.make_ref(command.data['category'],
-                                 command.data['id']).to_h
-    #############
-    # Rendering #
-    #############
-    when :fetch_footnotes
-      config.freeze
-      success footnotes.fetch_footnotes
-    when :fetch_note
-      config.freeze
-      success footnotes.fetch_note(command.data['category'],
-                                   command.data['id']).to_h
-    when :render_footnotes
-      config.freeze
-      success String footnotes.render_footnotes command.data
-    when :render_cite_sup
-      config.freeze
-      success String \
-        footnotes.render_cite_sup(**command.data.transform_keys(&:to_sym))
-    else
-      raise 'Invalid command'
-    end
+    result = machine.call command
+    success result
   rescue => e
     failure serialize_err e
   end
diff --git a/lib/referator.rb b/lib/referator.rb
index abd57f5..6ff1a36 100644
--- a/lib/referator.rb
+++ b/lib/referator.rb
@@ -12,6 +12,7 @@ require_relative 'referator/config/formats'
 require_relative 'referator/config/repo'
 require_relative 'referator/config/scripts'
 require_relative 'referator/footnotes'
+require_relative 'referator/machine'
 require_relative 'referator/note'
 require_relative 'referator/reference'
 require_relative 'referator/script'
diff --git a/lib/referator/machine.rb b/lib/referator/machine.rb
new file mode 100644
index 0000000..6f2dde1
--- /dev/null
+++ b/lib/referator/machine.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+module Referator
+  class Machine
+    attr_reader :workdir
+
+    def initialize(workdir)
+      self.workdir = workdir
+
+      @config = Config.new self.workdir
+      @footnotes = Footnotes.new @config
+    end
+
+    def call(command)
+      case command.name
+      ##################
+      # Administrative #
+      ##################
+      when :exit
+        exit
+      when :ping
+        :pong
+      ##########
+      # Config #
+      ##########
+      when :register_script
+        @config.scripts.register(**command.data.transform_keys(&:to_sym))
+        nil
+      when :register_category
+        @config.categories.register command.data
+        nil
+      when :register_format
+        @config.formats.register(**command.data.transform_keys(&:to_sym))
+        nil
+      when :register_ref
+        @config.repo.register_ref(**command.data.transform_keys(&:to_sym))
+        nil
+      ########
+      # Info #
+      ########
+      when :ref
+        @config.freeze
+        @config.repo[command.data['category'], command.data['id']].to_h
+      ############
+      # Creation #
+      ############
+      when :make_ref
+        @config.freeze
+        @footnotes.make_ref(command.data['category'], command.data['id']).to_h
+      #############
+      # Rendering #
+      #############
+      when :fetch_footnotes
+        @config.freeze
+        @footnotes.fetch_footnotes
+      when :fetch_note
+        @config.freeze
+        @footnotes.fetch_note(command.data['category'], command.data['id']).to_h
+      when :render_footnotes
+        @config.freeze
+        String @footnotes.render_footnotes command.data
+      when :render_cite_sup
+        @config.freeze
+        String \
+          @footnotes.render_cite_sup(**command.data.transform_keys(&:to_sym))
+      else
+        raise 'Invalid command'
+      end
+    end
+
+  private
+
+    def workdir=(workdir)
+      workdir = Pathname.new(workdir).expand_path.freeze
+      raise 'Expected absolute path' unless workdir.absolute?
+      raise 'Expected existing directory' unless workdir.directory?
+
+      @workdir = workdir
+    end
+  end
+end