diff --git a/lib/lyp.rb b/lib/lyp.rb
index 3da76a2..5b3ea41 100644
--- a/lib/lyp.rb
+++ b/lib/lyp.rb
@@ -1,14 +1,23 @@
-def req(f); require File.expand_path("lyp/#{f}", File.dirname(__FILE__)) end
+def req_int(f)
+  require File.expand_path("lyp/#{f}", File.dirname(__FILE__))
+end
 
-req 'base'
-req 'system'
-req 'settings'
+module Kernel
+  @@ext_requires = {}
+  def req_ext(l)
+    @@ext_requires[l] ||= require(l)
+  end
+end 
 
-req 'template'
-req 'resolver'
-req 'wrapper'
-req 'package'
-req 'lilypond'
-req 'transform'
+req_int 'base'
+req_int 'system'
+req_int 'settings'
 
-req 'windows' if Lyp::WINDOWS
+req_int 'template'
+req_int 'resolver'
+req_int 'wrapper'
+req_int 'package'
+req_int 'lilypond'
+req_int 'transform'
+
+req_int 'windows' if Lyp::WINDOWS
diff --git a/lib/lyp/lilypond.rb b/lib/lyp/lilypond.rb
index 1c71206..9e1d773 100644
--- a/lib/lyp/lilypond.rb
+++ b/lib/lyp/lilypond.rb
@@ -1,7 +1,3 @@
-require 'uri'
-require 'open3'
-require 'ruby-progressbar'
-
 module Lyp::Lilypond
   class << self
     NO_ARGUMENT_OPTIONS_REGEXP = /^\-([REnFOcSA]+)(.+)/
@@ -208,10 +204,14 @@ def select_default_lilypond!
     end
 
     def get_session_settings
-      YAML.load(IO.read(session_settings_filename)) rescue {}
+      req_ext('yaml')
+      settings = YAML.load(IO.read(session_settings_filename)) rescue {}
+      settings = {} unless settings.is_a?(Hash)
+      settings
     end
 
     def set_session_settings(settings)
+      req_ext('yaml')
       File.open(session_settings_filename, 'w+') do |f|
         f << YAML.dump(settings)
       end
@@ -314,7 +314,7 @@ def get_system_lilyponds_paths
 
     # Returns a list of versions of lilyponds available for download
     def search(version_specifier = nil)
-      require 'open-uri'
+      req_ext 'open-uri'
 
       platform = detect_lilypond_platform
       url = "#{BASE_URL}/#{platform}/"
@@ -452,12 +452,14 @@ def lilypond_install_url(platform, version, opts)
     end
 
     def temp_install_filename(url)
+      req_ext('uri')
       u = URI(url)
       "#{Lyp::TMP_ROOT}/#{File.basename(u.path)}"
     end
 
     def download_lilypond(url, fn, opts)
-      require 'httpclient'
+      req_ext 'ruby-progressbar'
+      req_ext 'httpclient'
 
       STDERR.puts "Downloading #{url}" unless opts[:silent]
 
@@ -700,6 +702,7 @@ def uninstall_lilypond_version(path)
     end
 
     def exec(cmd, raise_on_failure = true)
+      req_ext('open3')
       $_out = ""
       $_err = ""
       success = nil
diff --git a/lib/lyp/package.rb b/lib/lyp/package.rb
index a37fe69..d34d874 100644
--- a/lib/lyp/package.rb
+++ b/lib/lyp/package.rb
@@ -1,7 +1,3 @@
-require 'fileutils'
-require 'open-uri'
-require 'yaml'
-
 module Lyp::Package
   class << self
 
@@ -371,6 +367,8 @@ def list_lyp_index(pattern = nil)
     end
 
     def lyp_index
+      req_ext 'yaml'
+      req_ext 'open-uri'
       @lyp_index ||= YAML.load(open(LYP_INDEX_URL))
     end
 
diff --git a/lib/lyp/settings.rb b/lib/lyp/settings.rb
index b83fd14..a4c4b0e 100644
--- a/lib/lyp/settings.rb
+++ b/lib/lyp/settings.rb
@@ -1,12 +1,12 @@
-require 'yaml'
-
 module Lyp::Settings
   class << self
     def load
+      req_ext 'yaml'
       @settings = YAML.load(IO.read(Lyp.settings_file)) rescue {}
     end
 
     def save
+      req_ext 'yaml'
       File.open(Lyp.settings_file, 'w+') {|f| f << YAML.dump(@settings)}
     end
 
@@ -33,11 +33,13 @@ def []=(path, value)
     end
 
     def get_value(path, default = nil)
+      req_ext 'yaml'
       v = self[path]
       v ? YAML.load(v) : default
     end
 
     def set_value(path, value)
+      req_ext 'yaml'
       self[path] = YAML.dump(value)
     end
   end
diff --git a/lib/lyp/system.rb b/lib/lyp/system.rb
index 64a3f74..248dfb8 100644
--- a/lib/lyp/system.rb
+++ b/lib/lyp/system.rb
@@ -1,5 +1,3 @@
-require 'fileutils'
-
 module Lyp::System
   class << self
     RUGGED_REQ = Lyp.version_req('>=0.23.0')
@@ -26,7 +24,7 @@ def find_rugged_gem
     
     def require_rugged_gem
       gem 'rugged', RUGGED_REQ.to_s
-      require 'rugged'
+      req_ext 'rugged'
     end
     
     def use_git_based_rugged_gem
diff --git a/lib/lyp/templates/deps_wrapper.rb b/lib/lyp/templates/deps_wrapper.rb
index a5900b7..0d5fe3f 100644
--- a/lib/lyp/templates/deps_wrapper.rb
+++ b/lib/lyp/templates/deps_wrapper.rb
@@ -13,8 +13,6 @@
 `
 end
 
-require 'fileutils'
-
 user_filename = File.expand_path(_[:user_file])
 user_dirname = File.dirname(user_filename)
 
diff --git a/lib/lyp/transform.rb b/lib/lyp/transform.rb
index 594a3ce..32f4a22 100644
--- a/lib/lyp/transform.rb
+++ b/lib/lyp/transform.rb
@@ -1,5 +1,3 @@
-require 'fileutils'
-
 module Lyp::Transform
   class << self
     R = Lyp::DependencyResolver
diff --git a/lib/lyp/wrapper.rb b/lib/lyp/wrapper.rb
index 43491e2..8da1da5 100644
--- a/lib/lyp/wrapper.rb
+++ b/lib/lyp/wrapper.rb
@@ -1,5 +1,3 @@
-require 'tempfile'
-
 module Lyp
   WRAPPER_TEMPLATE = Lyp::Template.new(IO.read(
     File.expand_path('templates/deps_wrapper.rb', File.dirname(__FILE__))