diff --git a/Makefile b/Makefile
index e1b1009..b82ba64 100644
--- a/Makefile
+++ b/Makefile
@@ -55,3 +55,8 @@ install-fonts:
 .PHONY: compile
 compile:
 	@$(PWD)/fg42-new --script scripts/compiler.el
+
+.PHONY: clean
+clean:
+	@rm -rf $(shell find `pwd` -iname "*~")
+	@rm -rf $(shell find `pwd`/core -iname "*.elc")
diff --git a/core/fg42/extensions.el b/core/fg42/extensions.el
index 9710ad4..c8faea6 100644
--- a/core/fg42/extensions.el
+++ b/core/fg42/extensions.el
@@ -43,14 +43,14 @@ and call the `on-initialize'function of extensions in order to setup
 the autoloads and hooks."
   (cond
    ((symbolp ext)
-    (fg42-extensions/load-index system ext (fg42-extension/path system ext)))
+    (fg42-extensions/load-index system ext (fg42-extensions/path system ext)))
 
    ((listp ext)
     (fg42-extensions/load-index system (car ext) (cadr ext)))
    (t
     ;; TODO: instead of throwing and error, inject the error into the system
     (throw 'load-extension-failed
-           (format "Can't load extension %s" (str ext))))))
+           (format "Can't load extension %s" (->str ext))))))
 
 
 (defun fg42-extensions/load-system-extensions (system)
@@ -75,7 +75,7 @@ containing the `fg42-extension' instances."
 
 (defun fg42-extensions/initialize-extensions (system)
   "Initialize the extensions within SYSTEM and return a new system."
-  (mapcar
+  (mapc
    (lambda (ext) (fg42-extensions/initialize system ext))
    (fg42-system-extensions system))
   system)
diff --git a/core/fg42/extensions/core.el b/core/fg42/extensions/core.el
index 329d0b6..6a5a530 100644
--- a/core/fg42/extensions/core.el
+++ b/core/fg42/extensions/core.el
@@ -59,18 +59,18 @@
   ;; TODO: should we extract variables such as `fg42-home' to their
   ;;       dedicated ns in order to avoid the warning ?
   (let ((ext-name (symbol-name ext)))
-    (concat (fg42-system-root)
+    (concat (fg42-system-root system)
             "/extensions/" ext-name  "/" ext-name ".el")))
 
 
-(defun fg42-extension/path (system ext)
+(defun fg42-extensions/path (system ext)
   "Return the path to the given extension EXT in the given SYSTEM."
   (cond
-   ((symbolp ext) (fg42-extension/build-path system ext))
+   ((symbolp ext) (fg42-extensions/build-path system ext))
    ((fg42-extension-p ext)
     (or (fg42-extension-path ext)
-        (fg42-extension/build-path system
-                                   (intern (fg42-extension-name ext)))))))
+        (fg42-extensions/build-path system
+                                    (intern (fg42-extension-name ext)))))))
 
 
 (defmacro defextension (name docstring &rest args)
diff --git a/core/fg42/system.el b/core/fg42/system.el
index a1e8ae9..ac87e53 100644
--- a/core/fg42/system.el
+++ b/core/fg42/system.el
@@ -28,7 +28,7 @@
 ;;;###autoload
 (defun fg42-system/start ()
   "Start the system from `fg42-get-current-system'."
-  (require 'fg42/utils))
+  (require 'fg42/utils)
   (require 'fg42/system/core)
   (require 'fg42/system/utils)
 
@@ -37,25 +37,5 @@
     (funcall (fg42-system-start sys) sys)))
 
 
-(comment
-  (macroexpand-1 '(defsystem testsystem
-                    "docstring"
-                    :preloads '(2 43 4)
-                    :packages '(('elisp-extension :version "1.3.3"))
-                    :abilities '()))
-  (defsystem testsystem
-    "docstring1"
-    :packages '(('elisp-extension :version "1.3.3"))
-    :abilities '())
-
-  (make-fg42-system :name "asd" :preloads '(213 452) :abilities '(x y))
-  (aset testsystem 2 "sam")
-  (setf (fg42-system-abilities testsystem) '(3 3 3 3 3))
-  (fg42-set-current-system! testsystem)
-  (fg42-system-preloads testsystem)
-  (start-system)
-  (fg42-system-start testsystem))
-
-
 (provide 'fg42/system)
 ;;; system.el ends here
diff --git a/core/fg42/utils.el b/core/fg42/utils.el
index 49a4cee..ebbe37c 100644
--- a/core/fg42/utils.el
+++ b/core/fg42/utils.el
@@ -24,9 +24,13 @@
 ;; Each system has to have a `start' function to start the setup process.
 ;;
 ;;; Code:
+
 (require 'cl-lib)
 
-;;; Buffer helpers ------------------------------------------------------------
+(autoload 'seq-partition "seq")
+(autoload 'cl-reduce "cl-seq")
+
+
 (defun buffer-mode (buffer-or-string)
   "Return the major mode associated with a the given BUFFER-OR-STRING."
   (with-current-buffer buffer-or-string
@@ -46,6 +50,11 @@ with is the buffer."
         (funcall fn buf)))))
 
 
+(defun ->str (&rest args)
+  "Convert the given ARGS into string."
+  (funcall #'pp-to-string args))
+
+
 (defmacro inspect-expression (&rest body)
   "Pretty prints the result of the given BODY."
   `(pp-display-expression ,@body (get-buffer-create fg42/inspect-buffer)))
@@ -68,7 +77,7 @@ with is the buffer."
   (put-text-property 0 (length text) 'face face-symbol text))
 
 
-(defmacro comment (&rest body)
+(defmacro comment (&rest _body)
   "A macro similar to Clojure's comment macro that ignore the BODY."
   (declare (indent 0))
   `nil)
@@ -106,9 +115,9 @@ For example:
 or
  (funcall (compose #'some-fn #'message) some-value)"
   (lambda (&rest values)
-    (reduce 'funcall (butlast fns)
-            :from-end t
-            :initial-value (apply (car (last fns)) values))))
+    (cl-reduce 'funcall (butlast fns)
+               :from-end t
+               :initial-value (apply (car (last fns)) values))))
 
 
 (provide 'fg42/utils)