Revised tools/install-packages.el (#469) (#470)

- The function exercism//install-required-packages now perform
installation only if at least one of thte required applications has
not be installed.

Author: borderite

tools/install-packages.el

@@ -1,14 +1,15 @@
+(require 'cl-extra)
 (defun exercism//install-required-packages ()
   (require 'package)
   (package-initialize)
-  (unless package-archive-contents
-    (add-to-list
-     'package-archives '("gnu" . "https://elpa.gnu.org/packages/")
-     t)
-    (add-to-list
-     'package-archives '("melpa" . "https://melpa.org/packages/")
-     t)
-    (package-refresh-contents))
-  (dolist (pkg '(mustache ht string-inflection))
-    (unless (package-installed-p pkg)
-      (package-install pkg))))
+  (let ((required-packages '(mustache ht string-inflection)))
+    (when (not (cl-every #'package-installed-p required-packages))
+      (add-to-list
+       'package-archives '("gnu" . "https://elpa.gnu.org/packages/")
+       t)
+      (add-to-list
+       'package-archives '("melpa" . "https://melpa.org/packages/")
+       t)
+      (package-refresh-contents)
+      (dolist (pkg required-packages)
+	(package-install pkg)))))