Installing packages when needed

Question

I decided to create a portable Emacs config and install packages I use if it's necessary on a fresh computer.

Here is what I've done:

; loop through names of packages and install them if needed
(let ((packages '('use-package 'yasnippet 'expand-region 'bm 'undo-tree))
 (content-not-refreshed t)
 )
 (mapc
 (lambda (name)
 (unless (package-installed-p (eval name))
 (when content-not-refreshed
 (package-refresh-contents)
 (setq content-not-refreshed nil))
 (package-install (eval name))))
 packages
 ))
; load packages
(require 'use-package)
(require 'yasnippet)
(require 'expand-region)
(require 'bm)
(require 'undo-tree)

Is this code good? Can it be improved?

• mmmmmm: If you use use-package - then you don't need to list the other packages in this list - just use-package to load the packages
• Drew: emacs.stackexchange.com/tags/elisp/info
• user4035: @mmmmmm use-package won't install it from melpa if it's missing. And I think, we won't need use-package for this case: we know the package is installed.
• mmmmmm: @user4035 use-package does see the :ensure keyword in the manual jwiegley.github.io/use-package/keywords It even explicitl;y says " This is particularly useful if you share your .emacs among several machines; the relevant packages are downloaded automatically once declared in your .emacs. "

Answer 1

When quoting a list of symbols, it's redundant to quote each symbol within the list.

---

There's no need to eval a symbol.

---

This sequence looks strange:

(require 'use-package)
(require 'yasnippet)
(require 'expand-region)
(require 'bm)
(require 'undo-tree)

Since we're looping over those same names in the preceding loop, why not just (require name) as the last form within the lambda?

---

Addressing these issues gives somewhat improved code:

; loop through names of packages: install if needed, then load
(let ((packages '(use-package yasnippet expand-region bm undo-tree))
 (content-not-refreshed t)
 )
 (mapc
 (lambda (name)
 (unless (package-installed-p name)
 (when content-not-refreshed
 (package-refresh-contents)
 (setq content-not-refreshed nil))
 (package-install name))
 (require name))
 packages
 ))

---

Further improvement would maintain the list of packages as a customisable variable.