Configuring Emacs 27 for Common Lisp

custom.el

(custom-set-variables
 ;; custom-set-variables was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 '(package-selected-packages '(diff-hl magit treemacs project-explorer use-package))
 '(pe/cache-enabled nil)
 '(pe/inline-folders nil)
 '(pe/width 20)
 '(treemacs-python-executable "C:/Python310/python.exe"))
(custom-set-faces
 ;; custom-set-faces was added by Custom.
 ;; If you edit it by hand, you could mess it up, so be careful.
 ;; Your init file should contain only one such instance.
 ;; If there is more than one, they won't work right.
 )

init.el

;; Define the init file
(setq custom-file (expand-file-name "custom.el" user-emacs-directory))
(when (file-exists-p custom-file)
  (load custom-file))
(add-hook 'emacs-startup-hook 'toggle-frame-maximized)

;; Define and initialise package repositories
(require 'package)
(add-to-list 'package-archives '("melpa" . "https://melpa.org/packages/") t)
(package-initialize)

;; use-package to simplify the config file
(unless (package-installed-p 'use-package)
  (package-refresh-contents)
  (package-install 'use-package))
(require 'use-package)
(setq use-package-always-ensure 't)

(setq inhibit-startup-message t)
(tool-bar-mode -1)
(defalias 'yes-or-no-p 'y-or-n-p)

;; Customize EMACS to allow package search based on name
;; Taken from:
;; https://stackoverflow.com/questions/41204532/is-there-some-kind-of-package-search-function-available-for-emacs
;; USAGE: M-x apropose-package
(defun apropos-package--filter (string)
  (let (packages)
    (dolist (package-assoc package-archive-contents)
      (let ((package (cadr package-assoc)))
        (when (or (string-match-p (regexp-quote string) (package-desc-summary package))
                  (string-match-p (regexp-quote string) (prin1-to-string (package-desc-name package))))
          (push package packages))))
    packages))

(defun apropos-package (string)
  (interactive "sSearch for package: ")
  ;; Initialize the package system if necessary.
  (unless package--initialized
    (package-initialize t))
  (let ((packages (apropos-package--filter string)))
    (if (null packages)
    (message "No packages")
    (package-show-package-list (mapcar 'package-desc-name packages)))))
;; End package search function

(add-to-list 'custom-theme-load-path "~/.emacs.d/libs/theme/atom-one-dark-theme")
(load-theme 'atom-one-dark t)

;; This works nicely. It provides the parent, '..', directory unlike nav.
;;(use-package project-explorer
;;  :ensure t)
;;(project-explorer-open)
(use-package treemacs
  :ensure t)
(add-hook 'emacs-startup-hook 'treemacs)
(treemacs-git-mode 'deferred) ;; Enabling Treemacs to show Git status
;; Workaround to stop Treemacs from directory flattening
(with-eval-after-load 'treemacs
  (setf treemacs-collapse-dirs 0))

(add-hook 'shell-mode-hook 'ansi-color-for-comint-mode-on)

;; Integrating SLIME with EMACS for Common Lisp
(load (expand-file-name "~/quicklisp/slime-helper.el"))
(show-paren-mode 1)
(add-hook 'lisp-mode-hook (lambda () (slime-mode t)))
(add-hook 'inferior-lisp-mode-hook (lambda () (inferior-slime-mode t)))
;; Replace "sbcl" with the path to your implementation
(setq inferior-lisp-program "abcl")

;; For using Git with Magit
(use-package magit
  :ensure t)
(autoload 'magit-status "magit" nil t)
(use-package diff-hl
  :ensure t)
(add-hook 'magit-pre-refresh-hook 'diff-hl-magit-pre-refresh)
(add-hook 'magit-post-refresh-hook 'diff-hl-magit-post-refresh)