Quick Setup

(use-package evil-integrations
  :load-path "~/.emacs.d/fork/evil-integrations/"
  :ensure nil)

Strategy

For keymaps with not many keys bound, use the evil-define-key and supplement the keymap with original commands.

(defvar slime-popup-buffer-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "q") 'quit-window)
    ;;("\C-c\C-z" . slime-switch-to-output-buffer)
    (define-key map (kbd "M-.") 'slime-edit-definition)
    map))

(evil-define-key 'normal slime-popup-buffer-mode-map
  (kbd "q") 'quit-window
  (kbd "M-.") 'slime-edit-definition)

For keymaps that have an editing component to them, use evil-define-key.

(evil-add-hjkl-bindings ag-mode-map 'normal
  "gg" #'evil-goto-first-line
  "gr" #'recompile
  "gj" #'compilation-next-error
  "gk" #'compilation-previous-error
  "\C-j" #'compilation-next-error
  "\C-k" #'compilation-previous-error
  "0" #'evil-digit-argument-or-evil-beginning-of-line
  "n" #'evil-search-next
  "N" #'evil-search-previous)

For keymaps with many keys bound, use +evilify-map to use original keymap and then supplement them with additional evil keys.

(+evilify-map
 package-menu-mode-map
 :mode package-menu-mode
 "\C-h" #'help-command)