Fix & document set-pretty-symbols!

modules/ui/pretty-code/autoload/settings.el

@@ -40,21 +40,50 @@ universal way of getting the correct symbol as that area varies from font to
 font.")
 
 ;;;###autoload
-(defvar +pretty-code-symbols-alist nil
+(defvar +pretty-code-symbols-alist '((t))
   "An alist containing a mapping of major modes to its value for
 `prettify-symbols-alist'.")
 
-
-;;;###autoload
+;;;###autodef
 (defun set-pretty-symbols! (modes &rest rest)
+  "Associates string patterns with icons in certain major-modes.
+
+  MODES is a major mode symbol or a list of them.
+  PLIST is a property list whose keys must match keys in `+pretty-code-symbols',
+and whose values are strings representing the text to be replaced with that
+symbol. If the car of PLIST is nil, then unset any pretty symbols previously
+defined for MODES.
+
+The following properties are special:
+
+  :alist ALIST
+    Appends ALIST to `prettify-symbols-alist' literally, without mapping text to
+    `+pretty-code-symbols'.
+  :merge BOOL
+    If non-nil, merge with previously defined `prettify-symbols-alist',
+    otherwise overwrite it.
+
+For example, the rule for emacs-lisp-mode is very simple:
+
+  (set-pretty-symbols! 'emacs-lisp-mode
+    :lambda \"lambda\")
+
+This will replace any instances of \"lambda\" in emacs-lisp-mode with the symbol
+assicated with :lambda in `+pretty-code-symbols'.
+
+Pretty symbols can be unset for emacs-lisp-mode with:
+
+  (set-pretty-symbols! 'emacs-lisp-mode nil)"
+  (declare (indent defun))
   (dolist (mode (doom-enlist modes))
     (if (null (car-safe rest))
-        (setq var nil)
+        (delq (assq mode +pretty-code-symbols-alist)
+              +pretty-code-symbols-alist)
       (let (results merge key alist)
         (while rest
           (setq key (pop rest))
           (pcase key
-            (:merge (setq merge t))
+            (:merge (setq merge (pop rest)))
             (:alist (setq results (append (pop rest) results)))
             (_
              (unless (plist-member +pretty-code-symbols key)
@@ -63,5 +92,6 @@ font.")
                     (char (plist-get +pretty-code-symbols key)))
                (push (cons sym char) results)))))
         (unless merge
-          (assq-delete-all mode +pretty-code-symbols-alist))
+          (delq (assq mode +pretty-code-symbols-alist)
+                +pretty-code-symbols-alist))
         (push (cons mode results) +pretty-code-symbols-alist)))))