This is a mess

I'm sorry.  I really wanted to improve my commit discipline.  I know.  I can't
be fucked to comb this diff and split it into 8 properly-ordered commits, like I
know I should.  I'm not having a good time right now.  We'll do better moving
forward.

users/crumb/programs/emacs/lib/syd-handle-lookup.el

@@ -6,11 +6,59 @@
 
 (require 'better-jumper)
 
-(defvar syd-lookup-documentation-handlers '()
-  "An list of lookup handlers used to find documentation.  A lookup handler
+(defvar syd-lookup-online-documentation-backends
+  `(("Kagi" . "https://kagi.com/search?q=%s")
+    ("DuckDuckGo" . "https://duckduckgo.com/?q=%s")
+    ("Nixpkgs" . "https://search.nixos.org/packages?query=%s")
+    ("Hackage" . "https://hackage.haskell.org/packages/search?terms=%s"))
+  "A list of pairs (NAME . BACKEND) describing the various backends
+`syd-lookup-online-documentation' may delegate to.
+
+NAME is a string used when speaking to the user about BACKEND.
+
+If BACKEND is an interactive command, it will be called interactively.
+
+If BACKEND is a procedure, it will be called with the search string as the lone
+argument.
+
+If BACKEND is a string, the user's browser will be opened to the URL returned by
+(format BACKEND QUERY), where QUERY is the appropriately-encoded search
+string.")
+
+(defvar syd-lookup-documentation-handlers '(syd-lookup-online-documentation)
+  "A list of lookup handlers used to find documentation.  A lookup handler
 receives an identifier, and is expected to return nil on failure, and non-nil on
 success.  The specific return value is unused outside of the test for nil.")
 
+(defun syd-lookup--prompt-for-online-backend ()
+  (assoc-string
+   (completing-read "Search with: "
+                    (mapcar #'car syd-lookup-online-documentation-backends)
+                    nil
+                    t)
+   syd-lookup-online-documentation-backends))
+
+(cl-defun syd-lookup--call-online-backend (backend &key query-string)
+  (pcase-let ((`(,name . ,backend-fn) backend))
+    (cond ((functionp backend-fn) (if (commandp backend-fn)
+                                      (call-interactively backend-fn)
+                                    (funcall backend-fn query-string)))
+          ((stringp backend-fn)
+           (browse-url (format backend-fn
+                               (url-encode-url
+                                (read-string (format "Search for (on %s): "
+                                                     name)
+                                             query-string)))))
+          (t (signal 'wrong-type-argument `("backend" ,backend-fn))))))
+
+;;;###autoload
+(cl-defun syd-lookup-online-documentation (backend &key query-string)
+  (interactive (list (syd-lookup--prompt-for-online-backend)
+                     :query-string (when (use-region-p)
+                                     (syd-thing-at-point-or-region))))
+  (syd-lookup--call-online-backend (syd-lookup--prompt-for-online-backend)
+                                   :query-string query-string))
+
 ;;;###autoload
 (defun syd-lookup-documentation (identifier)
   "Try to find documentation on IDENTIFIER, and "
@@ -28,6 +76,8 @@ success.  The specific return value is unused outside of the test for nil.")
     (category identifier &key (display-fn #'switch-to-buffer))
   (let* ((handlers (alist-get category syd-lookup--handlers-by-category))
          (origin (point-marker))
+         ;; TODO: If called with a prefix argument, prompt the user to select a
+         ;; handler.
          (result (run-hook-wrapped handlers #'syd-lookup--run-handler
                                    identifier origin)))
     (message "result wrap hok: %S" result)