Prototype nrepl middleware for eval-in-emacs.

eval_in_emacs.clj

(ns org.kingtim.eval-in-emacs
  (:require
   [clojure.tools.nrepl.transport :as transport]
   [clojure.tools.nrepl.middleware :refer [set-descriptor!]]
   [clojure.tools.nrepl.middleware.session :refer [session]]
   [clojure.tools.nrepl.misc :refer [response-for]])
  (:import clojure.tools.nrepl.transport.Transport))

(def transports (atom {}))

(defn eval-in-emacs [form]
  (if-let [t (first @transports)]
    (do
      (clojure.tools.nrepl.transport/send (val t) {:eval form})
      true)))

(defn init-eval-in-emacs [{:keys [session transport] :as msg}]
  (let [id (-> session meta :id)]
    (swap! transports assoc id transport)
    (transport/send transport (response-for msg :status :done))))

(defn eval-result [{:keys [session transport] :as msg}]
  ;; TODO: not implemented yet
  (transport/send transport (response-for msg :status :done)))

(defn add-eval-in-emacs
  "eval-in-emacs middleware.  Returns a handler that supports eval-in-emacs."
  [h]
  (fn [{:keys [op] :as msg}]
    (cond
     (= op "init-eval")
       (init-eval-in-emacs msg)
     (= op "eval-result")
       (eval-result msg)
     :else
       (h msg))))

(set-descriptor! #'add-eval-in-emacs
  {:requires #{#'session}
   :handles {"init-eval" {:doc "Initialize eval in emacs"}
             "eval-result" {:doc "Result from eval (not implemented yet)"}}})

instructions

1. Use nrepl.el from "eval-in-emacs" branch published on github.
2. Build the above middleware add add it into your local repository.
3. Add the middleware into you project dependencies like so:
   ...
   :repl-options {:nrepl-middleware
                 [org.kingtim.eval-in-emacs/add-eval-in-emacs]}
  :profiles {:dev {:dependencies [[org.kingtim/eval-in-emacs "0.1.0-SNAPSHOT"]]}}
  ...
4. Connect up to your nrepl server using nrepl-jack-in or your preferred method.
   The server should now have the eval-in-emacs middleware.
   You can verify this by evalulating in emacs (nrepl-op-supported-p "init-eval").  Should return t.
4. From emacs connected to nrepl mode: M-x nrepl-init-eval-in-emacs
   This initializes the middleware with the correct transport for the current connection.  This was the best way I could find
   to get ahold of this with the current nrepl server.
5. Invoke (org.kingtim.eval-in-emacs/eval-in-emacs form) which will send the form to emacs to be evaled.
   e.g. (org.kingtim.eval-in-emacs/eval-in-emacs "(with-current-buffer nrepl-nrepl-buffer (insert \"hi\"))")

TODO:
- Should be controlled on the client side by a variable e.g. nrepl-enable-evaluate-in-emacs
- Need to complete round trip so that server side can get results of the eval.  I was thinking this could be modeled
  like the need-input/stdin interactions that currently exist in the nrepl server, with some kind of promise/future that
  that is fulfilled when the result is delivered.  Reference current eval in emacs implementation in swank-clojure and
  stdin handler in nrepl server.  Depends on your use cases.
- Possibly need synchronous version as well on the client side.  Again, not sure exactly what your use cases require.
- Would like a better way of getting a handle on the transport, but that may require changes to the core nrepl server.
  The other way I was able to do it was by getting a handle on the server and grabbing the transport from there, which
  I can provide an example of if you are interested.

Ah, nice thanks.

Is there a way to inject this from nrepl.el itself?

@samaaron Sorry, missed your comment.

I haven't found a good way to inject from nrepl.el yet.