osceval

evaluate Emacs Lisp code received over OSC. useful for controlling Emacs externally, e.g. using hardware controllers. (i use it to manipulate TidalCycles patterns)

Caution

careless configuration of osceval is a security risk — it will open up your system to remote code execution attacks!

first, consider emacsclient

Emacs' built-in emacsclient can also be used to control Emacs externally:

emacsclient --eval '(message "hello")'

using osceval might be preferable when any of the following apply:

• the controlling program runs on a different machine than Emacs
• the latency overhead of starting the emacsclient process and connecting to the Emacs server is too large

installation

you will also need the osc package.

using straight.el:

(use-package osceval
  :straight (osceval :type git :host github :repo "ahihi/osceval"))

or manually: place osceval.el in your load-path, then run

(require 'osceval)

usage

to start osceval: M-x osceval-start

with default settings, you can now send an OSC message with address /eval, and a single string argument containing the code to evaluate, to 127.0.0.1:9473.

to stop osceval: M-x osceval-stop

configuration

osceval can be configured via the following configuration variables:

osceval-host

IP address on which to listen for OSC messages (default: 127.0.0.1).

osceval-port

Port on which to listen for OSC messages (default: 9473).

osceval-buffer

The name of the osceval process buffer (default: *osceval*).

osceval-handler

Handler function to run on incoming OSC messages (default: #'osceval-default-handler).

the default handler handles messages of the form /eval <code>, directly evaluating the given code.

in many cases, it is useful to evaluate code in an interactive context, in the currently active window's buffer. the following custom handler defines an additional /eval-in-window message which achieves this:

(defun pulu-osceval-handler (path &rest args)
  (pcase path
    ("/eval" (let ((code (nth 0 args)))
               (osceval-message "%s %s" path code)
               (eval (read code))))
    ("/eval-in-window" (let ((code (nth 0 args)))
                         (osceval-message "%s %s" path code)
                         (eval `(call-interactively
                                 (lambda ()
                                   (interactive)
                                   (with-current-buffer (window-buffer)
                                     ,(read code)
                                     (run-hooks 'post-command-hook)))))))
    (t nil)))
(setq osceval-handler #'pulu-osceval-handler)

(note: the function osceval-message is used to print messages in the osceval process buffer)

examples

these are written in SuperCollider.

start a Tidal pattern with a MIDI CC button

(using tidal.el and the custom osceval-handler)

(
~emacsOsceval = NetAddr("127.0.0.1", 9473);

MIDIdef.cc(\tidalRunD1, { |val|
    if(val > 0) {
        ~emacsOsceval.sendMsg("/eval-in-window", "(tidal-run-d1)");
    }
}, ccNum: 32, chan: 1);
)

insert MIDI note numbers with MIDI keyboard

(
~emacsOsceval = NetAddr("127.0.0.1", 9473);

MIDIdef.noteOn(\insertNote, { |val, num|
    if(val > 0) {
        ~emacsOsceval.sendMsg("/eval-in-window", "(progn (insert (number-to-string %)) (insert \" \"))" .format(num));
    }
}, chan: 0);
)