Editing Chrome Textareas with Edwin


In this post, I’ll describe how to edit Chrome textareas with the Edwin text editor that comes built-in with MIT/GNU Scheme.

If you just want to see the end result, see the screenshot and video at the end of this post.

These instructions will also work with recent releases of the Opera browser (since the newer Chromium-based versions can run Chrome plugins). They may also work at some point with Firefox, when Mozilla implements the new WebExtensions API.

At a high level, the steps to edit Chrome textareas with Edwin are:

  1. Install a browser add-on
  2. Customize Edwin with a few hacks
  3. Write a shell script to make it easy to launch Edwin from the command line
  4. Run a local “edit server” that interacts with the browser add-on and launches Edwin

On This Page

Install the ‘Edit with Emacs’ add-on

Install the Edit with Emacs add-on from the Chrome Web Store.

Load some Edwin hacks

The default way to open Edwin is to run

$ mit-scheme --edit

This just launches an Edwin editor window. From there, you need to manually open files and edit them.

What we need is a way to launch Edwin and open a specific file automatically. Most editors you are familiar with already do this, e.g.,

$ vim /tmp/foo.txt
$ emacsclient /tmp/bar.txt

To be able to launch Edwin in this way, we need to hack a few procedures in the file editor.scm in the MIT/GNU Scheme source and load them from the Edwin init file. We’ll tackle each of these tasks separately below.

Hacking editor.scm

To get Edwin to open a file on startup, we need to tweak three procedures in editor.scm to accept and/or pass around filename arguments:

  • EDIT

Here’s the code; you can just paste it into a file somewhere. For the purposes of this post we’ll call it open-edwin-on-file.scm:

;;;; open-edwin-on-file.scm -- Rich's hacks to open Edwin on a specific file.

;;; These (minor) changes are all to the file `editor.scm'. They are
;;; all that is needed to allow Edwin to be opened on a specific file
;;; by adding a `filename' argument to the EDIT procedure.

(define (create-editor file . args)
  (let ((args
     (if (null? args)
           (set! create-editor-args args)
        (filename (if (file-exists? file)
    (event-distributor/invoke! editor-initializations)
    (set! edwin-editor
      (make-editor "Edwin"
               (let ((name (and (not (null? args)) (car args))))
             (if name
                 (let ((type (name->display-type name)))
                   (if (not type)
                   (error "Unknown display type name:" name))
                   (if (not (display-type/available? type))
                   (error "Requested display type unavailable:"
                 (default-display-type '())))
               (if (null? args) '() (cdr args))))
    (set! edwin-initialization
      (lambda ()
        (set! edwin-initialization #f)
        (if filename
                (standard-editor-initialization filename)
    (set! edwin-continuation #f)

(define (standard-editor-initialization #!optional filename)
   (lambda ()
     (if (and (not init-file-loaded?)
          (not inhibit-editor-init-file?))
       (let ((filename (os/init-file-name)))
         (if (file-exists? filename)
         (load-edwin-file filename '(EDWIN) #t)))
       (set! init-file-loaded? #t)
  (let ((buffer (find-buffer initial-buffer-name))
        (filename (if (not (default-object? filename))
                      ((ref-command find-file) filename)
    (if (and buffer
         (not inhibit-initial-inferior-repl?))
     (and (not (ref-variable inhibit-startup-message))
        (lambda (port)
          (identify-world port)
          (newline port)))
        "You are in an interaction window of the Edwin editor."
                "Type `C-h' for help, or `C-h t' for a tutorial."
                "`C-h m' will describe some commands."
                "`C-h' means: hold down the Ctrl key and type `h'.")))))))

(define (edit file . args)
   (lambda (continuation)
     (cond (within-editor?
        (error "edwin: Editor already running"))
       ((not edwin-editor)
        (apply create-editor file args))
       ((not (null? args))
        (error "edwin: Arguments ignored when re-entering editor" args))
        => (lambda (restart)
         (set! edwin-continuation #f)
         (within-continuation restart
           (lambda ()
             (set! editor-abort continuation)
     (fluid-let ((editor-abort continuation)
         (current-editor edwin-editor)
         (within-editor? #t)
         (editor-thread (current-thread))
         (editor-initial-threads '())
         (inferior-thread-changes? #f)
         (inferior-threads '())
         (recursive-edit-continuation #f)
         (recursive-edit-level 0))
       (editor-grab-display edwin-editor
     (lambda (with-editor-ungrabbed operations)
       (let ((message (cmdl-message/null)))
           (lambda (cmdl)
         cmdl       ;ignore
         (bind-condition-handler (list condition-type:error)
           (lambda ()
              (lambda (root-continuation)
            (set! editor-thread-root-continuation
            (with-notification-output-port null-output-port
              (lambda ()
                (do ((thunks (let ((thunks editor-initial-threads))
                       (set! editor-initial-threads '())
                     (cdr thunks)))
                ((null? thunks))
                  (create-thread root-continuation (car thunks)))
           `((START-CHILD ,(editor-start-child-cmdl with-editor-ungrabbed))
         (CHILD-PORT ,(editor-child-cmdl-port (nearest-cmdl/port)))

Update your Edwin init file

Then, you’ll need to tweak your Edwin init file (also known as ~/.edwin) to load this file into Edwin’s environment on startup:

(load "/path/to/open-edwin-on-file.scm" '(edwin))

Write a shell script to make it easier launch Edwin from the command line

Now that the EDIT procedure takes a filename argument, we can wrap this all up in a shell script that calls Edwin with the right arguments. There may be other ways to accomplish this than in the code shown below, but it works.

Note that the path to my local installation of MIT/GNU Scheme on Mac OS X is slightly tweaked from the official install location. What’s important is that Scheme is invoked using the right “band”, or image file. For more information, see the fine manual.

Take the code below and stick it somewhere on your $PATH; on my machine it lives at ~/bin/edwin.

#!/usr/bin/env sh


if [[ $(uname) == 'Darwin' ]]; then

if [[ $(uname) == 'Linux' ]]; then


touch $F
echo $SCHEME_CODE > $F

$CMD --load $F

Install an edit server

Although the extension is called ‘Edit with Emacs’, it can be used with any text editor. You just need to be able to run a local “edit server” that generates the right inputs and outputs. Since Chrome extensions can’t launch apps directly, the extension running in the browser needs to act as a client to a locally running server, which will launch the app.

Since we want to launch Edwin, we’ll need to run a local edit server. Here’s the one that I use:


To get the server to launch Edwin, I save the gist somewhere as editserver.psgi and run the following script (for more information on the environment variables and what they mean, see the comments in the gist):

#!/usr/bin/env sh
EDITSERVER_CMD='edwin %s' \
screen -d -m `which plackup` -s Starman -p 9292 -a ~/Code/mathoms/editserver.psgi

The relevant bit for running Edwin is the EDITSERVER_CMD environment variable, which we’ve set to run the edwin script shown above.

Note that this server is written in Perl and requires you to install the Starman and Plack modules. If you don’t like Perl or don’t know how to install Perl modules, there are other servers out there that should work for you, such as this one written in Python.

Edit text!

Once you’ve done everything above and gotten it working together, you should be able to click the “edit” button next to your browser textarea and start Edwin. It will look something like the following screenshot (which you saw at the beginning of this post):


If you prefer video, check out this short demo on YouTube.

Edwin `dired-do-shell-command’ on files

Evaluate this code in your Edwin REPL and you’re one step closer to being able to use Edwin as your primary file manager. I’ve reimplemented the Emacs `dired-do-shell-command’ function as an Edwin command (note that it puts these definitions in the `edwin dired’ environment’):

(ge '(edwin dired))

(define (string-join xs)
  (list->string (concatenate
    (map (lambda (s) (string->list s)) xs))))

(define (shell-command-prompt prompt)
  (prompt-for-string prompt #f
                            'DEFAULT-TYPE 'INSERTED-DEFAULT
                            'HISTORY 'SHELL-COMMAND))

(define (pathname->string pathname)
  (uri->string (pathname->uri pathname)))

(define-command dired-do-shell-command
  "Run a shell command on the file or directory at the current point."
  (lambda ()
    (list (shell-command-prompt "Shell command on file: ")
  (lambda (command pathname)
    ((ref-command shell-command)
      (list command " "
            (pathname->string (dired-current-pathname)) " &")) #f)))

(define-key 'dired #\! 'dired-do-shell-command)

Reading Email from Edwin/Imail

After much consternation, poring over of manuals, and scouring of the Interwebs for a decent, working `stunnel.conf’, I am finally able to read my mail from Edwin. And yes, it is amazing.

I think it’s probably time for me to make some documentation contributions to MIT Scheme and stunnel both.

Call it one more stumbling block overcome on the road to “Full Edwin”.

For the record, here are a few things to note when setting up Edwin’s IMail program:

– Read the manual! It’s available in a lovely linked PDF at

– Don’t fiddle with the value of `imail-default-imap-server’. Instead, configure your `stunnel.conf’ as shown below.

– Even after reading the manual, you need to play around in IMail to learn how best to do things. (I’m still working on this, as I literally just got it set up this morning.)

Finally, here’s my working stunnel.conf:


debug = 7
output = /home/rml/stunnel.log


[IMAP (Gmail) Incoming]
client = yes
accept =
connect = imap.gmail.com:993

[SMTP (Gmail) Outgoing]
client = yes
accept =
connect = smtp.gmail.com:465

Onward, aspiring Scheme wizards!

(Now to figure out how to send!)

Edwin Support for External Schemes

I’m pleased to announce an alpha release of support for using Edwin to interact with external Schemes. This is similar to the way Emacs can interact with REPLs from languages other than Emacs Lisp.

The code is available at http://github.com/rmloveland/edwin-external-scheme. The repository contains two Edwin modes, “External Scheme mode” and “External Scheme REPL mode”.


“External Scheme REPL mode” allows you to interact with an external Scheme REPL’s process from Edwin in the same way you would interact with a shell using `#\M-x shell’. Load the file `external-scheme-repl.scm’ and enter the command `#\M-x external-scheme-repl’. You’ll be asked to enter the name of the external Scheme you’d like to run, and away you go.

External Scheme mode inherits from Edwin’s Scheme mode for all of its formatting and editing commands, but provides its own commands for sending expressions to a running external Scheme REPL, if one exists.

Load the file `external-scheme-mode.scm’ and enter the command `#\M-x external-scheme-mode’ in a buffer containing Scheme code that you want to send to the external Scheme. Right now you can run only one external Scheme REPL, so be sure that the code you’re sending is going to be understood by that Scheme. It’s a simple matter of programming to extend this to multiple external Scheme buffers if you care to.


Right now you may run only one external Scheme REPL at a time. Any Scheme buffers in External Scheme mode will send their eval’d code to that REPL.

Finally, note that files containing Scheme code are automatically opened by Edwin in its own Scheme mode, no matter what Scheme they’re written in, so you’ll need to do `#\M-x external-scheme-mode’.


Finally, why bother? Isn’t MIT Scheme good enough? The answer is yes: it’s great. However, I often write scripts using Scheme Shell due to its tight integration with UNIX and excellent process notation. I could already write these programs in Emacs, but Edwin is my preferred editor.