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A low-level client for the Swank server of SLIME.


swank-protocol is a small, low-level client for Swank. It handles connections and reading/writing messages.

This is not a full client for Swank, it's a permissively-licensed library for building Swank clients. It doesn't match requests to responses, it doesn't asynchronously read responses and events from Swank. It just takes care of the low level details: Connecting, sending messages down the socket, reading and parsing incoming events and responses, and optionally logging.


First, load everything:

(ql:quickload :swank-protocol)

Run this to start a Swank server on localhost:5000:

(setf swank:*configure-emacs-indentation* nil)

(let ((swank::*loopback-interface* (uiop:hostname)))
  (swank:create-server :port 5000 :dont-close t))

Now we connect:

(defparameter connection
  (swank-protocol-make-connection (uiop:hostname)

(swank-protocol:connect connection)

Now we can start sending requests:

(swank-protocol:request-connection-info connection)

And reading responses:

(swank-protocol:read-message connection)

For instance, let's create a REPL. First, we require some modules:

(swank-protocol:request-swank-require connection
                                      '(swank-presentations swank-repl))
(swank-protocol:request-init-presentations connection)

(Don't worry about the symbols' package)

Now we actually create it:

(swank-protocol:request-create-repl connection)

Now we can send things for evaluation:

(swank-protocol:request-listener-eval connection "(+ 2 2)")

And receive the results:

(swank-protocol:read-all-messages connection)



The connection class has the following readers:

  • connection-hostname: The Swank server's hostname.
  • connection-port: The Swank server's port.

And the following accessors:

  • connection-request-count: The integer ID of the last request sent to the Swank server. Starts at zero.
  • connection-package: The package where things are evaluated. This should be changed when you send a request to Swank to change the current package.
  • connection-thread: This is the keyword ID of the thread to execute things in. t is used by default to tell Swank to pick the default thread.
  • connection-log-p: Whether to log messages as they are read/written.
  • connection-logging-stream: The stream to log things to, by default, *error-output*.

Instances of connection can be created with make-connection:

;; A regular connection
(make-connection "my-hostname" "1234")

;; A connection with logging
(make-connection "my-test-server" "1234" :logp t)

The connect function connects to the Swank server and returns t.


After connecting, you can do two things: Send messages or read them.

To write messages, you can use emacs-rex, which takes a connection and an S-expression to send to Swank. Implicit in this request, and stored in the connection object, are two bits of information: The current package and the request ID.

To read messages, you use read-message, which takes a connection and reads the next message coming from Swank. The result is an S-expression.

High-level Functions

There are higher-level convenience functions that call emacs-rex, to minimize repetition and error:


Requests connection information. The matching response is a plist with connection information.

Example response:

    (:pid 1234
     :style :spawn
     :encoding (:coding-systems ("utf-8-unix" "iso-latin-1-unix"))
     :lisp-implementation (:type "SBCL" :name "sbcl" :version "1.2.9" :program "/usr/local/bin/sbcl")
     :machine (:instance "laptop" :type "X86-64" :version "Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz")
     :features (:bordeaux-threads ... :x86-64)
     :modules ("SWANK-REPL" ... "uiop")
     :package (:name "COMMON-LISP-USER" :prompt "CL-USER")
     :version "2014-12-23"))

See Also


Copyright (c) 2015 Fernando Borretti

Licensed under the MIT License.

Fernando Borretti <eudoxiahp@gmail.com>
Fernando Borretti <eudoxiahp@gmail.com>