Dylan Language Server#

This is an implementation of the Language Server Protocol for Dylan.

Current Status#

As of 2024-04-19, the server implements

  • Jump to declaration

  • Jump to definition

  • Diagnostics (i.e., compiler warnings)

  • Hover (i.e., argument lists)

When applied to a symbol which is bound to a generic function, “jump to definition” will show a list containing the generic function and its specific methods, whereas “jump to declaration” will jump straight to the generic function.


  1. First install Open Dylan 2023.1 or newer.

  2. Clone the lsp-dylan repository:

    $ git clone --recursive https://github.com/dylan-lang/lsp-dylan
  3. Update the workspace so that dependencies are installed and the registry is created:

    $ cd lsp-dylan
    $ dylan update
  4. Build the dylan-lsp-server binary. This will install the binary in ${DYLAN}/bin. If DYLAN is not defined it defaults to ${HOME}/dylan.

    $ make install

    or just run these commands:

    $ dylan build --unify dylan-lsp-server
    $ cp _build/sbin/dylan-lsp-server /usr/local/bin/
  5. Make sure dylan-lsp-server is on your PATH.


The LSP server needs to be able to open a project (that is, a Dylan library) associated with the file you’re editing when you turn on LSP in your editor. It assumes you are using a dylan-tool workspace and searches for a project to open as follows:

  1. If there is a workspace.json file and that file has a “default-library” property, the specified library is opened.

  2. It uses the dylan tool to choose a library defined in the workspace. This is generally the test suite library, if one exists; otherwise it chooses a project arbitrarily.

Normally you shouldn’t need to set any environment variables; everything is derived from the full pathname to the dylan-compiler executable, which must be on your PATH.

When you open each new file in your editor the LSP client may try to start a new project if the file isn’t part of the same dylan workspace directory. If you want the client to use just one project, use a multi-package workspace.


Always run dylan update and dylan build -a in your workspace before starting the LSP server, or dylan-lsp-server may not be able to open your project. (This requirement will be removed in a future release.)

Emacs Usage#

  1. Make sure the dylan-lsp-server executable is on your PATH, or customize the lsp-dylan-exe-pathname elisp variable. See below for more on customization.

  2. Install lsp-mode and dylan-mode. Both of these are available from MELPA.

  3. When you jump to another .dylan file, that file does not automatically have LSP enabled so you must use M-x lsp again. To make this automatic, add this to your emacs init file:

    (add-hook 'dylan-mode-hook 'lsp)
  4. Start emacs and make sure that lsp-dylan.el is loaded. For example:

    emacs --load=/path/to/lsp-dylan/lsp-dylan.el

    You will probably want to modify your Emacs init file to load the file with

    (load "/path/to/lsp-dylan/lsp-dylan.el")
  5. Open a Dylan source file and type M-x lsp to start the client (unless you added the hook above, in which case it started automatically).

The client starts the LSP server (the dylan-lsp-server executable) and connects to it. You should see a message telling you what Dylan project was opened.

The emacs client has a customization group “lsp-dylan” which is a member of the “Language Server (lsp-mode)” group, and has the following variables:

  • lsp-dylan-exe-pathname

  • lsp-dylan-extra-command-line-options

  • lsp-dylan-log-pathname

  • lsp-dylan-open-dylan-release

These are documented in the customization interface within emacs. Use M-x customize-group lsp-dylan to customize these variables.


Emacs lsp-mode saves state in ~/.emacs.d/.lsp-session-v1. If you have a problem with Dylan’s LSP support it’s a good idea to delete this file and try again.

Visual Studio Code Usage#

These instructions were tested on Linux and macOS.

  1. Install Visual Studio Code and npm.

  2. The VS Code extension is in the folder vscode-dylan. It is necessary to run npm install in this folder before starting the extension for the first time, and any time a git pull updates the dependencies.

  3. Open the vscode-dylan folder in VS Code.

  4. In the debug viewlet, click the green play arrow (Launch Extension) or press F5.

  5. A build process will begin in ‘watch mode’; whenever the source is changed, the extension will be rebuilt. It is possible to debug the VS Code extension in this window, set breakpoints, watch variables and so on.

  6. A new VS Code window will open with the extension running.

  7. Open a folder with a Dylan project in it.

  8. If dylan-lsp-server is on the system path, it will be found. Otherwise, open the Settings in the new extension window, find the Dylan section under Extensions, and edit the path to the LSP server. The full, absolute pathname to the executable needs to be specified. It is usually better to set this in the ‘User’ scope, otherwise it will only apply to that particular project.

  9. It should now be possible to use the extension window to edit Dylan code using LSP.

  10. If the VS Code extension is changed, it is necessary to restart the extension host, or just close and re-open the extension window.

LSP Server Development#

This section contains notes for people interested in helping to improve LSP support for Dylan.

Open Dylan#

Unless you’re an Open Dylan expert already, you’ll probably find that you want to add debug statements in the Open Dylan IDE code to figure out what’s going on….

  1. Turn on the --debug-opendylan by customizing lsp-dylan-extra-command-line-options. This causes extra in the *lsp-dylan::stderr* buffer from calls to the debug-out macro.

  2. Create a multi-package workspace with both the lsp-dylan repo and the opendylan repo:

    $ mkdir lsp; cd lsp
    $ git clone --recursive https://github.com/dylan-lang/lsp-dylan
    $ git clone --recursive https://github.com/dylan-lang/opendylan
    $ echo '{ "default-library": "dylan-lsp-server" }' > workspace.json
  3. Sprinkle calls like debug-out(#"lsp", "your message here", ...) around in the Open Dylan code as needed.

  4. Remember to delete ~/.emacs.d/.lsp-session-v1` as needed. I (cgay) usually start a new emacs after rebuilding :program:dylan-lsp-server, like this:

    $ rm -f ~/.emacs.d/.lsp-session-v1; emacs &

    If you don’t start a new emacs, you probably want to at least kill the old dylan-lsp-server process. I (cgay) usually rebuild like this:

    $ pkill -f bin/dylan-lsp-server; make install


  • Intro to LSP from Microsoft - Besides being a quick introduction, this has links to some other tools that would help in developing VS Code integration for Dylan.

  • LSP v3.15 Specification - This is the version we are currently coding to.

  • langserver.org lists LSP implementations that support at least one of the six major LSP features.