Major mode for editing Mojo source code

It would be rather dull if Emacs did not have a major mode (for editing) and a REPL minor mode for Mojo. This is an attempt at providing both, albeit, by hacking on python.el.

Current working features:

• font-locking
• indentation
• movement
• REPL

At time of writing, a person writing Mojo code will likely have the Mojo language server available to them. This integrates nicely with eglot, yielding effortless ElDoc and imenu support.

In addition to the above, by analogy with rustic and cargo, support for mojo commands are included in mojo-mode's keymap.

(define-key map (kbd "C-c C-c C-r") #'mojo-run)
(define-key map (kbd "C-c C-c C-b") #'mojo-build)
(define-key map (kbd "C-c C-c C-f") #'mojo-format)
(define-key map (kbd "C-c C-c C-t") #'mojo-test)

The powerful convenience of using compile to run and display common commands be familiar to any user of rustic. Combined with a REPL, this yields a very enjoyable development experience.

Installation

Clone this repository

git clone https://github.com/andrewjradcliffe/mojo-mode.git

Then, add the following to your .emacs, init.el or however you configure your Emacs initialization.

(add-to-list 'load-path "/path/to/mojo-mode")
(require 'mojo-mode)
(require 'mojo-repl)
(add-hook 'mojo-mode-hook 'mojo-repl-mode)

eglot support

For the best experience, you should use eglot (lsp-mode may also work, I haven't tested it!) to provide language server support, which will include ElDoc, imenu and a host of other nice things.

Configuration looks something like:

;; Only if you need to activate eglot
(use-package eglot
  :ensure t)

;; Otherwise, just these two lines
(add-to-list 'eglot-server-programs '(mojo-mode . ("mojo-lsp-server")))
(add-hook 'mojo-mode-hook 'eglot-ensure)

REPL support

For the REPL to work, you will need vterm. vterm provides a high-performance virtual terminal, in contrast to the traditional alternatives -- though, I hear good things about eat.

If you don't have it already, add something like this to your init file:

(use-package vterm
  :ensure t
  :init
  (setq vterm-always-compile-module t)
  :config
  (setq vterm-max-scrollback 100000)
  (setq vterm-kill-buffer-on-exit nil)
  ;; If you want color support, configure
  (setq vterm-term-environment-variable "eterm-256color")
  )

Color support and font-locking with vterm works best with eterm-256color (or xterm-color). In my experience, minor adjustments to colors may be necessary, depending on the theme one uses.

Compatibility

At time of writing, the author has only tested this package with Emacs 29.3, compiled from source with essentially all features enabled; OS is Ubuntu 22.04 LTS.

Contributing

Contributions are welcome. Notably, many fancy features can be added; the current implementation is simple, but provides most of what one needs to get started.

Future improvements:

• fix some minor issues around font-locking for variable declarations and assignment
• font-locking for types and parameters
• mojo debug integration

Stability and roadmap

As the syntax and semantics of Mojo evolve, so must this package. Let us tentatively set an objective of being compatible with the latest stable release of Mojo.