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julia-repl: run an inferior Julia REPL in Emacs

MELPA build

This is a minor mode for interacting with a Julia REPL running inside Emacs. The julia process is started in an ANSI terminal (term), which allows text formatting and colors, and interaction with the help system and the debugger.

It is recommended that you use this minor mode with julia-mode.

screenshot

Installation and loading

Please make sure you have at least Emacs 27.1, as the package does not support earlier versions.

Place this in your Emacs initialization files (eg .emacs):

(add-to-list 'load-path path-to-julia-repl)
(require 'julia-repl)
(add-hook 'julia-mode-hook 'julia-repl-mode) ;; always use minor mode

If you want to use a Julia executable other than julia in your path, see below.

If you are experiencing problems with Unicode characters in the Julia REPL, try setting the relevant coding/language environment, eg

(set-language-environment "UTF-8")

Usage

M-x julia-repl, or C-c C-z from a buffer in which the julia-repl minor mode is active starts a new inferior Julia process. The keys below can be used to interact with this process.

key action
C-c C-a activate if there is a Project.toml in parent directories
C-u C-c C-a activate home project
C-c C-b send whole buffer to REPL (using include)
C-u C-c C-b send whole buffer to REPL (directly)
C-c C-c send region (when applicable) or line to REPL
C-c C-d invoke @doc on symbol
C-c C-e invoke @edit on region (when applicable) or line
C-c C-l list methods of a function
C-c C-m expand macro
C-c C-p change directory to that of the buffer
C-c C-s prompt for buffer name suffix
C-c C-t send whole buffer to REPL (using Revise.includet)
C-c C-v prompt for Julia executable
C-c C-z raise the REPL or create a new one (or switch back from REPL – only in vterm backend)
C-RET send line to REPL (without bracketed paste)

All actions that send something to the REPL terminate with a newline, triggering evaluation. If you want to avoid sending a newline (eg maybe because you want to edit an expression), use prefix arguments (C-- or C-u, currently both have the same effect). This of course does not apply to C-c C-b.

All commands send code using bracketed paste. When Julia is waiting for input, control characters like ^[[200~ may show up in your buffer, this is innocuous. If you input takes a long time to evaluate, you can step through it line-by-line with C-RET.

Options for this package are exposed via the customize interface (M-x customize-group julia).

Environment variables

You can set environment variables directly from your init.el in Emacs, eg

(setenv "JULIA_NUM_THREADS" "4")

Buffer-local inferior REPL and Julia executable

The minor mode allows the user to select a particular Julia executable and optionally a different inferior buffer for each source code buffer. This allows running two versions (eg stable and master) of Julia simultaneously, and/or running multiple inferior REPLs of the same Julia version. A typical use case is trying out something quickly, without changing the state of the current process.

Julia executables

Set julia-repl-executable-records to a list of keys and executables. For example,

(setq julia-repl-executable-records
      '((default "julia")                  ; in the executable path
        (master "~/src/julia-git/julia"))) ; compiled from the repository

provides two executables. The first entry is always the default (it can have any other key).

Use C-c C-v to select one of these (julia-repl-prompt-executable). You can also set the value of julia-repl-executable-key directly to a key in the julia-repl-executable-records, eg using file variables, but make sure you select a correct value.

The name of the inferior buffer will reflect your choice: the default is *julia* (indicator omitted), while the master executable would map to *julia-master*, and so on.

Executable suffix

You can also set a suffix for the inferior buffer, if you want multiple ones in parallel. This can be a number, which will show up as <number>, or a symbol, which appears as -symbol.

It is recommended that you use C-c C-s (julia-repl-prompt-inferior-buffer-name-suffix), which prompts for a string by default. Prefix arguments modify it like this:

  • numerical prefixes select that integer: eg C-3 C-c C-s set the suffix to 3.

  • the negative prefix picks the next unused integer: eg C- C-c C-s sets the suffix to 4 if 1, 2, 3 are in use.

Switches

Switches to the julia process can be provided in the global variable julia-repl-switches, for example

(setq julia-repl-switches "-p 4")

The function julia-repl-prompt-switches will prompt for new switches, you can bind it to a key.

File local variables

If you are using the same settings for a specific file, consider using file variables. For example, if you use add-file-local-variable to create a block at the end of the Julia source file similar to

# Local Variables:
# julia-repl-executable-key: master
# julia-repl-inferior-buffer-name-suffix: tests
# julia-repl-switches: "-p 4"
# End:

then the next time you open a REPL, it will have the name *julia-master-tests*, and 4 worker processes.

Terminal backends

julia-repl can use the terminal in different ways.

The default is ansi-term, which is included in Emacs, but it is recommended that you use vterm via emacs-libvterm (it is not the default since you need to install an extra package and the binary).

You can also use eat as a backend.

Note to Windows users: you may not be able to use eat and/or vterm directly from native Windows Emacs, but there have been reports of people using them successfully from WSL (Windows Subsistem for Linux) 2. Please understand that supporting those terminal emulators is outside the scope of this package; julia-repl merely provides bindings for them conditional on availability on your system.

Some hints on interacting with term

Note some keybindings for term:

  1. C-x C-j switches to line mode, where you can kill/yank, move around the buffer, use standard Emacs keybindings,
  2. C-c C-k switches back to char mode,
  3. for scrolling, use S-<prior> and S-<next>.

See the help of term for more.

Using vterm

vterm is now the recommended backend, but for now you have to enable it explicitly because dependencies need to be available. In the long run it is hoped that it will replace ansi-term as the default backend for this package, fixing many outstanding issues.

  1. Install emacs-libvterm and make sure you have a working installation (eg M-x vterm) should start a terminal

  2. Evaluate (julia-repl-set-terminal-backend 'vterm) in your config file after you load julia-repl, but before you use it (and of course vterm should be loaded at some point). Switching terminal backends with already running Julia processes is not supported.

  3. You may want to (setq vterm-kill-buffer-on-exit nil) to prevent the buffers associated with terminated Julia processes being killed automatically. This allows you to retain output and see error messages if the process does not start.

  4. You can also install EmacsVterm.jl package, which improves integration between Julia REPL and Emacs.

Using eat

Install eat and use (julia-repl-set-terminal-backend 'eat) in your config file.

Using the @edit macro

The @edit macro can be called with C-c C-e when the julia-repl-mode minor mode is enabled. The behavior depends on the value of the JULIA_EDITOR envoronment variable in the Julia session. The command julia-repl-set-julia-editor is provided to conveniently control this from emacs.

To use "emacsclient" as a default in each Julia REPL you open in emacs, add the following code to your ~/.julia/config/startup.jl:

if haskey(ENV, "INSIDE_EMACS")
    ENV["JULIA_EDITOR"] = "emacsclient"
end

If you cannot edit your startup.jl, you can configure the editor in each repl after starting it with:

(add-hook 'julia-repl-hook #'julia-repl-use-emacsclient)

More colors

Julia uses more colors than the ones supported by term by default. To get the full range of colors, use eterm-256color, available from MELPA.

Note for Windows users

ansi-term is not supported on some (most?) Windows versions of Emacs. It has been confirmed to work with Emacs running in Cygwin. You can test whether your version works with M-x ansi-term; if this errors then this package will not work for you.

Cygwin may require some rewriting of paths for include to work. After loading this package, customize the rewrite rules as

(setq julia-repl-path-rewrite-rules julia-repl-cygwin-path-rewrite-rules)

as a reasonable default, or write custom rules for julia-repl-path-rewrites.

Clickable error locations

Error locations in the inferior buffer should be clickable, implemented with compilation-shell-minor-mode.

The error printing syntax changed over time, and legacy forms are not included, they are not needed if you are using Julia 1.6 or later. To get them back, use

(setq julia-repl-compilation-location-legacy t)

If you find that a Julia error (warning, info, etc) message location is not clickable in Emacs, please open an issue.

Limitations

See the issues.

Comparison to ESS

A well-known alternative is ESS, which also supports Julia. ESS is however based on comint, which does not allow a fully functioning terminal and therefore does not support the Julia REPL modes (shell, Pkg, debuggers...) and features. julia-repl is instead based on term, and so gets all the features from Julia's native REPL for free.