Run an inferior Julia REPL in a terminal inside Emacs
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README.md

julia-repl: run an inferior Julia REPL in Emacs

MELPA

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 25. The term code changed a bit since Emacs 24, and the package does not support it. For example, Ubuntu users can get the latest Emacs snapshot here.

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.

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-c send region (when applicable) or line to REPL
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-z raise the REPL or create a new one
C-RET send line to REPL (without bracketed paste)
C-c C-e invoke @edit on region (when applicable) or line
C-c C-d invoke @doc on symbol
C-c C-m expand macro
C-c C-p change directory to that of the buffer
C-c C-a activate if there is a Project.toml in parent directories
C-u C-c C-a activate home project

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.

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.

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.

Limitations

See the issues.

Comparison to ESS

A well-known alternative is ESS, which also supports Julia. julia-repl was written because I could not use Gallium from ESS, which is based on comint, and thus does not allow a fully functioning terminal. Also, relying on the interactive features of the Julia REPL implies that I would not need to change this library to incorporate extensions and changes that rely on the terminal.