Emacs OCaml mode
Emacs Lisp OCaml Makefile


MELPA LGPL v2 Build Status

Tuareg: an Emacs OCaml mode

This archive contains files to help editing OCaml code, to highlight important parts of the code, to run an OCaml toplevel, and to run the OCaml debugger within Emacs.


README.md — This file.
HISTORY — Differences with previous versions.
tuareg.el — A major mode for editing OCaml code in Emacs.
ocamldebug.el — To run the OCaml debugger under Emacs.
sample.ml — Sample file to check the indentation engine.


The easier way to install Tuareg is though opam:

opam install tuareg

and follow the instructions given at the end of the opam installation.

There are versions of Tuareg in Melpa and in Marmalade but they may be older.

If you want to install from the Git checkout, just add to your Init Filethe line:

(load "path-to-git-checkout-dir/tuareg-site-file")

If you want to byte compile the files, issue make elc. If you do this in Darwin, make sure that the version of Emacs displayed at the end of make elc is the sole that you use (the .elc files may not be compatible with other versions of Emacs installed on your system).

Usage & Configuration

The Tuareg major mode is triggered by visiting a file with extension .ml, .mli, .mly, .mll, and .mlp or manually by M-x tuareg-mode.

Start the OCaml toplevel with M-x run-ocaml. You can evaluate a phrase in your buffer by typing C-c C-e when the cursor is on it (it will start the OCaml toplevel if needed).

Run the OCaml debugger with M-x ocamldebug FILE.


  • By default, Tuareg will align the arguments of functions as follows:

      function_name arg1

    If you prefer that arguments on the second line be indented w.r.t. the function name, put (setq tuareg-indent-align-with-first-arg nil) in your Init File. This may be convenient if you use the following style:

      function_name (fun x ->

    In both cases, if there are no argument on the line following the function name, the indentation will be:

  • To make easier to distinguish pattern-match cases containing several patterns, sub-patterns are slightly indented as in

      match x with
      | A
        | B -> ...
      | C -> ...

    If you prefer all pipes to be aligned as

      match x with
      | A
      | B -> ...
      | C -> ...

    use (setq tuareg-match-patterns-aligned t).

  • Emacs ≥ 24.4 turned on electric-indent-mode mode by default. If you do not like it, call (electric-indent-mode 0) in tuareg-mode-hook.

  • You can turn on and off the rendering of certain sequences of characters as symbols (such as and instead of +.and &&), use prettify-symbols-mode or use the check box in the Tuareg Options menu. To enable it by default when you start Tuareg, add the following to your Init File:

      (add-hook 'tuareg-mode-hook
                  (when (functionp 'prettify-symbols-mode)

    If you want more symbols to be prettified (such as -> being displayed as ) at the expense of modifying the indentation in incompatible ways with those not using that option, add (setq tuareg-prettify-symbols-full t) to your Init File.

Thanks to the work of Stefan Monnier, a new indentation engine based on SMIE was written. This changes the indentation somewhat w.r.t. the previous versions of tuareg. If you do not want that, you can use the old indentation engine by adding (setq tuareg-use-smie nil) to your Init File. It is discouraged however as the older indentation engine will not be updated (unless a PR is submitted) and will eventually be removed.

The standard Emacs customization tool can be used to configure Tuareg options. It is available from the Options menu and Tuareg's Customize sub-menu. Note that, at the moment, both customization options pertaining to the SMIE indentation mode and the old one are present.

You may also customize the appearance of OCaml code by twiddling the variables listed at the start of tuareg.el (preferably using tuareg-mode-hook, you should not patch the file directly). You should then add to your configuration file something like:

(add-hook 'tuareg-mode-hook
  (lambda () ... ; your customization code ))

For example:

(add-hook 'tuareg-mode-hook
          ;; Turn on auto-fill minor mode.
          (lambda () (auto-fill-mode 1)))

See dot-emacs.el for some examples.

Features, Known Bugs

Cf. online help.


Ian Zimmerman for the previous mode, compilation interface and debugger enhancement.

Jacques Garrigue enhanced Zimmerman's mode along with an adaptation to OCaml (and Labl) syntax. Although this work was performed independently, his useful test file and comments were of great help.

Michel Quercia for excellent suggestions, patches, and helpful emacs-lisp contributions (full, ready-to-work implementations, I should say), especially for Tuareg interactive mode, and browser capacities.

Denis Barthou, Pierre Boulet, Jean-Christophe Filliatre and Rémi Vanicat for intensive testing, useful suggestions, and help.

Ralf Treinen for maintaining the Debian GNU/Linux package.

Every people who sent me bug reports, suggestions, comments and patches. Nothing would have improved since version 0.9.2 without their help. Special thanks to Eli Barzilay, Josh Berdine, Christian Boos, Carsten Clasohm, Yann Coscoy, Prakash Countcham, Alvarado Cuihtlauac, Erwan David, Gilles Défourneaux, Philippe Esperet, Gilles Falcon, Tim Freeman, Alain Frisch, Christian Lindig, Claude Marché, Charles Martin, Dave Mason, Stefan Monnier, Toby Moth, Jean-Yves Moyen, Alex Ott, Christopher Quinn, Ohad Rodeh, Rauli Ruohonen, Hendrik Tews, Christophe Troestler, Joseph Sudish, Mattias Waldau and John Whitley.

Tuareg mode have been maintained by Albert Cohen until version 1.45.

Jane Street took over maintenance based on Albert Cohen's version 1.46 (later retracted by him), and released its first version as 2.0.


The official Tuareg home page is located at: https://github.com/ocaml/tuareg.

Bug reports & patches: use the tracker: https://github.com/ocaml/tuareg/issues.