A simple tool and library to indent OCaml programs, developed and maintained by OCamlPro (Louis Gesbert). License: LGPL 2.1 with linking exception

Installation

Using OPAM

The simplest way to install ocp-indent is using OPAM:

opam install ocp-indent

By hand

You can also compile and install ocp-indent from sources. You'll need ocaml (>= 3.12.1) and ocp-build (>= 1.99.6-beta):

./configure
make
make install

If you use opam and want it installed alongside ocaml, you may want to use ./configure --prefix $(opam config var prefix).

Usage

The above installation step copies elisp scripts to <prefix>/share/emacs/site-lisp/ and vim scripts to <prefix>/share/ocp-indent/vim/. You then need to load them in the editor of your choice to automatically use ocp-indent.

Installing OPAM package user-setup will trigger automatic configuration for popular editors (emacs and vim currently, but more are in the works). If you prefer to handle your configuration manually, read on.

Emacs

Run the following command to setup tuareg-mode or caml-mode to use ocp-indent for indentation:

echo '(load-file "'"$(opam config var share)"'/emacs/site-lisp/ocp-indent.el")' >>~/.emacs

The tab key should now reindent the current line using ocp-indent.

Vim

Use the following command to tell Vim to use ocp-indent to indent OCaml code:

echo 'set rtp^="'"$(opam config var ocp-indent:share)"'/vim"' >>~/.vimrc

Automatic indentation as you type should take place, depending on your configuration. Use == to reindent the current line, and =G to reindent until the end of buffer.

NeoVim

Use the following command to tell NeoVim to ocp-indent to indent OCaml code:

echo 'vim.opt.rtp:prepend("'"$(opam var ocp-indent:share)"'/vim")' >> ~/.config/nvim/init.lua

Automatic indentation as you type should take place, depending on your configuration. Use == to reindent the current line, and =G to reindent until the end of buffer.

Other editors

As ocp-indent is a command-line tool, you can easily integrate it with other editors.

ocp-indent <src-file> > <dst-file>

You can also tell it to indent only subsets of lines, and to output only the indentation level:

ocp-indent <src-file> --lines <l1>-<l2> --numeric

Configuration options

By default, ocp-indent comes with sensible default parameters. However, you can customize some of the indentation options using command-line arguments. For more details, see:

ocp-indent --help

Configuration file

The same parameters can be defined in a configuration file, allowing for user defaults and per-project parameters. The latter is particularly convenient to transparently ensure consistency in projects with many contributors, without requiring them to change their settings in any way (except that, obviously, they need to use ocp-indent !).

If a .ocp-indent file is found in the current directory or its ancestors, it overrides definitions from $XDG_CONFIG_HOME/ocp/ocp-indent.conf, ~/.ocp/ocp-indent.conf and the built-in default. The command-line can of course still be used to override parameters defined in the files.

Have a look at ocp-indent's own .ocp-indent file for an example.

In-file configuration

There is no built-in support for in-file configuration directives. Yet, some editors already provide these features, and with emacs, starting your file with a line like:

(* -*- ocp-indent-config: in=2 -*- *)

will enable you to have the indentation after in setup to 2 locally on this file.

Autoformat files with ocp-indent in dune

dune fmt or dune build @fmt can be used to format dune and OCaml files with ocamlformat. This can prove a convenient workflow for new projects so we made it available to ocp-indent users as well.

First you need to disable the default formatting rules for OCaml source files by adding the following to your dune-project:

(formatting (enabled_for dune))

dune fmt won't try to format your OCaml files with ocamlformat from there.

The ocp-indent formatting rules need to be enabled on a per-directory basis by adding the following dune rules to the dune file:

;; Auto indent files with `dune build @fmt`

(subdir
 run
 (dynamic_include ../rules/dune.ocp-indent))

(subdir
 rules
 (rule
  (deps
   (glob_files ../*.{ml,mli}))
  (target dune.ocp-indent)
  (action
   (run ocp-indent-gen-rules -o %{target}))))

ocp-indent-gen-rules will generate promotion based formatting rules for each .ml and .mli files in this folder. You can simply use the same dune build @fmt/dune promote workflow as with ocamlformat.

How does it compare to tuareg ?

We've run some benchmarks on real code-bases and the result is quite conclusive. Keep in mind that most of existing source files are either indented manually or following tuareg standards. You can see the results here.

Moreover, as ocp-indent has a deep understanding of the OCaml syntax it shines on specific cases. See for instance the collection of unit-tests here. The currently failing tests can be seen here.

Testing

It's hard to deliver a great indenter without tests. We've built ocp-indent based on a growing collection of unit-tests. If you find an indentation bug, feel free to send us a code snippet that we will incorporate into our test suite.

The tests are organized as follows:

• tests/passing contains tests that are properly indented and should be left unchanged by ocp-indent.
• tests/failing contains tests for which ocp-indent currently returns the results in tests/failing-output, hence meld tests/failing{,-output} should give an overview of currently known bugs (also available online here).
• tests/test.sh checks the current state against the reference state (checked into git).
• tests/test.sh --[git-]update updates the current reference state.
• See tests/test.sh --help for more

Please make sure to run make && tests/test.sh --git-update before any commit, so that the repo always reflects the state of the program.

Old Readme ocp-indent is a simple tool and library to indent OCaml code. ocp-indent is part of TypeRex, developed and maintained by OCamlPro. Documentation to install and use this tool is available on http://www.typerex.org/ocp-indent.html It is released under LGPL v2.1 with linking exception.