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Emacs Integration for OCaml LSP Server: Introducing ocaml-eglot

Emacs Integration for OCaml LSP Server: Introducing ocaml-eglot

TL;DR

ocaml-eglot provides full OCaml language support in Emacs through the Language Server Protocol (LSP) instead of direct Merlin integration. It offers the same features as merlin.el with simplified setup and enhanced capabilities like project-wide search. If you're starting fresh or want a more standardized approach, try ocaml-eglot, which is actively maintained. If your current merlin.el setup works well, you can continue using it.

Quick start: Install ocaml-lsp-server, add ocaml-eglot to your Emacs config, and get the same OCaml development experience with less configuration.

What is ocaml-eglot?

ocaml-eglot connects Emacs to ocaml-lsp-server using the Language Server Protocol, providing a standardized way to get OCaml language support.

Since the recent versions of Emacs (29), eglot, an LSP client, has been shipped with Emacs. However, merlin.el provides more features than LSP (which is designed to be generic), so relying solely on the features of LSP and eglot would limit functionality. Thus, we extended the LSP server to support more features, and ocaml-eglot allows you to benefit from these features in Emacs.

ocaml-eglot is a minor mode. It therefore works in conjunction with a major mode to edit Caml code. Examples of major modes include tuareg, caml-mode and the recent neocaml.

Who Should Use ocaml-eglot?

Use ocaml-eglot if you:

  • Are starting fresh with OCaml
  • If you use or want to use Emacs
  • Want simplified configuration with automatic setup
  • Use multiple editors and want consistent OCaml support
  • Want access to project-wide search and rename features
  • Want to rely on an actively maintained project that evolves over time

If your current setup is working perfectly and is heavily customised, merlin.el will still keep working, so there's no immediate need to migrate. However, for the moment, we don't plan to actively maintain merlin.el -- unless we receive a lot of requests.

Getting Started

Follow the installation instructions in the ocaml-eglot README.

When migrating from merlin.el to ocaml-eglot, your existing keybindings should work immediately!

Features

Error Navigation: Quick jump to next/previous errors

Type Information: Display types under cursor with adjustable verbosity, navigate enclosing expressions

Code Generation: Pattern matching construction, case completion, wildcard refinement via "destruct" feature

Navigation: Jump between language constructs (let, module, function, match), navigate phrases and pattern cases

Search: Find definitions, declarations, and references

For a detailed list of features, see the ocaml-eglot README.

Next Steps

  1. Try the basic setup with an existing OCaml project
  2. Explore all the features of ocaml-eglot
  3. Provide feedback at ocaml-eglot's GitHub Issues

Documentation

Related Releases

On January 17, 2025, ocaml-eglot version 1.0.0 was released, providing a new minor emacs mode to enable the editor features provided by ocaml-lsp-server. Subsequent releases 1.1.0 and 1.2.0 enable support for flycheck as a configurable alternative to flymake (1.0.0 release), Emacs 30.1 support, better user experience and error handling, as well as support for new features.