OCaml-LSP is a language server for OCaml that implements Language Server Protocol (LSP).
This project contains an implementation of a language server for OCaml and a standalone
library implementing LSP.
To install the language server in the currently used opam switch:
$ opam install ocaml-lsp-server
Note: you will need to install
ocaml-lsp-server in every switch where you would like
to use it.
To add the language server to an esy project, run in terminal:
$ esy add @opam/ocaml-lsp-server
This project uses submodules to handle dependencies. This is done so that users
ocaml-lsp-server into their sandbox will not share dependency constraints on
the same packages that
ocaml-lsp-server is using.
$ git clone --recurse-submodules http://github.com/ocaml/ocaml-lsp.git $ cd ocaml-lsp $ make all
ocaml-lsp-server is installed, the executable is called
now, the server can only be used through the standard input (
stdin) and output
stdout) file descriptors.
For an example of usage of the server in a VS Code extension, see
OCaml Platform Extension implementation here.
The server supports the following LSP requests:
Note that degrees of support for each LSP request are varying.
Integration with other tools
Formatters: OCamlFormat & Refmt
OCaml-LSP is dependent on external tools (OCamlFormat for OCaml and
refmt for Reason)
for formatting source files. You should have the necessary tool (OCamlFormat and/or Refmt)
installed in your opam switch or esy project to have formatting support. Note, however, that
OCaml-LSP requires presence of OCamlFormat configuration file (called
the project root to be able to format source files in your project.
Contributing to project
# clone repo with submodules git clone --recursive email@example.com:ocaml/ocaml-lsp.git # if you already cloned, pull submodules git submodule update --init --recursive # create local switch (or use global one) and install dependencies opam switch create . ocaml-base-compiler.4.12.0 --with-test # don't forget to set your environment to use the local switch eval ($opam env) # build make all # the ocamllsp executable can be found at _build/default/ocaml-lsp-server/src/main.exe
To run tests execute:
$ make test
Note that tests require Node.js and
Relationship to Other Tools
The lsp server uses merlin under the hood, but users are not required to have
merlin installed. We vendor merlin because we currently heavily depend on some
implementation details of merlin that make infeasible to upgrade the lsp server
and merlin independently.
The implementation of the lsp protocol itself was taken from
Previously, this lsp server was a part of merlin, until it was realized that the
lsp protocol covers a wider scope than merlin.
Comparison to other LSP Servers for OCaml
Note that the comparisons below make no claims of being objective and may be
entirely out of date:
This server supports
reason. However, this project does not
use merlin which means that it supports fewer versions of OCaml and offers less
"smart" functionality - especially in the face of sources that do not yet
This project is extremely similar in the functionality it provides because it
also reuses merlin on the backend. The essential difference is that this
project is written in typescript, while our server is in OCaml. We feel that
it's best to use OCaml to maximize the contributor pool.