OCaml: Setting Up Visual Studio Code for OCaml

Introduction

Visual Studio Code (hereinafter referred to as VS Code) is a powerful editor that supports multiple languages.
An extension for OCaml is also provided.
In this article, I will introduce how to set up an OCaml development environment in VS Code.

1. Installing OCaml Packages

1.1 Installing the LSP Server

In VS Code, the OCaml Platform extension uses LSP (Language Server Protocol).
We will install the OCaml LSP server package and verify its operation.

Install the LSP for OCaml with the following command:

opam install --yes ocaml-lsp-server

Note:
The --yes option is added to automatically install related packages.

To verify the LSP operation, run ocamllsp and check if error messages are output.
Follow these steps to verify the LSP:

1. Start the LSP server:
   Start the LSP server with the following command:

   ocamllsp
   

2. Check the error message:
   Press the [Enter] key and check if an error message is output from the LSP server.
   Note:
   This is to confirm that the LSP server is operating normally.

     # Press [Enter]
   
   /-----------------------------------------------------------------------
   | Internal error: Uncaught exception.
   | Error: content length absent
   

   An error message like the one above will be output.

3. Stop the LSP server:
   Enter [Ctrl+C] to stop the LSP.

   ^C  # Press [Ctrl+C] to stop
   
   0
   

If the error message is output as shown above, the LSP has been installed correctly.

1.2 Installing the Code Formatting Tool

Install the code formatting tool ocamlformat and verify its operation.
Use the following command to install the code formatting tool:

opam install --yes ocamlformat

Follow these steps to verify the operation of the code formatting tool:

1. Create a .ocamlformat file for the formatter:

   touch .ocamlformat
   

2. Create a program for code formatting:

   hello.ml

    (* my first OCaml program *)
    print_endline "Hello, OCaml!!"
   
   

3. Format the above OCaml program using the formatter:

   ocamlformat hello.ml
   (* my first OCaml program *)
   print_endline "Hello, OCaml!!"
   
   

   Note:
   If a Warning error occurs, add --enable-outside-detected-project.

If the formatted program is output as shown above, the formatter has been installed correctly.

2. Installing Extensions

2.1 Installing OCaml Platform

OCaml Platform uses LSP to provide features like tab completion and error checking during coding.
Follow these steps to install OCaml Platform:

1. Launch VS Code:

   code .
   

2. Open the [Extensions View]:
   Press [Ctrl+Shift+X] to display the [Extensions View].

3. Search for [OCaml Platform]:
   Enter ocaml in the search bar at the top to search for [OCaml Platform].

4. Install [OCaml Platform]:
   Click [Install] to install [OCaml Platform].

2.2 Installing Code Runner

Code Runner is an extension that allows you to easily run the program you are currently editing.
It executes the appropriate command according to the programming language being edited.

Follow these steps to install [Code Runner]:

1. Launch VS Code:

   code .
   

2. Open the [Extensions View]:
   Press [Ctrl+Shift+X] to display the [Extensions View].

3. Search for [Code Runner]:
   Enter code in the search bar at the top to search for [Code Runner].

4. Install [Code Runner]:
   Click [Install] to install [Code Runner].

2.3 Configuring Code Runner

To use [Code Runner], add OCaml-specific settings to the configuration file.

Follow these steps to add the settings for OCaml:

1. Launch VS Code:

   code .
   

2. Open the settings file:
   Press [Ctrl+Shift+P], select [Open User Settings (JSON)], and open the settings file (settings.json).

3. Add OCaml settings:
   Add the following lines to the settings file (settings.json).
   This ensures that the appropriate command is used when running an OCaml program.

settings.json

code-runner.executorMap": {
  "ocaml": "cd $dir && ocaml $fileName"
}

Note:
If you are setting up an environment for languages other than OCaml, add settings for those languages within the executorMap section.

With this, you can now run programs using Run Code.

Conclusion

In this article, I explained how to add the OCaml extension to VS Code.
Using extensions like this makes learning functional programming with OCaml much more convenient.

Let's use VS Code to learn functional programming with OCaml from now on.
By doing so, let's continue to improve our skills.

Now then, Happy Hacking!

Technical Terms and Notes

Here is an explanation of the main technical terms used in this article:

• OCaml:
  A functional programming language characterized by a powerful type system.

• VS Code (Visual Studio Code):
  A lightweight and powerful code editor developed by Microsoft.

• opam:
  The OCaml package manager that provides libraries and tools for OCaml.

• LSP (Language Server Protocol):
  A protocol that provides programming language support in a unified way for editors and IDEs.

• OCaml Platform:
  A VS Code extension that enhances OCaml language support for OCaml programming.

• Code Runner:
  A VS Code extension that allows you to easily run code snippets or files for any language.

References

Websites

• opam:
  Package manager for OCaml.

• ocaml-lsp:
  LSP server for OCaml.

• ocamlformat:
  Code formatting tool for OCaml.

• OCaml Platform:
  VS Code extension for OCaml.

• Code Runner:
  VS Code extension for code execution.