> ## Documentation Index
> Fetch the complete documentation index at: https://docs.codecrafters.io/llms.txt
> Use this file to discover all available pages before exploring further.

# OCaml

> Learn how to solve CodeCrafters challenges in OCaml

<Note>
  **New to OCaml?** We recommend checking out [A Tour of
  OCaml](https://ocaml.org/docs/tour-of-ocaml) to get up to speed.
</Note>

## Local development

To run the code for your challenge locally, you'll need [opam](https://opam.ocaml.org/) and [dune](https://dune.build/install) installed. Our test runners use Dune v3.16 (as of September 2024).

The script for your challenge (`./your_program.sh`) will run your code using these tools. It will look something like this:

```sh theme={null}
#!/bin/sh

dune build --build-dir /tmp/redis
exec /tmp/redis/default/main.exe "$@"
```

## File structure

* The files for your solution are placed in the `src/` directory.
* `src/main.ml` is the entry point for your OCaml program.

## Adding more files

You can organize your code by adding more `.ml` files in the `src/` directory. The test runner will include them when building and running your code.

For example, if you add a file at `src/foo.ml`, you can reference it in `main.ml` like this:

<CodeGroup>
  ```ocaml src/main.ml theme={null}
  let () = Foo.bar () (* Calls the bar function from foo.ml *)
  ```

  ```ocaml src/foo.ml theme={null}
  let bar () = Printf.printf "Hello World!\n"
  ```
</CodeGroup>

## Adding dependencies

If you're looking for OCaml libraries, you can browse the [opam package repository](https://opam.ocaml.org/packages/).

<Steps>
  <Step title="Specify dependencies">
    You need to specify dependencies in both the `dune-project` and `dune` files.

    For example, to add the `yojson` library for handling JSON, first update `dune-project` as follows:

    ```diff theme={null}
    (generate_opam_files true)

    (package
       (name codecrafters_redis)
    +  (depends yojson)
       (version 0.1))
    ```

    Then, update the `dune` file to include `yojson` as a library:

    ```diff theme={null}
    (executable
      (name main)
    - (libraries unix))
    + (libraries unix yojson))
    ```

    <Info>For more details, check the OCaml documentation on [Adding a Dependency](https://ocaml.org/docs/managing-dependencies#adding-a-dependency-to-your-dune-project-file).</Info>
  </Step>

  <Step title="Install dependencies">
    You need to regenerate the `.opam` file from `dune-project` before installing dependencies.

    First, run this command to update the `.opam` file:

    ```bash theme={null}
    dune build
    ```

    <Note>If you've already used the library in an `.ml` file, `dune build` will exit with an error. This is okay — it'll still update the `.opam` file (required for the next step).</Note>

    Then, run this command to install the dependencies:

    ```bash theme={null}
    opam install . --deps-only
    ```
  </Step>

  <Step title="Use dependencies">
    Here's an example of how to use the `yojson` library:

    ```ocaml theme={null}
    open Yojson.Basic

    let () =
      {| { "challenge": "Build your own Redis", "language": "OCaml" } |}
      |> from_string
      |> Util.member "language"
      |> Util.to_string
      |> print_endline

    (* This will print "OCaml" *)
    ```
  </Step>
</Steps>