Every library module must have an .mli file for:

Clear API boundaries
Proper encapsulation
Documentation surface

(* lib/user.mli *)

(** User management.

    This module provides types and functions for user operations. *)

type t
(** A user. *)

val create : name:string -> email:string -> t
(** [create ~name ~email] creates a new user. *)

val name : t -> string
(** [name u] is the user's name. *)

val pp : t Fmt.t
(** [pp] is a pretty-printer for users. *)

Documentation style:

Functions: [name args] is/does ...
Values: [name] is ...
End with period

Standard Module Interface

For modules with a central type t:

type t
val v : ... -> t                           (* pure constructor *)
val create : ... -> (t, Error.t) result    (* constructor with I/O *)
val pp : t Fmt.t                           (* pretty-printer - required *)
val equal : t -> t -> bool                 (* equality *)
val compare : t -> t -> int                (* comparison *)
val of_json : Yojson.Safe.t -> (t, string) result
val to_json : t -> Yojson.Safe.t

OCamlFormat Configuration

Required: .ocamlformat in project root.

version = 0.28.1

Run dune fmt before every commit.

Logging Setup

Each module using logging should declare a source:

let log_src = Logs.Src.create "project.module"
module Log = (val Logs.src_log log_src : Logs.LOG)

Log levels:

Log.app - Always shown (startup)
Log.err - Critical errors
Log.warn - Potential issues
Log.info - Informational
Log.debug - Verbose debugging

User Configuration

Read from ~/.claude/ocaml-config.json:

{
  "author": { "name": "Name", "email": "email@example.com" },
  "license": "ISC",
  "ci_platform": "github",
  "git_hosting": { "type": "github", "org": "username" },
  "ocaml_version": "5.2.0"
}

License Headers

Every source file starts with license header:

(*---------------------------------------------------------------------------
  Copyright (c) {{YEAR}} {{AUTHOR}}. All rights reserved.
  SPDX-License-Identifier: ISC
 ---------------------------------------------------------------------------*)

Project Structure

project/
├── dune-project
├── dune
├── .ocamlformat
├── .gitignore
├── LICENSE.md
├── README.md
├── lib/
│   ├── dune
│   ├── foo.ml
│   └── foo.mli         # Required for every .ml
├── bin/
│   ├── dune
│   └── main.ml
├── test/
│   ├── dune
│   ├── test.ml
│   └── test_foo.ml
├── .github/workflows/  # GitHub Actions
├── .gitlab-ci.yml      # GitLab CI
└── .tangled/workflows/ # Tangled CI

dune-project

(lang dune 3.21)
(name project_name)
(generate_opam_files true)

(license ISC)
(authors "Name <email@example.com>")
(maintainers "Name <email@example.com>")
(source (tangled user.domain/project_name))

(package
 (name project_name)
 (synopsis "Short description")
 (description "Longer description")
 (depends
  (ocaml (>= 5.2))
  (alcotest (and :with-test (>= 1.7.0)))))

Note: Don't add (version ...) - added at release time.

Tangled Source Syntax

For projects hosted on tangled.org, use the succinct source stanza:

(source (tangled user.domain/project-name))

Examples:

(source (tangled anil.recoil.org/ocaml-brotli))
(source (tangled user.example.org/my-library))

Tangled CI Configuration

For projects hosted on tangled.org, create .tangled/workflows/build.yml:

when:
  - event: ["push", "pull_request"]
    branch: ["main"]

engine: nixery

dependencies:
  nixpkgs:
    - shell
    - stdenv
    - findutils
    - binutils
    - libunwind
    - ncurses
    - opam
    - git
    - gawk
    - gnupatch
    - gnum4
    - gnumake
    - gnutar
    - gnused
    - gnugrep
    - diffutils
    - gzip
    - bzip2
    - gcc
    - ocaml
    - pkg-config

steps:
  - name: opam
    command: |
      opam init --disable-sandboxing -a -y

  - name: repo
    command: |
      opam repo add aoah https://tangled.org/anil.recoil.org/aoah-opam-repo.git

  - name: deps
    command: |
      opam install . --confirm-level=unsafe-yes --deps-only

  - name: build
    command: |
      opam exec -- dune build

  - name: test
    command: |
      opam install . --confirm-level=unsafe-yes --deps-only --with-test
      opam exec -- dune runtest --verbose

Tangled Workflow Syntax

Field	Description
`when`	Trigger conditions: `event` (push/pull_request) and `branch`
`engine`	Build engine, use `nixery` for Nix-based builds
`dependencies.nixpkgs`	List of Nix packages to include
`environment`	Global or per-step environment variables
`steps`	Build steps with `name` and `command`

Per-step environment variables:

steps:
  - name: test
    environment:
      MY_VAR: value
    command: |
      echo $MY_VAR

Templates

See templates/ directory for:

dune-project.template
dune-root.template
ci-github.yml
ci-gitlab.yml
ci-tangled.yml
gitignore
ocamlformat
LICENSE-ISC.md
LICENSE-MIT.md
README.template.md

File	Purpose
`dune-project`	Build configuration, opam generation
`dune` (root)	Top-level build rules
`.ocamlformat`	Code formatting (required)
`.gitignore`	VCS ignores
`LICENSE.md`	License file
`README.md`	Project documentation
CI config	GitHub Actions / GitLab CI / Tangled

ocaml-project-setup

OCaml Project Setup

Required Files

Interface Files (.mli)