Overview
Dune is a build tool that has been widely adopted in the OCaml world - it plays nicely with lots of other tools like opam and mdx. The documentation is very thorough - but do checkout the key concepts to get a high-level overview of how dune works and how to get started building your OCaml project.
Welcome to dune's documentation! - dune documentation
Key Concepts
Compositional Builds
Dune builds projects in a modular way generally based on file structure. This is somewhat different to say how npm would build Javascript projects more or less only based on the package.json at the root of the project. Looking at Typical Project Layout the compositionality is portrayed by the dune files in each directory. Each part is doing something different (building tests, the library, the unix version of the library etc.).
Declarative
Unlike say Makefiles, dune is declarative. You tell it what you want and dune handles the nitty-gritty details but provides escape-hatches and a lot of customisability in your dune file to build complex projects.
This allows dune to be a great build tool no matter what your project size or complexity is.
Build Types
There tend to be three main types of builds that will suffice for most projects: executables, libraries and tests. Each has its own stanza reference. The executable stanza will by default build a binary that you can run in the _build/default folder. Libraries are units of reusable code for other projects to benefit from packaged up under a module.
Typical Project Layout
The following file structure is taken from ocaml-yaml and has been trimmed to show only the relevant dune-related parts and still be readable.
.
|-- CHANGES.md
|-- LICENSE.md
|-- README.md
|-- dune
|-- dune-project
|-- fuzz
| |-- dune
| `-- fuzz.ml
|-- lib
| |-- dune
| |-- stream.ml
| |-- types.ml
| |-- yaml.ml
| `-- yaml.mli
|-- tests
| |-- dune
| |-- test.ml
| |-- test_emit.ml
| |-- test_parse.ml
| `-- yaml
|-- unix
| |-- dune
| |-- yaml_unix.ml
| `-- yaml_unix.mli
`-- yaml.opam
In the Wild
Dune is used in a lot of OCaml projects thanks to its flexibility, integration with opam and lightweightness. Below are just a few projects using dune: