Add a doc entry for setting up an OxCaml project with dune pkg

Signed-off-by: Sudha Parimala <sudharg247@gmail.com>

Author: Sudha247

doc/tutorials/dune-package-management/index.md

@@ -24,4 +24,5 @@ setup
 dependencies
 pinning
 repos
+oxcaml
 :::

doc/tutorials/dune-package-management/oxcaml.md

@@ -0,0 +1,80 @@
+# Example: Setting up an OxCaml project
+
+As an example to adding custom repositories and pinning projects, let's look at
+setting up a basic OxCaml project. [OxCaml](https://oxcaml.org/) is a compiler
+branch with fast moving set of extenstions to OCaml. Some tweaks are required to
+set up an OxCaml project with dune package management.
+
+## Setting up the workspace
+
+OxCaml has a custom `opam-repository` that we need in order to pull in its
+dependencies. This is specified in the `dune-workspace`.
+
+::::{dropdown} `dune-workspace`
+:icon: file-code
+
+:::{literalinclude} oxcaml/dune-workspace
+:language: dune
+:emphasize-lines: 3-5
+:::
+
+::::
+
+In the `dune-project`, we also need to add a constraint to depend on the OxCaml
+compiler. Otherwise, the solver may pick up the latest upstream compiler, which
+does not support the OxCaml extensions.
+
+::::{dropdown} `dune-project`
+:icon: file-code
+
+:::{literalinclude} oxcaml/dune-project
+:language: dune
+:::
+
+::::
+
+Let's add a test program that uses OxCaml syntax.
+
+::::{dropdown} `main.ml`
+:icon: file-code
+
+:::{literalinclude} oxcaml/main.ml
+:language: dune
+:::
+
+::::
+
+And to build it, we add a `dune` file.
+
+::::{dropdown} `dune`
+:icon: file-code
+
+:::{literalinclude} oxcaml/dune
+:language: dune
+:::
+
+::::
+
+## Building the project
+
+As usual, let's lock the dependencies and build the project with:
+
+```
+$ dune pkg lock
+Solution for dune.lock:                                                        
+- conf-autoconf.0.2
+- conf-which.1
+- ocaml-variants.5.2.0+ox
+
+$ dune build && dune exec ./main.exe
+...
+43
+```
+We have successfully built the project with the OxCaml compiler.
+
+## Developer tools
+
+Note that OxCaml provides its own forks of the developer tools
+`ocaml-lsp-server`, `ocamlformat`, etc. Make sure to include constraints for the
+tools in the `dune-workspace` if you intend to use them for your development
+workflows.

doc/tutorials/dune-package-management/oxcaml/dune

@@ -0,0 +1,2 @@
+(executable
+ (public_name main))

doc/tutorials/dune-package-management/oxcaml/dune-project

@@ -0,0 +1,7 @@
+(lang dune 3.20)
+
+(package
+ (name hello-oxcaml)
+ (depends
+  (ocaml-variants
+   (= 5.2.0+ox))))

doc/tutorials/dune-package-management/oxcaml/dune-workspace

@@ -0,0 +1,8 @@
+(lang dune 3.20)
+
+(repository
+ (name oxcaml)
+ (url git+https://github.com/oxcaml/opam-repository))
+
+(lock_dir
+ (repositories overlay oxcaml upstream))

doc/tutorials/dune-package-management/oxcaml/main.ml

@@ -0,0 +1,5 @@
+let () =
+  let local_ i = 42 in
+  let j = i + 1 in
+  print_endline (Printf.sprintf "%d" j)
+