Building an OCaml Project with Dependencies in a Conda Environment Using Dune

This workflow shows how to create and build an OCaml project with dependencies inside a Conda environment using Dune.

Key Benefits

• No Opam needed:
  • Dune handles dependency resolution and build steps.
  • No use of a global ~/.opam.
  • All dependencies and builds stay inside your project directory.
• Portable: Easy to reproduce and use in shell scripts, CI, or Docker.

Make sure you have a Conda environment with OCaml and Dune. To build OCaml and Dune in a Conda environment, follow the instructions here.

Steps

Create a New OCaml Project

Use dune to initialize your project:

dune init proj my_project
cd my_project

This sets up:

my_project/
├── dune-project
├── bin/
│   ├── dune
│   └── main.ml
└── lib/
    └── dune

Write Your Code

Executable Code (bin/main.ml)

open Hardcaml;;

let circuit = 
        let a = Signal.input "a" 8 in
        let b = Signal.input "b" 8 in
        let c = Signal.output "c" (Signal.(a +: b)) in
        Circuit.create_exn ~name:"adder" [ c ]
;;

Rtl.print Verilog circuit;;

let sim = Cyclesim.create circuit;;

let a = Cyclesim.in_port sim "a";;
let b = Cyclesim.in_port sim "b";;
let c = Cyclesim.out_port sim "c";;

a := Bits.of_int ~width:8 10;;
b := Bits.of_int ~width:8 20;;

Printf.printf "a: %d\n" (Bits.to_int !a);;
Printf.printf "b: %d\n" (Bits.to_int !b);;

Cyclesim.cycle sim;;

Printf.printf "c: %d\n" (Bits.to_int !c);;

Edit your bin/dune file to include used libraries:

(executable
 (public_name my_project)
 (name main)
 (libraries my_project hardcaml) ; Add space-separated libraries
 (preprocess (pps ppx_jane ppx_hardcaml))) ; Add other directives based on library READMEs

Declare Project Dependencies

Edit dune-project:

(lang dune 3.22)
(name my_project)
(generate_opam_files true)

(package
 (name my_project)
 (synopsis "A short synopsis")
 (description "A longer description")
 (depends ocaml hardcaml hardcaml_waveterm ppx_hardcaml)) ; Add dependencies based on libraries in `bin/dune`, refer to library READMEs

Lock Dependencies

Run:

dune pkg lock

• This will generate a lock directory.
• Dune will resolve, fetch, and build compatible versions for your declared dependencies.

Build the Project

dune build

This will download, build, and install all your locked dependencies and then use those to build your project. This means that the first time building it will take longer than usual, as the dependencies need to be built first. Subsequent builds where all dependencies have been built before will be fast.

Run the Executable

dune exec my_project

or

./_build/default/bin/main.exe

You should see:

module adder (
    b,
    a,
    c
);

    input [7:0] b;
    input [7:0] a;
    output [7:0] c;

    wire [7:0] _4;
    assign _4 = a + b;
    assign c = _4;

endmodule
a: 10
b: 20
c: 30