Dune is a Ocaml build system

Here is my attempt to properly build a toy Ocaml project using Dune.

Since this is the learning phase the Ocaml code may not be idiomatic.

My unit test framework is Alcotest

As is the case with other Ocaml tools and techniques information about this is sketchy. I wish there were more articles and examples as it is fun to work with this language..

I will add more details as I research this further. But for now here is a brief description of the dune build file.

  • dune runtest executes  all the tests
  • Dune does not install dependencies automatically . So, for example, I have to execute ‘opam install alcotest’. That is how one installs any opam package we need generally.


This looks like the file in which one specifies the framework versions and build instructions.

opam-version: "2.0"
authors: [ "Mohan" ]
synopsis: "Learning Dune"
description: """
Learning Dune
tags: []
depends: [
"ocaml" {
>= "4.02.3"}
"alcotest" {with-test}
build: [
["dune" "subst"] {pinned}
["dune" "build" "-p" name "-j" jobs]
["dune" "runtest" "-p" name "-j" jobs] {with-test}

Dune dependencies

This specifies the dependencies and the modules. My code module is ‘graph‘ and my test module is ‘kruskaltest‘.

(modules graph)
(name graph)
(name kruskaltest)
(modules kruskaltest)
(libraries alcotest graph))
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Main module

type edge = ( int * int * int ) list
module type EDGECOMPARE = sig
type t
val compare : 'a list -> 'a list ->bool
module EDGECOMPARE_weight : EDGECOMPARE with type t = edge = struct
type t = edge
let compare l r = ( List.nth l ( List.length l/ 2 )) == ( List.nth r (List.length r/2))
view raw kruskal.ml hosted with ❤ by GitHub


let testcompare () = Alcotest.(check bool) "Test for weight comparison" true (Graph.EDGECOMPARE_weight.compare [1,2,4] [ 5,6,7] )
let () =
Alcotest.run "Weights"
("test compare weights of edges", [
Alcotest.test_case "Compare weights" `Quick testcompare;
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mirage@mirage:~/theorem$ dune runtest
kruskaltest alias runtest
Testing Weights.
This run has ID `D7DAB7A8-A60A-4522-9732-54FAE2331A72`.
[OK] test compare weights of edges 0 Compare weights.
The full test results are available in `/home/mirage/theorem/_build/default/_build/_tests/D7DAB7A8-A60A-4522-9732-54FAE2331A72`.
Test Successful in 0.000s. 1 test run.

Joy of OCaml


I have spent most of last week with my Emacs editor and the OCaml development environment. Since I have some OCaml code to complete I will add more details soon.

Suffice it to say that this setup taxed me so much. OPAM does not seem to install easily in Windows. As is my wont in such cases I started with Cygwin and after two days switched to a Ubuntu VM. I didn’t think I was gaining much by reporting Cygwin permission issues to owners of OPAM Windows installers.

Emacs company mode for autocompletion

The toolchain includes company as well as Merlin
and Tuareg.


Utop is a toplevel for OCaml


Emacs elisp

It looks like this at this time and I use Gist because WordPress does not support Lisp or OCaml or Haskell yet. Filed a support ticket.

(load "/home/mohan/.opam/4.02.1/share/emacs/site-lisp/tuareg-site-file")
(let ((opam-share (ignore-errors (car (process-lines "opam" "config" "var"
(when (and opam-share (file-directory-p opam-share))
;; Register Merlin
(add-to-list 'load-path (expand-file-name "emacs/site-lisp" opam-share))
(autoload 'merlin-mode "merlin" nil t nil)
;; Automatically start it in OCaml buffers
(add-hook 'tuareg-mode-hook 'merlin-mode t)
(add-hook 'caml-mode-hook 'merlin-mode t)
;; Use opam switch to lookup ocamlmerlin binary
(setq merlin-command 'opam)))
(add-to-list 'load-path "/home/mohan/.opam/4.02.1/share/emacs/site-lisp")
(require 'ocp-indent)
(autoload 'utop-minor-mode "utop" "Minor mode for utop" t)
(autoload 'utop-setup-ocaml-buffer "utop" "Toplevel for OCaml" t)
(autoload 'merlin-mode "merlin" "Merlin mode" t)
;; Important to note that setq-local is a macro and it needs to be
;; separate calls, not like setq
(setq-local merlin-completion-with-doc t)
(setq-local indent-tabs-mode nil)
(setq-local show-trailing-whitespace t)
(setq-local indent-line-function 'ocp-indent-line)
(setq-local indent-region-function 'ocp-indent-region)
;; custom-set-variables was added by Custom.
;; If you edit it by hand, you could mess it up, so be careful.
;; Your init file should contain only one such instance.
;; If there is more than one, they won't work right.
'(package-selected-packages (quote (company))))
;; custom-set-faces was added by Custom.
;; If you edit it by hand, you could mess it up, so be careful.
;; Your init file should contain only one such instance.
;; If there is more than one, they won't work right.
; Make company aware of merlin
(with-eval-after-load 'company
(add-to-list 'company-backends 'merlin-company-backend))
; Enable company on merlin managed buffers
(add-hook 'merlin-mode-hook 'company-mode)

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More about OCaml code later. This creates an associative list of tuples containing characters and the number of times they occur in a String. MultiSet is a module that is not shown either but as I mentioned I have more to write about this wonderful programming language.

let insert l a =
if List.mem_assoc a l
let n = List.assoc a l in (a, n+1)::(List.remove_assoc a l)
else (a, 1)::l
let letters (word : string) : char MultiSet.t =
let rec insert (l : char MultiSet.t) (c : string) (i : int) : char MultiSet.t =
if ( String.length c > 1 ) then
insert ( MultiSet.insert l (String.get c i) ) ( String.sub c 1 ((String.length c) 1) ) 0
MultiSet.insert l (String.get c 0)
in insert MultiSet.empty word 0

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