# Tips on advent-of-code project structure

**URL:** <https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920>\
**Category:** Learning\
**Created:** [December 5, 2020, 9:27pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920 "2020-12-05T21:27:32Z")\
**Posts on this page:** 20\
**Page:** 1

<div class="post-metadata">

**Author:** ![cdaringe](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cdaringe/32/2419_2.png) [@cdaringe](https://discuss.ocaml.org/u/cdaringe)\
**Post date:** [December 5, 2020, 9:27pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/1 "2020-12-05T21:27:32Z")

</div>

Hi all,

I’m doing [AOC](https://adventofcode.com/2020) this year in OCaml, and have found that my routine for setting up the daily challenge involves:

- copying a folder
- renaming a series of files (because filenames = module names)
- updating my dayX/dune files to rename symbols
- updating my dayX/dayXbin.ml file to have the right X value

I.e.:

```auto
$ tree
├── day1
│ ├── day1bin.ml
│ ├── day1lib.ml
│ ├── day1test.ml
│ ├── dune
│ └── input.txt
...
├── day5
│ ├── day5bin.ml
│ ├── day5lib.ml
│ ├── day5test.ml
│ ├── dune
│ ├── index.md
│ └── input.txt
├── dune
├── dune-project
├── fixture.ml
└── readme.md

```

I’d prefer if all of my daily challenges had the same module basenames and libs names, just living in different child directories. Im 100% sure there is a better way to do this than what I’m doing now. I’d like to just `cp -r dayX dayY` and be done with it. Each day I’m fine having `Lib` be my module name, where I can import Lib into my bin file and my test file.

Here’s my repo: [https://github.com/cdaringe/aoc-2020](https://github.com/cdaringe/aoc-2020)

Have some hot 🔥 tips? If you have time to burn and want to critique my code, oh boy I’d _love that_ too 🙂

related, but not sufficiently relevant:

- [Filesystem structure for Ocaml project](https://discuss.ocaml.org/t/filesystem-structure-for-ocaml-project/2273)
- [Structure the code in modules](https://discuss.ocaml.org/t/structure-the-code-in-modules/5401)
- [How would you structure a dune project for web development with opium and js\_of\_ocaml?](https://discuss.ocaml.org/t/how-would-you-structure-a-dune-project-for-web-development-with-opium-and-js-of-ocaml/2441/2)

---

<div class="post-metadata">

**Author:** ![yawaramin](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/yawaramin/32/3384_2.png) [@yawaramin](https://discuss.ocaml.org/u/yawaramin)\
**Post date:** [December 5, 2020, 11:39pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/2 "2020-12-05T23:39:58Z")

</div>

Maybe `dune init` is what you are looking for?

---

<div class="post-metadata">

**Author:** ![cdaringe](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cdaringe/32/2419_2.png) [@cdaringe](https://discuss.ocaml.org/u/cdaringe)\
**Post date:** [December 5, 2020, 11:47pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/3 "2020-12-05T23:47:50Z")

</div>

Thx for the response. I realized that I didn’t articulate my target state very well. Ive applied an edit to the above post. Really, what I’m after, is each day having the exact same file name structure, and each being able to use a common fixture module from the root of the project. I’m not sure dune init plays a role in making that now clarified objective possible.

---

<div class="post-metadata">

**Author:** ![yawaramin](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/yawaramin/32/3384_2.png) [@yawaramin](https://discuss.ocaml.org/u/yawaramin)\
**Post date:** [December 5, 2020, 11:54pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/4 "2020-12-05T23:54:17Z")

</div>

Oh I see. You want a project structure like:

```auto
day01/
  bin.ml
  dune
  lib.ml
day02/
  bin.ml
  dune
  lib.ml
...

```

Instead of:

```auto
day01/
  day01.ml
  dune
  lib.ml
day02/
  day02.ml
  dune
  lib.ml
...

```

I don’t think dune works like that, but maybe someone else can chime in. In any case, repetitive daily projects like this is _probably_ not the use case dune is trying to optimize for. Personally I think the latter project structure (above) is not too bad. It should be a directory copy & rename, followed by one file rename at most.

Edit: also the dune file edit, true.

---

<div class="post-metadata">

**Author:** ![darrenldl](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/darrenldl/32/291_2.png) [@darrenldl](https://discuss.ocaml.org/u/darrenldl)\
**Post date:** [December 6, 2020, 4:00am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/5 "2020-12-06T04:00:11Z")

</div>

Is using a bash script/Makefile acceptable?

---

<div class="post-metadata">

**Author:** ![yawaramin](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/yawaramin/32/3384_2.png) [@yawaramin](https://discuss.ocaml.org/u/yawaramin)\
**Post date:** [December 6, 2020, 4:03am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/6 "2020-12-06T04:03:03Z")

</div>

For new projects, dune is the recommended build tool.

---

<div class="post-metadata">

**Author:** ![darrenldl](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/darrenldl/32/291_2.png) [@darrenldl](https://discuss.ocaml.org/u/darrenldl)\
**Post date:** [December 6, 2020, 4:05am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/7 "2020-12-06T04:05:19Z")

</div>

That is true. Just it seems that this is much simpler to handle in more general scripting than in dune, since you need access to non-static information (day number).

EDIT: I still think what you want is outside of what dune was intended for (as mentioned by other people above), and rolling dune files and folders via script would be the most straightforward approach.

---

<div class="post-metadata">

**Author:** ![mseri](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/mseri/32/91_2.png) [@mseri](https://discuss.ocaml.org/u/mseri)\
**Post date:** [December 6, 2020, 8:23am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/8 "2020-12-06T08:23:29Z")

</div>

If the dune file declares a different name/public\_name for the binary and library in each folder, that should work fine. You still have to change the dune files but that is about it. Otherwise you would need to make each folder a separate dune project.

---

<div class="post-metadata">

**Author:** ![SkySkimmer](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/skyskimmer/32/1672_2.png) [@SkySkimmer](https://discuss.ocaml.org/u/SkySkimmer)\
**Post date:** [December 6, 2020, 10:42am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/9 "2020-12-06T10:42:08Z")

</div>

I use the same filenames everyday, and there’s no issue.  
I don’t use public\_name so that may be a factor.

Typically I have

```auto
XX
├── input.txt
├── ocaml
│ ├── dune
│ ├── mainA.ml
│ └── mainB.ml
├── resultA.txt
└── resultB.txt

```

where `XX` is the day, `input.txt` from the AOC website, `resultY.txt` created manually for posterity.  
`dune` is always

```auto
(executable
 (name mainA)
 (libraries utils)
 (modes byte exe)
 (modules MainA))

(executable
 (name mainB)
 (libraries utils)
 (modes byte exe)
 (modules MainB))

```

(I have some `utils` library in another folder, shared across days)  
`mainA` and `mainB` contain something like

```ocaml
let input = 
  let input = open_in "../input.txt" in
  let res = input_line input in
  close_in input;
  res

(* do stuff *)

let () = Printf.printf "%s\n" (whatever result I got)

```

Workflow is

- cp -r $yesterday $today
- rm $today/\*.txt; create fresh $today/input.txt
- cd $today/ocaml
- edit mainA.ml, run with `dune exec -- ./mainA.ml # possibly extra args, eg -debug`
- eventually get a solution, paste into the website, also paste into $today/resultA.txt
- cp mainA.ml mainB.ml
- edit mainB.ml until solution, paste into website and $today/resultB.txt
- `git add $today; git commit; git push

Typical result [https://github.com/SkySkimmer/AdventOfCode/blob/master/2019/25/ocaml/mainA.ml](https://github.com/SkySkimmer/AdventOfCode/blob/master/2019/25/ocaml/mainA.ml)

I don’t have an equivalent to `day1lib/day1test`, everything specific to the day is in mainA/mainB, copied if used in both. Last year there were the “intcode” recurring problems for which I created a separate library.

---

<div class="post-metadata">

**Author:** ![cdaringe](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cdaringe/32/2419_2.png) [@cdaringe](https://discuss.ocaml.org/u/cdaringe)\
**Post date:** [December 6, 2020, 9:04pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/10 "2020-12-06T21:04:40Z")

</div>

Money. I will do something similar. I think my biggest obstacle was having `dune` file in the root, which seemed to want to include all other subdirs in compilation. Even if compiling in a dayXX subdir, the root project would assess all other sub dune projects and complain about `bin`, `lib`, and `test` collisions. You made `utils` a standalone lib, in a non-rooty folder. I was hoping to find a way to just have my utils live in root with a dune file, but i dont think that works. I tried using `data-only-dirs`, which of course failed.

Thanks for the ref to your project. Man, `Scanf.sscanf`! Who knew!

---

<div class="post-metadata">

**Author:** ![darrenldl](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/darrenldl/32/291_2.png) [@darrenldl](https://discuss.ocaml.org/u/darrenldl)\
**Post date:** [December 7, 2020, 12:29am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/11 "2020-12-07T00:29:39Z")

</div>

You can use a rule in dune to copy the file over during build if you don’t mind hacking.

```auto
(rule
 (targets utils.ml)
 (deps ../utils.ml)
 (action (copy %{deps} %{targets}))
)

```

---

<div class="post-metadata">

**Author:** ![cdaringe](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cdaringe/32/2419_2.png) [@cdaringe](https://discuss.ocaml.org/u/cdaringe)\
**Post date:** [December 7, 2020, 1:23am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/12 "2020-12-07T01:23:11Z")

</div>

> [@darrenldl](#):
>
> ```auto
> (rule
> (targets utils.ml)
> (deps ../utils.ml)
> (action (copy %{deps} %{targets}))
> )
> 
> ```

Using a relative file seems to not take:

```auto
File "dune", line 1, characters 0-88:
1 | (rule
2 | (targets fixture.ml)
3 | (deps ../fixture.ml)
4 | (action (copy %{deps} %{targets}))
5 | )
Error: File unavailable: _build/fixture.ml

```

Replacing `../fixture.ml` with an absolute path `/Users/cdaringe/path/to/aoc-2020/fixture.ml` works, though is undesirable for obvious reasons. Even though my `../fixture.ml` 100% exists relative to my `dayXX/dune` file, it seems the path is evaluated from a dir inside of the `_build` dir, instead of the working dir from which the process is executed or the dirname of the `dune` file.

---

<div class="post-metadata">

**Author:** ![darrenldl](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/darrenldl/32/291_2.png) [@darrenldl](https://discuss.ocaml.org/u/darrenldl)\
**Post date:** [December 7, 2020, 1:26am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/13 "2020-12-07T01:26:36Z")

</div>

> Even though my `../fixture.ml` 100% exists relative to my `dayXX/dune` file, it seems the path is evaluated from a dir inside of the `_build` dir, instead of the working dir from which the process is executed or the dirname of the `dune` file.

Hm…it seems to work on my side, let me try it on your actual repo real quick…

---

<div class="post-metadata">

**Author:** ![darrenldl](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/darrenldl/32/291_2.png) [@darrenldl](https://discuss.ocaml.org/u/darrenldl)\
**Post date:** [December 7, 2020, 1:39am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/14 "2020-12-07T01:39:24Z")

</div>

Hm…I can’t seem to replicate your `File unavailable` issue on my fork: [https://github.com/darrenldl/aoc-2020/tree/test-dune](https://github.com/darrenldl/aoc-2020/tree/test-dune)

EDIT: possibly silly idea - do you happen to be building on something other than Linux? (Judging from your absolute path). In which case dune might being doing things differently I’m guessing(?

---

<div class="post-metadata">

**Author:** ![cdaringe](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cdaringe/32/2419_2.png) [@cdaringe](https://discuss.ocaml.org/u/cdaringe)\
**Post date:** [December 7, 2020, 1:51am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/15 "2020-12-07T01:51:12Z")

</div>

Ya, ok, so the trick is… if you remove the `<root>/dune` file, the problem should surface. Somewhat confusingly, at the moment in time you forked, the root dune existed _just_ to build `fixture`, which was also the point of the `rule`. Thus, `rm dune dune-project` from root should create a repro. Edit: building on osx 🙂

---

<div class="post-metadata">

**Author:** ![Cjen1](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/cjen1/32/1731_2.png) [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\
**Post date:** [December 7, 2020, 11:08am UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/16 "2020-12-07T11:08:22Z")

</div>

I’m currently using a similar style of project structure and just copying it over each day. That means that in each subdirectory for each day there is:

```auto
day01
├── dune-project
├── dune
├── .ocamlformat
├── lib.ml
├── bin.ml
day02
├── ...

```

This nicely means that each subdirectory is in some sense its own separate project which feels about right from a philosophical direction. Unfortunately this means that any utilities written end up accumulating over the days in the `lib.ml` file but otherwise is fine 🙂.

---

<div class="post-metadata">

**Author:** ![bcc32](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/bcc32/32/203_2.png) [@bcc32](https://discuss.ocaml.org/u/bcc32)\
**Post date:** [December 7, 2020, 6:00pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/17 "2020-12-07T18:00:05Z")

</div>

I’m using a template directory which I copy into a new day’s directory each time. Having the template as a separate directory means I can update and test the template itself.

I also have a script at the root of my repo that automatically fetches my input (I saved my cookies in a gitignored file in the repo) and copies over the template. It renames my dune library to the day number, but the file structure is the same each day.

```auto
(library
 (name day_7_solution)
 (libraries async bignum core expect_test_helpers re topological_sort)
 (inline_tests
  (deps input.txt))
 (preprocess
  (pps ppx_jane)))

```

```auto
day_7
├── dune
├── import.ml
├── input.txt
├── main.ml
└── main.mli

```

I haven’t gotten to the point yet this year, but when I will inevitably write some shared library between solutions, I’ll put it in the root of the project and create a new dune library that I can just depend on in each day’s solution dune file, rather than trying to copy over individual files. That lets dune think about the dependencies instead of me trying to write them out 🙂

> **[bcc32/advent-of-code-2020](https://github.com/bcc32/advent-of-code-2020)**
>
> Contribute to bcc32/advent-of-code-2020 development by creating an account on GitHub.

---

<div class="post-metadata">

**Author:** ![yawaramin](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/yawaramin/32/3384_2.png) [@yawaramin](https://discuss.ocaml.org/u/yawaramin)\
**Post date:** [December 7, 2020, 6:49pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/18 "2020-12-07T18:49:13Z")

</div>

> [@bcc32](#):
>
> I’ll put it in the root of the project and create a new dune library that I can just depend on in each day’s solution dune file, rather than trying to copy over individual files. That lets dune think about the dependencies instead of me trying to write them out 🙂

I did exactly this, working well 🙂 My repo: [GitHub - yawaramin/aoc2020: Advent of Code 2020](https://github.com/yawaramin/aoc2020)

---

<div class="post-metadata">

**Author:** ![lefessan](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/lefessan/32/2293_2.png) [@lefessan](https://discuss.ocaml.org/u/lefessan)\
**Post date:** [December 8, 2020, 5:23pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/19 "2020-12-08T17:23:56Z")

</div>

You may want to use `drom` ([https://github.com/ocamlpro/drom](https://github.com/ocamlpro/drom)) at some point: it has a notion of skeleton, and is able to perform substitutions on these skeletons to instantiate them for every new project.  
If you look at the `master` branch, it currently has skeletons for `library`, `program`, `mini-lib` (same as `library` without docs, tests, etc.), `mini-prg` and now `ppx_rewriter`. The substitution language is far from perfect, but is being improved for every new skeleton.

With `drom`, you can define your own skeletons in `~/.config/drom/skeletons/`, by mimicing the same structure as the `share/drom` folder in the sources.

---

<div class="post-metadata">

**Author:** ![anuragsoni](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/anuragsoni/32/1107_2.png) [@anuragsoni](https://discuss.ocaml.org/u/anuragsoni)\
**Post date:** [December 8, 2020, 5:28pm UTC](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920/20 "2020-12-08T17:28:03Z")

</div>

I’ve kept things simple. Instead of separate projects for each day, I just have one library project. Each day i add a new module `day_one`, `day_two` etc, and I run tests using [https://github.com/janestreet/ppx\_expect](https://github.com/janestreet/ppx_expect) that run the two problems for each day. I’ve found this to be a pretty nice setup, as I can still keep some shared code in modules that are used by each day’s specific task.

[Next page](https://discuss.ocaml.org/t/tips-on-advent-of-code-project-structure/6920.md?page=2)