# Dune: depending on local module "Library not found" **URL:** \ **Category:** Learning\ **Tags:** dune\ **Created:** [May 17, 2020, 9:53pm UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793 "2020-05-17T21:53:37Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![evanm](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/evanm/32/2222_2.png) [@evanm](https://discuss.ocaml.org/u/evanm)\ **Post date:** [May 17, 2020, 9:53pm UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/1 "2020-05-17T21:53:37Z")
Under my project root I have two folders, one for library code and one for the final binary built from main.ml. Unfortunately I’m missing something since dune can’t seem to find the library code ``` File "bin/dune", line 3, characters 12-15: 3 | (libraries lib)) ^^^ Error: Library "lib" not found. Hint: try: dune external-lib-deps --missing @@default ``` Here’s the folder structure: ```auto . |-- bin | |-- dune | |-- dune-project | `-- main.ml |-- dune-project `-- lib |-- dune `-- math.ml ``` Here’s bin/dune: ```auto (executable (name main) (libraries lib)) ``` And lib/dune ```auto (library (name lib)) ``` From the dune [documentation](https://dune.readthedocs.io/en/stable/concepts.html#library-deps) on library dependencies it seems like dune should automatically find libraries defined within the current scope / workspace. What am I doing wrong? ---
**Author:** ![evanm](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/evanm/32/2222_2.png) [@evanm](https://discuss.ocaml.org/u/evanm)\ **Post date:** [May 18, 2020, 12:47am UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/2 "2020-05-18T00:47:35Z")
I ended up getting this to work after investigating a bit further, although I’m still not exactly sure why it works now. I modified main.ml and added `open Lib`, after which dune built everything without complaint. I thought perhaps dune throws an error to prevent unused dependencies from being included, but I’ve also listed base as a dependency in the dune file, without opening it in `main.ml`, and dune is fine with that. If anyone knows why I’m observing this behavior, I’d be curious to know. ---
**Author:** ![Leonidas](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/leonidas/32/4039_2.png) [@Leonidas](https://discuss.ocaml.org/u/Leonidas)\ **Post date:** [May 18, 2020, 2:03pm UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/3 "2020-05-18T14:03:17Z")
Do you have a git repo where we could test that without having to reproduce it ourselves? You should not be required to use `open Lib`, a practice that I find pretty bad for readability of code in any case. ---
**Author:** ![evanm](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/evanm/32/2222_2.png) [@evanm](https://discuss.ocaml.org/u/evanm)\ **Post date:** [May 18, 2020, 4:53pm UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/4 "2020-05-18T16:53:17Z")
Unfortunately when I tried this again today I couldn’t reproduce the error. However, as I wrote that last sentence I realized the difference between the code now and before is that previously I had a stray `dune-project` file in the bin directory. If you clone the sample repository I created and copy the `dune-project` file into the bin directory you can reproduce the error. To your point about not needing to `open Lib` - you’re right. I tested things out today and it works properly without opening the library. > **[emesterhazy/dune\_test](https://github.com/emesterhazy/dune_test)** > > Contribute to emesterhazy/dune\_test development by creating an account on GitHub. Thanks! ---
**Author:** ![Leonidas](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/leonidas/32/4039_2.png) [@Leonidas](https://discuss.ocaml.org/u/Leonidas)\ **Post date:** [May 19, 2020, 12:43pm UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/5 "2020-05-19T12:43:59Z")
Yes, so `dune-project` acts as “anchor” to determine where the project root is, and if it finds it in a folder from where there is no subfolder with a `lib` library this is exactly what happens. I am glad we could figure out the reason for this weird behaviour you were seeing! ---
**Author:** ![Luc\_ML](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/luc_ml/32/1671_2.png) [@Luc\_ML](https://discuss.ocaml.org/u/Luc_ML)\ **Post date:** [May 20, 2020, 2:38am UTC](https://discuss.ocaml.org/t/dune-depending-on-local-module-library-not-found/5793/6 "2020-05-20T02:38:27Z")
> [@Leonidas](#): > > Yes, so `dune-project` acts as “anchor” to determine where the project root is, and if it finds it in a folder from where there is no subfolder with a `lib` library this is exactly what happens. Yes, and dune doesn’t tell you what it does. @evanm: you may reproduce something like your problem if your try to build one of the example that are still within dune source 2.5.1, say [dune/example/sample-projects/hello\_world at 2.5.1 · ocaml/dune · GitHub](https://github.com/ocaml/dune/tree/2.5.1/example/sample-projects/hello_world) . Doing `dune build` does nothing (with no message, which is puzzling and disappointing). Doing `dune build --root .` (dot for current directory) from within the hello\_world directory works (you have to dig in \_build/default because nothing is visible). You should also think about doing `dune runtest --root .` and `dune clean --root .` to make something happen. What happens if you try `--root .` your files tree? Also, try `--verbose` to gain visibility and let us know.