examples

The examples show some concrete uses of opam2nix, and should be buildable as long as you have a recent nixpkgs.

Layout

Each example has:

• default.nix: self-contained derivation which imports opam2nix and <nixpkgs> explicitly
• opam-selection.nix: generated information for all opam packages in use
• nix/default.nix: a parameterised derivation as you might find in nixpkgs - i.e. all dependencies injected. Uses the opam2nix API to build opam-selection.nix
• Makefile: commands for building the actual derivation, and for (re)generating opam-selection.nix

The examples reference ./examples/opam2nix.nix, which imports opam2nix directly from the parent directory. In your own repository, you would import it from github instead (see the toplevel README for instructions).

Building

(e.g. for ./simple)

cd simple
make
./result/bin/main

To get a shell instead, run nix-shell

Scenario 1. simple

The simple use case is where all dependencies are in OPAM, you just want to build them via nix.

Scenario 2. opam-library

If you're developing more complex software, you may need to integrate ocaml dependencies from outside the official opam repository.

This example uses the vdoml library, which is not in the opam repositories.

The main change is that the source for vdoml is required when building the initial selections document, as well as at build time. This is achieved by making nix/default.nix return an attribute set instead of a single derivation.

The make target which builds the opam-selections.nix document passes in the path to vdoml which it generated with nix-build --attr vdoml, and the final build runs on nix-build --attr hello (the demo program).

Scenario 3. dev-dependencies

An extension of scenario 1 where you want to add development dependencies. It's almost idential to simple, see the comments in nix/default.nix for how it includes two different types of dependencies (ofrcing depopts to be installed, and adding packages which aren't even depopts).

Utility. package

This is less of an example and more of a simple way to check that an opam package builds correctly.

You can run ./build.sh packagename, and it'll build that package into result/