Spago2Nix: generate Nix expressions from Spago

justinw · June 19, 2019, 12:50pm

At ZuriHac, I put together a utility to generate Nix expressions from Spago. It requires Spago 0.8.5.0, which is available now either via npm or from easy-purescript-nix

https://github.com/justinwoo/spago2nix

How do I use this?

From https://github.com/justinwoo/spago2nix#usage

First, generate the spago-packages.nix:

$ spago2nix generate
getting packages..
got 65 packages from Spago list-packages.
# ...
wrote spago-packages.nix

Then install these, optionally with more jobs provided to Nix:

$ spago2nix install -j 100
/nix/store/...-install-spago-style
installing dependencies...
# ...
done.
Wrote install script to .spago2nix/install

Then build the project:

# SOON: spago --no-install
$ spago2nix build
/nix/store/...-build-spago-style
building project...
done.
Wrote build script to .spago2nix/build

How does this work?

I call Spago list-packages
I generate Nix derivations for each package
I give you ways to generate bash scripts that will ensure these inputs are available:

github.com

justinwoo/spago2nix/blob/be7e3a785be20bf052223e91bbd07ceccfc334c2/spago-packages.nix#L808-L826


installSpagoStyle = pkgs.runCommand "install-spago-style" {} ''
    >>$out echo "#!/usr/bin/env bash"
    >>$out echo
    >>$out echo "echo installing dependencies..."
    >>$out echo "${builtins.toString (
      builtins.map cpPackage (builtins.attrValues inputs))}"
    >>$out echo "echo done."
    chmod +x $out
'';


buildSpagoStyle = pkgs.runCommand "build-spago-style" {} ''
    >>$out echo "#!/usr/bin/env bash"
    >>$out echo
    >>$out echo "echo building project..."
    >>$out echo "purs compile \"\$@\" ${builtins.toString (
      builtins.map getGlob (builtins.attrValues inputs))}"
    >>$out echo "echo done."
    chmod +x $out
'';

This means that once you have these, you really don’t need much more than to run nix-build spago-packages.nix -A installSpagoStyle to install these packages in your Nix store and get the bash script to copy these packages from your store to your project.

Of course, since I make this expression readily available to you, you can also choose to manipulate these in ways you see fit.

Why?

I also needed this to replace my usage of Psc-Package2Nix with spago psc-package-insdhall on some of my projects.

Further questions

You should ask any specific questions in issues on the repo.

justinw · June 22, 2019, 4:05pm

Here’s a post about this project: https://github.com/justinwoo/my-blog-posts/blob/master/posts/2019-06-22-spago2nix-why-and-how.md