Start with cabal2nix.
The workflow roughly looks like:
$ cabal2nix --sha256=ignoreme file:///path/to/package.cabal > ./my-app/default.nix
$ vim ./my-app/default.nix # remove sha256 stuff and add src reference:
# src = git-repo-filter <my-app>;
# now add to the packages attrset:
my-app = pkgs.haskellPackages.callPackage ./my-app {};You'll have to double-check if the dependencies inferred by cabal2nix actually exist
in your pkgs collection and if not, you have to repeat the procedure for it.