An option for package-dhall inputs.

[philderbeast]

I've stopped using package.yaml in favour of package.dhall in flare-timing, making good use of hpack-dhall from @sol. Could we please have an option of supplying snack with a package in dhall format?

> snack --help
- Usage: snack (--snack-nix PATH | --package-yaml PATH) COMMAND
+ Usage: snack (--snack-nix PATH | --package-yaml PATH | --package-dhall PATH) COMMAND

[philderbeast]

I want to try writing a DhallToJson.hs module similar to the existing YamlToJson.hs module.

snack/snack-lib/YamlToJson.hs

Line 4 in 5d52a2d

import qualified Data.Yaml as Yaml

This module will need to make some Dhall.* imports.

import qualified Dhall.Parser
import qualified Dhall.Import
import qualified Dhall.TypeCheck
import qualified Dhall.JSON

@nmattia how do I add packages that are missing so that those imports resolve?

[philderbeast]

I'm now maintainer of hpack-dhall. The executable dhall-hpack-json in that package might be just what we need instead of using dhall-to-json. It resolves imports and pretty prints JSON equivalent to running yaml2json on a package.yaml.

snack/snack-lib/hpack.nix

Line 30 in fa50d9b

"dhall-to-json <<< ${writeText "d2j" text} > $out"

[nmattia]

@philderbeast I missed your comment above (#51 (comment)). You can add them like this:

snack/snack-lib/hpack.nix

Line 10 in 90e27fc

[ (haskellPackages.ghcWithPackages (ps: [ ps.aeson ps.yaml ])) glibcLocales ];

It resolves imports and pretty prints JSON equivalent to running yaml2json on a package.yaml.

I see two solutions:

1. We use the import resolution to then cherry-pick the imported files and feed them to nix
2. We simply handle the dhall parsing/evaluation on the Haskell side and only feed the generated JSON to nix