Architecture

There are multiple components that play a part in the haskell.nix infrastructure. These are nix-tools, haskell.nix, hackage.nix, and stackage.nix.

                                             .-------------.     .-------------.
.- nix-tools ------.                         | haskell.nix |  .- | hackage.nix |
| .--------------. |   .----------------.    '-------------'  |  '-------------'
| | stack-to-nix |---> | stack-pkgs.nix |-.         |         |         |
| '--------------' |   '----------------' |         v         |         v
| .-------------.  |   .----------.       '--> .----------. <-'  .--------------.
| | plan-to-nix |----> | plan.nix |------.---> | pkgs.nix | <--- | stackage.nix |
| '-------------'  |   '----------'      |     '----------'      '--------------'
| .--------------. |   .--------------.  |          |
| | cabal-to-nix |---> | $package.nix |--'          v
| '--------------' |   '--------------'       .-------------.
'------------------'                          | default.nix |
                                              '-------------'
                                                    |
                                                    v
                                              .-------------.
                                              | release.nix |
                                              '-------------'

haskell.nix diagram

nix-tools

nix-tools is a Haskell package that provides the following tools:

• cabal-to-nix: a .cabal to .nix transformer that retains conditional expressions.

• stack-to-nix: a stack.yaml to .nix transformer that will read in a stack.yaml expression an generate a pkgs.nix file suited for use with haskell.nix.

• plan-to-nix: a plan.json to .nix transformer that will read in a plan.json file and generate a pkgs.nix file suited for use with haskell.nix.

as well as a few other tools used to generate hackage.nix and stackage.nix.

haskell.nix

Haskell.nix is the runtime system for this Haskell infrastructure. It contains the component builder, as well as the system package and license mapping. Without haskell.nix the expressions generated by either of the nix-tools tools make little sense on their own.

hackage.nix

hackage.nix provides all cabal expressions from hackage as nix expressions. It is periodically updated to keep in sync with the set of packages available on hackage.

stackage.nix

stackage.nix is similar to hackage.nix but provides all stackage snapshots (lts, and nightly) as nix expressions. It naturally depends on hackage.nix to resolve package names, versions and revisions to the respective packages from hackage.nix.