There are two types of Elm projects, one for applications and another one for packages. The elm.json is different in each case, so they are modeled as ApplicationInfo and PackageInfo types.

The contents of an elm.json with "type": "application".

The dependencies for a project. The order is preserved from JSON.

The contents of an elm.json with "type": "package".

There are two ways to specify "exposed-modules" field in an elm.json for packages. In one you just list the exposed modules. In the other, you provide headers for chunks of module names. In either case, the package website preserves this information to make the presentation nicer.

Turn a Project into the JSON that goes in elm.json

Decode the contents of elm.json into a Project.