The motivation for this change is:
* To catch build failures in downstream packages whenever we make a breaking
change to the `dhall` API
* To reduce the amount of work I need in order to cut a release for all of
these packages
* To better share Nix/CI-related logic between the projects
Note that I have not yet migrated `dhall-nix` in. I'm waiting for
https://github.com/dhall-lang/dhall-nix/issues/17 to be fixed since
`dhall-nix` is incompatible with later versions of `megaparsec` due to
`hnix`.
* rename previous lts-11 yaml file and add needed extra-deps
* use new lts-12.4
* add import of Data.Monoid.(<>) to make it compilable with base < 4.11 (and stack lts-11)
* add needed extra-deps
Not sure if this is a change you’re interested in. IMO, it’s nice for stack
users even if they don’t use Nix, since it makes the dependencies explicit.
prettyprinter doesn't match on lts-9.0. You get the following error
with stack:
```
Error: While constructing the build plan, the following exceptions were encountered:
In the dependencies for dhall-1.6.0:
prettyprinter-1.1 must match >=1.1.1 && <1.2 (latest applicable is 1.1.1)
needed since dhall-1.6.0 is a build target.
```
